Greening the Blue Revolution - Burren Smokehouse



Omega-3 fatty acids — a key component in a healthy diet

Graham Look, updated 17 March 2005

The substantial library of evidence that the fatty acids found in oily fish such as salmon have significant health benefits continues to grow and to expand in the number of benefits identified.

Benefits range from the well-known advantages for cardiovascular health to relief from arthritis and inflammatory diseases and a central role in mental health and brain development, on to emerging bodies of evidence that they are important in preventing or moderating cancers. More recently, these fatty acids have been linked with further benefits such as reducing the risk of gallstones. In addition, as the UN Food and Agriculture Organization (FAO) reports, “Fish is a food of excellent nutritional value, providing high quality protein and a wide variety of vitamins and minerals, including vitamins A and D, phosphorus, magnesium, selenium and iodine in marine fish.”

In the face of increasing obesity and decreasing health standards, governments and food and health advisory bodies in Europe and the USA are actively encouraging their populations to consume more fish in their diet.

Omega-3 fatty acids

Central to the health benefits being observed are the omega-3 polyunsaturated fatty acids, also referred to as n-3 fatty acids. The two key fatty acids are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Fatty acids are building blocks for eicosanoids, which are precursors for hormones such as prostaglandins and are involved in the formation of cell membranes, blood clotting, wound healing and inflammation. They are termed ‘essential’ because we need them to live a healthy life but cannot synthesise them effectively.

Fatty acids are based on a chain of linked carbon atoms and are classified as saturated or unsaturated. In a saturated fatty acid there are only single bonds between the carbon atoms — hydrogen atoms take up all other bonds. The term unsaturated means that the fatty acid has at least one carbon-carbon double bond. Polyunsaturated means there are two or more double bonds.

The 3 and 6 in omega-3 and omega-6 fatty acids indicates where the first double bond is in the carbon atom chain. Unsaturated and polyunsaturated fats have lower melting points and are liquid at room temperature. Typically they are found in vegetable oils and fish oils, but it is the fish oils in particular that are rich in EPA and DHA. The omega-3 fatty acids from vegetable sources need to be converted into EPA and DHA in the body before they can be converted into beneficial eicosanoids.

EPA can be synthesised in the human body to a limited extent from alphalinolenic acid (ALNA), an unsaturated fatty acid of plant origin, but even less is converted to DHA[i]. Research at the Institute of Human Nutrition in the UK indicates women convert more than men[ii]. The authors comment,” Since the capacity of adult males to convert ALNA to DHA was either very low or absent, uptake of pre-formed DHA from the diet may be critical for maintaining adequate membrane DHA concentrations in these individuals.” Thus in human nutrition, fish is an important source of omega-3 fatty acids.

Human evolution

The reasons for this valuable health contribution from fish oils are possibly becoming clearer with the latest theories of the origins of mammalian life forms. Evidence gathered in recent years in particular shows the probable route being the development of terrestrial forms, tetrapods, in the extensive swamps of the late Devonian age around 360 million years ago. Given that origin, on the edges of the waters, our early ancestors would have eaten a diet based substantially on seafood. As Professor Michael Crawford, Director of the Institute of Brain Chemistry and Human Nutrition, University of North London, UK, observes, “Six hundred million years ago, the evolution of the human brain and nervous system originated in the marine environment in a rich supply of DHA. This essential fatty acid has been conserved since then for the structure and function of neurological and visual membranes.”(from an article by Professor Crawford on the US National Institutes of Health web site; ).

Since mankind (Homo sapiens) first appeared some million years ago, our diet has changed and one significant change has been in the ratio of plant-derived omega-6 fatty acids (e.g. arachidonic and linoleic acids) with omega-3 fatty acids. It is estimated that the ratio for early man was 1:1[iii] whereas in the western diet it is now around 10:1: probably higher in many individuals, up to 15:1 and even 20:1 according to some estimates in the US. The fall in fish consumption over the past decades and the imbalance between omega-6 and omega-3 acids may account for the apparent rise in occurrence of those diseases where omega-3 consumption has been demonstrated to bring benefits.

The following review highlights some typical and important examples of many thousands of research publications linking fish oils with human health benefits.

Reducing heart attacks and strokes

Cardiovascular diseases (CVD) are responsible for an estimated 16.6 million deaths a year worldwide according to the World Health Organization (WHO Cardiovascular Disease Fact Sheet). This is one third of the global total. In addition, at least 20 million people survive heart attacks and strokes every year, a significant proportion of these subsequently require costly clinical care, placing a huge burden on long-term care resources. There is compelling evidence, reports WHO, that at least three dietary strategies are effective in preventing CVD. One of these is an increase in the consumption of omega-3 fatty acids as found in oily fish.

