In Reply Peiris and colleagues commented on the null effect of vitamin D supplementation on incident cancer in the ViDA study,1 which is based primarily on possible differential effects on disease risk between daily vs monthly doses of vitamin D supplementation. In our article,1 we acknowledged that monthly dosing may be less effective than daily dosing for preventing cancer, and we agree that if this finding is true, increased variability in vitamin D levels associated with monthly dosing would be a possible mechanism. For example, daily or weekly dosing of vitamin D is more effective than bolus dosing (ie, monthly) in preventing acute respiratory infections, particularly in people with vitamin D deficiency.2 However, the recent null findings for incident cancer reported in the VITAL study,3 in which a daily dose of vitamin D was administered, suggest that the frequency of dosing is not important for cancer prevention.
Scragg R, Camargo CA. Role of Monthly High-Dose Vitamin D Supplementation in Cancer Prevention—In Reply. JAMA Oncol. Published online February 14, 20195(4):572–573. doi:10.1001/jamaoncol.2018.7233
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