Data from 4839 participants of the National Health and Nutrition Examination Survey (NHANES) showed that the prevalence of PAD was 4.4 per cent lower in people with blood levels of vitamin D above 29.2 nanograms per millilitre (ng/mL) than in people with blood levels below 17.8 ng/mL. PAD is associated with decreased blood flow in the legs, and occurs when arteries in the legs become narrowed or clogged with fatty deposits. According to 2008 statistic from the American Heart Association, PAD affects about 8 million Americans and is associated with significant disease and death. The authors of the study are careful to point out that the link does not prove vitamin D is protective in itself (causality), and recommend increasing intake of the vitamin from fortified foods and not supplements. "We would not recommend people start taking vitamin D supplements without talking to their doctors," stated lead researcher Michal Melamed, MD, from the Albert Einstein College of Medicine in New York City. "However, we recommend eating a balanced diet. People obtain vitamin D either through exposure to the sun or from foods, especially fish and fortified milk and other fortified foods." The results are published in the journal Arteriosclerosis, Thrombosis, and Vascular Biology, and were also presented at the American Heart Association's Arteriosclerosis, Thrombosis and Vascular Biology Annual Conference 2008. Study details Blood levels of 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form of the vitamin, was correlated to the prevalence of PAD among the participants. The average age of the "large nationally representative study sample" was 61.2. When the researcher divided the sample into four groups according to their 25(OH)D levels, and found that increasing levels of the vitamin were associated with lower prevalence of PAD, from 8.1 per cent in the group with the lowest 25(OH)D levels, to 5.4, 4.9, and 3.7 per cent across the 'quartiles' with increasing vitamin D levels. When the researchers adjusted for age, sex, race and co-existing health problems, they found that PAD was 64 per cent more common in the group with the lowest vitamin D levels compared with the group with the highest levels. For each 10 ng/mL drop in vitamin D level, the risk for PAD increased by 29 per cent. Moreover, the relationship was consistent across the difference subgroups. "The consistency of the results in these subgroups is noteworthy," wrote the researchers. The authors note that the relationship does not prove that increased levels of vitamin D protect against PAD directly, and that higher vitamin D levels may be a marker of general or specific lifestyle practices. Mechanism The potential mechanism by which vitamin D may improve cardiovascular health is not known and is "controversial," wrote the authors. "In some studies, low 25(OH)D levels have been associated with increased prevalence of coronary heart disease (CHD), stroke, and congestive heart failure. However, low 25(OH)D has been associated with a protective association in other studies," they stated. Dr. Melamed added: "We know that in mice, vitamin D regulates one of the hormone systems that affects blood pressure. Since cells in the blood vessels have receptors for vitamin D, it may directly affect the vessels, although this has not been fully worked out." The researchers called for large randomised clinical trials to address if vitamin D supplementation could offer protection against PAD. 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(OH)D, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body. Source: Arteriosclerosis, Thrombosis, and Vascular Biology Published online ahead of print, April 2008, doi:10.1161/ATVBAHA.108.165886 "Serum 25-Hydroxyvitamin D Levels and the Prevalence of Peripheral Arterial Disease. Results from NHANES 2001 to 2004" Authors: M.L. Melamed, P. Muntner, E.D. Michos, J. Uribarri, C. Weber, J. Sharma, P. Raggi
Increased levels of vitamin D may improve cardiovascular health and reduce the prevalence of peripheral arterial disease (PAD), suggests a new study.