Researchers from the Wolfson Medical Center and Tel Aviv University in Israel report that daily doses of vitamin D of 1,000 IU for one year significantly decreased the central aortic augmentation index, a predictor of adverse cardiovascular events.
“The findings of the present study may have clinical implications for the usual recommended daily allowance for vitamin D in diabetic patients,” they wrote in Clinical Nutrition .
“Since the levels of vitamin D are extremely low in this population, more appropriate daily supplementation doses of > 1.000 IU/day might be recommended to achieve optimal levels of vitamin D.”
The study adds to an ever-growing body of science supporting the cardiovascular benefits of the sunshine vitamin in people with or at risk of diabetes. A study published in Diabetes Care last year reported that people with metabolic syndrome may be at a lower risk of dying from cardiovascular disease if they have optimal vitamin D levels.
Optimal levels of vitamin D – defined as having blood levels of 25-hydroxyvitamin D (25[OH]D) of at least 75 nmol/L – were associated with a 66% reduction in the risk of cardiovascular disease mortality, compared with people with severe vitamin D deficiency (Diabetes Care, May 2012, Vol. 35, pp. 1158-1164).
The Israeli researchers recruited 47 type-2 diabetic patients to participate in their randomized, placebo-controlled study. Participants received either a daily dose of vitamin D (1,000 IU per day) or placebo for one year.
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), the biologically active form that is tightly controlled by the body.
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.
Results showed that the augmentation index decreased significantly in the vitamin D group (a decrease of 7 units), compared with placebo (a decrease of 0.31 units).
No changes were observed in other measures, such as maintaining a health blood sugar level (glucose homeostasis). However, levels of adiponectin were found to increase over the 12 months of vitamin D supplementation, while no such changes were observed in the placebo group.
“The change in circulating adiponectin, a collagen-like protein specifically expressed in human adipose cells which plays an important role in insulin sensitivity, inflammation and atherogenesis, observed in the vit D group but not in the placebo group, is of interest,” wrote the researchers.
“Since adiponectin emerged as an important link between atherosclerosis and insulin resistance as well as an independent predictor of atherosclerotic vascular disease, the increase even marginal in circulating adiponectin levels during vitamin D supplementation as a potential mechanism of improved arterial stiffness may also be considered.”
Since the study included a small number of participants, and a relatively large number of these people dropped out, the researchers called for larger studies to establish the benefits of vitamin D supplementation on vascular health as well as its clinical impact on cardiovascular outcomes in type-2 diabetics.
Source: Clinical Nutrition
Published online ahead of print, doi: 10.1016/j.clnu.2013.01.020
“Effect of high doses of vitamin D on arterial properties, adiponectin, leptin and glucose homeostasis in type 2 diabetic patients”
Authors: A. Breslavsky, J. Frand, Z.Matas, M. Boaz, Z. Barnea, M. Shargorodsky