Dietary choices, some drugs may reduce incidence of colorectal cancer

Aspirin, NSAIDs, magnesium, folate, a high consumption of fruits and vegetables, fiber, and dairy products are associated with a decreased incidence of colorectal cancer in an average-risk population, according to a recent systematic review.

The review evaluated 80 meta-analyses of interventional and observational studies of colorectal cancer prevention using medications, vitamins, supplements, and dietary factors. Any studies on specific high-risk populations, such as those with previous adenoma removal, diabetes, chronic inflammatory bowel disease, or a genetic background that increases colorectal cancer risk, were excluded. Results were published online on Sept. 28 by Gut.

Seven interventions were associated with a decreased incidence of colorectal cancer. For aspirin, the relative risks (RRs) ranged from 0.71 to 0.86 (moderate certainty of evidence). A protective effect was seen for doses as low as 75 mg/d, with a dose-response effect reported up to 325 mg/d. For NSAIDs, the RR ranged from 0.57 to 0.74 (low certainty of evidence). The effect was consistently significant for at least five years. For magnesium, the RR ranged from 0.78 to 0.87 (low certainty of evidence) when at least 255 mg/d was consumed. For folic acid, the RR ranged from 0.85 to 0.88 (very low certainty of evidence) with high intake, although a protective dose could not be determined. For consumption of fruit and/or vegetables, the RR ranged from 0.48 to 0.92, with an incremental benefit for any 100 g/d intake (very low certainty of evidence). For fiber consumption, the RR ranged from 0.57 to 0.78 (very low certainty of evidence), although the optimal daily dose and duration of intake were undetermined. For consumption of dairy products, the RR ranged from 0.81 to 0.87 (very low certainty of evidence), although there were too many products to allow for conclusion of optimal dose or duration. An increased incidence of colorectal cancer was seen with frequent consumption of alcohol or meat. There was no evidence of a protective effect for tea, coffee, garlic, fish, or soy products.

Limitations of the study include the inability to pool the results of the different meta-analyses included for each component due to high between-study heterogeneity, the authors noted. They concluded that clinicians should encourage use of the seven interventions associated with decreased colorectal cancer incidence in average-risk individuals.

“It is our hope that despite all aforementioned limitations, this comprehensive umbrella meta-analysis will assist clinicians in counselling patients, and help to guide the future research on the topic that is required in many instances, to better characterise the impact of a nutritional, supplement, or chemical intervention in [colorectal cancer] prevention in an average-risk population,” the authors wrote.