Condition - Insufficient vitamin D linked to severe asthma in children
According to the results of a new UK study, published in the American Journal of Respiratory and Critical Care Medicine, asthmatic children with low vitamin D levels in their blood are at greater risk of suffering from severe, therapy-resistant asthma than those with higher levels of the vitamin.
Asthma is a chronic inflammatory disorder of the airways, which causes an increase in airway hyper-responsiveness. Asthma is the most common chronic condition in children, and the prevalence of asthma in children is on the rise. If not well controlled, asthma can cause coughing, wheezing, chest tightness, trouble breathing or shortness of breath, fatigue, nigh-time coughing and noisy breathing. Asthma symptoms can make it hard for children to exercise, concentrate and sleep. Inadequate sleep has been linked with poor school performance. In fact, asthma is one of the most common reasons for children's absence from school.
One hypothesis for the rising prevalence of asthma involves lower vitamin D levels.
Vitamin D is best known for its important role in calcium absorption and bone health. New research suggests that vitamin D may also be involved in regulating blood pressure, lowering cancer risk, and mediating a shift to amore anti-inflammatory immune response.
Some experts believe that vitamin D may also enhance the anti-inflammatory function of steroid hormones – both the body’s natural supply and the synthetic versions used to treat asthma.
Vitamin D is naturally produced when ultraviolet rays from sunlight strike the skin, but long winter months of little sun exposure and sun avoidance mean that many children may not get enough vitamin D this way. In addition, vitamin D synthesis is less efficient in children with darker skin. Overweight children also appear to be at a greater risk of deficiency because vitamin D is stored in body fat, which means less of the active vitamin is in the blood.
Researchers led by Dr Sejal Saglani, of the Royal Brompton Hospital, London, carried out a study examining the relationship between blood vitamin D levels and airway structure and function in children.
Blood levels of 25-hydroxyvitamin D, the main metabolite of vitamin D and a marker of vitamin D status, were measured in 86 children with an average age of 11 years, who were either severe therapy-resistant asthmatics, moderate asthmatics, or non-asthmatic controls.
The researchers found that severely asthmatic children had significantly lower vitamin D levels (22-38 nmol/L) than those with moderate asthma (29-63 nmol/L) or non-asthmatic controls (45-67 nmol/L), and that higher vitamin D levels correlated with reduced airway inflammation and improved airway structure and lung function. Conversely, reduced vitamin D levels were associated with lower lung function, poor asthma control, increased medication use and exacerbations.
The results of this study suggest that detection and treatment of low blood vitamin D levels may be of benefit to children with severe therapy-resistant asthma.
Further research should be directed at determining whether vitamin D supplementation affects the degree of severity of asthma.
Gupta A, Sjoukes A, Richards D et al. Am J Respir Crit Care Med. 2011 Sep 15.