THE DIET of our ancestors, as is often the case,

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1 Dr Carrie Ruxton BSc, PhD, is a freelance dietician and registered public health nutritionist. Contact: Online archive For related articles and author guidelines visit our online archive at: and search using the key words below. Key words Children: development Heart disease Mental health Nutrition These key words are based on the subject headings from the British Nursing Index. This article has been subject to double-blind review. Health benefits of omega-3 fatty acids Ruxton C (2004) Health benefits of omega-3 fatty acids. Nursing Standard. 18, 48, Date of acceptance: July Summary Evidence suggests that omega-3 polyunsaturated fatty acids play an integral role in cell membrane function and development of the brain and eyes. Optimising intake appears to confer many benefits, including reduced risk of heart disease and possibly a reduced likelihood of behavioural problems, depression and inflammatory conditions such as rheumatoid arthritis. Although there is some disagreement on what level of intake is optimal, British diets are low in omega-3 fatty acids. Good sources include oily fish and novel sources include fortified eggs and oils derived from microalgae. THE DIET of our ancestors, as is often the case, can teach us a lesson about modern nutrition. Palaeontologists suspect that early man consumed a diet rich in marine foods, with women gathering shellfish and sharing their catch with the children of the community (Crawford 1992). It is thus a coincidence that most abundant fatty acids in marine foods, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), are key components of our eyes and brain, and are particularly important during infant development (Ruxton et al 2004). EPA and DHA are parts of a family of polyunsaturated fatty acids called omega-3 (or sometimes n- 3). Table 1 summarises the key types of dietary fatty acids. The array of fatty acids and the terminology that applies to them can be daunting. A simple approach is to look at their chemical structure. All fats, and their constituent fatty acids, are made up of an even-numbered chain of carbon atoms with hydrogen and oxygen molecules tacked on to the sides. Those fatty acids with only single bonds between the carbon atoms are called saturated fatty acids. They tend to be solid at room temperature, for example, butter or meat fat. Fatty acids with one double bond in the carbon chain (C=C) are called unsaturated, while those with two or more double bonds are called polyunsaturated. Unsaturated and polyunsaturated fatty acids tend to be liquid at room temperature, for example, olive oil or sunflower oil. Their fluidity makes them useful in human cells where flexible membranes are vital for the transport of oxygen, glucose and other molecules around the body (Yehuda et al 1999). Foods normally contain a mixture of different types of fatty acids with one type dominating the mix. The polyunsaturates alpha-linolenic acid (ALA), arachidonic acid (AA) and linoleic acid are essential fatty acids because they cannot be made in the body and must be obtained in the diet. ALA can be used as a precursor in the body to create EPA and DHA, but the latter process is ineffective in preterm babies. Although DHA is not an essential fatty acid, the inefficiency of its synthesis from ALA combined with its role in fetal and infant development make it an important nutrient during pregnancy, lactation and infanthood (SACN 2004). Dietary sources As Table 1 shows, the dietary sources of omega-3 fatty acids vary for ALA, DHA or EPA. ALA is a key component of dark green leafy vegetables, such as broccoli, cabbage and spinach (Thomas and Jefferson 2001). It is also found in abundance in seed oils, meats and cereal products (Table 1). Until recently, DHA and EPA have only been found in animal products, particularly oil-rich fish such as tuna, salmon and trout, animal offal and game meats but food technology has progressed to the stage where microalgae called Crypthecodinium cohnii, which are rich in DHA, can be harvested for their fatty acids. This opens up the benefits of DHA and EPA to vegetarians and those who prefer not to eat fish. Although oily fish are a rich source of omega-3 fatty acids, tinned varieties, particularly tuna, lose much of their natural oils during processing (Ruxton et al 2004). Some products detail the omega-3 content on the nutrition label. Other good sources are eggs produced by chickens which have been fed omega-3-rich diets and supplements based on fish oils not fish liver oils or algae-derived omega- 3 fatty acids. Game meats tend to be higher in omega-3 fatty acids than domesticated meats, and plant sources include linseeds and walnuts and their oils although only a small amount of their ALA is converted in the body to the more useful DHA and EPA (SACN 2004). Table 2 shows the DHA and EPA content of a range of foods. Intake of omega-3 fatty acids Over the past few decades, the balance of fatty acids in the diet has shifted away from omega-3s 38 nursing standard august 11/vol18/no48/2004

