You would need to control every factor of a person's life to see if D makes the difference: food, culture, stressors, exercise, etc. Since it’s not possible to

You would need to control every factor of a person's life to see if D makes the difference: food, culture, stressors, exercise, etc. Since it’s not possible to do this should we give up studying these sorts of things? Scientists study theses types of things the best way they know how. They search for clues, evidence. Then more studies are done. Eventually, hopefully, enough evidence has been amassed to make a conclusion that has a very good chance of being correct. It’s not perfect but it’s much better than doing nothing. The authors acknowledge the limitations of the conclusions that can be made. They write: Vitamin D supplementation might reduce the incidence of major cardiovascular events, although the absolute risk difference was small and the confidence interval was consistent with a null finding. These findings could prompt further evaluation of the role of vitamin D supplementation, particularly in people taking drugs for prevention or treatment of cardiovascular disease.