Fish oil pills during pregnancy may lower asthma risk in children

    3 January 2017

    Taking omega-3 fatty acid supplements during pregnancy can reduce the risk of childhood asthma by almost a third, according to a study published in the New England Journal of Medicine.

    The research, at the University of Waterloo in Canada, found that women who were prescribed 2.4 grams of ‘long-chain’ omega-3 supplements during the third trimester of pregnancy reduced their children’s risk of asthma by 31 per cent.

    Long-chain omega-3 fatty acids, which include eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are found in cold water fish and help to regulate immune system response.

    During the study, researchers measured levels of EPA and DHA in pregnant women’s blood. It was found that those with low levels of EPA and DHA at the beginning of the study benefitted the most from the supplements. In these women, it reduced their children’s relative risk of developing asthma by 54 per cent.

    Researchers analysed blood samples of 695 Danish women at 24 weeks of pregnancy and again one week after delivery. They then monitored the health status of each participating child for five years, which is the age at which asthma symptoms can be clinically established.

    Professor Hans Bisgaard, the study’s lead author, said: ‘We’ve long suspected there was a link between the anti-inflammatory properties of long-chain omega-3 fats, the low intakes of omega-3 in Western diets and the rising rates of childhood asthma. This study proves that they are definitively and significantly related.

    ‘Asthma and wheezing disorders have more than doubled in Western countries in recent decades. We now have a preventative measure to help bring those numbers down.’

    The researchers told the New York Times they were not ready to advise pregnant women to take fish oil supplements. The doses in the study were high — 15 to 20 times typical intake from food.

    Instant analysis
    It must be noted that the authors happily disclosed a conflict of interest at the outset. One contributor is named on a forthcoming patent related to childhood asthma and the assessment of blood levels of the two long-chain fatty acids, EPA and DHA. The other has received consulting fees from various pharmaceutical companies on undisclosed subjects.

    The paper initially discussed the increasing rate of childhood asthma, and suggested this was related to diet — in particular, to an increase in the intake of omega-6 fatty acids and a decrease in long-chain omega-3s. (However, prior studies in this area returned underpowered and ambiguous results.)

    This study was a double-blind randomised controlled trial of omega-3 fatty acid supplementation during the third trimester of pregnancy in pregnant women to assess whether there was an association between these levels and eventual childhood asthma.

    Parents completed a diary card every day from birth. The end point was determined by the presence of troublesome lung symptoms (cough, dyspnoea, wheeze) within the preceding six months, each lasting for three consecutive days, as well as usage of asthma medication.

    However, there is an issue of recall bias in asking parents to fill out diaries for their children and a possible over-emphasising of symptoms, which can be confused with the symptoms of colds.

    Women were either given long-chain polyunsaturated fatty acids or placebo from week 24 to one week after delivery. Maternal variation for genes involved in encoding fatty acid desaturase were also noted which could have an implication in how this is passed on to the child in breast milk, for example, or via genetics.

    Statistically, the study underperforms. It looks only at 700 or so women and splitting these groups down leaves massive margins of difference.

    In addition, little discussion is made about the women recruited. Did they have family histories of atopy (a tendency to be hyperallergic)? Did they have childhood asthma also? Do any of their other children have any issues? The inclusion criteria for the study was quite succinct. Exclusions and selection weren’t significantly discussed.

    The results suggest a slightly lower incidence of persistent wheeze/asthma in children of mothers supplemented with the long-chain fatty acids (seven per cent, in very low study numbers — translates as 31 per cent in terms of relative risk), but the biggest impact was for mothers who had low levels of EPA and DHA. Where the study didn’t seem to show much of a difference was where the levels were similar in women prior to supplementation.

    As the paper notes, ‘further studies are required’.

    Take-home message: eat oily fish regularly, ideally around once a week — current advice already given out by your friendly GP.
    Research score: 2/5