Subgroup analyses in the observational studies indicated that risk of mortality was significantly higher in studies with lower baseline use of vitamin D supplements .
The effects observed for vitamin D3 supplementation remained unchanged when grouped by various characteristics .
However , for vitamin D2 supplementation , increased risks of mortality were observed in studies with lower intervention doses and shorter average intervention periods .
Conclusions Evidence from observational studies indicates inverse associations of circulating 25-hydroxyvitamin D with risks of death due to cardiovascular disease , cancer , and other causes .
Objective To evaluate the extent to which circulating biomarker and supplements of vitamin D are associated with  mortality from cardiovascular , cancer , or other conditions  , under various circumstances .
Dietary vitamin D intake and serum 25‐hydroxyvitamin D level in relation to disease outcomes in head and neck cancer patients
Low pretreatment vitamin D status has been associated with worsened disease outcomes in patients with cancer at various sites . Its prognostic significance in head and neck cancer ( HNC ) patients has not been studied . Patients with HNC who participated in a r and omized trial were evaluated for : ( i )  total intake of vitamin D from diet and supplements using a vali date d food frequency question naire ( all trial participants , n = 540 ) and ( ii )  pretreatment serum 25‐hydroxyvitamin D through a radioimmunoassay ( n = 522 ) . The association of dietary/serum measures of vitamin D status with HNC recurrence , second primary cancer ( SPC ) incidence , and overall mortality was evaluated using multivariate Cox proportional hazard models . There was no significant association between dietary or serum vitamin D measures and the three HNC outcomes . The hazard ratios ( HRs ) comparing the highest with the lowest quartile of dietary/supplemental vitamin D intake were 1.10 ( 95 % confidence interval ( CI ) : 0.66–1.84 ) for recurrence , 1.05 ( 95 % CI : 0.63–1.74 ) for SPC , and 1.27 ( 95 % CI : 0.87–1.84 ) for overall mortality . HRs comparing the uppermost to the lowest quartile of serum 25‐hydroxyvitamin D levels were 1.12 ( 95 % CI : 0.65–1.93 ) for recurrence , 0.72 ( 95 % CI : 0.40–1.30 ) for SPC , and 0.85 ( 95 % CI : 0.57–1.28 ) for overall mortality . There was no effect modification by cancer stage , season of initial treatment , or trial arm . Among patients with HNC , vitamin D status before treatment does not influence disease outcomes . Our results contrast with those from most published studies , which suggest prognostic significance of vitamin D status in cancer patients at least in subgroups
Subgroup analyses in the observational studies indicated that risk of mortality was significantly higher in studies with lower baseline use of vitamin D supplements .
The effects observed for vitamin D3 supplementation remained unchanged when grouped by various characteristics .
However , for vitamin D2 supplementation , increased risks of mortality were observed in studies with lower intervention doses and shorter average intervention periods .
Conclusions Evidence from observational studies indicates inverse associations of circulating 25-hydroxyvitamin D with risks of death due to cardiovascular disease , cancer , and other causes .
Objective To evaluate the extent to which circulating biomarker and supplements of vitamin D are associated with  mortality from cardiovascular , cancer , or other conditions  , under various circumstances .