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Researchers say children with higher vitamin D levels in their blood have fewer asthma symptoms. Getty Images

Vitamin D may help ease asthma symptoms for obese children living in urban environments with high indoor air pollution.

Recent research from the Johns Hopkins University School of Medicine in Maryland found that having low levels of vitamin D was associated with respiratory problems from indoor air pollution in obese children in urban areas.

The researchers examined 120 children over a 9-month period in the Baltimore area. They tested the vitamin D levels in the blood of the children, their asthma symptoms, and the level of air pollution in their homes.

Of the 120 children involved in the research, all had preexisting asthma, and 1/3 were obese.

“Baltimore is one example where urban minority populations in the U.S. suffer disproportionately heavy burden of asthma. We know from our prior work that indoor air pollution is a significant contributing factor to asthma symptoms, especially among urban children who spend the majority of their time indoors,” Sonali Bose, MD, study author and assistant professor of medicine in the Division of Pulmonary, Critical Care and Sleep Medicine at the Icahn School of Medicine at Mount Sinai in New York, told Healthline.

“There’s emerging scientific literature in support of the protective role of vitamin D in asthma, and therefore we wondered if low vitamin D levels in children with asthma might make them more vulnerable to the effects of indoor air pollution,” added Dr. Bose, who’s also on the adjunct faculty at Johns Hopkins. “By identifying individual risk factors, such as dietary factors, that may potentially be modifiable, we can begin to find ways to protect children from harmful effects of air pollution in the future.”

The researchers found that in homes with the highest levels of indoor air pollution, children who were obese and had higher blood vitamin D levels had fewer asthma-related symptoms.

According to the U.S. Centers for Disease Control and Prevention, 6.1 million American children, or about 1 in 12 children, have asthma. Asthma disproportionately affects urban minorities, including African-American children.

Bose says the reasons behind the higher rates of asthma among African-American children remain a puzzle to researchers, but it is likely due to multiple reasons, including vitamin D deficiency.

“There are many factors that may contribute to the heavy burden of asthma in urban blacks, including but not limited to disproportionate exposures to environmental factors such as pollution, obesity, poor diet, genetics, and other yet-unidentified factors,” she said. “Vitamin D deficiency is also disproportionately present among black children, potentially due to a combination of poor diet and darker skin pigmentation, which blocks the production of vitamin D in comparison to lighter skin tones.”

In 2015, nearly 2.6 million non-hispanic blacks reported having asthma. In 2014, African-Americans were nearly three times more likely to die from complications due to asthma than their white counterparts.

African-American children were 10 times more likely than white children to die from complications due to asthma than those in the white population in 2015. Black children are also four times more likely to be admitted to a hospital due to asthma than white children.

Tonya Winders, president and chief executive officer of the Allergy and Asthma Network, says further research into why African-American children are disproportionately impacted by asthma is important.

“We truly do not fully understand if it is genetics, environment, or both that cause higher rates of asthma in children of color. It could be higher rates of pollution or allergens. It could also be lack of access to adequate healthcare or financial resources,” she told Healthline.

Urban children are particularly vulnerable to indoor air pollution due to the significant amount of time they spend indoors.

Incense, smoke from cooking, cigarette smoke, and candles can all worsen symptoms of asthma in children. Such environmental triggers can cause wheezing, tightness in the chest, and breathlessness.

“A child with asthma has inflammation in their airways along with constriction of the muscle in their airways, causing narrowing of these breathing tubes, making it much harder to breathe. It is essentially like breathing out of a straw,” Purvi Parikh, MD, a spokesperson for the Allergy and Asthma Network, and an allergist in New York City, told Healthline.

Recent research has suggested there may be a link between vitamin D levels and asthma.

In one study, researchers compared asthma diagnoses, vitamin D levels. and lung function in 10,000 children and more than 24,000 adults. They found that low levels of vitamin D among those studied were associated with a diagnosis of asthma as well as reduced lung function.

The role of vitamin D in bone strength has been well established, but researchers believe the vitamin also plays an important role in the production of insulin as well as in the functioning of the immune system.

Experts says it isn’t just obese children in urban environments whose asthma, and overall health, may be influenced by their vitamin D levels.

“Many studies have shown vitamin D helps not only asthma but all inflammatory conditions,” Dr. Parikh said.

“Both obesity and air pollution are risk factors for poor asthma control. Vitamin D, however, may help mitigate that risk. This underscores the importance of normal levels,” she said.