Vitamin D and Cancer Mortality: Not to be Taken Lightly

Craig A. Elmets, MD

Introduction

Ultraviolet radiation has various deleterious effects but a positive influence on vitamin D metabolism.
Dermatologists typically recommend that patients use sunscreen and take other precautions to prevent sunburn, nonmelanoma skin cancer, melanoma, and cutaneous photoaging.
This practice is increasingly being scrutinized because much of the population is vitamin D deficient and because several healthful effects have been attributed to vitamin D, including a potential cancer-protection effect.
To assess the association between baseline serum 25-hydroxyvitamin D levels (25[OH]D) and cancer mortality, researchers prospectively examined data on 16,819 participants in the Third National Health and Nutritional Examination Survey (NHANES III). Levels of 25(OH)D were measured once, in spring or summer in higher latitudes and in fall or winter in lower latitudes.

During a mean follow-up of 13.4 years, 884 participants died of cancer.
Cancer mortality did not correlate with serum 25(OH)D in the total population or in men and women analyzed separately.
However, men with 25(OH)D levels >80 nmol/L had a significantly higher cancer mortality rate than those with levels <50 nmol/L.
Among women in the summer/higher-latitude group, the overall cancer risk trended significantly lower with higher 25(OH)D level.
Serum 25(OH)D levels were not associated with cancer mortality among non-Hispanic white, non-Hispanic black, and Mexican-American subgroups.
Colon cancer deaths trended nonsignificantly lower with higher 25(OH)D levels.
In men, but not women, elevated baseline serum 25(OH)D was associated with increased deaths from lung cancer and from digestive tract cancers other than colorectal cancer. No clear trend was apparent for female breast cancer, prostate cancer, or combined deaths from non-Hodgkin lymphoma or leukemia.

Comment

The large NHANES III database provides a unique opportunity to evaluate in detail the relation between vitamin D and diseases in the U.S. Study limitations include the measurement of vitamin D levels only at baseline. The findings suggest that we don't yet have the final word on the relationship between vitamin D and human health and that claims that vitamin D protects against specific cancers are not necessarily supported by the facts. Dermatologists can use this information to counter people's presumption that sun exposure or tanning bed use will protect against cancer mortality; in fact, such exposure may actually increase deaths from some cancers.