A long-term observational study of data from the Nurses’ Health Study suggests that high intake of supplemental vitamin D and calcium can significantly lower the risk of type 2 diabetes in women (Diabetes Care. 2006;29:650-656).
This study, which was started in 1976, is the first to look at the joint effects of vitamin D and calcium on diabetes risk. Included were 83,779 women (median age, 46 years) with an average body mass index of 24.2 kg/m2 who were followed for 20 years. Participants had no history of diabetes, cardiovascular disease, or cancer at study onset. Dietary and supplemental vitamin D and calcium intake were assessed at 2- and 4-year intervals. Overall, 4843 (5.8%) new cases of type 2 diabetes occurred during the study. Follow-up began in 1980 and was completed in June 2000.
Mean daily cumulative intake of vitamin D over the 20-year follow-up period was 309 IU; mean daily calcium intake was 867 mg. Average total vitamin D intake increased from 291 to 342 IU/day during the follow-up period, while calcium intake increased from 731 to 980 mg. Even with these increases, when the final dietary assessment was obtained at the end of 1998, only 3% of the women were consuming sufficient amounts of vitamin D, and 24% were consuming sufficient amounts of calcium, based on the most recent guidelines from the Institute of Medicine.
The incidence of diabetes is on the increase in the United States and worldwide.
This study shows that high intake of supplemental, but not dietary, calcium and vitamin
D could reduce the risk of diabetes by one third.
Greatest risk reduction was seen with >1200 mg supplemental calcium and >800 IU vitamin D.
Dietary and supplemental vitamin D and calcium were analyzed. Women who took Ž400 IU/day of supplemental vitamin D had a 13% lower risk of developing diabetes compared with those whose intake was 100 IU/day. Women who took Ž1200 mg/day total (dietary and supplemental) calcium lowered their risk of developing diabetes by 21% compared with women whose intake was <600 mg/day.
Similar benefits were not observed in women whose calcium intake came only from food. Whereas the majority (90%) of the women were not taking calcium supplements in 1980, almost half (48%) were taking them in 1998.
There was an inverse association between calcium intake from supplements only and the occurrence of diabetes, even after adjusting for all covariates. This extended to women with lower supplemental calcium intakes; those who took Ž500 mg/day had an 18% lower risk of diabetes compared with those who took 250 mg/day.
An analysis of the combined effects of vitamin D and calcium showed that the combination of >1200 mg of calcium and >800 IU of vitamin D reduced the risk of type 2 diabetes by 33% compared with intakes of <600 mg and 400 IU, respectively.
“For both vitamin D and calcium, intakes from supplements rather than from diet were significantly associated with a lower risk of type 2 diabetes,” wrote lead investigator Anatassios G. Pittas, MD, of Tufts-New England Medical Center, Boston, and colleagues.
If confirmed, these results will have “important public health implications, because both of these interventions can be implemented easily and inexpensively to prevent type 2 diabetes,” they added.