Vitamin D protective against pollution-associated asthma, study shows

Vitamin D may be protective among asthmatic obese children living in urban environments with high indoor air pollution, according to a new study published in The Journal of Allergy and Clinical Immunology: In Practice.

The study by researchers at the John Hopkins University School of Medicine in Baltimore, Maryland, and funded by the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health, identified factors that make children susceptible to health problems from air pollution throughout Baltimore's inner city.

The researchers tested three factors, which included air pollution levels in homes, blood vitamin D levels, and asthma symptoms, in 120 school-aged children with preexisting asthma in the Baltimore area. One-third of the study participants were also obese. The children were evaluated at the start of the study and three times over the next nine months, according to the study abstract.

Researchers found that having low blood vitamin D levels was related to the harmful respiratory effects of indoor air pollution among obese children with asthma. Conversely, in homes that had the highest indoor air pollution, higher blood vitamin D levels were linked to fewer asthma symptoms in obese children.

According to the Centers for Disease Control and Prevention, one in 12 children in the U.S. have asthma, which totals 6.1 million children nationally. Additionally, asthma disproportionately impacts urban minority populations, such as black children. Higher indoor air pollution, from sources such as cigarette smoke, cooking, burning of candles, and incense, is linked to greater respiratory problems, including worsening of asthma symptoms and more hospital visits.

Asthma is an immune-mediated disease, according to Sonali Bose, MD, lead author of the study and assistant professor of medicine, pulmonary, critical care, and sleep medicine at the Icahn School of Medicine at Mount Sinai, and adjunct faculty at Johns Hopkins. Based on previous scientific studies, the researchers already knew that vitamin D was a molecule that may influence asthma by impacting antioxidant or immune-related pathways.

Bose explained that at the time the study was being conceived, researchers were seeing vitamin D deficiencies across the U.S.. Certain populations were at higher risk for vitamin D deficiency, particularly African American children, the researchers said.

They were also noticing a heavy burden of asthma in inner city minority children. It seemed as though vitamin D deficiency and asthma were coincident and interacting in some way, Bose said.

"What surprised us the most was that the findings of the study showed the effects were most pronounced among obese children," Bose said. "This highlights a third factor at play here - the obesity epidemic - and helps bring that risk to light when considering individual susceptibility to asthma."

Bose said they will work to identify ways to increase blood vitamin D levels in these children, helping them be more resilient to environmental insults.

"One way to increase blood vitamin D levels is to increase sun exposure, but that isn't always possible in urban environments, or in people with darker skin pigmentation," she said. "Another way is through dietary supplements or eating more foods that are high in vitamin D, such as fatty fish, mushrooms, or foods fortified with vitamin D, such as bread, orange juice, or milk."