A doctor at Massachusetts General Hospital led a study of 322 healthy hospital workers and students in New Zealand. Half received a placebo. The other half received more than five times the adult recommended daily allowance of vitamin D.
It didn't help the avoid colds. Study co-author Dr. Carlos Camargo says, "if you take healthy adults with normal levels of Vitamin D in their blood and you boost them up significantly with a supplement given every month it has no apparent effect on the frequency or severity of upper respiratory infections."
Dr Camargo says it's important to remember that people in the study had normal levels of vitamin D to start with, so results of the study may not apLly to people with a deficiency of the vitamin. Past studies involving daily dosing of vitamin D did help reduce respiratory infections in children.