Eighty children between the ages of six and 14 (50 asthmatic and 30 non-asthmatic) participated in the study, which was led by the Environmental Health Center for Asthma.
Researchers measured and compared serum vitamin D levels between the two groups of children, observing that the asthmatic group had less serum vitamin D than the non-asthmatic group. Of the former, 86% had a serum vitamin D deficiency, compared to just 19% of the latter.
The study, published by the Korean Society of Environmental Health and Toxicology, stated: “We observed that the serum vitamin D level in asthmatic children was significantly lower than that in non-atopic children.”
The study also found that an “insufficient level of serum vitamin D increased the risk of developing asthma in children”, with the results being “very consistent with those of numerous existing epidemiological researches which examined the association between serum vitamin D level and the risk of developing asthma”.
Asthma is among the most common allergy-related chronic respiratory illnesses in children, and has become more widespread over the last two decades. While it is now generally understood that both environmental and genetic factors are contribute to the condition, its root cause is yet to be determined.
Since melanin, age, body fat, latitude, season, time spent outdoors and sunscreen use affect serum vitamin D levels, the study examined its participants’ housing types, floor of residence and time spent outdoors. However, sunlight exposure was the only environmental factor found to be associated with serum vitamin D levels.
Reverse causality was also noted: asthmatics are more likely to remain indoors, minimising their exposure to sunlight and therefore, their serum vitamin D levels. Simultaneously, lifestyle changes were taken into account: Korean children and teenagers in school spend less time outdoors, leading to lower levels of serum vitamin D and in turn, a possible higher prevalence of asthma.
However, the study did not account for the use of vitamin D supplements among its participants or the effect such supplements might have on serum vitamin D levels. As such, the link between lower serum vitamin D levels and a higher risk or prevalence of paediatric asthma remains inconclusive.
The study concluded that “more cautious consideration” and “more comprehensive research for exploring the causal relationship” between serum vitamin D levels and asthma was still necessary.
Source: The Korean Society of Environmental Health and Toxicology
“Are children with asthma in South Korea also associated with vitamin D deficiency?”
Authors: Yu-Ri Kim, Sung Chul Seo, Young Yoo, Ji Tae Choung