Whether or not outcomes such as osteoporosis ( or low bone mass ) and specific types of cancer may be prevented by ' generous ' vitamin D supplementation is unclear and mostly based on indirect epidemiologic data not clearly substantiated by r and omized controlled trials SUMMARY The dose of daily vitamin D supplements needed to prevent rickets is probably much lower than that recommended by most expert committees .
PURPOSE OF REVIEW To underst and the basis for current recommendations for  vitamin D supplementation in childhood and the differences between the recommendations published by major expert committees , using the Medline engine of the US National Library of Medicine and the National Institutes of Health .
Most trials have examined the question of whether a specific daily vitamin D dose is capable or not to prevent rickets ( by study ing surrogate markers of rickets ) .
Vitamin D, calcium supplementation, and colorectal adenomas: results of a randomized trial.
BACKGROUND Calcium and vitamin D both appear to have antineoplastic effects in the large bowel . Although these nutrients are inter-related metabolically in bone and in the normal intestine , their potential interactions in large-bowel carcinogenesis are not well understood . METHODS We assessed independent and joint effects of calcium supplementation and vitamin D status on  adenoma recurrence in 803 subjects in a multi-center , placebo-controlled r and omized clinical trial of calcium supplementation for the prevention of colorectal adenoma recurrence . Serum levels of 25-hydroxy [ 25-(OH ) ] vitamin D and 1,25-dihydroxy [ 1,25-(OH)2 ] vitamin D levels were determined , and the Taq I and Fok I polymorphisms in the vitamin D receptor ( VDR ) gene were analyzed by polymerase chain reaction . Risk ratios ( RRs ) for any adenoma recurrence were computed for calcium supplementation within groups defined by serum vitamin D levels and for serum vitamin D levels within treatment groups . Associations of VDR polymorphisms with recurrence risk were also evaluated . All statistical tests were two-sided . RESULTS Among subjects with baseline 25-(OH ) vitamin D levels at or below the median ( 29.1 ng/mL ) , calcium supplementation was not associated with adenoma recurrence , whereas among those with levels above the median , calcium supplementation was associated with a reduced risk ( RR = 0.71 , 95 % confidence interval [ CI ] = 0.57 to 0.89 , P for interaction = .012 ) . Conversely , serum 25-(OH ) vitamin D levels were associated with a reduced risk only among subjects receiving calcium supplements ( RR per 12 ng/mL increase of vitamin D = 0.88 , 95 % CI = 0.77 to 0.99 , P for interaction = .006 ) . VDR polymorphisms were not related to adenoma recurrence and did not modify the associations with vitamin D or calcium . CONCLUSIONS Calcium supplementation and vitamin D status appear to act largely together , not separately , to reduce the risk of colorectal adenoma recurrence . VDR genotype does not appear to be associated with risk
Whether or not outcomes such as osteoporosis ( or low bone mass ) and specific types of cancer may be prevented by ' generous ' vitamin D supplementation is unclear and mostly based on indirect epidemiologic data not clearly substantiated by r and omized controlled trials SUMMARY The dose of daily vitamin D supplements needed to prevent rickets is probably much lower than that recommended by most expert committees .
PURPOSE OF REVIEW To underst and the basis for current recommendations for  vitamin D supplementation in childhood and the differences between the recommendations published by major expert committees , using the Medline engine of the US National Library of Medicine and the National Institutes of Health .
Most trials have examined the question of whether a specific daily vitamin D dose is capable or not to prevent rickets ( by study ing surrogate markers of rickets ) .