Diet and coronary health

The first suggestions of the cardiovascular benefits to be derived from eating oily fish came from the observation that populations that eat fish regularly, such as the Eskimos, Japanese and Koreans, have lower rates of heart disease[iv],[v]. This has been substantiated through a series of studies over the past twenty years and more. The mechanism appears to include counteracting a tendency for blood clots to form in the blood stream. It is also linked with decreased atherosclerosis (narrowing of the arteries by deposition of fatty material), especially, as indicated in a study using fish oil supplements, if combined with exercise[vi]. These benefits may be augmented by the effect demonstrated in an African study[vii], of lowering plasma leptin levels, which also has been shown to reduce CVD risk.

Several major studies have examined the link between diet and coronary health. One of these followed 20,551 male physicians, aged from 40 to 84, who were free from myocardial infarction, cerebrovascular disease and cancer. They completed a questionnaire on fish consumption and were checked 11 years later. Using the incidence of sudden cardiac death (within one hour) as the metric, the authors concluded that dietary fish intake was associated with a reduced risk of sudden cardiac death, with the threshold being one meal a week.

In the Netherlands, part of what is known as the Zutphen study[viii], which began in 1960, looked at the diet of 552 men in Zutphen who would be 50–69 in 1970. The incidence of stroke in this group was recorded from 1970 to 1985 and it was reported that men who ate an average 20g of oily fish a day had a significantly reduced risk of stroke than those who ate less.

In the UK, the DART study investigated the influence of dietary advice, to eat fish, on a recurrence of myocardial infarction in 2,033 patients and concluded “the subjects advised to eat fatty fish had a 29% reduction in two-year all-cause mortality compared with those not so advised” [ix].

Supplements also

In Italy, the GISSI trial, published in The Lancet[x], reported the initial outcome of a study relating fish oil consumption in the form of dietary supplements to the incidence of heart attack. Nearly 12,000 survivors of heart attacks were randomly assigned fish oil. Three and a half years later 20% fewer of the group taking fish oil had died. The fish oil group consumed 1g per day of DHA and EPA; equivalent to two meals a week of oily fish. The trial continues to be reported, with consistent results.[xi]

Using data from this study together with that from Finland and the Netherlands (Zutphen) — all part of a combined Seven Countries Trial — it has been calculated that oily fish consumption reduces the relative risk of coronary heart disease mortality in the observed populations by 34%[xii].

Women’s health

The Nurses Health Study led from Harvard University, by a team including Walter Willet, brought some equivalent information in women’s health. Initiated in 1976 at Brigham and Women’s Hospital it was the longest major women’s health study ever undertaken. Around 85,000 women aged 30–55 at recruitment were monitored from 1980 to 1994. One of many findings was that those who ate fish 2–4 times a week showed an incidence of stroke 48% less than those who ate fish once a month or less[xiii].

Diabetics

People suffering from diabetes type 2 are especially vulnerable to CVD. Information derived from the Nurses Health Study indicates that regular consumption of fish can reduce that risk by more than half[xiv]. Also, hypertriglyceridemia (fasting serum triglycerides of 200 mg/dl or higher) is a common lipid abnormality in individuals with type 2 diabetes and it is a negative indication; a number of randomised controlled trials have found that fish oil supplementation significantly lowers serum triglyceride levels in diabetic individuals[xv].

An added dimension to this was reported by Denkins, Lovejoy and Smith from the Pennington Biomedical Research Institute in Louisiana to the Experimental Biology conference in New Orleans in April 2002. They had found that daily doses of 1.8g DHA taken over a three-month period by a small sample of overweight people produced a clinically significant improvement in the insulin resistance, a pre-diabetic condition, in half of the sample and measurable improvements in a further 20 percent. While none of the participants had full type 2 diabetes, they all suffered from insulin resistance.

Measurable physiological effects

Fish consumption was linked with a lower heart rate by a French study on 9,758 men recruited in France and Ireland. The men, who did not have coronary heart disease, were divided into four fish consumption groups. Fish consumption was clearly associated with decreased heart rate and therefore the risk of sudden death from CVD[xvi].

