THE RELATIONSHIP BETWEEN VITAMIN D AND HIP FRACTURE

Abstract

Low levels of vitamin D are a frequent finding in old people, and several studies have

linked this diminution of vitamin D, with an increase in osteoporotic fractures. Vitamin D

insufficiency promotes serum calcium decrease, secondary hyperparathyroidism, high

bone remodeling and low bone mass, increasing the risk of fractures. On the contrary,

Chapuy et al. (1992) and Dawson-Hughes et al. (1997) in remarkable studies have

observed that the supplementation with 800 IU/day or 700 IU/day of vitamin D and

calcium, significantly decreases the number of hip fractures in an old population.

Nevertheless, this protective effect was not found by Lips et al. (1996) in another

randomized, placebo-controlled study using 400 IU/day, which is a lower dose of

vitamin D than the one used in the studies mentioned above, and without calcium

supplementation. So, the question is whether the positive effects found in the

populations treated with calcium and vitamin D were due to the combination of both or

just one of the two nutrients. Providing only vitamin D, at a dose of 400 IU/day, Meyer

et al. (2002) did not find any preventive effect of osteoporotic fractures. On the

contrary, the results provided by Trivedi et al. (2003) showed that a supplement of

100,000 IU of vitamin D every 4 months during 5 years, decreased the incidence of

fractures in men and women over 65 years of age. Failure to demonstrate a reduction

in the rate of fractures may be related to the dose of vitamin D used, since Chapuy,

Dawson-Hughes and Trivedi used higher doses than Lips and Meyer. The protective

effect of vitamin D on the ocurrence of hip fractures is probably due to both the

improvement in bone mineral density and the diminution in the bone remodeling. An

alternative explanation could be that vitamin D also affects directly factors related to the

falls, such as muscle strength.