Strong links between vitamin D status and insulin secretion, and with diabetes, have been shown in recent studies, but now a large US study from the Harvard School of Public Health suggests vitamin D status may also be important in earlier “pre-diabetes”.
Pre-diabetes is the name doctors have given to the condition where fasting blood glucose is high, but not high enough for a diagnosis of type 2 diabetes. Many people with pre-diabetes will go on to develop full-blown diabetes some 5 to 10 years down the track if they don't make lifestyle changes.
Using data from the Framingham Offspring Study, which follows children of the original Framingham (Massachusetts) longitudinal study, 2571 men and women averaging 54 years of age were followed for an average of 7 years. None had any evidence of diabetes. Body mass index (BMI) was recorded at the start, together with fasting blood glucose (blood sugar) level and vitamin D level.
Fasting blood glucose levels are done after at least 8 hours of fasting, and a high level of glucose can indicate pre-diabetes or diabetes.
As expected, blood glucose levels rose with advancing age. However, those in the highest third for vitamin D levels at the start of the study had a significantly lesser rise in fasting glucose level over the 7-year period than those in the lowest third of vitamin D. In fact, the average rise in fasting blood glucose level (0.23 mmol/L) in the “high vitamin D” group was only 66 per cent of that for the “low vitamin D” group (a 0.35 mmol/L rise). All the results were corrected for the effects of age, gender and BMI at the start of the study.
While this type of evidence does not offer any mechanism for the observed findings, it does suggest that vitamin D status in healthy older adults is important in preventing the onset of early metabolic changes that lead towards diabetes. In view of current knowledge about vitamin D and insulin metabolism, this is not perhaps surprising.
It worthwhile remembering that Framingham (MA) lies in a part of the US which has a substantial variation in sunlight hours over the year (and therefore variation in the ability of the body to produce vitamin D). Recent Australasian research shows that, contrary to what might be expected in our sunnier climate, less-than-optimum vitamin D levels are actually quite common, even in young children. This effect may be exacerbated in some people by efforts to limit sunlight exposure because of our higher rates of melanoma and skin cancer. Vitamin D is not present in significant amounts in most people’s diet, and some experts consider that, overall, supplements may be the correct approach for most people.
Last Reviewed: 23 February 2012