Extending the observed cardiovascular benefits of oily fish, in 1988, Australian researchers observed that omega-3 fatty acids modified the electrical problems that lead to arrhythmia[xvii]. This was taken an important step further by a pilot study in Munich, published in 2004, where patients at high risk of sudden cardiac death were infused with omega-3 fatty acids and this clearly reduced susceptibility to sustained ventricular tachycardia[xviii].

Strong recommendations

The above references are a very small proportion of the many reports available. A review published in 2002 lists 119 key references[xix]. The U.S. National Library in Bethesda monitored research papers on the subject and picked up over 700 references a year on fish oils and cardiovascular disease. The wealth of information available led Professor Walter Willet of Harvard School of Public Health and Harvard Medical School, to comment at the Diet and Optimum Health Conference, in May 2001[xx], “The evidence that higher intake of omega-3 fatty acids can reduce coronary heart disease mortality due to sudden death is conclusive.”

In May 2003 the Office of Management and Budget in Washington urged the Departments of Health and Human Services (HHS) and Agriculture (USDA) to include new information that omega-3 fatty acids may reduce the risk of coronary heart disease, while trans-fatty acids may increase the risk. “Since CHD kills over 500,000 Americans a year, even a small improvement in dietary habits could save thousands of lives,” states the letter. The 2005 dietary guidelines from these departments, released 12 January, have doubled the recommended consumption of fish to include two meals a week of 110g of oily fish such as trout, salmon or herring. In September 2004, the US Food and Drug Administration (FDA) announced that conventional foods containing EPA and DHA could make qualified health claims for a reduced risk of coronary heart disease.

The American Heart Association now specifically recommends people without documented coronary heart diseases (CHD) to eat a variety of fish, preferably oily, at least twice a week. Patients with CHD should consume 1g/day of EPA+DHA, preferably from oily fish (equivalent to two meals a week of oily fish) but adds that supplements can be considered in consultation with the physician. The AHA shows a clear preference for a balanced nutritious diet including fish over supplements. However, patients needing to lower triglycerides are recommended to take 2–4 g/day EPA+DHA, as capsules and under the care of a physician. The benefits listed by AHA are decreased arrhythmias, which can lead to sudden cardiac death, decreased triglyceride levels, decreased growth rate of atherosclerotic plaque and slightly lower blood pressure.

Following a review of the risk: benefit balance, in 2004 the UK Food Standards Agency (FSA) revised upwards its recommendations concerning oily fish. The FSA website states, “Aim to eat at least two portions of oily fish a week because fish are a good source of protein, vitamins and minerals, and they are low in saturated fat.” It continues, “Oily fish are a healthy choice because they also contain omega-3 fatty acids.” For most sections of the population the FSA suggests they can eat up to four portions a week.

The UK Joint Health Claim Initiative works to ensure that health claims are scientifically substantiated. In 2005 it ruled that consumption of long chain polyunsaturated omega-3 fatty acids, such as those found in oily fish, can be promoted as beneficial to heart health.

In 2004, the Dutch State Institute for Public Health and Environment (RIVM) published an extensive review of risks and benefits from a wide variety of foods. Risks and benefits were compared using the Disability Adjusted Life Years (DALYs). For fish, the heart health benefits were weighed against risks represented by contaminants such as dioxins. The conclusion was that the benefits are far greater than the risks (consumption of oily fish once a week brings a health gain of 82,000 DALYs compared with risks rated from probably low to absent)[xxi].

In the light of concerns over potential risks, the Michigan Department of Community Health has also assessed the balance of benefits and risks[xxii]. The conclusion was that the consumption of fish in accordance with the State of Michigan Fish Advisory Guidelines (which refer to eating fish meals two to three times a week) is safe and should be encouraged.

The Healthy Eating Club in Australia, headed by Professor Mark Wahlqvist – President of the International Union of Nutrition Sciences, suggests, “adult Australians should include one to two fish or seafood meals per week”, citing cardiac benefits and possible relief from the effects of rheumatoid arthritis.

Preparation affects benefits

The results of a 12-year study among 4,775 adults aged 65 or over at the outset suggest that the way in which food is prepared has a bearing on its health influences. Those who regularly ate fried fish or fish sandwiches (fish burgers) had an increased risk of stroke while those that regularly ate their fish baked or grilled had a lower risk of stroke[xxiii].

Easing inflammatory and auto-immune diseases

The first scientific publication relating the benefits of fish oils on an inflammatory disease, rheumatoid arthritis, was in The London Medical Journal in 1783, describing the then current practice at Manchester Infirmary. Over the past 20 years interest has been re-awakened and data has steadily been accumulated detailing these benefits. It appears that the EPA component has particular impact and that it is associated with ameliorating the inflammatory effects of excess omega-6 fatty acids, or of an imbalance between the two fatty acid groups. Omega-3 fatty acids compete with linoleic acid in the arachidonic acid pathway, thereby reducing the metabolism of arachidonic acid to prostaglandin E2 and thromboxane A2, both of which are associated with inflammation.

