According to a new study, patients with diabetes can double their risk of heart disease if their diets do not contain enough vitamin D.

The study explains that the mechanism by which this occurs involves cholesterol and a special kind of cell called a microphage. The cells are dispatched by the immune system to deal with inflammation, but people with diabetes tend to dispatch them much more readily.

"When people are deficient in vitamin D, the macrophage cells eat more cholesterol, and they can’t get rid of it," says Dr Carlos Bernal-Mizrachi, a Washington University endocrinologist at Barnes-Jewish Hospital. "The macrophages get clogged with cholesterol and become what scientists call foam cells, which are one of the earliest markers of atherosclerosis."

The researchers discovered this by feeding cholesterol to macrophages in both low and high vitamin D environments. They found that the ones in low vitamin D environments showed a greater tendency to become foam cells.

Vitamin D is produced by the skin when it is exposed to sunlight, but in certain parts of the world, regular exposure to sunlight is difficult to get. Even so, the researchers are hopeful that the risk can be reduced or reversed by increasing vitamin D levels, which can be done with a supplement.