Hypertension (High Blood Pressure)

The results of epidemiologic and clinical studies suggest an inverse relationship between serum 1,25(OH)2D levels and blood pressure, which may be explained by recent findings that 1,25(OH)2D decreases the expression of the gene encoding renin (see Function). Data from epidemiologic studies suggest that conditions that decrease vitamin D synthesis in the skin, such as having dark skin and living in temperate latitudes, are associated with increased prevalence of hypertension. A controlled clinical trial in 18 hypertensive men and women living in the Netherlands found that exposure to UVB radiation three times weekly for six weeks during the winter increased serum 25(OH)D levels and significantly decreased 24-hour ambulatory systolic and diastolic blood pressure measurements by an average of 6 mm Hg. In randomized controlled trials of vitamin D supplementation, a combination of 1,600 IU/day of vitamin D and 800 mg/day of calcium for eight weeks significantly decreased systolic blood pressure in elderly women by 9% compared to calcium alone, but supplementation with 400 IU/day or a single dose of 100,000 IU of vitamin D did not significantly lower blood pressure in elderly men and women over the next two months. At present, data from controlled clinical trials are too limited to determine whether vitamin D supplementation will be effective in lowering blood pressure or preventing hypertension.

Osteoporosis

Although osteoporosis is a multifactorial disease, vitamin D insufficiency can be an important contributing factor. Without sufficient vitamin D, calcium absorption cannot be maximized and the resulting elevation in PTH secretion by the parathyroid glands results in increased bone resorption, which may lead to osteoporotic fracture . A prospective cohort study that followed more than 72,000 postmenopausal women in the U.S. for 18 years found that those who consumed at least 600 IU/day of vitamin D from diet and supplements had a risk of osteoporotic hip fracture that was 37% lower than women who consumed less than 140 IU/day . The results of most clinical trials suggest that vitamin D supplementation can slow bone density losses or decrease the risk of osteoporotic fracture in men and women who are unlikely to be getting enough vitamin D.

Supplementation of postmenopausal women in the U.S. with 500 mg/day of calcium and either 100 IU/day or 700 IU/day of vitamin D for two years slowed bone density losses at the hip only in the group taking 700 IU/da . Daily supplementation of elderly men and women with 500 mg/day of calcium and 700 IU/day of vitamin D for three years reduced bone density losses at the hip and spine and reduced the frequency of nonvertebral fractures. When the calcium and vitamin D supplements were discontinued, the bone density benefits were lost within 2 years. In Denmark, supplementation of elderly women with 400 IU/day of vitamin D for two years increased bone density at the hip.

An annual injection of 150,000-300,000 IU of vitamin D2 (ergocalciferol) for four years decreased the incidence of fracture in elderly Finnish women, and oral supplementation with 800 IU/day of vitamin D and 1,200 mg/day of calcium for three years decreased the incidence of hip fracture in elderly French women. Oral supplementation of elderly adults in the U.K. with 100,000 IU of vitamin D once every four months (equivalent to about 800 IU/day) for five years reduced the risk of osteoporotic fracture by 33% compared to placebo. However, oral supplementation with 400 IU/day of vitamin D for more than 3 years did not affect the incidence of fracture in a study of elderly Dutch men and women. Overall, the evidence to date suggests that vitamin D supplements of about 800 IU/day may be helpful in reducing bone loss and fracture rates in the elderly. In order for vitamin D supplementation to be effective in preserving bone health, adequate calcium (1,000 to 1,200 mg/day) should also be consumed.

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