Biomarkers of Bone Turnover in Vegetarians and Omnivores

A cross-sectional study on fasting serum and 24-hour urine samples were used to determine whether biochemical markers of bone turnover, resorption and formation, differed in a group of 50 healthy premenopausal Caucasian women eating vegan, lactoovovegetarian(LOV) and omnivorous diets. The women, ages 20-42, had participated in a study of bone mineral density(BMD). The three groups were comparable in mean age, BMI, calorie intake, calories spent in exercise, kcal/kg body weight, protein/day, protein/kg body weight and urinary creatinine. Biomarkers included those of bone resorption—pyridinoline, deoxypyridinoline, and N-telopeptides, and of bone turnover—serum and urinary osteocalcin(OC), skeletal alkaline phosphatase, and propeptide-type-I-carboxyterminal-procollagen(PICP). In all subjects, biomarker levels were significantly lower in women ages 27-33yr compared to women 20-26yr and 34-38yr. Selected resorption and turnover biomarkers were significantly and negatively correlated with BMD, and with Ca:Protein and Ca:P ratios. Findings suggest women with both higher resorption and higher turnover rates are more likely to have lower BMD of the spine and lower calcium intake in relationship to protein and phosphorus, but not to calcium alone. Higher resorption and turnover were seen where these ratios were lower, as in vegans. A consistent trend was observed with vegans having the highest levels of bone resorption and bone turnover markers while consuming the lowest Ca:Protein and Ca:P ratios. Serum osteocalcin, a marker of bone turnover in adults, was significantly higher in vegans than in LOVs. BMD, Ca:Protein, and Ca:P were significantly lower in vegans than in LOVs. Higher bone turnover and an inadequate diet is consistent with the significantly lower BMD found in vegans. Increased biomarkers of turnover and resorption may be early predictors of future osteopenia, especially in premenopausal women with low Ca:Protein and low Ca:P ratios. This study found vegans were at risk, possibly because they consumed a diet very low in calcium, particularly in relationship to protein and phosphorus. Such a diet may have resulted in the significantly higher turnover rates found in the vegans as well as the significantly lower BMD. A vegetarian diet that contains recommended levels of calcium may help to achieve peak skeletal mass at maturity and provide a more stable bone mass during menopause