Key learning points
- The role of different fatty acids in the body
- Intakes, recommendations and authorised health claims
- Evidence for benefit during pregnancy and early life
Fatty acids, such as omega-3 polyunsaturated fatty acids (LCn3FA), have a proven role in foetal development, but the main dietary source, oily fish, is under-consumed in the UK and use of supplements is fairly low. While pregnant women appear to demonstrate good awareness of the benefits of oily fish and LCn3FA,1 much of their information is sourced from the media rather than from healthcare professionals (HCPs) perhaps leading to misconceptions about appropriate sources during pregnancy and their safety. This article will examine the evidence for consumption of LCn3FA and other fatty acids during pregnancy and early life, and will explore the role of HCPs in delivering practical advice to women.
FATTY ACIDS AND SOURCES
The fatty acid ‘family’ is made up of several branches as shown in Figure 1. Both monounsaturated and polyunsaturated fatty acids (PUFA) are viewed by health experts as healthier choices than saturated fatty acids. Key examples of beneficial fatty acids are the essential fatty acids linoleic acid (LA) found in vegetable oils and nuts and alpha-linolenic acid (ALA) found in nuts and seeds, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), found in oily fish, seafood and dietary supplements. Small amounts of LCn3FA are also found in meat, offal and eggs.
Fatty acids are an essential part of human cell membranes and are particularly important during pregnancy when foetal tissue is being formed. The brain and retina have the largest requirements for fatty acids, particularly DHA and n6 arachidonic acid, during the last trimester of pregnancy. Deficiency studies in experimental animals, and observational studies on premature infants fed low- LCn3FA formula milks, have concluded that adequate levels of LCn3FA in early life are vital for the normal development of eyesight, brain development and learning.
Health benefits for women
There may be mental health advantages for women consuming high intakes of oily fish and/or LCn3FA during pregnancy. A UK survey of 9,530 pregnant women2 found a 50% lower risk of anxiety symptoms in those who consumed at least 1.5g LCn3FA weekly from seafood compared with women who ate no seafood. Other surveys have reported associations between peri-natal depression and low intakes of oily fish.3,4
However, intervention trials during pregnancy have produced conflicting results. A recent meta-analysis5 combined the effects of seven randomised controlled trials (RCTs) but found no significant impact on symptoms of post-natal depression when LCn3FA supplements were given, although there was evidence of efficacy in a subgroup of women with major depression. The lack of consistent findings could be due to small sample sizes, the relatively low LCn3FA content of the supplements, and the ratio between EPA and DHA. Interestingly, a meta-analysis6 based on 28 RCTs in non-pregnant populations, found that high EPA supplements appeared more effective at reducing symptoms of depression than high DHA supplements. Clearly, further evidence from larger RCTs is needed to determine whether LCn3FA supplementation have a role in managing perinatal depression.
Health benefits for infants
Much interest has focussed on the role of maternal fish or LCn3FA intake in programming foetal development, particularly in relation to brain, eye and immune function. There is now a large body of evidence indicating positive findings, especially for immune function where several studies have reported a link between low fish consumption in pregnancy and increased risk of childhood allergic disease.7 Relevant RCTs are summarised in Table 1 and suggest good results for at risk infants, ie. those born to mothers who themselves have allergic conditions. The mechanism probably relates to the anti-inflammatory properties of LCn3FA compared with other fatty acids.
Less consistency has been seen in studies of maternal supplementation and infant cognitive function, although individual studies suggest promising results. For example, one RCT found a significant increase in mental processing in children at age four years when their mothers were supplemented with 2g EPA + DHA daily from 18 weeks gestation until three months after delivery.12 Others have reported benefits in neurodevelopmental tests following maternal DHA supplementation, or positive associations between maternal DHA status and cognitive function in young children.13 However, a recent meta-analysis on 11 large RCTs14 was unable to draw any firm conclusions on whether LCn3FA supplementation during pregnancy influences child cognitive and visual development due to study limitations, although it was noted that two RCTs showed significantly better cognitive scores in children aged two to five years when mothers had consumed additional LCn3FA. The inconsistent findings could be due to differences in baseline maternal fatty acid status, dosage and compliance. A practical approach would be to assume that LCn3FA can offer benefit to individuals, particularly by reducing the risk of allergic disease, and is a low risk intervention when supplemental intakes are below 2.7g EPA + DHA.
In the 12 months following delivery, infants grow rapidly and retain their high reliance on fatty acids for building new cell structures, particularly in the brain. This has been recognised by expert bodies which recommend that formula-fed infants receive 0.2-0.5% of their total fat from DHA; breast-fed infants would obtain sufficient levels from breast milk as long as their mothers are consuming 0.2g DHA daily.15 In addition, several health claims for DHA-rich infant products have been authorised in Europe as shown in Table 2.
Recommendations and intakes
Fatty acid targets in the UK are expressed in several ways. PUFAs should provide 6.5% of energy on average (currently 5%) while monounsaturated fatty acids should provide 12% of energy (currently 12%). Saturated fats should provide no more than 10% of energy (currently 13%). Targets for fish consumption16 are two portions weekly, one of which should be oily (for example salmon, trout or mackerel). However, average intakes are 1.8 portions a week, including just half a portion of oily fish, and less than 25% of adults eat oily fish regularly. The ‘two portion’ target equates to 0.45g LCn3FA daily, while other expert groups recommend daily intakes of 0.25g for general health17 or 0.5g to promote cardiovascular health.18
There are no UK recommendations for LCn3FA in pregnant women, although it has been estimated that an additional 22-25g of DHA is needed to support the increased requirements of pregnancy and lactation.16 At present, typical diets contain around 9g of DHA in the last trimester of pregnancy and 18g during lactation, which would seem inadequate. An international committee recommended that pregnant women should aim for a LCn3FA intake that supplies at least 0.2g DHA daily.19 This would be possible if pregnant women met the UK target for oily fish.
