Vitamin DSupplementation with vitamin D3 may reduce a patient’s risk of developing respiratory tract infections (RTIs), according to research published last week in the online scientific journal BMJ Open. Investigators found that symptoms of RTIs declined by almost a quarter and the use of antibiotics by almost half. Vitamin D treatment was also tolerated well by all patients and gave no serious side effects, according to study results.

“Our research can have important implications for patients with recurrent infections or a compromised immune defense, such as a lack of antibodies, and can also help to prevent the emerging resistance to antibiotics that come from overuse,” says Peter Bergman, researcher at Karolinska Institutet’s Department of Laboratory Medicine (Stockholm, Sweden) and doctor at Karolinska University Hospital’s Immunodeficiency Unit. “On the other hand, there doesn’t seem to be anything to support the idea that vitamin D would help otherwise healthy people with normal, temporary respiratory tract infections.”

This study contradicts findings from an unrelated New Zealand study published in JAMA earlier this year. Researchers note the current study differs from the JAMA study in several important respects, which could explain their different results. Specifically, the JAMA study examined a group of healthy people with initially normal levels of vitamin D in the blood, using bolus dose administration (ie, large doses on fewer occasions), which is thought to be less effective than daily doses.

“However, the most important difference is probably due to the fact that our participants had much lower initial levels of vitamin D than those in the New Zealand study,” says Anna-Carin Norlin, MD, doctoral student and co-lead author of the study along with Bergman. “There is evidence from previous studies that vitamin D supplements are only effective in patients who fall well below the recommended level, which also suggests that it would be wise to check the vitamin D levels of patients with recurrent infections.”