For example, 25(OH)D3 levels are determined by sun exposure

and diet that may be affected by a range of factors including SEP and outdoor physical activity, which may confound relationships with bone outcomes. Although the association between 25(OH)D3 and endosteal adjusted for periosteal circumference was unaffected by adjusting for observed measurements click here of these additional factors, unmeasured confounders may be important. For example, D2 intake is related to consumption of fruits and vegetables, which is positively associated with childhood BMD as measured by DXA [30]. In addition, fruit and vegetable intake is related to a ‘prudent’ or ‘healthy’ diet [31], of which intake in pregnancy is positively associated with BMD in subsequent childhood [19]. Limitations In terms of limitations of this study, our pQCT measurements comprised a single slice, namely, the 50% mid-tibia, which is unable to provide any information about trabecular bone. In the study of 171 girls aged 9–15 years described Combretastatin A4 above, the relationship between baseline total 25(OH)D and subsequent gain in BMD across puberty was particularly strong at the lumbar spine [16] which is rich in trabecular bone. Whereas

the present study suggests that 25(OH)D status has minimal buy ARN-509 effects on cortical bone, it may be that stronger effects exist for trabecular bone which we were unable to evaluate here. A further Benzatropine limitation is the relatively long interval between measurement of 25(OH)D and measurement of cortical bone from pQCT scans, which may have reduced the strength of associations observed between these sets of parametres. Finally, the generalisability of our findings is limited by the fact that the subset of 3,579 subjects forming the basis of the present study is likely to differ in important ways from the original cohort drawn from the general population. For example, maternal social class in the subset on which this paper is based was higher compared with those who were not included (P = 0.0001).

In conclusion, we found that in contrast to 25(OH)D2, 25(OH)D3, as measured in childhood, was positively related to BMCC, cortical thickness and resistance to buckling as assessed 5 years later. These different associations suggest that supplementation with vitamin D3 in childhood is likely to prove more beneficial for subsequent cortical bone development compared to vitamin D2, presumably reflecting important differences between the actions of these two isoforms on bone, the basis of which is currently unclear. Interventional studies are justified in which effects of these two forms of vitamin D are directly compared in the same population, in order to test the conclusions from this observational study, given that we are unable to exclude confounding as a possible explanation for our findings.