Dietary vitamin C and bone mineral density in postmenopausal women in Washington State, USA

Study objective - To examine the relationship between dietary vitamin C and hip bone mineral density (BMD) in postmenopausal women. Design - This was a cross sectional study using retrospective diet and vitamin supplement data. Setting - The Seattle area of Washington State. Participants - Screenees for a clinical trial of a drug to prevent osteoporotic fractures; 1892 women aged 55-80 years who had hip bone densitometry and osteoporosis risk factor information. Main results - Mean energy adjusted dietary intake of vitamin C was 113 mg/day; including supplement use, mean intake was 407 mg/day. There were no differences in BMD according to diet-only vitamin C intake or combined dietary and supplemental vitamin C intake. Longer duration of vitamin C supplement use was associated with higher BMD in women who had not used oestrogen replacement therapy (trend p = 0.02) and among women aged 55-64 years (trend p = 0.01). Women aged 55-64 years who used vitamin C supplements for ≤ 10 years had a higher BMD than non-users aged 55-64 years (multivariate adjusted mean BMD 0.699 (0.017)g/cm² versus 0.655 (0.007)g/cm², p= 0.02). Benefits were not evident in older age groups or in women who had used oestrogen in the past. Frequent intake of foods rich in vitamin C was not associated with BMD. Conclusion - There was no evidence that vitamin C from the diet was associated with BMD, although long term use of vitamin C supplements was associated with a higher BMD in the early postmenopausal years and among never users of oestrogen.