PURPOSE: Young men and women accrue the majority of their bone mass in their teens and twenties, where their bone mass peaks (PBM), yet little is known about the roles of physical exercise, vitamin D levels and bone mineral density (BMD) near PBM.

METHODS: To comparatively examine the effect of physical exercise and two vitamin D levels (insufficient s-25[OH]D <50 nmol/L and sufficient s-25[OH]D >80 nmol/L) on the BMD measured at the femoral neck, total hip (bilaterally) and the lumbar spine (L2-L4) in male and female participants approaching PBM.

RESULTS: The insufficient s-25[OH]D group, median age 21.6 (19.8-22.8) years, and BMI 24.2 ± 5.0 kg/m(2) had BMD 0.10 (0.03, 0.17) g/cm(2) (p = 0.008) lower at all DXA-scan sites compared to the sufficient s-25[OH]D group, median age 19.5 (19.0-22.3) years, and BMI of 22.6 ± 1.8 kg/m(2). Exercise was positively associated with the BMD at all DXA-scan sites (p trend = 0.0001) and with equal benefit; there was no interaction between exercise and the DXA-scan site (p = 0.09). The male participants did not have a systematically higher BMD than the female participants for all scan sites; only for hips total and femoral neck bilaterally, while it was equal at the lumbar spine.

CONCLUSION: The BMD in young healthy adults is associated with physical exercise, independent of sex and s-25[OH]D status. A sufficient s-25[OH]D status was systematically associated with a higher BMD for all levels of exercise. For both sexes and vitamin D levels exercise was equally positively associated with BMD.