Childhood asthma and vitamin D deficiency: what you need to know about it

The concentration of vitamin D in the blood of asthmatic children is lower than that found in healthy toddlers, suggesting how deficiency of the vitamin may be a risk factor for childhood asthma. If this association is confirmed by other studies, intervention on vitamin D levels in young patients may be a suitable strategy to counteract the symptoms of the disease.

This is reported in new research conducted by Korean scholars at Korea University Medical Center in Seoul and published in the journal Environmental Health and Toxicology.

Childhood asthma: the most common chronic disease in children

Asthma is one of the most common chronic respiratory diseases in pediatric age; its prevalence is steadily increasing and so are the number of patients with severe asthma and acute complications. Asthma is an inflammatory airway disease, and the most common symptoms are wheezing, dyspnea, chest tightness, and coughing. Although it is now known that environmental and genetic factors contribute to the condition, the main cause has yet to be determined. 

The major environmental factors that stimulate the onset of asthma are dust mites, mold, animal allergens, tobacco smoke and pollutants. Recently, much research has also focused on the role of vitamin D deficiency in the onset of asthma. In addition to contributing to bone growth and health, vitamin D is known to play a key role in the prevention and treatment of osteoporosis as it is an essential hormone for maintaining phosphorus and calcium homeostasis. 

However, recent epidemiological studies have reported that serum vitamin D deficiency may be linked to an increased risk of autoimmune disorders and diseases such as asthma, atopic dermatitis, and allergic rhinitis. Numerous epidemiological investigations regarding the causes of childhood asthma have reported the association between vitamin D deficiency and increased rates of asthmatic disease. The results of a study involving Qatari children revealed that vitamin D levels in asthmatics were significantly lower than in healthy children. As well as another research on African American children confirmed a correlation between vitamin D deficiency and asthma.

A study of boys with asthma in North America also reported that vitamin D deficiency is associated with an increased rate of emergency room visits due to symptoms of the disease. Insufficiency of the vitamin in serum is more common among urban dwellers, where exposure to sunlight is reduced due to the "Western" lifestyle. Although vitamin D deficiency in some countries has been reduced by food fortification, much research has shown that vitamin D deficiency is highly prevalent even in sunny areas of the world and that supplementation and fortification are not always sufficient to prevent it.

86% of asthmatic children manifest vitamin D deficiency

The results reported by the Korean study showed that children with asthma have insufficient levels of vitamin D, suggesting that this deficiency could be a risk factor for developing the disease. During the research, which involved subjects between the ages of 6 and 14, researchers measured and compared the serum vitamin D concentrations of children with asthma and healthy children, observing that the vitamin in the young sufferers was significantly lower than in unaffected children.

As many as 86 percent of patients with childhood asthma showed a serum vitamin D deficiency, while only 19 percent of nonasthmatics had insufficient levels; results, which as stated by the authors themselves, are very consistent with those of numerous epidemiological studies that have examined the association between vitamin D concentrations and the risk of developing asthma. Since the amount of melanin, age, body fat percentage, latitude, season, time spent outdoors, and use of sunscreen can influence vitamin D concentrations, the study examined participants' housing types and time spent outdoors. 

However, exposure to sunlight was found to be the only environmental factor associated with vitamin D amount in the blood. Regarding the link between asthma symptoms, vitamin D and sunlight, the researchers also took into account reverse causality: asthmatics have a greater tendency to stay indoors, minimizing their exposure to sunlight and thus their levels of vitamin D, which is known to be produced in the skin by sunlight. Korean children and adolescents in school spend little time outdoors, which could promote lower serum vitamin D concentrations and, in turn, a higher prevalence of asthma.

Some details of the study

A total of 80 children participated in this study, including 50 asthmatics and 30 healthy children (controls). Serum vitamin D levels were measured and compared between the two groups and, they were examined in relation to lung function test results and details of environmental factors, collected through a questionnaire submitted to the children. 

The results showed that vitamin D in the blood of subjects with childhood asthma (16.63 ng/mL) was significantly lower than that of healthy controls (24.24 ng/mL). Increased time spent outdoors seemed to significantly influence the increase in vitamin D levels, while no associations were observed between it and lung function and residential environmental factors such as type of housing, floor of the house, and "indoor" activity time.

More comprehensive research will confirm link between asthma and vitamin D deficiency

According to the scientists who conducted the study, these findings suggest that low serum concentrations of vitamin D are associated with childhood asthma in Korean children, and managing the level of this nutrient could be a promising approach to preventing the disease from worsening. 

The study did not consider the use of vitamin D supplements among its participants, or the effect of such supplements on levels of this vitamin. For this reason, the link between vitamin deficiency and increased risk of childhood asthma will need to be investigated further. Indeed, as stated by the authors themselves, the data should be interpreted with caution, and more comprehensive research will be needed to explore the causal relationship between vitamin D levels and childhood asthma.   

Source: Yu-Ri Kim, Sung Chul Seo, Young Yoo, Ji Tae Choung. "Are children with asthma in South Korea also associated with vitamin D deficiency?" The Korean Society of Environmental Health and Toxicology.