Average intakes of LCn3FA in the UK have been estimated as 0.1-0.2g per day in women of child-bearing age20 and 0.15g per day in pregnant women, with a range of 0g to 2.2g.21 In this survey, only 12% of women ate no fish during pregnancy, while 65% consumed 0g-340g weekly (around two portions, although it was unclear how much of this was oily fish).
An important aspect of the UK fish target was protecting vulnerable groups from any risks relating to marine contamination (eg. dioxins, mercury). Thus, as well as setting a specific target for pregnant women and children of one to two portions weekly, advice was given on fish species that should be avoided (shark, swordfish, marlin) or restricted (fresh tuna, tinned tuna). This may have had the unintended consequences of dissuading women from eating fish during pregnancy or limiting their intakes. Indeed, one UK study,21 which found beneficial effects on child verbal development when women consumed more than 340g seafood weekly during pregnancy, suggested that advice to limit seafood consumption during pregnancy could be detrimental to infants. In addition, any risks associated with increased fish consumption were more than offset by the benefits.
For the majority of women who do not eat oily fish regularly, dietary supplements provide an alternative source. Yet, official advice given to women warns against the use of cod liver oil in pregnancy (due to the high vitamin A content which may be teratogenic in the first trimester) without pointing out that vitamin A-free formulations are widely available. Surveys show that LCn3FA supplements are used by less than 2% of pregnant women but can be just as beneficial as oily fish in relation to infant neurological development as reported in one large study.21 Supplements should ideally contain both DHA and EPA as EPA is needed for the transport of DHA through the placenta to the foetus.22
Certain fatty acids are vital during normal pregnancy and lactation for supporting normal foetal growth and development. There is good evidence that maternal intakes of LCn3FA can help to ‘program’ the foetal immune system and lower the risk of allergic disease. Other evidence suggests benefits for foetal and infant cognitive development, and eyesight, although the small size of many studies, and differences in methods, hamper firm conclusions. However, expert bodies recommend additional LCn3FA during pregnancy and lactation to meet the undoubted higher requirements of rapid infant development during the last trimester, and in the first 12 months of life. This can only be met by increased intakes of oily fish and/or regular use of fortified foods and dietary supplements. Suggested HCP advice for pregnant women, and parents of young children, is summarised in Table 3.
Women with asthma, eczema or food allergy may need more LCn3FA than is generally recommended to help lower the risk of allergic conditions in their infants, and should consult their doctor about appropriate supplements. Once breast-feeding or formula-feeding has been discontinued, oily fish and/or age-appropriate fish oil supplements can meet the high fatty acid requirements of infants in the first few years of life
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2. Vaz Jdos S, Kac G, Emmett P et al. Dietary patterns, n-3 fatty acids intake from seafood and high levels of anxiety symptoms during pregnancy: findings from the Avon Longitudinal Study of Parents and Children. PLoS One 2013; 8:e67671.
3. Golding J, Steer C, Emmett P et al. High levels of depressive symptoms in pregnancy with low omega-3 fatty acid intake from fish. Epidemiology 2009;20:598-603.
4. Miyake Y, Tanaka K, Okubo H et al. Fish and fat intake and prevalence of depressive symptoms during pregnancy in Japan: baseline data from the Kyushu Okinawa Maternal and Child Health Study. J Psychiatr Res 2013;47:572-8.
5. Jans LA, Giltay EJ, Van der Does AJ. The efficacy of n-3 fatty acids DHA and EPA (fish oil) for perinatal depression. Br J Nutr 2010;104:1577-85.
6. Martins JG. EPA but not DHA appears to be responsible for the efficacy of omega-3 long chain polyunsaturated fatty acid supplementation in depression: evidence from a meta-analysis of randomized controlled trials. J Am Coll Nutr 2009;28:525-42.
7. Kremmyda L-S, Vlachava M, Noakes PS et al. Atopy risk in infants and children in relation to early exposure to fish, oily fish, or long-chain omega-3 Fatty acids: a systematic review. Clin Rev Allergy Immunol 2011;41:36-66.
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16, Scientific Advisory Committee on Nutrition, Committee on Toxicity. Advice on fish consumption: benefits and risks. London: HM Stationery Office;2004.
17. European Food Safety Authority. Labelling reference intake values for n-3 and n-6 polyunsaturated fatty acids. The EFSA Journal 2009;1176:1-11.
18. ISSFAL. Report on dietary intake of essential fatty acids. 2004; Available at: www.issfal.org/news-links/resources/publications/PUFAIntakeReccomdFinalReport.pdf
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20. Givens DI, Rymer C, Gibbs RA Long-chain n-3 PUFA: intakes in the UK and the potential of a chicken meat prototype to increase them. Proc Nutr Soc 2010;69:144-155.
21. Hibbeln JR, Davis JM, Steer C et al.Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood (ALSPAC study): an observational cohort study. Lancet 2007;369:578-85.
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