Which came first? The disease, or the vitamin deficiency?

Data shows that people with a wide range of diseases and health issues — from weight gain to multiple sclerosis — also have lower-than-normal levels of Vitamin D in their system. But a couple of new reviews of multiple studies suggest that the cause/effect relationship here might not be what we think it is. It's possible the lowered Vitamin D levels are a result of poor health, not a cause of it.