This growing body of evidence indicates that the moderating effects of omega-3 fatty acids on inflammation are beneficial in the management of a wide range of inflammatory and autoimmune diseases. Significant research reports up to early 2002 were reviewed by Dr Artemis Simopoulos of the Center for Genetics, Nutrition and Health in Washington DC[xxiv]. The 100 papers cited cover a broad range of conditions including inflammatory bowel disease, psoriasis and asthma as well as rheumatoid arthritis.

Current interest in omega-3 fatty acids and rheumatoid arthritis began in the mid-80s. Since then many randomised controlled clinical trials have shown a benefit from fish oil supplements in patients with rheumatoid arthritis, most of which show a reduction in symptoms, the number of tender joints and in morning stiffness. Many patients taking the supplements reduced their use of the pain-relieving anti-inflammatory drugs. The dosage rates used in these studies vary widely, for example one study used daily doses of 1.8g EPA and 0.9g DHA while another used 3.6g EPA and 2.4g DHA. Clear benefits were observed in both. In his conclusions, Dr Simopoulos observed that a better balance of omega-3 with omega-6 is important — current western diets being too low in the former and too high in the latter and he suggests eating fish two to three times a week or taking fish oil supplements.

Inflammatory bowel diseases, which include Crohn’s disease and ulcerative colitis, appear to be on the increase in the western world. They are treated usually by using anti-inflammatory products. Fish oils have led to lessening of symptoms and the need for drugs. The therapeutic effects reported in the review range from a ‘trend towards improvement’ to ‘significant improvement in clinical activity’. For example supplementation with 2.7g omega-3 fatty acids per day gave a reduced rate of relapse in cases of Crohn’s disease that were in remission.

Psoriasis is a chronic recurring inflammatory disease of the skin, characterised by elevated, discoloured patches. Fish oils have been found to enhance the effects of treatments with UV-light and with drugs, and to decrease side effects from the latter.

Asthma

Asthma is also reported to be increasing in industrialised societies and fish oils have been clearly linked with reductions in its effects. For example, Dr Bipen Patel, a clinical epidemiologist at Cambridge University in the UK, reported to the British Thoracic Society meeting in December 2002 on an investigation of the links between oily fish consumption and asthma-related symptoms. In 770 people, 333 of whom had a history of asthma, there was a clear correlation in that the asthma group had far fewer fish consumers. Dr Patel noted that asthma has become more common in the UK over the past 30 years and that the amount of oily fish in the diet had declined over the same period.

In another example, fish oil supplementation was demonstrated in a joint UK American trial to reduce exercise-induced bronchorestriction (EIB) in elite athletes[xxv]. EIB is a condition suffered by some athletes after intense exercise and not by others. Ten from each group participated in a randomised, double-blind crossover study in which half received fish oil capsules containing 3.2g EPA and 2.2g DHA daily for three weeks. The authors concluded that dietary fish oil supplementation had a markedly protective effect in suppressing EIB.

Asthma is more common in children. A six-country survey of nutrition and respiratory health of children in central and eastern European countries has shown a clear link with the consumption of fish[xxvi]. A total of 20,271 children aged from seven to eleven years were surveyed on respiratory health and food intake. The authors concluded that low fish intake, less than once a month, was the most consistent predictor of poor respiratory health.

The respiratory benefits for children of oily fish consumption probably begin even before birth. Frank Gilliland, professor of preventive medicine at the University of Southern California, reported to the American Thoracic Society in May 2004 on analyses of data drawn from the Children’s Health Study, coupled with further research on maternal diets[xxvii]. Researchers selected 300 asthmatic children and 400 non-asthmatics. The results indicated children born to asthmatic women who had eaten oily fish “at least a few times a month” during pregnancy were 71% less likely to develop asthma by their fifth birthday than those born to similar women who consumed no fish.

Cancer clues

The links between cancer and omega-3 fatty acids are less clear but evidence is being found.

When animals are implanted with human tumours and are fed fish oils, the tumours are fewer, smaller and less likely to spread[xxviii]. When just DHA is fed, tumour growth decreases and tumour cell death increases, provided there is only a low level of linoleic acid in the diet[xxix]. In a study investigating the influence on drug treatments, DHA enhanced the effectiveness of the cancer therapeutic drug doxorubicin[xxx].

