Low vitamin D is common among infants with bronchiolitis and is associated with an increase in the severity of the disease, according to a new Spanish study.

Bronchiolitis is a lung infection common in young children. About one in three infants develop bronchiolitis in the first year of their life.

The disease causes the small airways, known as bronchioles, to become congested which leads to cold-like symptoms and possibly wheezing and difficulty breathing.

In epidemiological research, the prevalence of various conditions is often associated with time of year. This may relate to a variety of factors, with one of those factors being vitamin D production.

During winter in the northern hemisphere, the Earth is tilted away from the sun making vitamin D production much more difficult in many locations. The UV wavelengths responsible for vitamin D production in the skin have a harder time reaching the Earth in winter. This leads to a higher seasonal prevalence of vitamin D deficiency.

Bronchiolitis is also much more common in the winter, leading researchers to speculate whether vitamin D plays a role.

In a new study, the vitamin D status of 48 infants with bronchiolitis were compared to the vitamin D status of 30 healthy infants.

They found that nearly twice as many infants with bronchiolitis had levels lower than 30 ng/ml compared to healthy infants (52.1% vs. 26.6%). Low vitamin D levels were also significantly associated with a more severe disease state.

“In the present study, serum vitamin D levels in infants with bronchiolitis were significantly lower than in the control group,” the researchers concluded.

“The severity of acute bronchiolitis increases with a decline in serum [vitamin D] level.”