The growth years provide an important window of opportunity for building peak bone mass. More than one-fourth of adult bone mass is acquired between the ages of 12 to 14 years in girls and 13 to 15 years in boys. Although genetics determine 60-80% of peak bone mass, lifestyle choices including diet and physical activity are also predictors of bone accrual during growth. Calcium and vitamin D are two nutrients that are most likely to be deficient. Dietary calcium predicts 10-15% of skeletal calcium retention during adolescence with race and sexual maturity in the models. Boys retain more calcium than girls and black girls retain more calcium than whites girls. The role of Vitamin D status on peak bone mass is not well understood. Results of randomized, controlled trials are mixed and the effects of vitamin D supplementation on calcium absorption in children has not been studied. Dietary salt increases urinary calcium excretion. Exercise can enhance the effect of dietary calcium through enhanced bone geometry.