2 towards omega-6s. These are polyunsaturates, derived from the essential fatty acid, linoleic acid, which differ from omega-3s in their metabolic effects (Table 1). Explanations for this could include: Changing farming practices have resulted in domesticated animal flesh being less rich in omega-3 fatty acids. The rising cost of oil-rich fish makes it a luxury rather than a staple food. Developments in food technology have brought a huge array of omega-6 sunflower and soybean oil products. Misplaced nutrition advice has encouraged preference for omega-6 products rather than oil-rich fish. Intake of EPA and DHA in the UK and other developed countries has been falling steadily over the past couple of decades (Sanders 2000). Makrides et al (1995) studied the fatty acid composition of breast milk in Australian women between 1981 and 1994 and found that DHA levels had fallen from 0.32 per cent to 0.21 per cent, while omega-6 levels had increased from 11 per cent to 14 per cent. The shift towards omega-6 fatty acids was blamed on increased intake of vegetable oils rich in linoleic acid combined with decreased oily fish intake. Similarly, in the UK DHA levels in breast milk have steadily fallen over the past 30 years (Sanders 2000). Some nutrition scientists believe the rise in chronic diseases, such as coronary heart disease, rheumatoid arthritis, certain cancers and dementia could be linked to escalating intakes of omega-6 fatty acids (Thomas and Jefferson 2001). In countries where the prevalence of these diseases is low, for example Japan, the ratio between omega-6 and omega-3 fatty acids is around 4:1 (Simopoulos 2001). By comparison, in the US, where the prevalence of chronic disease is high, the ratio between omega-6 and omega-3 fatty acids is around 17:1. The UK has a middling figure of 6:1 (BNF 1999), but this is increasing in favour of omega-6 fatty acids, no doubt because only a third of British adults eat oily fish on a regular basis (BNF 1999). Recommendations for omega-3 fatty acids In 1994, the Department of Health published a report on heart disease risk which mentioned the beneficial impact of fish oils and their constituent omega-3s. The 1994 recommendation of 220mg per day EPA + DHA has recently been superseded by FSA advice on fish intakes. The new advice (SACN 2004) recommends that people eat one to four oilrich fish meals a week, while pregnant and lactating women should restrict their intake to one or two. This translates to a daily recommendation of 450mg to 900mg EPA + DHA. The restriction on pregnant and lactating women is designed to prevent high intakes of contaminants such as dioxins, polychlorinated biphenyls (PCBs) and mercury, known Table 1. Key dietary fatty acids Family Examples Dietary sources Saturated no Stearic acid Meat double bonds Palmitic acid Coconut oil Monounsaturated Oleic acid Olive oil, omega-9 (n-9) rapeseed oil one double bond Polyunsaturated Linoleic acid Sunflower, soya, omega-6 (n-6) sesame and rape seed oils more than one Arachidonic acid Lean meats, offal, double bond poultry Polyunsaturated Alpha-linolenic acid Green leafy omega-3 (n-3) vegetables, the oils of more than one flaxseed, linseed, double bond rapeseed and soya, some meats and cereal products Eicosapentaenoic acid Tuna, salmon, trout, fish oil, animal liver Docosahexaenoic acid As above but also fortified products made from vegetarian algae docosahexaenoic acid Eggs from chickens fed an omega-3-rich diet (Thomas and Jefferson 2001) to be present in some fish stocks. Marlin, swordfish and shark the most commonly contaminated should be avoided by these women, while tuna should be restricted to once a week. It is worth noting that the DHA and EPA sources used in fortified products are sourced from microalgae or purified tuna oil and, thus, are contaminant-free. These foods could provide an alternative omega-3 source for women. Other respected bodies have made recommendations about omega-3 intakes. BNF (1992) recommended 1,140mg a day for women and 1,400mg a day for men. The International Society for the Study of Fatty Acids and Lipids suggests that a minimum of 500mg a day should be consumed for cardiovascular health (ISSFAL 2004). Role in the body during development The fluidity of omega-3 fatty acids has already been described. This makes them an ideal building block for cell walls whose job is to regulate the transport of oxygen and nutrients across cell membranes. Two major areas where omega-3 fatty acids, particularly DHA, play a role are in brain and eye function. DHA accounts for 25 per cent of the phospholipids present in cerebral grey matter, where it supports neural activity and learning (Ruxton et al 2004). august 11/vol18/no48/2004 nursing standard 39

3 Table 2. Some key food sources of docosahexaenoic acid and eicosapentaenoic acid Food Average docosahexaenoic Average eicosapentaenoic acid per serving* (mg) acid per serving* (mg) Cod Haddock Mackerel 1,700 1,136 Canned salmon Fresh salmon 1, Trout Sardines Prawns Canned tuna in oil Fresh tuna 1, Fortified eggs 150 per egg 0 Cod liver oil (1 teaspoon = 5ml) *Average serving sizes: 80g-120g DHA also accounts for 50 per cent of the total fatty acid content in the retina, where it probably maintains the normal functioning of photoreceptor cells (Giusto et al 2000). Omega-3 fatty acids are critical during fetal development, particularly in the third trimester of pregnancy when fetal DHA requirements reach their maximum (SACN 2004). Women with low omega- 3 stores, perhaps due to multiple pregnancies or a vegetarian diet, can pass on this suboptimal status to their newborns (Otto et al 1997). By comparison, women who consume more omega-3 fatty acids