Those who have lower blood levels of vitamin D may be at a higher risk of developing diabetes, according to a new study. Researchers with the Australian Diabetes, Obesity and Lifestyle Study followed over 5,000 adults for five years and found that those with lower levels of vitamin D were more likely to develop type 2 diabetes than those with vitamin D levels in the recommended range.

Twice as many people with low vitamin D levels developed diabetes compared to those with normal levels of vitamin D.

The researchers measured the vitamin D blood levels in over 5,000 people who did not have diabetes. Five years later approximately 200 of the study participants had developed type 2 diabetes, and vitamin D levels were tested again. Twice as many people with low vitamin D levels developed diabetes compared to those with normal levels of vitamin D. Other risk factors for diabetes were taken into consideration such as age, waist circumference, and family history, but those with low vitamin D levels were 57% more likely to develop type 2 diabetes.

The study suggests that blood levels of vitamin D recommended for bone health may not be high enough to reduce the risk of developing type 2 diabetes. According to the Office of Dietary Supplements, a definite level for vitamin D adequacy has not been developed, but based on its review of data, a committee at the Institute of Medicine concluded that those with vitamin D levels <12 ng/mL (nanograms per milliliter) are at risk of deficiency, while a level between 12–20 ng/mL is generally considered inadequate for bone and overall health. Vitamin D levels ≥ 20 ng/mL are considered adequate for bone and overall health.

Vitamin D is manufactured by the body when exposed to sunlight but is naturally found in few foods. Eggs, fish, and fortified dairy products are good sources of vitamin D. The recommended dietary allowance is 600 IU per day for adults.

Previous studies have linked vitamin D to lower risks of asthma, some types of cancer, and heart disease, but there isn’t enough evidence that supplements of vitamin D can help treat these conditions. Neither is there evidence that supplementing with vitamin D will prevent diabetes.

The best way to prevent type 2 diabetes is to maintain a healthy body weight, eat right, and exercise. More research is needed to determine if vitamin D supplements really do reduce the risk of developing diabetes, and if it does, to determine the optimal blood level of vitamin D to minimize the risk.

The study was published online on March 23, 2011 in Diabetes Care.