Prevalence of Cardiovascular Risk Factors and the Serum Levels of 25-Hydroxyvitamin D in the United States

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Abstract
Cardiovascular disease (CVD) is a major cause of mortality and morbidity in the United States.1 Hypertension and diabetes mellitus are among the leading risk factors for CVD.2 Several epidemiologic and clinical studies3-5 have suggested that there is an excess risk of hypertension and diabetes mellitus among persons with suboptimal intake of vitamin D. Dietary sources of vitamin D are very few and are limited to fatty fish liver and fortified food sources, such as cereals and milk. The synthesis of vitamin D in the skin after exposure to type B UV light remains a major source of vitamin D in humans. The primary circulating form of vitamin D is 25-hydroxyvitamin D (25[OH]D), formed in the liver by the hydroxylation of vitamin D. The active form of the vitamin is 1,25-dihydroxyvitamin D, formed by a second hydroxylation of vitamin D, primarily in the kidneys, and is responsible for the physiologic functions of vitamin D. The nutritional status of vitamin D has always been assessed by the circulating level of 25(OH)D, but the data for the historical reference range for the circulating level of 25(OH)D originated from sun-deprived human populations with suboptimal vitamin D intake and may have underestimated the physiologic demands for vitamin D.6,7 Recommended optimum levels of vitamin D have been established without accounting for the ubiquitous nature of the vitamin D receptor and the possible salutary affects of vitamin D on other organ systems that may affect CVD.8,9 Indeed, even the adequacy of present recommendations for vitamin D to prevent osteomalacia has been questioned.10