during pregnancy can enhance maternal DHA status, potentially benefiting the fetus. Connor et al (1996) reported that pregnant women who consumed regular amounts of sardines or fish oil increased their own plasma DHA levels and transferred additional DHA to their fetuses. It is also known that a good maternal DHA status can delay birth by about six days and increase birth weight, both potentially beneficial for the baby (Smuts et al 2003). Premature babies lack the ability to synthesise DHA (Clandinin et al 1981). Early formula milks used to sustain premature babies were lacking in DHA and AA a derivative of the omega-6 linoleic acid key components of breast milk. This was only discovered when researchers compared learning and eye function in breastfed premature babies with that of babies fed formula milks (O Connor et al 2001). The breastfed babies, who were receiving a natural source of DHA and AA, performed much better in tests of visual acuity and basic learning. DHA and AA are now added routinely to specialist preterm formula milk, and to many formulas marketed for term babies. Omega-3 supplementation and brain and eye function If low intakes of omega-3 fatty acids during pregnancy can theoretically have an impact on development, can high intakes confer benefits to the fetus? Jørgensen et al (2001) examined oily fish consumption in pregnant women and found that the infants of high-fish consumers had better visual acuity than the infants of low-fish consumers. Two randomised controlled trials of low-dose omega-3 supplementation during pregnancy found no effect on cognitive function at age four and seven years (Bakker et al 2003, Ghys et al 2002). However, a longer-term study by Helland et al (2003) found a relationship between omega-3 supplementation of mothers during their third trimester of pregnancy and child IQ at age four. This finding needs to be confirmed by other studies. In older children, some studies of omega-3 supplementation have found benefits for children with behavioural problems, for example, attention deficit hyperactivity disorder (ADHD) (Richardson and Puri 2000), while others have found no significant effect (Voigt et al 2001). Omega-3 fatty acids and heart disease The lower rate of heart disease in ethnic groups who traditionally consume higher amounts of fish (Dewailly et al 2003) prompted researchers to investigate whether dietary components were responsible. Hu et al (2002) followed 84,688 women enrolled in the Nurses Health Study for 16 years. Coronary deaths were 50 per cent lower in women who ate fish five times per week compared with women who did not eat fish. Even a once-a-month fish meal was related to a 20 per cent reduction in cardiovascular events. When women with diabetes were considered, the protective effect of fish was even stronger (Hu et al 2003). A Cochrane review found that omega-3 fatty acids lower triglycerides in people with type 2 diabetes (Farmer et al 2004), and this is likely to be an important mechanism for heart disease risk reduction. Stronger evidence of the health benefits for the heart of omega-3 fatty acids was provided by intervention studies using dietary means extra fish meals and supplementation of DHA and EPA, for example, the famous DART study (Burr et al 1989). A meta-analysis of 11 high-quality intervention studies involving a total of 7,951 patients in the intervention groups concluded that omega- 3 fatty acids can reduce overall mortality, mortal- 40 nursing standard august 11/vol18/no48/2004

4 ity due to myocardial infarction (MI), and sudden death in patients with coronary heart disease (Bucher et al 2002). When comparing the relative benefits for different types of patients, Bucher et al calculated that patients who had previously had an MI could benefit about 10 times more than lower-risk patients. It is now well accepted that EPA and DHA have a favourable impact on heart disease risk by reducing platelet aggregation, reducing triglycerides and by having an anti-inflammatory effect. The major European and American heart foundations have now incorporated advice to include regular fish meals in their recommendations (for more information see Krauss et al 2000 and Second Joint Task Force of European and Other Societies on Coronary Prevention 1998). Inflammatory conditions Recently, it has been suggested that omega-3 fatty acids may control or prevent inflammatory conditions, such as asthma, cystic fibrosis and inflammatory bowel disease. While individual studies show promising effects, systematic reviews do not back routine supplementation with omega-3 fatty acids in patients with these conditions because of the lack of randomised trials. The Cochrane review on asthma (Thien et al 2004) commented that, since no adverse effects of increased omega-3 intake were found, it would be safe for patients with asthma to try fish oil supplementation alongside conventional therapy. A more promising area is the management of rheumatoid arthritis (RA), for which good evidence on omega-3 fatty acids exists. Fortin et al (1995) conducted a meta-analysis of 10 clinical trials of fish oil supplementation in RA, representing 395 patients in control and intervention groups. While no effect was seen on indices of disease activity or progression of RA, there was a significant reduction in the number of tender joints and in duration of morning stiffness after three months of