Expectant mothers who want to reduce their children's chances of developing asthma should spend more time outdoors and in the sun during the second trimester.
For this study, researchers headed by David Slusky at the University of Kansas wanted to test out a medical hypothesis that higher vitamin D levels during the second trimester can affect a fetus' risk of asthma. The hypothesis was presented by Scott Weiss and Augusto Litonjua, who are physicians at Brigham and Women's Hospital in Boston.
"This is the golden age in the way that data about hospital discharges, insurance claims, birth certificates and death certificates are more and more available and more and more set up for researchers," Slusky said. "And that allows economists to get really large sample sizes with not a lot of cost."
Slusky and colleagues used hospital data taken from two states that were gathered through a national survey. They also looked at where and when children were born in relation to the amount of sunlight that their mothers were most likely exposed to specifically during the second trimester.
"We're not looking at sunny places versus non-sunny places," said Slusky, whose findings will be published in the American Journal of Health Economics. "We looked at the relative differences of the level of sunlight at a particular place at a particular time of year."
The researchers found that mothers who had more sunlight, which meant they had higher levels of exposure to vitamin D, were more likely to have children who were not afflicted with asthma. The researchers could not explain why sunlight and vitamin D appeared to reduce an unborn child's risk of asthma. They argued that since sunlight is free, it would not hurt pregnant women to get a little bit of sun every day.
The researchers, however, cautioned that expectant mothers should be aware of the risks involved with too much sunlight. Sun exposure without protection can lead to skin cancer, which is why people who plan on spending an extended period of time in the sun should always use sunscreen.
The researchers added that people in general would benefit from getting extra sunlight since vitamin D deficiency is pretty common. The Centers for Disease Control and Prevention (CDC) reported that from 2001 to 2006, only about two-thirds of the population had sufficient vitamin D levels.
Vitamin D deficiency can lead to weak and brittle bones.