A letter to The Lancet in June 2001[xxxi], reported a link observed in the 30-year Health Professionals Follow-up Study, associating fish consumption with reduced prostate cancer in men in Sweden. This was elaborated in 2003 to show men who ate no fish (or less than twice a month) had a two- to three-fold higher frequency of prostate cancer than those who ate fish more than three times a week. The effect is highest with respect to the advanced metastatic form of the cancer. Further analysis of the information, comparing omega-3 fatty acid intake via other dietary sources than fish, showed a positive but weaker correlation, suggesting that the omega-3 fatty acids may not be the only factor in fish contributing to this reduction in risk[xxxii].

In Japan, data on medical history, dietary habits (including fish consumption), smoking and exercise of 5,885 men and women were gathered from 1985 to 1999[xxxiii]. A clear link between fish consumption and lung cancer was found. After figures were adjusted for age, occupation, sex and smoking, households in which fish was consumed three or more times a week had 77% lower risk of lung cancer. It was 57% less where fish was eaten once or twice a week.

The Singapore Chinese prospective health study followed 35,298 women from 1993 to 1998, with a follow up in 2000, and monitored the occurrence of breast cancer. It was 26% lower in the top three quartiles of fish and shellfish consumption (over 44g/day) compared with occurrence in the lowest quartile[xxxiv].

Fish oils may also provide a benefit in lessening cachexia; the severe wasting and weight loss associated with some cancers such as pancreatic cancer. A seven-country study led by the Edinburgh Royal Infirmary, UK, investigated the influence of dietary supplements with and without fish oils on 200 patients with pancreatic cancer. While weight loss stopped in all cases, only the omega-3 fatty-acid-enriched supplement resulted in a net weight gain, lean tissue and improved quality of life[xxxv]. The patients with the omega-3 enriched diets also showed an increase in physical activity[xxxvi].

There is some indication that EPA may reduce the susceptibility of human skin to cancer caused by UV light (photocarcinogenesis). An Australian population-based study compared the diets of 41 women in Brisbane with cutaneous malignant melanoma with those of 297 healthy women from the same community. There was a strong inverse relationship between intakes of polyunsaturated fatty acids and melanoma. The authors concluded the reduction in risk seen among those eating the most fish suggested the effects of marine oils and omega-3 fatty acids deserved specific attention[xxxvii]. In 2003, a study in Manchester, UK, reported more detail of a possible link. Forty-two healthy subjects were given 4g/day of purified EPA for three months. This caused an eight-fold increase in bioavailability in the skin. Sunburn sensitivity and other early markers of skin cancer were reduced by 20–50%[xxxviii].

In 2004 researchers at the Karolinska Insitute in Sweden published a comprehensive review of current knowledge regarding the role of polyunsaturated acids in carcinogenesis. Their conclusion was that the omega-3 fatty acids are protective against the progression of cancers while omega-6 fatty acids, notably arachidonic acid and its derivatives, help promote the growth of cancer. They put forward several specific mechanisms of action for the omega-3 fatty acids[xxxix].

Mental health and development

The old adage that fish is good for the brain has more sense in it than many people realised. There is an increasing amount of evidence that the DHA component of omega-3 fatty acids in oily fish does indeed have a key role in brain function, as suggested by Professor Crawford. Research studies illustrate a wide range of effects.

Dementias now affect nearly half of the western population aged over 80, with Alzheimer’s disease (AD) being a leading and growing cause. There is no cure and its causes are not well understood. Researchers in at the University of Guelph[xl], Canada, have found only low levels of long-chain fatty acids, notably DHA, in people suffering from dementias, including Alzheimer’s. The study looked at 84 people aged 80 and over. Nineteen were diagnosed as having AD, 10 had non-AD dementia, 36 did not have dementia but were cognitively impaired and 19 had normal cognitive functioning. Levels of EPA and DHA were significantly higher in the final group than in those with dementias or cognitive impairment. The Guelph researchers concluded that efforts should be made to increase the intake of fish or fish oils in the population in general and in the elderly in particular.

A prospective study in the US followed 815 people aged over 65 from 1993 to 2000. Initially none had Alzheimer’s disease. During the study period 131 developed the disease. When incidence was compared with diet it was seen that those who consumed fish at least once per week had 60% less risk of developing Alzheimer’s disease than those who consumed it less often or not al all[xli].

