Having low levels of vitamin D worsens asthma symptoms and makes asthmatics less likely to respond to steroid treatment, a new study has found.

Researchers at National Jewish Health in Denver took the vitamin D levels of 54 asthmatics and tested them for lung function, constriction of the airways and responsiveness to steroid treatment.

They found that those with low vitamin D levels did worse on every measure and airway constriction almost doubled in those with vitamin D levels below 30 nanograms/ml.

Those with low vitamin D also produced more of a pro-inflammatory cytokine called TNF-alpha, indicating vitamin D may play a role in reducing inflammation.

“There is a potential that restoring normal vitamin D levels in people with asthma may help improve their asthma,” lead researcher D.E. Rand Sutherland said.

The researchers also noted that the heaviest participants in the study had the lowest levels of vitamin D.