Dont count on extra vitamin D to get you through cold and flu season sniffle-free. Results from a large new clinical trial show no significant difference in upper respiratory tract infections between people randomly assigned to vitamin D supplements and those getting a placebo. The study, published in Clinical Infectious Diseases, also found no benefit from calcium supplements, either in duration of infection or severity of symptoms. The 759 generally healthy participants, ages 45-75, received either 1,000 IU of vitamin D, 1,200 milligrams of calcium, vitamin D plus calcium, or a placebo daily. Their days of illness and symptom severity were tracked over four winters.
Although some prior observational studies have suggested a benefit for vitamin D against upper respiratory tract infections, researchers pointed out that such studies cant eliminate the effects of lifestyle from causing bias. A randomized trial is designed to avoid those problems.