Reports

This report is based on medical evidence presented at sanctioned medical congress, from peer reviewed literature or opinion provided by a qualified healthcare practitioner. The consumption of the information contained within this report is intended for qualified Canadian healthcare practitioners only.

June 2007

For clinicians who may not be familiar with the omega-3 fatty acid story, it is important to appreciate that mammals cannot produce either omega-3 or omega-6 fatty acids themselves, so whatever they need must come from the diet. Despite the fact that flax and canola oil are good sources of alpha-linolenic (ALA) omega-3 fatty acid, it is often mistakenly believed that this vegetable omega-3 is equivalent to marine omega-3 sources, especially eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids.

Some of the confusion arises because although mammals have the necessary enzymes to make EPA and DHA from the vegetable precursor (ALA), recent studies that used tracers in humans showed that this conversion is a very inefficient way to increase DHA in tissues, since <0.5% of ALA is converted to DHA.

In contrast, marine sources, especially salmon, mackerel and herring, are important sources of biologically viable DHA: it is this DHA that is critical for human growth and development. When the level of DHA falls in the brain and retina, there is a concomitant increase in the omega-6 docosapentaenoic acid (DPAn-6). However, this reciprocal replacement has adverse effects on brain structure and function, therefore, DPAn-6 cannot functionally replace DHA, indicated researchers from the National Institutes of Health, Bethesda, Maryland.

Ensuring Adequate Levels in Pregnancy and Beyond

Studies in infants indicate that there is a growth spurt in the human brain during the last trimester of pregnancy and during early postnatal months, with a large increase in the cerebral content of both DHA and arachidonic acid. Mothers are the sole source of the fatty acids infants require and if they are deficient themselves in omega-3, they are more likely to be unable to meet an infant’s needs.

Infants are usually born with a reserve of DHA, but if not nourished with adequate levels from either breast milk or fortified formula, they quickly become deficient in DHA. The consequences of pregnant women consuming diets rich in EPA and DHA have not been widely studied, but a recent effort provides some confirmation that maternal seafood consumption in pregnancy appears to improve child development (Hibbeln et al. Lancet 2007;369(9561):578-85).

In this observational cohort study, 11,875 pregnant women completed a food questionnaire assessing seafood consumption at 32 weeks’ gestation. After adjusting for 28 potential confounders, investigators found that maternal seafood intake of <340 g/week during pregnancy was associated with an increased risk of their child being in the lowest quartile for verbal intelligence quotient compared with mothers who consumed >340 g/week (a mother who ate seafood three times a week would typically have a fish intake of 347 g/week). Low maternal seafood intake was also associated with an increased risk of suboptimal outcomes for pro-social behaviour as well as fine motor, communication and social development scores. For each of these outcome measures, the lower the maternal intake of seafood during pregnancy, the higher the risk of suboptimal developmental outcome.

The outcomes of this study are important, in that in 2004, the US federal government advised pregnant women to restrict their overall consumption of seafood to 340 g/week in order to avoid exposing the fetus to trace amounts of neurotoxins. But as Hibbeln et al. stressed, they found that children whose mothers ate <340 g of seafood a week were more likely to have suboptimal neurodevelopmental outcomes than children whose mothers ate more seafood than is currently recommended.

An earlier study appears to support these findings and again argues in favour of maternal intake of very long-chain omega-3 polyunsaturated fatty acids (PUFAs) (Helland et al. Pediatrics 2003;111(1):e39-44). Investigators examined the effect of giving pregnant and lactating women either cod liver oil or corn oil on the subsequent mental development of their children. Pregnant women were recruited in week 18 of their pregnancy and took 10 mL of either cod liver oil or corn oil until three months after delivery. The cod liver oil contained 1183 mg/10 mL of DHA and 803 mg/10 mL EPA, while the corn oil contained 47 mg/10 mL of linoleic acid and 92 mg/10 mL of ALA. The amount of fat-soluble vitamins in each oil was identical.

Infants born to this cohort of women were scheduled to undergo cognitive function tests at six and nine months of age, and a small proportion of them were again assessed when they were four years old. Results showed that children born to mothers who had taken cod liver oil during pregnancy and lactation scored higher on the mental processing composite of the Kaufman Assessment Battery for Children compared to those whose mothers had taken corn oil. Children’s mental processing scores at four years of age also correlated significantly with maternal intake of DHA and EPA during pregnancy. In fact, maternal intake of DHA during pregnancy was the only variable of statistical significance for the children’s mental processing scores at four years of age when analyzed in a multiple regression model. As the authors pointed out, higher maternal intake of DHA resulted in higher maternal plasma levels and thus increased transfer of DHA to the fetus.

Another interesting study involved children with developmental coordination disorder (Richardson AJ, Montgomery P. Pediatrics 2005;115(5):1360-6). As the authors reported, this condition is associated with difficulties in learning, behaviour and psychosocial adjustment that persist into adulthood. In this study, children between the ages of five and 12 were randomized to three months of supplementation with omega-3 and omega-6 fatty acids or placebo, then crossed over to the alternative arm. Supplementation had no effect on motor skills but investigators noted a significant improvement in reading, spelling and behaviour during the three months when children were on active supplements, suggesting that omega-3 and omega-6 fatty acids may help children with this constellation of behavioural symptoms.

Integrating Options for Optimal DHA

According to investigators, current typical DHA status among Canadian women is not necessarily very good. In a survey conducted by epidemiologist/nutritionist Michel Lucas, Université Laval, in June 2006, only 17% of women of child-bearing age in Quebec had a DHA intake of 300 mg/day as recommended by the International Society for the Study of Fatty Acids and Lipids. DHA levels in breast milk in Canadian women are also among the lowest in the world, at a mean of only 0.14% compared with a world-wide median of 0.3 to 0.4%. According to several expert panels, pregnant and lactating women should consume at least 200 mg of DHA/day—optimally 300 mg—to ensure infants receive an adequate supply. It is assumed that this is derived from marine sources of DHA, as flaxseed supplementation has no effect on DHA levels in breast milk.

The safest way to ensure women ingest adequate amounts of omega-3 is to recommend they consume at least two servings (three servings for more than 340 g/week, ) of fish per week, mainly the oily species, as indicated in American Heart Association guidelines. Otherwise, women may consider a perinatal supplement, fish oil capsules or omega-3-fortified foods such as Danino yogurt, formulated specifically for children but when consumed in high enough quantities, may help supplement a woman’s DHA supply as well.

The American Academy of Pediatrics recommends children over the age of two eat more fish, especially oily fish, broiled or baked. Omega-3-fortified foods that are likely to be more palatable than fish for many children may help them achieve adequate amounts of essential fatty acids for optimal health. Danino yogurt, for example, contains 40 mg of DHA in every 100-g serving.

According to investigators, the typical Canadian diet has a ratio of omega-3 to omega-6 fatty acids of approximately 1:10, where the optimal ratio should be 1:3. Consequently, omega-6 supplementation is essentially redundant as we already have too much in our diet and should concentrate on improving the omega-3 fatty acid content of our diet.