Osteoporotic fractures in adults are a substantial cause of morbidity and mortality, and they cost the health services about £2.3bn (€2.8bn; $3.6bn) a year in the United Kingdom and $30bn in the United States. Prevention, which includes manipulation of the development of bone mass during childhood and adolescence, is therefore important. Increasing peak bone mass in young adults might have a longstanding effect on the risk of osteoporosis in later years. Although genetic factors account for 50-85% of the variance in adult bone density, modification of environmental factors during childhood might have an effect on peak bone mass. One such factor is vitamin D⇓.

In a linked systematic review and meta-analysis (doi:10.1136/bmj.c7254), Winzenberg and colleagues assess the impact of vitamin D supplementation on bone density in children.1 They show that overall vitamin D supplementation had no significant effect on bone density in the whole body, hip, or forearm (with a trend to a small effect in the lumbar spine). However, in children with low serum vitamin D (defined as <35 nmol/L) supplements …