MIAMI BEACH — High maternal vitamin D intake in pregnancy may help protect children from asthma and wheezing illnesses during early childhood, results of a large, prospective study suggest.
In multivariate analyses, every 100-IU increase in maternal vitamin D intake was associated with about a 10% lower risk for any wheeze (odds ratio 0.90) and with nearly a 20% lower risk of having a child at high risk for asthma (OR 0.82). This inverse association was present whether vitamin D came from diet or nutritional supplements and remained after controlling for 10 confounding factors, Dr. Carlos A. Camargo Jr. reported at the annual meeting of the American Academy of Allergy, Asthma and Immunology.
“This is a new hypothesis, but the vitamin D story is going to be one that you're going to hear more and more about in the years ahead,” he told reporters at the meeting. “Already this year there is a lot of discussion going on about vitamin D and cancer. But to link this to asthma and allergic diseases is very exciting.”
The best explanation for the observed protective effect is that vitamin D, which is known to have some immunologic effects, influences IL-10 secretion by regulatory T cells, said Dr. Camargo of the department of epidemiology at Harvard Medical School in Boston.
The findings suggest that vitamin D insufficiency is a reality, particularly in northern parts of the country. Exactly what the correct amount of daily vitamin D intake is remains unclear, in part because of emerging data from this and studies in other specialties, he said. “Most people in the field would recommend 800–1,000 IU/day, and yet you'll see recommendations of 200–400 IU in the literature,” he said.
The mean vitamin D intake during pregnancy was 548 IU/day in the study, which included 1,194 mother-child pairs in Project Viva, a prospective prepartum cohort study in Massachusetts. Intake was assessed using a validated food questionnaire in the first and second trimesters and was averaged for analyses.
Dr. Camargo and his colleagues defined any wheeze as a mother-reported wheeze or physician-diagnosed asthma, wheezing, or reactive airway disease at ages 1, 2, or 3 years. High risk of asthma was defined as the subset of children with two or more reports of wheezing at 1, 2, or 3 years, plus either parental history of asthma or child diagnosis of eczema.
Most people in the field would recommend 800–1,000 IU/day, yet recommendations of 200–400 IU are in the literature. DR. CAMARGO