Vitamin D Levels Linked to Colorectal Cancer Risk

Experimental and epidemiological studies suggest a protective role for vitamin D in colorectal carcinogenesis, but evidence is inconclusive. Circulating 25-hydroxyvitamin D (25(OH)D) concentrations that minimize risk are unknown.

Vitamin D, known for its role in maintaining bone health, is hypothesized to lower colorectal cancer risk via several pathways related to cell growth and regulation. Previous prospective studies have reported inconsistent results for whether higher concentrations of circulating 25-hydroxyvitamin D, the accepted measure of vitamin D status, are linked to lower risk of colorectal cancer.

A large team of scientists led by those working at the American Cancer Society (Atlanta, GA, USA) pooled participant-level data from 17 cohorts, comprising 5,706 colorectal cancer case participants and 7,107 control participants with a wide range of circulating 25(OH)D concentrations. For 30.1% of participants, 25(OH)D was newly measured. Previously measured 25(OH)D was calibrated to the same assay to permit estimating risk by absolute concentrations.

The scientists found that compared with the lower range of sufficiency for bone health (50–<62.5 nmol/L), deficient 25(OH)D (<30 nmol/L) was associated with 31% higher colorectal cancer risk; 25(OH)D above sufficiency (75–<87.5 and 87.5–<100 nmol/L) was associated with 19%, and 27% lower risk, respectively. These associations persisted even after adjusting for known colorectal cancer risk factors. Protective associations were seen in all subgroups examined. However, the association was noticeably stronger in women than men at concentrations above bone health sufficiency. The lifetime risk of colorectal cancer is 4.2% (1 in 24) in women and 4.5% (1 in 22) in men.

The authors concluded that higher circulating 25(OH)D was related to a statistically significant, substantially lower colorectal cancer risk in women and non–statistically significant lower risk in men. Optimal 25(OH)D concentrations for colorectal cancer risk reduction, 75-100 nmol/L, appear higher than current recommendations. Regina G. Ziegler, PhD, an epidemiologist and co-author of the study, said, “In the past, substantial differences between assays made it difficult to integrate vitamin D data from different studies. This calibration approach enabled us to systematically explore risk over the broad range of vitamin D levels seen internationally.”

Related Links:
American Cancer Society