Obese people with low levels of vitamin D in their bodies are at an increased risk of developing diabetes, a new study indicates.

According to US scientists, obesity is already a well known risk factor for diabetes. Insufficient vitamin D levels are also seen as a risk factor. However both of these together ‘increase the odds of insulin resistance' even more.

Insulin resistance is a precursor to diabetes.

The scientists studied data on almost 6,000 people. They found that obese people with healthy levels of vitamin D in their body were 20 times more likely to have insulin resistance compared to people in the general population.

However, the risk of insulin resistance in obese people with low levels of vitamin D was 32 times higher.

"Vitamin D insufficiency and obesity are individual risk factors for insulin resistance and diabetes. Our results suggest that the combination of these two factors increases the odds of insulin resistance to an even greater degree than would have been expected based on their individual contributions," the scientists from Drexel University in Pennsylvania explained.

Vitamin D is essential for healthy bones, but is present in very few foods. It is also known as the sunshine vitamin, because it is made in the body when ultraviolet rays from sunlight strike the skin. However, Ireland's northerly latitude and lack of winter sunlight means that we cannot make enough vitamin D in this way. As a result, some people choose to take supplements.

The scientists said that more research is needed to ascertain whether taking supplements could reduce the risk of developing insulin resistance and diabetes in people who are obese.

If this was proven, it could become a simple and inexpensive prevention strategy, the team added.

Details of these findings are published in the journal, Diabetes Care.