Dietary recommendations and r and omized trials on vitamin D supplementation should evaluate whether increases in circulating 25-hydroxyvitamin D levels match expectations -- for instance , the average increases obtained by trials on vitamin D3 without concomitant calcium supplements
CONTEXT Few studies in subjects over 50 yr of age have evaluated the influence of variable doses of vitamin D supplementation on serum 25-hydroxyvitamin D levels .
OBJECTIVE We performed a meta- analysis of changes in circulating 25-hydroxyvitamin D level associated with vitamin D supplementation in Caucasian subjects over 50 yr old .
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 . )
Dietary recommendations and r and omized trials on vitamin D supplementation should evaluate whether increases in circulating 25-hydroxyvitamin D levels match expectations -- for instance , the average increases obtained by trials on vitamin D3 without concomitant calcium supplements
CONTEXT Few studies in subjects over 50 yr of age have evaluated the influence of variable doses of vitamin D supplementation on serum 25-hydroxyvitamin D levels .
OBJECTIVE We performed a meta- analysis of changes in circulating 25-hydroxyvitamin D level associated with vitamin D supplementation in Caucasian subjects over 50 yr old .