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Newborns with low vitamin D have infection risk

Newborns with low vitamin D levels may have a heightened risk of developing a certain type of lung infection before their first birthday, a new study suggests.
/ Source: Reuters

Newborns with low vitamin D levels may have a heightened risk of developing a certain type of lung infection before their first birthday, a new study suggests.

The infection is caused by a bug known as respiratory syncytial virus (RSV). RSV can cause the small airways in the lungs to become inflamed, in a condition called bronchiolitis; it can also cause pneumonia. In fact, RSV is the most common cause of pneumonia and bronchiolitis in infants, according to the U.S. Centers for Disease Control and Prevention.

Researchers found that infants with inadequate vitamin D levels at birth were about six times more likely than others to develop RSV bronchiolitis in their first year of life.

The findings, the researchers say, raise the possibility that getting enough vitamin D during pregnancy could prevent some RSV infections.

However, studies to test that idea are still needed. In the meantime, it's just a theory.

The study's senior researcher, Dr. Louis Bont of Wilhelmina Children's Hospital in Utrecht, the Netherlands, told Reuters Health in an email that for now, pregnant women should stick with experts' general recommendations on vitamin D intake. In the U.S., the Institute of Medicine recently bumped up the recommended dose to 600 IU per day, and set an upper limit of 4,000 IU per day.

Nearly all children become infected with RSV by the time they are 2, and most have mild symptoms. But for every 10 kids, about 1 or 2 develop bronchiolitis - and about 1 in 10 of those end up in the hospital, Bont said.

The current study, scheduled for publication today in the journal Pediatrics, focused on more-serious cases of RSV where infants developed symptoms of bronchiolitis, including wheezing and a moderate to severe cough.

At the start of the study, Bont's team measured vitamin D levels in umbilical-cord blood from 156 newborns.

Overall, 27 percent had vitamin D levels that are generally considered inadequate. Another 27 percent had mid-range levels which some experts consider too low - although there's some controversy over their definition. The rest of the newborns -- 46 percent -- had adequate vitamin D levels.

Overall, 18 infants had a confirmed RSV infection during their first year of life.

The researchers found that babies with vitamin D levels in the lowest range at birth were about six times more likely to develop an RSV infection than those with adequate levels.

There was no increased risk among babies with vitamin D levels in the controversial mid-range levels.

However, the findings do not prove that higher vitamin D at birth, per se, prevents RSV infections. Instead, there could be other explanations for the link, according to Bont.

One possibility is that newborns from low-income families could be more likely to have inadequate vitamin D levels. And infants from those families may, for some yet-unknown reason, have a higher risk of severe RSV infection, Bont said.

He also noted that pregnant women with high vitamin D levels may spend more time outdoors; the body naturally synthesizes vitamin D when the skin is exposed to the sun. And those women may be more physically active or have generally healthier lifestyles.

On the other hand, vitamin D is believed to affect immune system function and inflammation. So it's plausible that the vitamin could play a role in the risk of RSV illness.

A researcher not involved in the study said that he thinks that vitamin D may indeed have a "real" effect on infants' respiratory infections. "But we have to do clinical trials," said Dr. Carlos Camargo, an associate professor of medicine at Harvard Medical School in Boston.

In a study recently published in Pediatrics, Camargo and his colleagues found that higher newborn vitamin D levels were linked to a lower risk of respiratory infections, in general, during the first three months of life.

So the current findings are "very consistent" with that study, Camargo told Reuters Health.

He and his colleagues have begun to study different doses of vitamin D for mothers during pregnancy, and vitamin D supplements for infants, to see whether they have an effect on respiratory infections.

But, Camargo said, there are already reasons for pregnant women to make sure they are getting enough vitamin D -- including their own bone health.

He suggested that women who might not have enough vitamin D in their blood -- such as those who are obese, have dark skin or get little sun -- might want to talk with their doctors about whether they should have their blood levels of the vitamin measured.

"It's possible that if you start super-low, you'll need more (supplemental vitamin D)," Camargo said.

The prenatal vitamins recommended for pregnant women contain vitamin D. Food sources include fortified cereals, milk and orange juice, and fatty fish like salmon and tuna (although pregnant women should limit themselves to two serving per week because the fish can contain traces of mercury).