In a recent international study, researchers found higher vitamin D concentrations in the blood are strongly linked to lower colorectal cancer risk.
The research is reported by the American Cancer Society.
Colorectal cancer is the third most common cancer and the third leading cause of cancer-related deaths in both men and women in the United States, with about 140,250 new cases and 50,630 deaths expected during 2018.
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 studies have shown 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.
The few clinical trials of vitamin D supplementation and colorectal cancer completed thus far have not shown an effect.
Study size, supplementation duration, and compliance may have contributed to their null findings.
In the current study, the researchers analyzed data collected before colorectal cancer diagnosis from 17 prospective cohorts and used standardized criteria across the studies.
The analysis included over 5,700 colorectal cancer cases and 7,100 controls from the United States, Europe, and Asia.
A single, widely accepted assay and laboratory were used for new vitamin D measurements and calibration of existing vitamin D measurements.
The team found that compared to participants with circulating vitamin D concentrations considered sufficient for bone health, those with deficient concentrations of vitamin D had a 31% higher risk of colorectal cancer during follow-up, which averaged 5.5 years.
Similarly, concentrations above bone health sufficiency were associated with a 22% lower risk. However, the risk did not continue to decline at the highest concentrations.
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.
Currently, health agencies do not recommend vitamin D for the prevention of colorectal cancer.
This study adds new information that agencies can use when reviewing evidence for vitamin D guidance.
It suggests that the concentrations recommended for bone health may be lower than would be optimal for colorectal cancer prevention.
Vitamin D can be obtained in the diet, particularly from fortified foods, from supplements, and from sun exposure.
Experts recommend vitamin D be obtained through diet whenever possible because excessive ultraviolet radiation is a major risk factor for skin cancer.
The study is published in the Journal of the National Cancer Institute.
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