There is currently no firm evidence that vitamin D supplementation decreases or increases cancer occurrence in predominantly elderly community-dwelling women .
Vitamin D₃ supplementation  decreased cancer mortality  and vitamin D supplementation  decreased all-cause mortality , but these estimates are at risk of type I errors due to the fact that too few participants were examined , and to risks of attrition bias originating from substantial dropout of participants .
Combined vitamin D₃ and calcium supplements  increased nephrolithiasis , whereas it remains unclear from the included trials whether vitamin D₃ , calcium , or both were responsible for this effect .
BACKGROUND The evidence on whether vitamin D supplementation is effective in decreasing cancers is contradictory .
OBJECTIVES To assess the beneficial and harmful effects of vitamin D supplementation for prevention of cancer in adults .
The effect of various vitamin D supplementation regimens in breast cancer patients
Vitamin D deficiency in the patients treated for breast cancer is associated with numerous adverse effects ( bone loss , arthralgia , and falls ) . The first aim of this study was to assess vitamin D status , determined by 25-OH vitamin D levels , among women diagnosed with breast cancer according to demographic/ clinical variables and bone mineral density ( BMD ) . The second aim of this study was to evaluate the effect of daily low-dose and weekly high-dose vitamin D supplementation on 25-OH vitamin D levels . This retrospective study included 224 women diagnosed with stage 0–III breast cancer who received treatment at the James P. Wilmot Cancer Center at the University of Rochester Medical Center . Total 25-OH vitamin D levels ( D2 + D3 ) were determined at baseline for all participants . Vitamin D deficiency was defined as a 25-OH vitamin D level < 20 ng/ml , insufficiency as 20–31 ng/ml , and sufficiency as ≥32 ng/ml . BMD was assessed during the period between 3 months before and 6 months following the baseline vitamin D assessment . Based on the participants ’ baseline levels , they received either no supplementation , low-dose supplementation ( 1,000 IU/day ) , or high-dose supplementation ( ≥50,000 IU/week ) , and 25-OH vitamin D was reassessed in the following 8–16 weeks . Approximately 66.5 % had deficient/insufficient vitamin D levels at baseline . Deficiency/insufficiency was more common among non-Caucasians , women with later-stage disease , and those who had previously received radiation therapy ( P < 0.05 ) . Breast cancer patients with deficient/insufficient 25-OH vitamin D levels had significantly lower lumbar BMD ( P = 0.03 ) . Compared to the no-supplementation group , weekly high-dose supplementation significantly increased 25-OH vitamin D levels , while daily low-dose supplementation did not significantly increase levels . Vitamin D deficiency and insufficiency were common among women with breast cancer and associated with reduced BMD in the spine . Clinicians should carefully consider vitamin D supplementation regimens when treating vitamin D deficiency/insufficiency in breast cancer patients
There is currently no firm evidence that vitamin D supplementation decreases or increases cancer occurrence in predominantly elderly community-dwelling women .
Vitamin D₃ supplementation  decreased cancer mortality  and vitamin D supplementation  decreased all-cause mortality , but these estimates are at risk of type I errors due to the fact that too few participants were examined , and to risks of attrition bias originating from substantial dropout of participants .
Combined vitamin D₃ and calcium supplements  increased nephrolithiasis , whereas it remains unclear from the included trials whether vitamin D₃ , calcium , or both were responsible for this effect .
BACKGROUND The evidence on whether vitamin D supplementation is effective in decreasing cancers is contradictory .
OBJECTIVES To assess the beneficial and harmful effects of vitamin D supplementation for prevention of cancer in adults .