Find Information About:

Drugs & Supplements

Get information and reviews on prescription drugs, over-the-counter medications, vitamins, and supplements. Search by name or medical condition.

Pill Identifier

Pill Identifier

Having trouble identifying your pills?

Enter the shape, color, or imprint of your prescription or OTC drug. Our pill identification tool will display pictures that you can compare to your pill.

Get Started

My Medicine

Save your medicine, check interactions, sign up for FDA alerts, create family profiles and more.

Get Started

WebMD Health Experts and Community

Talk to health experts and other people like you in WebMD's Communities. It's a safe forum where you can create or participate in support groups and discussions about health topics that interest you.

  • Second Opinion

    Second Opinion

    Read expert perspectives on popular health topics.

  • Community


    Connect with people like you, and get expert guidance on living a healthy life.

Got a health question? Get answers provided by leading organizations, doctors, and experts.

Get Answers

Sign up to receive WebMD's award-winning content delivered to your inbox.

Sign Up

Colorectal Cancer Health Center

Font Size

Colorectal Cancer Prevention (PDQ®): Prevention - Health Professional Information [NCI] - Description of the Evidence


A meta-analysis of 106 observational studies found a RR (ever smokers compared with nonsmokers) for CRC incidence of 1.18 (95% CI, 1.11-1.25), with an absolute risk increase of 10.8 cases per 100,000 person-years (95% CI, 7.9-13.6). There was a statistically significant dose-response effect. In 17 studies with data on CRC mortality, cigarette smoking was associated with CRC death, with a RR (ever smokers vs. never smokers) of 1.25 (95% CI, 1.14-1.37), and an absolute increase in the death rate of 6.0 deaths per 100,000 person-years. For both incidence and mortality, the association was stronger for rectal cancer than for colon cancer.[28]


At least three large cohort studies have found an association between obesity and CRC incidence or mortality.[29,30,31] The Nurses' Health Study found that women with a body mass index (BMI) of more than 29, compared with women with a BMI of less than 21, had an adjusted RR for CRC incidence of 1.45 (95% CI ,1.02-2.07).[29] In the CPS II [31], men and women with a BMI of 30 to 34.9 had an adjusted RR for CRC mortality (compared with people with a BMI of 18.5-24.9) of 1.47 (95% CI, 1.30-1.66), with a statistically significant dose-response effect.[31] The effects were similar in men and women.

Factors associated with a decreased risk of colorectal cancer

Physical activity

A sedentary lifestyle has been associated in some [32,33] but not all [34] studies with an increased risk of CRC. Numerous observational studies that have examined the relationship between physical activity and colon cancer risk.[35] Most of these studies have shown an inverse relationship between level of physical activity and colon cancer incidence. The average RR reduction is reportedly 40% to 50%. Large U.S. cohort studies have found statistically significant adjusted RR of 0.54 (95% CI, 0.33-0.90) [29] and 0.53 (95% CI, 0.32-0.88) [30] when comparing people with high versus low average energy expenditure. A meta-analysis of 52 observational studies found an overall adjusted RR of 0.76 (95% CI, 0.72-0.81), with similar results for men and women.[36]

Next Article:

Today on WebMD

Colorectal cancer cells
The right diagnosis is the most important factor.
man with a doctor
Our health check will steer you in the right direction.
sauteed cherry tomatoes
Fight cancer one plate at a time.
bladder cancer x-ray
Do you know the warning signs?
Colon vs Rectal Cancer
New Colorectal Treatments
can lack of sleep affect your immune system
Cancer Facts Quiz
Virtual Colonoscopy
Picture of the Colon
Vitamin D