Vitamin C supplementation may decrease diabetes risk

Frequent users of vitamin C or calcium supplements may have a lower risk of type 2 diabetes, a new US study suggests.

In the observational study, the dietary supplement use of 232,007 elderly people was examined in relation to diagnosed diabetes after five years (1). Supplement use was assessed by food frequency questionnaire and diabetes by self-report. In the study, 14,130 diabetes cases were diagnosed. In total, 54% of the men and 65% of the women studied took multivitamin supplements. Among them, 79% of the men and 78% of the women reported daily uses. Of the individual micronutrient supplements, vitamin C (35%) was the most commonly used, followed by vitamin E (32%), calcium (29%), beta-carotene (13%), zinc (10%), vitamin A (10%), iron (8%), folic acid (7%) and selenium (6%).

The study results showed a significantly lower risk of diabetes for participants using vitamin C or calcium supplements frequently (seven times a week) compared with nonusers. The frequent use of multivitamins, vitamin E or other individual vitamin and mineral supplements was not associated with diabetes risk. The researchers commented that a potential reason for this is that multivitamins contain lower amounts of single antioxidants, such as vitamin C, than individual vitamin supplements, and thus might not be sufficient to be effective in reducing diabetes risk. However, the fact that findings suggest a lower diabetes risk among frequent users of vitamin C or calcium supplements appears to warrant further evaluations.

Several observational studies have found correlations between high antioxidant intakes and high levels of antioxidants in the blood and low concentrations of biomarkers for type 2 diabetes (2). However, there have been only few randomized controlled trials on vitamin supplements for primary prevention of type 2 diabetes that suggest no effects (3).

1. Song Y. et al. Multivitamins, individual vitamin and mineral supplements, and risk of diabetes mellitus among older U.S. adults. Diabetes Care. 2010.
2. Montonen J. et al. Dietary antioxidant intake and risk of type 2 diabetes. Diabetes Care. 2004; 27:362–366.