Newborns with the lowest vitamin D levels are twice as likely to develop respiratory infections as babies with normal levels, according to new research.
Vitamin D is called the sunshine vitamin because the body produces it when exposed to sunlight. It helps build strong bones and bolster the immune system. And, now, a new international study finds it can also lower the risk of respiratory infections in babies.
Carlos Camargo and his colleagues at Harvard Medical School in Boston, Massachusetts, measured vitamin D levels in frozen umbilical cord blood samples from more than 900 children in the New Zealand cities of Wellington and Christchurch. They followed the children from the age of 3 months until they were 5 years old.
"And what we found," says Camargo, "was that children who had the lowest levels of vitamin D had a high risk of developing infections and wheezing throughout childhood."
Children with vitamin D levels below 25 nanomoles per liter were twice as likely to develop respiratory infections, some requiring hospitalization, compared to infants in the study who had vitamin D levels of 75 or higher. However, low vitamin D levels were not associated with being diagnosed with asthma.
While fortified cow's milk and cheese contain abundant amounts of vitamin D, the sun is the easiest and most reliable source.
So it was no surprise to that investigators found the lowest vitamin D levels among children who were born in the winter. "If you don't have high stores (of vitamin D) built up or you don't take a supplement, you're going to sort of drift downward," says Camargo.
Very few children in the study took vitamin D supplements.
Vitamin D deficiency is usually most common in countries furthest away from the Equator. But Camargo says the problem is becoming more common even in warm, sunny climates.
"People are moving more and more indoors," he says. "They work indoors. They play indoors. Everything's indoors. So we're actually starting to see low levels of vitamin D in areas where the sun is plentiful."
The study linking vitamin D levels in infants to respiratory infection in childhood is published in the January issue of the journal Pediatrics.