The U.S. recommendation for daily calcium intake is 800 to 1,300 mg, but it is unclear whether dietary calcium helps prevent osteoporosis. Fracture rates in the United States are high in spite of high dairy consumption. Although dietary protein supports bone growth, it also is associated with calcium loss because 6 mg of calcium are required to offset the urinary loss of calcium that occurs with 1 g of protein intake. These and other factors (e.g., body weight, pubertal status, exercise) need to be accounted for in studies that evaluate the effect of calcium on bone integrity. Lanou and colleagues conducted a review of the effect of dairy product consumption and calcium supplementation on bone integrity in children, adolescents, and young adults (ages one to 25 years).

The authors performed a MEDLINE search of studies controlling for factors that might influence bone integrity and health. They found 17 cross-sectional studies that met the inclusion criteria. Four of these studies included information on dairy or milk consumption; the rest reported on total calcium intake. Of the four studies reporting on dairy product consumption, three showed no relationship between dairy product consumption and bone mineral density (BMD). In the study that did show a correlation, milk and vitamin D were significant predictors of BMD, but there was no correlation between total calcium intake and BMD. Of the remaining 13 cross-sectional studies, nine showed no relationship between calcium intake and bone health. Body weight, physical activity, pubertal or menarchal status, height, and age were the main predictors of BMD in these studies.

Seven retrospective studies were included in the review. Milk consumption had no impact on fracture risk, bone mineral content, or BMD in these studies. Total calcium consumption lowered fracture risk in one study; in another study, calcium consumption was associated with BMD in a midpuberty group but not in a pre- or postpuberty group. Lower bone mineral content also was found in children who had consumed a macrobiotic diet compared with those who had not consumed a macrobiotic diet in the first six years of life.

Of the 10 prospective studies included in the review, one estimated the specific effects of dairy products on bone mass and density. In this study, there was no significant correlation between dairy calcium intake and BMD. Of the nine studies measuring total calcium intake, one study showed a positive correlation between cumulative calcium intake from birth to five years of age, but current calcium intake was not associated with BMD.

Of the 12 randomized controlled trials (RCTs) included in the review, one measured vitamin D intake and found increases in lumbar spine and total bone mineral content in girls who increased their dairy product consumption over one year, but the study found no difference in average BMD. In another RCT, BMD was slightly greater in the group treated with one pint of milk per day. In 10 RCTs assessing calcium supplementation, nine showed a 1 to 6 percent increase in BMD or bone mineral content at one or more bone sites.

The authors state that there is no evidence to support the idea that milk is the preferred source of calcium. A positive correlation between dairy product consumption and bone health was found in three of 11 trials. A positive correlation between calcium intake and bone health was found in seven of 26 studies. A total of nine trials showed a positive correlation with calcium intake, although the correlations were small and seemed to be transient. Physical activity appeared to have the greatest impact on bone health in these studies.