Scientists from the Universities of Aberdeen and Dundee in Scotland and the University of Auckland in New Zealand report that 800 IU per day of vitamin D were associated with lower risks of heart failure, but had no impact on heart attack or stroke.
“Results suggested that there is insufficient evidence to support vitamin D supplementation for the reduction of cardiovascular events but raised the possibility that vitamin D supplementation might have an effect on heart failure,” they wrote in the American Journal of Clinical Nutrition.
The researchers analyzed data from the Randomised Evaluation of Calcium Or vitamin D (RECORD) randomized controlled trial (RCT), and also performed a systematic review and meta-analysis.
Data from RECORD, which had 5,292 participants randomized to one of four groups (800 IU/d of vitamin D3, 1,000 mg/d of calcium, vitamin D and calcium, or placebo), indicated that the risk of heart failure was reduced by 25% for the vitamin D groups compared to no vitamin D. No significant effects were observed for heart attack or stroke.
Results from the 21 studies with 13,033 people included in the systematic review and meta-analysis found similar results, with the risk of heart failure reduced by 18% for vitamin D groups, compared with the placebo or control. Again, no significant effects were observed for heart attack or stroke.
“Sufficiently powered, high-quality RCTs are needed to investigate the relation between cardiovascular disease and vitamin D,” wrote the researchers. “An ongoing trial will randomly assign 1000 participants with cardiac failure to received vitamin D or a control and measure the symptom improvement and mortality at 3 years.
“However, to our knowledge, no studies are currently aiming to prevent heart failure in patients at high risk (eg, MI with a reduced ejection fraction). These trials are using high doses of vitamin D, although none of them have set vitamin D deficiency as an entry criterion.”
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D).
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
Vitamin D deficiency in adults is reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 and -2 diabetes.
Low 25-hydroxyvitamin D status has been associated with increased cardiovascular events in epidemiologic studies.
However, while much growth in vitamin sales is driven by the sunshine vitamin (according to the Nutrition Business Journal), there is resistance to the use of vitamin D to fortify foods.
In her Food Politics blog, Marion Nestle from the Department of Nutrition, Food Studies, and Public Health at New York University, writes, “’Vitamin’ D is not a vitamin; it is a hormone synthesized by the action of sunlight on skin. For this reason alone, it does not belong on the food label.
“Vitamin D fortification must be understood as a form of hormone replacement therapy,” she continues. “As such, it raises questions about efficacy, dose, and side effects that should be asked about all such therapies.
“Fortification and supplementation provide hormone Vitamin D by the oral route. This is not physiological. Active vitamin D is synthesized in the body through a series of reactions that begin with the action of sunlight on skin. Sunlight on skin produces ample Vitamin D, is regulated to promote synthesis as needed and avoid toxicity, and may lead to synthesis of other useful biological components; the unphysiologic oral route does not produce the same benefits.”
To read all of Prof Nestle’s blog post, please click HERE.
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi:10.3945/ajcn.113.082602
“Cardiovascular disease and vitamin D supplementation: trial analysis, systematic review, and meta-analysis”
Authors: J.A. Ford, G.S. MacLennan, A. Avenell, M. Bolland, A. Grey, M. Witham, and for the RECORD Trial Group