Prevention of Asthma: Fish or Fish Oil?

Probiotics, antihistamines, inhaled glucocorticosteroids, allergen and/or irritant avoidance, allergen immunotherapy, and even biologics have been investigated to prevent its onset, with mixed results.1 However, fish oil, enriched in n−3 polyunsaturated fatty acids (PUFA), for example, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), used during pregnancy, may prevent asthma in progeny. The proposed mechanism is that EPA and DHA replace arachidonic acid on cell membranes and result in a reduction of arachidonic acid transformation into proinflammatory leukotrienes, known to cause airway inflammation and bronchoconstriction.2 A 2015 Cochrane review demonstrated limited evidence to support fish oil supplementation during pregnancy to reduce asthma onset in offspring, although the conclusion was based on few studies with various supplementation dosages, research quality, and statistical power.3 However, 2 publications, one by Bisgaard et al4 (study A) and another by Hansen et al5 (study B), published in 2016 and 2017, respectively, in which high-dose fish oil supplementation was used during the third trimester, were successful to prevent pediatric asthma.Methods Study A Pregnant women at 24 weeks of gestation were double-blind, placebo-controlled, randomized to receive 2.4 g of n−3 PUFA (N = 346) or placebo olive oil (N = 349) daily until 1 week after delivery in the years 2008 to 2010. Rather than instituting this complicated scenario, a better alternative way may be to recommend consuming fish during pregnancy. Because EPA and DHA are almost exclusively from fish and shellfish, it is reasonable to hypothesize that enough fish consumption could provide the same benefit as fish oil. [...]8 to 12 ounces per week of fish, with an average mercury concentration less than or equal to 0.15 μg/g, can be safely consumed.11 Four species of fish with high mercury levels that should be avoided include tilefish from the Gulf of Mexico and shark, swordfish, and king mackerel from throughout the world.