Three European studies reinforce these observations. A French team tracked a cohort of 1,674 people aged 68 to 75 for seven years. Participants who ate fish or seafood at least once a week had a 44% lower risk of being diagnosed with dementia than those who ate it less often, and a 31% lower risk of being diagnosed with Alzheimer’s disease[xlii].

The middle aged can also benefit. In the Netherlands, data was extracted from a cross-sectional population-based study among 1,613 people ranging from 45 to 70 years of age. The authors concluded that consumption of fatty fish and omega-3 fatty acids was associated with a reduced risk of impaired cognitive function, whereas consumption of cholesterol and saturated fat was associated with an increased risk[xliii].

Looking for more direct evidence, another team in France used fatty acid levels in red blood cell membranes as a surrogate means of assessing levels in the brain of 246 subjects aged 63–74. These were compared with cognitive status over a four-year period (1995–2000). Those whose cognition declined had significantly lower levels of DHA and EPA and significantly higher levels of omega-6 fatty acids[xliv].

The accumulating evidence has led, for example, to the American Alzheimer’s Association including the following in its dietary recommendations, “Eat more oily fish such as salmon, halibut, trout and tuna. They are rich in beneficial omega-3 fatty acids.”

Depression

One of the first reports to correlate the incidence of depression with the consumption of fish was from a multi-country review led by Joseph Hibbeln at the US National Institutes of Health in Maryland[xlv]. The incidence of major depression per 100 people was recorded from nine countries together with the average consumption of fish.

Typically, a high incidence of depression occurred in those countries with a low consumption of fish. For example, in New Zealand, with fish consumption around 18kg per annum, depression was scored at 5.8%. In Japan, with a fish consumption of 68kg per annum, depression was 0.12%. Since then further evidence has been gathered. A survey of 3,204 residents of Kuopio in Finland revealed that frequent consumers of fish (twice or more a week) were significantly less likely to suffer from depression and suicidal tendencies than those who ate fish less often or not at all[xlvi].

Taking this another step, in the UK researchers administered EPA to 70 depressed patients for 12 weeks. The patients, who had all previously tried conventional treatments such as Prozac, reported improvements with sadness, anxiety and sleeping problems[xlvii]. With respect to the effective dose, relatively low levels, just 1g/day of EPA alone, provided marked improvements. In a similar study, researchers in Israel used the EPA supplement in addition to established anti-depression therapy over a four-week period. The authors reported significant benefits by week three[xlviii]. There also is evidence of DHA involvement in depression.

A study of 247 healthy adults in Greece (Crete) found that mildly depressed individuals had 35% lower levels of DHA in their adipose tissues than participants who had no depressive symptoms[xlix]. However, one study has indicated that DHA alone did no better than placebo at alleviating depressive symptoms[l].

In a Taiwanese study over two months, a daily dosage of 4.4g EPA and 2.2g DHA alleviated depression in patients for whom antidepressants were not working[li].

Depression is a significant problem with women just after giving birth; the baby blues. Because of the emerging body of information showing that DHA in particular is important for the development of the child’s brain, the possibility that a depletion of DHA in the mother may be associated with the depression has been widely investigated. In 2002 Joseph Hibbeln reported on a study of 14,541 pregnancies in published results from 23 countries. Both lower DHA content in mothers’ milk and lower seafood consumption were associated with higher rates of postpartum depression[lii].

Investigators in the Netherlands reported in 2003 that the levels of available DHA were measured in 112 women at the time of delivery and 32 weeks later. The levels were significantly lower in those mothers assessed to be “possibly depressed” than in the non-depressed group. The authors suggested, “increasing dietary DHA during pregnancy and post-partum seems prudent”[liii].

Bipolar disorder

Bipolar disorder (previously known as manic depression) has increased dramatically in its rate of incidence over the past century, by as much as 100%. It is, however, rare in fish-eating societies such as Japan, Korea, Malaysia and Taiwan. One may also plot a decline in fish consumption in the average Western diet over that same 100-year period. Joseph Hibbeln has surveyed the evidence from multiple countries relating the occurrence of bipolar disorders to seafood consumption[liv]. The authors concluded that the data show a robust correlation between greater seafood consumption and lower prevalence of bipolar disorders.

In a study carried out at the Harvard Medical School[lv], 30 patients suffering from bipolar disorder were split into two groups and one group was given EPA and DHA in daily fish oil supplement and the other was given a placebo. Twelve of the 14 patients in the fish-oil group completed the four-month study without major episodes of mania or depression, compared with only six of the 16 in the placebo group. Nine members of the placebo group experienced a worsening of their condition; none of the fish oil group did.

