Bone health in children
Authors: Amy Joy Lanou
Journal: BMJ (2006)

Conventional wisdom, public policy on nutrition in many westernised countries, and advertisements for dairy products link increased consumption of calcium to better bone health and prevention of osteoporosis in later life. However, a meta-analysis by Winzenberg and colleagues in this week's BMJ shows that calcium supplementation in children is unlikely to result in a clinically relevant decrease in the risk of fracture in childhood or in later life.1

Previous research has questioned whether increasing calcium intake through diet or supplements benefits children's or young adults' bones. Exercise significantly increased bone density and bone strength, but calcium intake between 500 and 1500 mg had no effect on the same outcomes in adolescent girls studied prospectively for 12 years as they passed into young adulthood.2 Of three qualitative reviews of literature published in this decade, two concluded that it is not known whether the modest increments in rate of bone gain after supplementation with calcium or dairy produce will translate into clinically meaningful reductions in the risk of osteoporosis later in life or even persist beyond the treatment period.3,4 The third concluded that increases in dairy or total dietary calcium intake did not reliably increase bone mineral density or reduce fracture rate in children or adolescents.5

None the less, the recommended intake of calcium in children remains high in the United Kingdom, the European Union, Australia, the United States, and Canada (350-800 mg/day for children and 800-1300 for adolescents).6 Consequently, policy guidelines and nutrition programmes promote the intake of two to four servings of dairy products daily. For example, the US government promotes the consumption of three or more servings of cow's milk or other dairy products daily, and it subsidises the distribution of dairy products through the national school lunch programme and the women's, infants', and children's nutrition programme. The justification has been to avert a so called “calcium crisis” (a mismatch between calcium intake and recommendations) thought to be responsible for high rates of osteoporosis later in life.

What if we—researchers, paediatricians, marketers, and policy experts—have been wrong? What if increasing calcium intake in youth has no significant impact on fracture risk in early or later life as Winzenberg and colleagues conclude? Populations that consume the most cow's milk and other dairy products have among the highest rates of osteoporosis and hip fracture in later life.6,7 Given this fact, it is important to ask whether sufficient evidence exists to continue assuming that consumption of these foods is part of the solution.

Furthermore, we need to ask the question of whether we are doing children a disservice by encouraging them to meet recommendations. Childhood obesity is on the rise in westernised countries, and dairy products—the main source of calcium recommended by nutrition guidelines—contribute greatly to the intake of fat and sugar in children.8 Nearly three quarters of the world's population are estimated to be lactose intolerant after the age of weaning and therefore do not tolerate the consumption of milk and other dairy products well. In addition, some studies suggest that the consumption of cow's milk increases the risk of some types of cancer.9,10

The meta-analysis by Winzenberg and colleagues strengthens previous evidence that calcium or dairy products do not have a clinically relevant impact on bone health in youth. The focus on calcium recommendations in nutrition policy and research draws attention away from more comprehensive research on how to promote long term bone health among young people. Public health would be better served by researching how other dietary and lifestyle factors affect children's bones. Promising areas include the effect of regular exercise, vitamin D status, increasing fruit and vegetable consumption, limiting salt intake, limiting or avoiding animal protein, and avoiding smoking.

It is time to revise our calcium recommendations for young people and change our assumptions about the role of calcium, milk, and other dairy products in the bone health of children and adolescents. While the policy experts work on revising recommendations, doctors and other health professionals should encourage children to spend time in active play or sports, and to consume a nutritious diet built from whole foods from plant sources to achieve and maintain a healthy weight and provide an environment conducive to building strong bones.