BACKGROUND: Persons following plant-based diets have lower bone mineral density (BMD) and higher fracture risk, possibly due to suboptimal nutrient supply. However, anthropometric measures were not considered as potential confounders in many previous studies, and body mass index (BMI) is positively associated with BMD but also generally lower among vegans and vegetarians.
OBJECTIVES: Our objective was to investigate if BMD measurements differ between vegetarians and nonvegetarians from the adult general population when accounting for important determinants of BMD, especially BMI and waist circumference.
METHODS: Using data from the NHANES (cycles 2007-2008 and 2009-2010), we evaluated the differences in BMD (femoral neck, total femoral, and total lumbar spine) between adult vegetarians and nonvegetarians. Linear regression models were used to determine the associations between BMD and diet. Statistical models were adjusted for important factors, i.e., age, sex, race/ethnicity, smoking status, alcohol consumption, serum vitamin D and calcium concentrations, waist circumference, and BMI.
RESULTS: In statistical models adjusted for age, sex, race/ethnicity, menopausal status, and education level, BMD values were significantly lower among vegetarians than among nonvegetarians (P < 0.001). These differences were attenuated upon adjustment for lifestyle factors, and became statistically nonsignificant upon adjustment for anthropometric variables (BMI and waist circumference) for femoral neck (0.77 compared with 0.79 g/cm2 among vegetarians versus nonvegetarians, P = 0.10) and total femoral BMD (0.88 compared with 0.90 g/cm2, P = 0.12). A small but statistically significant difference remained for total lumbar spine BMD (1.01 compared with 1.04 g/cm2, P = 0.005).
CONCLUSIONS: These findings suggest that lower BMD among adult vegetarians is in larger parts explained by lower BMI and waist circumference.