Higher vitamin D needed for diabetes benefits?

By Stephen Daniells

- Last updated on GMT

Related tags: Diabetes, Vitamin d

Combined supplementation with vitamin D and calcium may not reduce
the risk of diabetes, suggests new research that challenges
previous studies.

However, researchers using data from the Women's Health Initiative (WHI) do not rule out benefits for the vitamin-mineral combination, leaving the door open for further studies to investigate the role of higher doses. "Higher doses of vitamin D may be required to affect diabetes risk, and/or associations of calcium and vitamin D intake with improved glucose metabolism observed in non-randomised studies may be the result of confounding or of other components of foods containing these nutrients,"​ wrote lead author Ian de Boer from the University of Washington. An estimated 19 million people are affected by diabetes in the EU 25, equal to four per cent of the total population. This figure is projected to increase to 26 million by 2030. In the US, there are over 20 million people with diabetes, equal to seven per cent of the population. The total costs are thought to be as much as $132 billion, with $92 billion being direct costs from medication, according to 2002 American Diabetes Association figures. The new research, published in the journal Diabetes Care, challenges previous experimental and epidemiologic studies that reported a reduction in risk of developing type-2 diabetes by calcium and vitamin D supplementation. The WHI calcium/vitamin D trial randomly assigned 33,951 postmenopausal women to receive daily supplements of calcium (1000 mg) plus vitamin D3 (400 IU), or placebo. After seven years of follow-up, 2,291 women were diagnosed with diabetes. After adjusting for confounding factors, no association was found between the groups, suggesting the vitamin-mineral combination was ineffective. "Calcium plus vitamin D3 supplementation did not reduce the risk of developing diabetes over seven years of follow-up in this randomized, placebo-controlled trial," they concluded. However, by not discounting the possibility that higher doses may illicit an effect, the door remains open on the potential of vitamin D and calcium to impact diabetes risk. Indeed, a recent meta-analysis of data from observational studies and clinical trials in adults showed a "relatively consistent association"​ between low intakes of calcium, vitamin D, or dairy intake and type-2 diabetes. (Journal of Clinical Endocrinology & Metabolism, Vol. 92, pp. 2017-2029) Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive. The latter is derived from plants and only enters the body via the diet, from consumption of foods such as oily fish, egg yolk and liver. Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body Source: Diabetes Care​ Published online ahead of print, 30 January 2008, doi: 10.2337/dc07-1829 "Calcium plus vitamin D supplementation and the risk of incident diabetes mellitus in the Women's Health Initiative" ​Authors: Ian H. de Boer, B. Kestenbaum, D.S. Siscovick, N.S. Weiss, L.F. Tinker, S. Connelly, J.D. Curb, B.V. Howard, J.C. Larson, J.E. Manson, K.L. Margolis

Related topics: R&D

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