Folic acid may increase the risk of asthma, study suggests

In Norway all women planning a pregnancy and those in the early stages of pregnancy are told to take a folic acid supplement to promote normal fetal development. The reason for this is that folic acid supplements taken during pregnancy reduce the risk of spina bifida in newborns.

A recent study, carried out with funding from the Research Council and data from the large-scale Norwegian Mother and Child Cohort Study (MoBa), indicates that the effects of folic acid may not be as categorically positive as had been thought.

Too early to be sure

Pregnant women should continue to take folic acid supplements with a clear conscience, says Siri Eldevik Håberg, MD Ph.D. at the Norwegian Institute of Public Health. "We have compared the levels of folic acid in the blood of nearly 2 000 pregnant women with the incidence of asthma in their children at the age of three. The results show that the higher the level of folic acid in the woman's blood, the greater the risk of the child having asthma," explains Siri Eldevik Håberg, MD Ph.D. at the Norwegian Institute of Public Health.

The study is the first to examine the connection between the level of folic acid in the blood of pregnant women and the occurrence of asthma in their children. The researchers have also checked a number of other factors such as the mother's level of education, the mother's body mass index (BMI), smoking during pregnancy and whether the mother herself has suffered from asthma.

However, Ms Håberg is quick to point out that there may be other factors present in the women with high folic acid levels that have an impact on the child's risk of developing asthma. So it is still too early to say with certainty that there is a direct causal relationship between folic acid and asthma.

Inspired by US studies on mice

Ms Håberg also stresses that pregnant women should continue to take folic acid supplements with a clear conscience.

The results of a recent study show that the higher the level of folic acid in the woman's blood, the greater the risk of the child having asthma. "Folic acid is recommended because we know that it prevents neural tube defects such as spina bifida. If, in time, our research has implications for the guidelines on folic acid supplementation, it will probably be a matter of adjusting the recommended dose, possibly limited to specific groups of women."

In the next phase of the research Ms Håberg and her colleagues plan to study the mechanisms behind a possible connection between folic acid and asthma. Studies on mice carried out in the US led the Norwegian researchers to the idea that folic acid can lead to epigenetic changes, and thereby affect how our genes function.

Folic acid carries small carbon compounds called methyl groups. By transferring these methyl groups onto DNA the folic acid can help regulate DNA activity. This in turn can result in some genes being switched off or on.