Anorexia nervosa

Of all psychiatric disorders, anorexia nervosa carries the highest risk of morbidity and mortality. The nature of the condition, usually occurring in adolescents, is characterised by self-induced starvation. In the typical western diet, where omega-3 fatty acid is already very low, this can lead to serious deficiencies of these essential nutrients.

Researchers in the UK explored the possibility that the low success rate with re-feeding programmes may be because they do not take the lack of omega-3 fatty acids into consideration. In an initial trial, seven patients were provided with ethyl-EPA supplements (1g/day) and were followed for three months. Three recovered and the other four improved[lvi]. In one case report from the group, a 15-year old girl who was suffering so severely that she had to be detained under the Mental Health Act, was given the supplement, together with micronutrients to correct a diagnosed imbalance. Within a few weeks improvements were clear. At the end of three months she could take responsibility for her own diet. Her abnormal attitude to her weight and shape had disappeared and she took an interest in her environment and future. At this point she was discharged to return home, where she took on a summer job and enrolled in college for the next term[lvii].

Schizophrenia

Schizophrenia is an even more complex area. Current understanding suggests there must be a genetic predisposition involving several genes for the disease to develop. Even so, omega-3 fatty acids do appear to play a role. Researchers at the Imperial College of Medicine in London, UK, reported on the case of a 30-year old man who had suffered from schizophrenia for ten years[lviii]. He had hallucinations at least daily and suffered from persecutory delusions and thought disorder. He was put on 2g/day of EPA. After six months he was showing an 85% reduction in schizophrenia severity. Delusions were eliminated and there was an 88% reduction in hallucinatory episodes.

In India, 28 male and female schizophrenic patients who were taking medication were given low-dose supplements of omega-3 fatty acids (600mg/day) together with vitamins C and E. In a pre-treatment assessment in comparison with a control group of normal people of similar age, the patients had significantly lower levels of DHA and EPA in their red blood cell membranes; a measure of its availability in the body. After four months the levels in the patients had risen significantly compared with the controls. The patients also had significantly improved psychiatric ratings and quality of life ratings[lix].

Aggression

A study in Japan[lx] that was published in 1996 showed students consuming fish oil had reduced tendencies to become aggressive under stress, in comparison with non-fish oil consumers.

More recently, in 2004, information emerged from an observational study begun in New York in the 1990s. The information on hostility among 3,581 urban white and black young adults again showed a link with fish consumption. Low fish consumption correlated with the higher levels of hostility[lxi].

Similarly, in the UK, dietary supplements with vitamins and fish oils were given to young prisoners in a maximum security institution. The prisoners were aged 18–21 and typically serving long sentences for serious offences. A group of 231 was divided into those given supplements (1260mg linoleic acid, 80mg gamma linoleic acid, 80mg EPA and 44mg DHA) and others receiving placebo for 142 days. Participants receiving the supplements became 26% less likely to be reported for antisocial behaviour than the control group[lxii].

In Boston, women suffering borderline personality disorder were recruited to an eight-week trial using supplementation with ethyl EPA or placebo. Those taking ethyl-EPA experienced a significant decrease in aggression as well as diminished symptoms of depression[lxiii].

Behaviour and learning difficulties in children

Turning to the mental well being of children, it seems that problems such as attention-deficit hyperactivity disorder (ADHD), dyslexia and similar problems are on the increase in western society. It is now estimated that 3–5% of school-age Americans suffer from ADHD and 10% in the US and UK suffer from dyslexia to some extent. A link between these problems and essential fatty acids was suggested some 15 years ago.

Research indicates a sub-clinical deficiency of DHA is the key in ADHD[lxiv], and DHA deficiency has also been linked with dyslexia and dyspraxia[lxv]. Dr Alexandra Richardson of the University Laboratory of Physiology, Oxford has reviewed the clinical trial data available to date[lxvi]. A typical example is her work reported in 2002, where, in a school-based study, 41 dyslexic children with ADHD features were given either fish oil (with some evening primrose oil) or placebo for three months. The children receiving supplement showed significant reductions in a range of ADHD symptoms, particularly cognitive problems. In a second stage, the placebo group were switched to the supplement, without their knowledge. After three months, they showed similar improvements[lxvii].

In the 2004 review, Richardson concluded the current evidence suggests that omega-3 fatty acids, and EPA in particular, may be of benefit in the management of common neurodevelopmental conditions such as dyslexia, dyspraxia and ADHD. She also reports that a similar rationale exists for fatty acid treatment in autistic spectrum disorders. At the time of writing the first trials are underway.

