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People with asthma should not be taking vitamin D supplements as a means of reducing their risk of developing a cold, a new study reported.

"Other studies of vitamin D and colds have produced mixed results. Most of those studies were conducted among healthy patients," study leader Dr. Loren Denlinger, an associate professor of medicine at the University of Wisconsin, said in a journal news release reported by Medical Xpress. "We wanted to ask the same question of a patient population in which the impact of a cold carries greater risk."

For this study, the researchers set out to see if vitamin D supplements could either prevent a cold or reduce the severity of a cold in asthmatic adults. They recruited more than 400 participants with mild to moderate asthma. All of the participants had low vitamin D levels as well.

The participants were assigned to either a vitamin D supplement group or a placebo group for 28 weeks. Throughout the experiment, about 50 percent of them had at least one case of the common cold. Cold symptoms were assessed every day using the Wisconsin Upper Respiratory Symptom Survey-21 scores.

At the 12-week mark, the researchers found that 82 percent of the participants from the vitamin D supplement group had normal levels of vitamin D. Despite getting their levels up, their risk of developing a cold was still the same as the other participants.

Denlinger concluded that they could not recommend vitamin D supplements "for the prevention of colds."

Vitamin D, which can be sourced from direct sunlight, is vital for bone health and other body functions.

The study's findings were published in the American Journal of Respiratory and Critical Care Medicine.