Benefits Outweigh Risks

Abstract

The recent review of vitamin D for cancer prevention (1) was based on the IARC review [Ref. 6 in (1)]. My critical review of the IARC review pointed out that the evidence for beneficial effects of solar UVB and vitamin D was much stronger than concluded in the review (2). Ecological studies (epidemiological studies researching disease outcome and risk-modifying factors averaged by geographical region) are better for studying the effects of UVB and vitamin D in reducing the risk of cancer than observational studies and randomized controlled trials (RCTs) for several reasons: solar UVB is the primary source of vitamin D for most people there is a long lag time between cancer initiation and detection or death RCTs and observational studies often use too little vitamin D too short a time period, and too few people. An ecological study for Spain illustrates this. The two factors used for vitamin D were nonmelanoma skin cancer (NMSC) mortality rate and latitude, for 48 provinces. NMSC was inversely correlated and/or latitude directly correlated with mortality rates for 15 types of cancer after adjustment for lung cancer mortality rates, included to account for the effect of smoking (3). Death rates were much higher for internal cancers than for NMSC.