therapy. Similar findings and a reduction in use of non-steroidal antiinflammatory drugs (NSAIDs) were reported by a review of 14 clinical trials on omega-3 use in patients with RA (Cleland et al 2003). Omega-3 fatty acids, mental function and mood Research has linked lower intakes of omega-3 fatty acids with mental ill-health. Epidemiological studies have found that countries with a high fish consumption tend to have a low prevalence of major depression (Hibbeln 1998). Adams et al (1996) also observed a relationship between low blood DHA in depressed patients and severity of symptoms. More convincing evidence comes from the use of omega-3 supplementation in cases of depression. Although research is limited at present, these studies, such as Stoll et al (1999) suggest that high doses of EPA and DHA can reduce symptoms in patients who have clinical or manic depression. The Food Standards Agency (FSA) is currently funding a large trial of fish oil supplementation in England to gauge the benefits for people with depression (FSA 2004a). Just as the increasing prevalence of depression might be linked to low oily fish consumption, the same may be said for dementia, a condition on the rise in Western countries. Large epidemiological studies, such as that by Kalmijn et al (1997), have identified fish consumption as a potential protective factor against this disabling condition. In a prospective study of 5,386 Dutch citizens aged 55 or older, those who ate two moderate portions of oil-rich fish a week had a reduced risk of cognitive impairment, cognitive decline, dementia and Alzheimer s disease. A more recent study found a strong inverse link between fish intake and Alzheimer s disease (Morris et al 2003). Older people who ate oil-rich fish at least once a week had a 60 per cent lower risk of developing the disease over a fouryear period. Plasma studies also support the link between low omega-3 fatty acid intake and dementia. Conquer et al (2000) found lower levels of plasma phospholipid DHA in patients with Alzheimer s disease and other dementias, while Heude et al (2003) found that older people with high plasma omega-6 and low plasma omega-3 levels were most likely to experience cognitive decline over a four-year period. Intervention studies attempting to lower dementia risk with fish oil supplementation are scarce and need to be performed to exploit this promising area of preventive medicine. How to use omega-3 fatty acids in practice The new FSA guidelines on oil-rich fish consumption were mentioned previously (SACN 2004). These would translate into an intake of 450mg to 900mg EPA + DHA per day, with pregnant women at the lower end due to concerns about fish contamination. However, there is debate about whether this level is high enough to provide an optimal intake for the population as a whole, and particularly for certain subgroups. Research suggests that higher omega-3 intakes could benefit pregnant women, infants, and people with heart disease or RA. However, the FSA currently advises pregnant and lactating women and young children to limit oilrich fish consumption. This limits the benefit that these vulnerable groups can gain from DHA. The FSA states that there is no reason to avoid eating Scottish farmed salmon or any other salmon. Research carried out by the FSA has shown no significant difference in levels of contaminants between farmed and wild salmon from the UK. It is carrying out further research in this area (FSA 2004b). Other sources of DHA, such as cod liver oil and liver, are not recommended because their vitamin A content could be teratogenic. august 11/vol18/no48/2004 nursing standard 41

5 Nurses have a role to play in stressing the importance of DHA intake in pregnancy and suggesting safe alternatives to these foods. These could include salmon, trout, sardines and products fortified with DHA from microalgae or tuna oil. Note that the high intakes of omega-3 fatty acids suggested for conditions such as RA will be difficult to obtain from food sources, but it is important to encourage obtaining these nutrients by eating a healthy balanced diet. It is unwise to suggest supplementation because research is not conclusive. Instead, nurses should refer patients to a suitably qualified dietician or nutritionist. People considering very high intakes of these fats should consult their doctor about the possible interaction with medications because high intakes can increase clotting times. Another factor to consider is the increased requirement for antioxidant vitamins because polyunsaturated fats, such as omega- 3 fatty acids, are particularly susceptible to oxidation (Thomas and Jefferson 2001). A good intake of vitamin C can be obtained from citrus fruits and juices, melons, tomatoes and peppers, while vitamin E can be obtained from sources such as wheatgerm oil. Conclusion The British diet is known to be low in omega-3 polyunsaturated acids, however there are many health benefits to be gained from their consumption. Nurses can play an important role in encouraging their intake in appropriate patients REFERENCES Adams P et al (1996) Arachidonic acid to eicosapentaenoic acid ratio in blood correlates positively with clinical symptoms of depression. Lipids. 31, Suppl, S157-S161. Bakker E et al (2003) Long-chain polyunsaturated fatty acids at birth and cognitive function at 7 y of age. 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