Studies show that the children of mothers who consumed high doses of omega-3 fatty acids every day during their third trimester of pregnancy have reduced odds of developing asthma. However, it also turns out that pregnant women following the recommendations from the EPA and FDA to eat 8 to 12 ounces of low-mercury fish per week see the same benefit.
A review of the two studies was recently published in the Journal of Allergy and Clinical Immunology: In Practice. In the first study, from the New England Journal of Medicine, nearly 350 women who were in their third trimester of pregnancy took omega-3 fatty acids on a daily basis, while a similar number were given a placebo. The trial group was also divided into groups according to the women’s blood levels of omega-3 fatty acids. Those who had the lowest blood levels of omega 3 got the most benefits from supplementing with fish oil.
The other study was published in the Journal of Allergy and Clinical Immunology. It entailed a group of pregnant women in their third trimester who were randomly placed into fish oil, “no oil”, and placebo groups. The fish oil group was given omega-3 fatty acids every day. In the “no oil” group, participants were told about the trial proposal and given the option of consuming either fish or fish oil. The researchers found that those in the no oil and fish oil groups ended up taking less asthma medication as they reached the age of 24, which would infer they developed less asthma.
The University of South Florida’s Dr. Chen Hsin Lin, a co-author of the scientific review of the two studies in question, emphasized that omega 3 fatty acids are essential nutrients derived solely from marine sources that the body cannot synthesize on its own. She said that recommending pregnant women take a high dose of fish oil supplements each day in their third trimester may be a bit premature, however. Co-author Dr. Richard Lockey pointed out that consuming 8 to 12 ounces of fish per week can offer the same protection against asthma while also boosting nutritional benefits for infant growth and development.
A primary concern for pregnant women is avoiding toxins, so for many, the choice may come down to whichever option is lower in mercury. Mercury is a highly toxic heavy metal that can harm fetuses as well as children, even at very low levels.
Studies have shown that exposure to mercury in the womb can increase a child’s chances of developing ADHD-related behavioral problems later in life. On top of that, mothers who ate a high amount of low-mercury fish in pregnancy actually had children with a lower risk of developing ADHD-related conditions.
Some supplements contain mercury, so it’s important to buy from trusted sources. When it comes to fish, there are a few rules of thumb to follow. Most fish have at least a small amount of mercury in them, but some have much higher levels than others.
Bigger, older and predatory fish tend to have the highest levels of mercury as levels of the heavy metal build up in their bodies throughout their lives. Good low-mercury choices include salmon, trout, sardines, herring and anchovies. Pregnant women should avoid high-mercury fish like tuna, swordfish, shark and king mackerel.
Be sure to choose wild fish over farmed fish for fewer toxins and more nutrition. Beyond pregnancy, it’s a good idea to avoid high-mercury fish in general, and this is especially true if you’re breastfeeding.