Because the Framingham Heart Study is not a randomized controlled trial, it's still not clear if vitamin D is the real reason for the link (the vitamin's levels could drop in unhealthy people for other reasons), or if taking a supplement would lower the risk. However, experts agree that a connection is likely. Vitamin D appears to regulate insulin production in the pancreas, and a deficiency could raise diabetes risk. Low levels of vitamin D can also raise blood pressure and increase inflammation in the arteries, "a recipe for disaster," says O'Keefe.