Higher circulating vitamin D levels appeared associated with a lower risk for colorectal cancer among women, according to findings published in Journal of the National Cancer Institute.
“Currently, health agencies do not recommend vitamin D for the prevention of colorectal cancer,” Marji L. McCullough, ScD, epidemiologist at the American Cancer Society, said in a press release. “This study adds new information that agencies can use when reviewing evidence for vitamin D guidance and suggests that the concentrations recommended for bone health may be lower than would be optimal for colorectal cancer prevention.”
The researchers reviewed pooled data from 17 cohorts comprised of 5,706 patients with colorectal cancer and 7,107 controls (women, 50.6%; white, 83.9%). Participants had a wide range of circulating 25-hyrdoxyvitamin D — or 25(OH)D — levels. Median 25(OH)D level among controls was 56 nmol/L (range, 31-85).
Researchers examined newly measured vitamin D levels from 30.1% of participants, and they calibrated previously measured levels to the same assay used to measure those of the others.
Compared with patients whose vitamin D levels were in the lower-sufficient range for bone health (50 to < 62.5 nmol/L), vitamin D deficiency (< 30 nmol/L) appeared associated with a 31% increased risk for colorectal cancer (RR = 1.31; 95% CI, 1.05-1.62).
Conversely, vitamin D levels above sufficiency appeared associated with a decrease in colorectal cancer risk: 25(OH)D of 75 nmol/L to more than 87.5 nmol/L associated with a 19% reduced risk (RR = 0.81; 95% CI, 0.67-0.99), whereas levels of 87.5 nmol/L to more than 100 nmol/L associated with a 27% reduced risk (RR = 0.73; 95% CI, 0.59-0.91).
However, at levels greater than 100 nmol/L, the risk was not statistically significantly reduced (RR = 0.91; 95% CI, 0.67-1.24; 3.5% of control participants).
Adjusting for BMI, physical activity and other risk factors had a minimal effect on associations between risk and 25(OH)D.
Among women, each 25-nmol/L increment in vitamin D reduced colorectal cancer risk by 19% (RR = 0.81; 95% CI, 0.75-0.87). Among men, risk fell by 7% (RR = 0.93; 95% CI, 0.86-1).
“Our study suggests that optimal circulating 25(OH)D concentrations for colorectal cancer risk reduction are 75 to 100 nmol/L, higher than current Institute of Medicine recommendations for bone health,” the researchers wrote. “Although our results are relevant to future recommendations for optimal vitamin D status, the effects of vitamin D on health outcomes other than colorectal cancer also need to be evaluated and integrated into public health guidance.” – by Andy Polhamus
Disclosures: The authors report no relevant financial disclosures.