An epidemiological investigation into the influence of nutritional factors on bone mineral density and bone metabolism
A food frequency questionnaire (FFQ) was developed for a study investigating dietary influences on bone mineral density (BMD) and bone metabolism (BM). The percentage contribution of food groups to nutrients of interest were identified from 20 7d weighed records (WR) and incorporated to form a 98 food item FFQ. The FFQ was validated against a further 20 7d WR, and the short (6 weeks) and long-term (1 year) reproducibility tested. Mean nutrient intakes by 7d WR and FFQ, and initial and repeat FFQ were similar and cross-classification showed few women to be grossly misclassified. Information was also collected on past intakes of milk and fruit, weight, height, smoking, social class and physical activity. The effect of dietary intake on BMD was investigated in 994 healthy premenopausal women aged 45-49 years. BMD was measured using dual energy X-ray absorptiometry at the lumbar spine (LS) and hip (femoral neck [FN], trochanter [FT], Wards [FW]). Nutrient intakes were adjusted for energy intake by calculating the residual from regression analysis. Positive relationships were found between BMD and intakes of Mg, K, Zn and vitamin C, remaining significant after adjustment for confounding variables. LS BMD was lower in women who reported a low intake of milk and fruit in their childhood and early adulthood. The influence of dietary intake on BM was assessed in 62 healthy peri-menopausal women aged 45-55 years. Bone resorption was determined by urinary excretion of pyridinoline (Pyd) and deoxypyridinoline (Dpd) using reversed-phase HPLC, and bone formation by serum osteocalcin (OC) using an ELISA. Energy adjusted intakes of K, Mg, carotene and vitamin C were negatively associated with Pyd and Dpd concentrations, remaining significant after appropriate adjustment including menopausal status. OC was positively associated with energy intake and weight. Twenty-six women were measured after one year, but no relationships were found between changes in bone mass and baseline bone metabolism markers or dietary intake. Results suggest there is a higher bone mass and lower bone resorption in women with high intakes of K, Mg, carotene and vitamin C, independent of confounding factors. Positive effects on acid-base balance, Mg deficiency or the role of vitamin C in collagen liydroxylation may provide some explanations for these findings.