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Fish oil supplementation during pregnancy prevents childhood asthma

Fish oil supplementation during pregnancy prevents childhood asthmaAsthma is the leading disease among children and adolescents in the Western world, and the rate has been going up for the past 20 years. A new Danish study that is published in the New England Journal of Medicine shows that pregnant women who take supplements of fish oil are much less likely to give birth to children that develop asthma later on. The question is how much fish oil it takes to obtain the positive effect.

Around 300 million people worldwide suffer from asthma, a chronic inflammatory condition of the lungs. Symptoms include repeated bouts of breathlessness, coughing, and chest pain caused by constricted bronchi. Asthma patients are more prone to respiratory tract infections, fatigue, and poor sleep because of their coughing and breathing difficulty. Asthma can affect all age groups, and half of the patients are younger than 10 years of age. The condition impairs quality of life, and the medicine used to treat asthma is lifesaving but often associated with side effects. It is therefore important to take all necessary steps to prevent the disease as early as possible.

30 percent fewer cases of asthma and fewer respiratory tract infections

When mothers take fish oil supplements in the last third of their pregnancy, their children seem to get a better start to life, as their risk of asthma and other types of breathing difficulty is reduced. This is what scientists observed in a Danish study of 736 women and 596 children. The study was double-blind and placebo-controlled, and half the pregnant women received a daily supplement containing four grams of fish oil, while the other half got the same dose of olive oil. Neither the pregnant women nor the researchers knew who got what, and this information remained undisclosed for the first three years of the children’s lives.

The study showed that the risk of chronic breathing difficulty or asthma among children in the fish oil group was 16.9 percent, while 23.7% of children in the control group were affected. The difference between the two groups translates into a 30.7 percent relative reduction of asthma and breathing difficulty. Children of mothers who took fish oil also had fewer respiratory tract infections that often trigger an asthma attack. Lead researcher, Professor Hans Bisgaard from the University of Copenhagen, has been investigating causes of childhood asthma for many years. He calls the results of this study a turning point that may help improve future prevention of this widespread disease.

The most pronounced effect is seen in women who don’t eat fish and who are genetically predisposed

At baseline, the researchers measured blood levels of the omega-3 fatty acids, EPA and DHA, in the pregnant women, and they compared this information with their genetic profile. The measurements showed that women who had the smallest fish consumption and also had a specific variant of a gene called FADS that metabolizes fish oil in the body, benefited the most from taking the supplement. In this group, the risk of asthma among their offspring was 50% lower than among children of women who got a placebo.

Does fish oil prevent other diseases?

Inflammation is involved in asthma and many other diseases that are widespread today. It is therefore plausible that fish oil has the potential to prevent an array of conditions. According to Professor Hans Bisgaard, fish oil’s effect on asthma is bound to apply to other conditions such as inflammatory rheumatism and gastro-intestinal diseases where genes and risk factors overlap with asthma. Preliminary results from the large fish oil study also show that fish oil supplementation is associated with higher IQ in boys, which helps them keep up with the girls during the first years of childhood.

Several reasons to start early with fish oil

The researchers behind the study encourage pregnant women to start supplementing with fish oil early in pregnancy for the simple reason that the organs of the fetus start developing in the second month of pregnancy. The expecting mother also benefits from fish oil. Studies have shown that it helps prevent postpartum depression. It is already known that the brain contains quite a lot of omega-3 that is of vital importance to the nervous system.

Salmon with omega-3 may also reduce childhood asthma

Professor Philip Calder from the University of Southampton conducted a study (Salmon in Pregnancy), in which a group of pregnant women consumed salmon twice a week, starting from the 19th week of their pregnancy. The children underwent various allergy tests six months after birth and again when they were two to three years of age. The results were compared with a control group consisting of children whose mothers had not consumed salmon during their pregnancy.
No difference was detected in terms of their allergy rate at six months of age. However, when the children were two to three year old, the rate of asthma was lower among those whose mothers had consumed salmon during pregnancy.

Get omega-3 and other nutrients from fish and supplements

On the one hand, oily fish contain omega-3 fatty acids, selenium, zinc, and other vital nutrients that are important for the developing fetus. On the other hand, fish also contain mercury and other environmental toxins that may harm the development of the fetus, especially the brain. Fish at the top of the food chain contain the most pollution, which is why health authorities warn pregnant women against eating tuna and other predatory fish. There are no warnings for smaller fish and salmon, however. Nonetheless, it is a good idea to avoid salmon from the Baltic Sea, as fish from this region is known to contain larger concentrations of heavy metals. An option is to buy organic salmon. Pregnant women who dislike the taste of fish can even take high-quality fish oil supplements as an alternative. This is also a viable option for others who feel that they eat too little fish and want to be on the safe side.

Omega-3 content in salmon and capsules

100 grams of salmon contain around three grams of fish oil, which corresponds with three large fish oil capsules. In the Danish study, the participants got four grams of fish oil daily, which is far more than the official recommendations and far more than the amount used in the Salmon in Pregnancy study. Everyone agrees that pregnant women need the essential omega-3 fatty acids, but the optimal dose in terms of benefiting the health of the expecting mother and her child has not been established at this point.

Inflammation is controlled by omega-3 and omega-3 fatty acids

Omega-3 fatty acids, which we typically get from fish oil, work in an intricate, biochemical interplay with omega-6, which we get from plant oils, meat, and dairy products. For instance, the type of omega-3 called EPA is in direct competition with arachidonic acid (omega-6) over the production of some hormone-like compounds (prostaglandins) that regulate inflammation and other processes in the body. It is therefore vital that the two types of fatty acids are consumed in the right balance.

Too little omega-3 and too much omega-6 increases the risk of inflammation and asthma

Farmed fish, beef cattle, chickens, and dairy cattle are fed a diet that contains more omega-6 than omega-3. Therefore, fish, meat, eggs, and dairy products typically contain higher amounts of omega-6 and smaller amounts of omega-3 compared with earlier. Animal feed, limited consumption of fish, ready meals, and margarine all contribute to our higher intake of omega-6 and our low intake of omega-3, an imbalance that may explain the increasing rate of asthma and other conditions where inflammation is part of the picture.

Modern (western) diets often contain omega-6 and omega-3 in a 10:1 ratio. In some cases, the ratio may even be 30:1. The optimal ratio is believed to be 4:1, possibly even lower.
Dietary changes with less omega-6 and more omega-3 from oily fish and fish oil supplements can correct this imbalance, thereby reducing our risk of asthma and several other diseases where inflammation is known to be involved.


Bisgaard Hans et al. Fish Oil-Derived Fatty Acids in Pregnancy and Wheeze and Asthma in Offspring. New England Journal of Medicine 2017

University of Southampton: Oily fish eaten during pregnancy may reduce risk of asthma in offspring. ScienceDaily 2016

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