THE RELATION OF DIETARY VITAMIN-C INTAKE TO BONE-MINERAL DENSITY - RESULTS FROM THE PEPI STUDY

Ascorbic acid is a required cofactor in the hydroxylations of lysine a nd proline necessary for collagen formation; its role in bone cell dif ferentiation and formation is less well characterized. This study exam ines the cross-sectional relation between dietary vitamin C intake and bone mineral density (BMD) in women from the Postmenopausal Estrogen/ Progestin Interventions Trial. BMD (spine and hip) was measured using dual energy X-ray absorptiometry (DXA). The PEPI participants (n = 775 ) included in this analysis were Caucasian and ranged in age from 45 t o 64 years. At the femoral neck and total hip after adjustment for age , BMI, estrogen use, smoking, leisure physical activity, calcium and t otal energy intake, each 100 mg increment in dietary vitamin C intake, was associated with a 0.017 g/cm(2) increment in BMD (P = 0.002 femor al neck; P = 0.005 total hip). After adjustment, the association of vi tamin C with lumbar spine BMD was similar to that at the hip, but was not Statistically significant (P = 0.08). To assess for effect modific ation by dietary calcium, the analyses were repeated, stratified by ca lcium intake (>500 mg/ day and less than or equal to 500 mg/day). For the femoral neck, women with higher calcium intake had an increment of 0.0190 g/cm(2) in BMD per 100 mg vitamin C (P = 0.002). No relation b etween BMD and vitamin C was evident in the lower calcium stratum. Sim ilar effect modification by calcium was observed at the total hip: the beta coefficient in the higher calcium stratum was similar to that fo r the total sample (beta = 0.0172, P = 0.01), but no statistically sig nificant relation between total hip BMD and vitamin C was found in the lower calcium subgroup. Although the relation between vitamin C and l umbar spine BMD was of marginal statistical significance in the total sample, among women ingesting higher calcium, a statistically signific ant association was observed (beta = 0.0199, P = 0.024). These data ar e consistent with a positive association of vitamin C with BMD in post menopausal women with dietary calcium intakes of at least 500 mg.