Natural development

As the FAO indicates on its web site, fish is much more than an alternative source of animal protein. Fish oils in fatty fish are the richest source of a type of fat that is vital to normal brain development in unborn babies and in infants. Without adequate amounts of these fatty acids, normal brain development does not take place. Again, the evidence to support this assessment of the importance of omega-3 fatty acids is accumulating.

Investigators in Dundee[lxviii] in the UK studied the effect of DHA on the problem solving capabilities of infants. For a period of four months 23 children were fed infant formula (baby milk) supplemented with DHA (0.15–0.25g/100g fat in the formula) and 21 were fed the formula without. At the end of the trial, the children, then aged ten months, were given a problem to solve. This involved removing a barrier and cover to find a toy. The DHA group solved the problem faster and more often than their non-DHA counterparts.

In Norway, investigators have shown that benefits in IQ ratings, relating to DHA during later pregnancy and lactation, are still present at four years of age[lxix].

Other work has demonstrated enhanced sleep patterns suggesting greater maturity of the central nervous system in infants whose mothers had higher DHA levels during pregnancy[lxx]. Visual function also has clearly been related to DHA levels in pregnancy[lxxi].

Further benefits

Benefits associated with fish consumption and unsaturated fats such as the omega-3 fatty acids continue to grow in number. Four examples unrelated to the above groups cover gallstones, osteoporosis, weight loss and premature birth.

Data gathered in the Health Professional Follow-up Study in the US provides an indication that there is a long-term relationship in an energy-balanced diet between the consumption of unsaturated fats (both mono- and polyunsaturated, which includes the omega-3 fatty acids) and a reduced risk of gallstones. The data is drawn from a 14-year follow-up of 45,756 men aged 40 to 75 in 1986 and free of gallstones. In that time 2,323 new cases were diagnosed[lxxii].

With respect to osteoporosis, a condition related to reduced bone mass, studies suggest that omega-3 fatty acids such as EPA help increase levels of calcium in the body, deposition of calcium in the bones, and improvement in bone strength[lxxiii]. In addition, studies also show that people who are deficient in certain essential fatty acids (particularly EPA and gamma-linolenic acid [GLA], an omega-6 fatty acid) are more likely to suffer from bone loss than those with normal levels of these fatty acids. In a study of women aged over 65 and with osteoporosis, those who given EPA and GLA supplements experienced significantly less bone loss over three years than those who were given a placebo. Many of these women also experienced an increase in bone density[lxxiv].

Research using animal models at the Charles University in Prague indicates that omega-3 fatty acids of marine origin and rich in DHA increase the oxidation of fat in the body and reduce the number of fat cells[lxxv]. This approach to aiding weight loss has been tested in a pilot study that was presented at the North American Association for Study of Obesity annual meeting in November 2004. Twenty women with severe obesity, body mass index (BMI) over 40, and already on a very low calorie diet were given the same DHA-rich omega-3 supplement used in Prague or placebo. After three weeks the group given the supplement had lost 20 percent more weight than those in the control group and BMIs were down by as much as 15%[lxxvi].

Low consumption of fish in early pregnancy was linked with higher risks of preterm delivery and low birth weight in a Danish study of 8,700 pregnant women. Those that said they ate no fish were three times more likely to have a preterm delivery than the fish eaters[lxxvii].

Optimising diets

At the time the findings on the importance of DHA and EPA began to emerge, there was a strong move in the world of nutrition to encourage a reduction of fats in the diet, to counter the rising incidence of heart disease. In general this worked, but it was perhaps a case of throwing out the baby with the bathwater as the role of EPA and DHA was, for a while, ignored.

To return to an optimum presence of omega-3 fatty acids in the diet, the Western population must reverse that trend. This can be achieved most conveniently through the consumption of more oily fish. However, it is clear the wild catch cannot sustainably meet an increasing demand. As the FAO has observed, the gap between the wild harvest and a growing demand can only be met in the long term through the output of aquaculture. The need for oily fish will be satisfied mainly through the farming of Atlantic salmon, which are particularly well suited to aquaculture, to provide a reliable supply of consistent, safe, healthy and appetising food.

A clear conclusion from this collection of studies, and many others pointing the same way, is that if you wish to stay as fit and alert as nature intended, make oily fish a regular part of your balanced diet.

Graham Look, Nutreco Tel +32 9 223 2382 Mobile +32 495 526766

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