Asthma patients obtain limited benefits from Vitamin D supplements, according to a study conducted by researchers at the Washington University School of Medicine.

Mario Castro, lead author of the study said that previous studies have found that low levels of vitamin D in blood weakens the lung function and heightens their risk of more asthma attacks and emergency room visits than those with higher vitamin D levels.

The researchers conducted the study to determine whether the inclusion of vitamin D supplements could relieve asthma patients from the symptoms. They found that vitamin D supplements were associated with restricted benefits.

"This is the first randomized-controlled trial to investigate whether taking vitamin D supplements can improve asthma control," Castro said in a press release.

According to Dr. Frank Lipman Vitamin D deficiency causes several diseases like Osteoporosis, cancer, heart diseases, obesity, diabetes, high blood pressure and asthma among others.

For the study, researchers analysed the medical reports of 408 adult patients, who suffered from mild to moderate asthma and had vitamin D deficiency, from nine major U.S. medical centers.

Average Vitamin D level in patients was 18 nanograms per ml of blood. Vitamin D level below 30 is deemed abnormal. All the patients took a steroid daily to control their asthma and were equipped with rescue inhalers in the event of an asthma attack.

The researchers divided the patients into two groups. One group received a loading dose of 100,000 international units of vitamin D3 and then a daily dose of 4,000 units. On the other hand the second group were treated with vitamin-free placebo pill.

The researchers found no difference between both the groups in asthma control, asthma attacks and need for emergency care. There was also no difference in the number of treatment failures.

However, researchers discovered that the group that received vitamin dose subsequently reduced their daily dosage of the steroid.

"The difference was small - 15 micrograms of steroid per day - but statistically significant," said Castro. "Over long term, even that small amount may have an important impact on reducing side effects of inhaled steroids. Although inhaled steroids work very well in controlling asthma, patients don't like them because they cause weight gain and increase the risk of diabetes and high blood pressure. Anything we can do to reduce the amount they need is important."