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High vitamin C linked to lower hip fracture risk.

MONTREAL -- Consumption of vitamin C at sufficiently high levels is associated with nearly a 50% decrease in the risk of hip and nonvertebral osteoporotic fractures in elderly men and women, according to a 15- to 17-year follow-up of participants in the Framingham Osteoporosis Study.

Previous studies of menopausal and postmenopausal women have shown that dietary intake of vitamin C is associated with increased bone mineral density (BMD), and that a high vitamin C serum level is associated with a decreased prevalence of fracture. Poor dietary intake of vitamin C also has been associated with an increased risk of hip fracture, Marian T. Hannan, D.Sc., said at the annual meeting of the American Society for Bone and Mineral Research.

Vitamin C, an antioxidant, plays an important role in the formation of collagen, which is a major component of connective tissue. Published evidence suggests that oxidative stress may result in increased osteoclast formation, resulting in greater bone resorption, said Dr. Hannan, who presented the study on behalf of Shivani Sahni of Tufts University, Boston, who performed the research for her thesis but could not attend the meeting.

Of 5,209 men and women in the original Framingham Heart Study cohort, the investigators identified 958 individuals who had participated in the beginning of the osteoporosis study in 1988-1989, had answered a food-frequency questionnaire, and had no history of a hip fracture. These individuals had a mean age of 75 years and experienced 100 hip fractures and 180 non-vertebral osteoporotic fractures during the follow-up period, Dr. Hannan reported.

For the study, participants were divided into three groups based on their intake of vitamin C. The relative risk of hip fracture was significantly lower for individuals who had the highest total intake of both dietary and supplemental vitamin C (a median of 305 mg/day) than it was for people with the lowest total intake (median of 97 mg/day). This translated into a 44% decrease in relative risk of hip fracture, according to Dr. Hannan of Harvard Medical School's Institute for Aging Research, Boston.

Those with the highest total intake of vitamin C also had a 36% lower relative risk of having a nonvertebral osteoporotic fracture than did individuals with the lowest total intake.

When the investigators looked at supplemental vitamin C intake alone, the highest users (median of 260 mg/day) had a 70% lower relative risk of hip fracture than did nonusers. Supplements accounted for about 28% of the individuals' total vitamin C intake, Dr. Hannan said. The investigators found no effect for dietary intake of vitamin C alone.

All of the comparisons were adjusted for age, sex, body mass index, height, smoking status, estrogen use in women, physical activity, alcohol use, multivitamin use, femoral neck BMD, and total intake of energy, calcium, vitamin D, and potassium.

One audience member suggested that the discrepancy between the effects of supplemental and dietary vitamin C intake could mean that there are residual confounding effects from factors that were not accounted for in the study, such that supplemental use of vitamin C may be a marker for people who care more about their health and take better care of themselves. This is a problem that can only be answered with a randomized, controlled trial. Dr. Hannan noted.

"We were intrigued by the lack of a BMD effect on [the association between] vitamin C and fracture, and we believe that it implies that vitamin C may affect a different pathway or other fracture risk factors, for example, fall risk factors or mobility risk factors," Dr. Hannan said.

Future research should investigate "alternative mechanisms for vitamin C that are independent of BMD [and] whether an increase in the recommended dietary intake for vitamin C should take into account the preventive effects seen in this study."


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Author:Evans, Jeff
Publication:OB GYN News
Date:Oct 1, 2008
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