Vitamin D protects against asthma, reduces attacks by 50%

Vitamin D protects against asthma, reduces attacks by 50%

 Vitamin D supplements reduce the risk of severe asthma attacks by 50 percent, according to a recent research review by the world-renowned Cochrane Collaboration.

The Cochrane Collaboration is an independent, international network of researchers, health professionals and patients who work together to review existing scientific research in order to promote evidence-based treatment.

Fewer severe attacks

Vitamin D has long been known to play an important role in preserving bone health, but in the 1980s researchers learned that vitamin D receptors are found throughout the body – particularly in white blood cells and in the epithelial layer of the respiratory system. This sparked an interest in whether the vitamin might play a role in immune or respiratory health.

Since then, numerous studies have confirmed that vitamin D plays a key role in immune regulation. Low levels of vitamin D have been strongly linked to a wide variety of autoimmune diseases, which share many physiological characteristics with allergies and asthma. Observational studies have also confirmed that asthma patients with lower blood levels of vitamin D are more likely to suffer from asthma attacks.

For the new studies, the researchers examined 81 separate studies into the connection between vitamin D and asthma attacks. From these, they identified nine that were double-blind, placebo controlled, randomized trials – considered the gold standard in medical research.

The researchers looked at several different asthma-related outcomes, including a worsening of symptoms severe enough to require an emergency room visit, hospital admission, or oral corticosteroid treatment; day-to-day asthma symptoms; lung function; exhaled nitric oxide; and biomarkers of airway inflammation.

The researchers found that people who took vitamin D supplements were 50 percent less likely to suffer from asthma attacks severe enough to require emergency room visits or hospital admission. They also reduced the risk of treatment with oral steroids.

Notably, vitamin D showed no effect on day-to-day asthma symptoms or any of the other biomarkers that the researchers examined.

Vitamin D fights infection, inflammation

Because of the design of the initial studies, the researchers were not able to determine whether vitamin D supplementation helped all patients, or merely those who were deficient in vitamin D before the study began. They have now partnered with the principal investigators of the nine initial studies to be able to review individual patient data.

The researchers hope that this collaboration will indicate a threshold above which vitamin D is shown to reduce the risk of severe asthma attacks, which will in turn allow them to make a clinical recommendation.

Although it is impossible to say exactly why vitamin D supplementation reduced the risk of attacks, prior studies showing a strong link between vitamin D and asthma are able to offer several possibilities. Some studies have shown, for example, that vitamin D can suppress inflammatory responses, including those that produce asthma attacks.

Studies have also shown that vitamin D helps induce immune responses when the body detects infection with an upper respiratory virus, like a cold or flu. These viruses are major triggers of asthma attacks.

Martineau offered two main cautions regarding the research. First, he noted that only about half of asthma patients suffer from a form severe enough to be at risk of the attacks examined in the study. It is unclear if or how vitamin D might affect people with these more mild forms of the disease.

He also noted that all the trials used vitamin D supplementation in addition to regular treatment, not as a replacement. Severe asthma attacks can be life-threatening.