Introduction: Studies on the association of vitamin D and bone mineral density (BMD) in adolescence and young adults have shown contrasting results. None of these studies have examined the course and baseline in vitamin D intake. The purpose of this study was to examine the association between baseline and the course of dietary vitamin D intake on the BMD.
Methods: Vitamin D intake was assessed 3-8 times between the age of 13 and 36 years in 152 men and 168 women from the Amsterdam Growth and Health Longitudinal Study. The BMD of the femoral neck, lumbar spine, total hip and total body was measured at the age of 36 years with dual-energy X-ray absorptiometry. Linear regression analyses were used to determine the vitamin D intake pattern in time for each subject. The models provide a baseline, course and fluctuation of the vitamin D intake for each subject. These were used in separate regression analyses with the dependent variable BMD.
Results: Mean baseline vitamin D was 6.86 (SD: 2.18) microg/day for men and 4.90 (1.19) microg/day for women. Mean course of vitamin D was -0.10 (0.12) microg/day/year and -0.05 (0.18) microg/day/year for men and women respectively. After adjustment for potential confounders and correcting for the other parameters of vitamin D intake, the associations between baseline vitamin D intake and BMD were significant in the total hip (0.018 g/cm(2) per -1 microg/day; 95% CI 0.001-0.035) and total body (0.015 per -1 microg/day; 0.001-0.029). The course of vitamin D intake was associated with BMD in the lumbar spine (0.50 g/cm(2) per -1 microg/day/year; 0.130-0.867), femoral neck (0.42 g/cm(2) per -1 microg/day/year; 0.10-0.743), total body (0.34 g/cm(2) per -1 microg/day/year; 0.09-0.59) and total hip (0.44 g/cm(2) per -1 microg/day/year; 0.11-0.77) in men. No significant associations were found in women.
Conclusion: In men, the level of vitamin D intake in adolescence and the course of vitamin D intake from adolescence into adulthood are positively related with BMD in adulthood. In women, however, no significant associations are found.