“The family of long-chain omega-3 polyunsaturated fatty acids (LC n-3 PUFA) are comprised of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA), which are all derived from alpha-linolenic acid(ALA). While the ratios of these vary depending on the food source, DPA is typically less prevalent than EPA and DHA. Metabolically, ALA can be converted to EPA in humans, but conversion to DHA is inefficient. This is why it is important to obtain LC n-3 PUFA direct from dietary sources. Seafood is the richest natural source of LC n-3 PUFA, although other sources include human milk, marine algae, marine mammals and krill. Unfortunately, mean UK intakes of oily fish are well below guidelines, with older adults aged over 65 years eating just 85 g per week instead of 140 g (1). For these reasons, food supplements and enriched foods can be important sources of LC n-3 PUFA (2). Currently, mean intakes of EPA + DHA in Europe range from 127 to 1,278 mg per day, when foods and supplements are taken together (3). In the UK, this figure is only 410 mg per day in people aged 65 years and over, with lower amounts in younger people. More recently, the European Food Safety Authority (EFSA) advised that long-term intakes of up to 5.0 g per day EPA + DHA from supple- ments and up to 1.8 g per day of EPA alone from supplements were safe for adults (3).
Cardiovascular (CV) disease is one of the leading causes of death worldwide. LC n-3 PUFA consumption is viewed as protective, an effect most likely due to reductions in triacylglycerol (TAG) concentrations, improv- ed plaque stability and anti-thrombotic or anti-arrhythmic effects (4). This is supported by good evidence, with one meta-analysis of 47 randomized controlled trials (RCTs) finding that fish oils (average intake of 3.25 g EPA and/or DHA per day) significantly reduced TAG levels in patients with high lipid levels (5). Similarly, a RCT on 40 healthy 51- to 72-year-olds found that 3.0 g per day fish oil significantly reduced TAG levels and systolic blood pressure (6). Finally,a US cohort of 2,692 adults (mean age 74 years) found that increased individual and total LC n-3 PUFA levels were significantly associated with decreased mortality, especially CHD-related death (7). Several meta-analyses considering the effects of LC n-3 PUFA on other markers of CV health have generated mixed results. A number of factors may have influenced the data, e.g. 1) different levels of omega-3 fatty acid red blood cell levels at baseline, 2) variations in the source, type, combination and dose of omega-3 fatty acids, 3) differences in patients groups, i.e., primary vs. secondary prevention trials and 4) the inclusion of different quality studies within meta-analyses. Considering this, LC n-3 PUFA, at higher levels of intake and from fish oils appear to be effective for improving markers of heart health.
In terms of clinical guidelines, EFSA advise that intakes of 0.25 to 0.5 g/day of EPA + DHA may exert cardio- protective effects, while the International Society for the Study of Fatty Acids and Lipids recommends that at least 0.5 g/ day EPA + DHA should be consumed to support CV health. The American Heart Association advises 1.0 g per day of EPA + DHA per day for patients diagnosed with coronary heart diseases and a supplement of 2.0–4.0 g/day of EPA + DHA for patients with raised triglycerides. Two heart health claims were approved by the European Commission (8): DHA/EPA contribute to the maintenance of normal blood triglyceride levels and normal blood pressure. Maintaining optimal cognitive health is central to healthy ageing. As with heart health, different omega-3 fatty acids may have distinct but complementary roles in the brain (9). A systematic review (10), which included 14 studies, mainly epidemiological, found that diets with a higher omega-6:omega-3 ratio were associated with an increased risk of cognitive decline and dementia. The beneficial role of omega-3 fats may be because DHA is a major component of brain phospholipids and helps to regulate the uptake of brain glucose, ion transport, signal transmission, neurotransmitter release (and uptake) and the sequestration of free radicals, preventing oxidative stress (9). In addition, ALA is thought to support the production of ketone bodies and EPA the oxidation of fatty acids, both of which are central to providing a supply of brain glucose. The OPAL study of healthy elderly found that higher fish intakes at baseline were associated with better cognitive function (11). Equally, a five-week RCT of 40 healthy middle-aged and elderly subjects revealed that supple- mentation with fish oil (3 g LC n-3 PUFA per day) significantly improved working memory (6). Some but not all studies on the management of cognitive dysfunctions – such as dementia, Alzheimer’s disease and de- pression – have shown benefits of increased intakes of DHA+EPA (12-14). Overall, there seem to be cogni- tive benefits for omega-3 fatty acids but study results are varied, possibly due to recruitment of healthy participants, poor retention, failure to screen for low baseline LC n-3 PUFA status, different doses and ratios of EPA/DHA and inappropriate study size or duration. In conclusion, there is good evidence that LC n-3 PUFA can help to support heart health and cognitive func- tion. Unfortunately, LC n-3 PUFA and their main natural source, oily fish, are under-consumed by most people. Dietitians can play an important role in helping older people to meet LC n-3 PUFA intake recommen- dations by encouraging oily fish consumption and by providing impartial advice about fish oil supplements.”