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 ) .
Calcium plus vitamin D supplementation and the risk of colorectal cancer.
BACKGROUND Higher intake of calcium and vitamin D has been associated with a reduced risk of colorectal cancer in epidemiologic studies and polyp recurrence in polyp-prevention trials . However , r and omized-trial evidence that calcium with vitamin D supplementation is beneficial in the primary prevention of colorectal cancer is lacking . METHODS We conducted a r and omized , double-blind , placebo-controlled trial involving 36,282 postmenopausal women from 40 Women 's Health Initiative centers : 18,176 women received 500 mg of elemental calcium as calcium carbonate with 200 IU of vitamin D3 [ corrected ] twice daily ( 1000 mg of elemental calcium and 400 IU of vitamin D3 ) and 18,106 received a matching placebo for an average of 7.0 years . The incidence of pathologically confirmed colorectal cancer was the design ated secondary outcome . Baseline levels of serum 25-hydroxyvitamin D were assessed in a nested case-control study . RESULTS The incidence of invasive colorectal cancer did not differ significantly between women assigned to calcium plus vitamin D supplementation and those assigned to placebo ( 168 and 154 cases ; hazard ratio , 1.08 ; 95 percent confidence interval , 0.86 to 1.34 ; P=0.51 ) , and the tumor characteristics were similar in the two groups . The frequency of colorectal-cancer screening and abdominal symptoms was similar in the two groups . There were no significant treatment interactions with baseline characteristics . CONCLUSIONS Daily supplementation of calcium with vitamin D for seven years had no effect on the incidence of colorectal cancer  among postmenopausal women . The long latency associated with the development of colorectal cancer , along with the seven-year duration of the trial , may have contributed to this null finding . Ongoing follow-up will assess the longer-term effect of this intervention . ( Clinical Trials.gov number , NCT00000611 . )
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 ) .