A study published in the American Journal of Respiratory and Critical Care Medicine, (April 2009) suggested that low levels of Vitamin D may be linked to severity of asthma in children. (1)

 

The study examined the blood levels of Vitamin D in children with asthma and found that lower levels of Vitamin D were associated with more severe asthma.

Participants included 616 children with asthma between the ages of 6 and 14. Of the participants, 175 had insufficient levels of Vitamin D. John Brehm, MD, from Brigham and Women's Hospital, and colleagues found that low Vitamin D levels were associated with more asthma hospitalizations in the previous year, more airway hyperactivity in lung function tests, more use of anti-inflammatory asthma medications such as inhaled steroids in the previous year, and higher blood levels of allergy markers.

While the study doesn't confirm a cause-effect relationship, the researchers note that Vitamin D may influence asthma in different ways, such as its effect on the immune system and muscle cells of the airways.

 

Then in January 2010, another study published in American Journal of Respiratory and Critical Care Medicine, (2) also demonstrated that low Vitamin D levels were associated with worse lung function compared to higher Vitamin D levels in people with asthma. Researchers compared Vitamin D levels and asthma severity in 54 people with asthma.

 

The results showed that people with higher Vitamin D levels had better lung function than people with lower Vitamin D levels. In particular, people with low Vitamin D performed worse on tests of lung function and airway hyper-responsiveness, two hallmarks of asthma.

Vitamin D levels were shown to be directly related to participants' score on the breathing tests: the lower the Vitamin D levels, the worse their performance.
For example, airway hyper-responsiveness was nearly twice as poor in people with Vitamin D insufficiency (below the threshold level of 30 nanograms/milliliter) as compared to those with higher Vitamin D levels.

In addition, the study showed that people with low Vitamin D levels didn't respond as well to asthma treatments as compared to people with higher Vitamin D levels.

 

The study also showed that low Vitamin D levels were associated with increased production of a pro-inflammatory protein in the blood, which raises the possibility that low vitamin D levels could be related to increased inflammation in people with asthma.

"Our findings suggest that Vitamin D levels influence a number of important features of asthma, including lung function, bronchospasm, and therapeutic response to steroids," researcher E. Rand Sutherland, MD, MPH, chief of the pulmonary division at National Jewish Health in Denver, says in a news release.