According to the results of a study published in the Journal of the National Cancer Institute, a protective effect of calcium supplementation on risk of colorectal adenoma recurrence persisted for up to five years after the end of the study.
Colorectal cancer is the second leading cause of cancer-related deaths in the U.S. The disease develops in the colon (the longest part of the large intestine) or the rectum (the last several inches of the large intestine). It may start as a precancerous growth known as an adenomatous polyp or adenoma. It is thought that a reduction in the development of adenomas would ultimately reduce the risk of developing colorectal cancer.
Among individuals who have been diagnosed with an adenoma, studies have suggested that calcium supplementation reduces the risk of adenoma recurrence. It is uncertain, however, how long the protective effect of calcium supplementation lasts.
To explore the long-term effects of calcium supplementation on risk of adenoma recurrence, researchers evaluated follow-up information from a clinical trial known as the Calcium Polyp Prevention Study. In this study individuals with a previous colorectal adenoma were assigned to receive either a calcium supplement (1200 mg of elemental calcium daily) or a placebo for four years.
Subjects were then followed for an average of seven years after the end of the study. During this period some subjects chose to continue using calcium supplements and some did not.
- During the first five years after the study ended, individuals who had been assigned to the calcium group continued to have lower rates of adenoma recurrence than individuals who had been assigned to the placebo group. Risk of recurrence was 37% lower in the calcium group than in the placebo group.
- A protective effect of calcium supplementation was observed even among study participants who did not take calcium after the study was over.
- By five to ten years after the end of the study, the protective effect of calcium supplementation had disappeared.
The researchers concluded that the protective effect of calcium supplementation on adenoma recurrence persisted for up to five years after the end of the study, even among study participants who stopped taking calcium supplements after the study was over.
Reference: Grau MV, Baron JA, Sandler RS et al. Prolonged Effect of Calcium Supplementation on Risk of Colorectal Adenomas in a Randomized Trial. Journal of the National Cancer Institute. 2007;99:129-36.
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