Vitamin D, calcium may prevent, improve diabetes

By Stephen Daniells

Combined supplementation with vitamin D and calcium may improve blood sugar and insulin levels, suggests a new meta-analysis and review

Although the evidence to date suggests that vitamin D and calcium deficiency influences post-prandial glycaemia and insulin response while supplementation may be beneficial in optimizing these processes, our understanding of the exact mechanisms by which vitamin D and calcium may promote beta cell function, or ameliorate insulin resistance and systemic inflammation is incomplete," wrote lead author Anastassios Pittas."It is also not clear whether the effects are additive or synergistic," he added.

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

Writing in the Journal of Clinical Endocrinology & Metabolism, Pittas and co-workers reviewed data from observational studies and clinical trials in adults with results related to the control of glucose.

The data from observational studies showed a "relatively consistent association" between low intakes of calcium, vitamin D, or dairy intake and type-2 diabetes, with highest levels associated with a 64 per cent lower prevalence of the disease, and a 29 per cent lower prevalence of metabolic syndrome among non-blacks.

When intake of calcium and vitamin D was combined, the inverse associations were still observed, with the highest versus lowest combined intake being associated with an 18 per cent lower incidence of diabetes.

"Evidence from trials with vitamin D and/or calcium supplementation suggests that combined vitamin D and calcium supplementation may have a role in the prevention of type-2 diabetes only in populations at high risk (i.e. glucose intolerance)," wrote the reviewers from Tufts-New England Medical Center.

They noted that research into this area remains limited and called for future research to focus on clarifying and quantifying the link between calcium intake and 25(OH)D levels and the incidence of type-2 diabetes.

"Additionally, there is a need for randomized trials to examine the effects of vitamin D and/or calcium supplementation with intermediary endpoints (glucose tolerance, insulin secretion, insulin sensitivity) and ultimately with incident type-2 diabetes," they added.

"The results of future studies will define the clinical role of vitamin D and calcium as potential interventions for prevention and management of t2DM, which will have significant public health implications since vitamin D and calcium insufficiency is common in US adults and both interventions can be implemented easily and inexpensively in clinical practice."

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.

Source: Journal of Clinical Endocrinology & Metabolism

June 2007, Volume 92, Number 6, Pages 2017-2029. doi:10.1210/jc.2007-0298

"The Role of Vitamin D and Calcium in type 2 diabetes. A systematic Review and Meta-Analysis"

Authors: A.G. Pittas, J. Lau, F. Hu, B. Dawson-Hughes