People over 75 should weigh the risks and benefits of colon cancer screening. (Image credit: Getty Images)

Screening is the best way to prevent colon cancer. But should everyone get a colonoscopy? Not so fast.

The recommendations for colorectal cancer screening are pretty clear: Start screening at age 50 and continue through age 75 with a colonoscopy every 10 years, a sigmoidoscopy every five years or a fecal blood test every year. Those who have a high risk for colon cancer should be screened more often and starting at a younger age.

For people over 75, it all comes down to benefits and risks.

The benefit of colon cancer screening is that it can detect precancerous polyps before they have a chance to develop into cancers. Removing the polyps takes care of the problem. However, most polyps develop into cancers quite slowly, and the procedure to spot and remove them carries risks like bleeding, infection and perforation of the colon.

Why worry about detecting a cancer that will do no harm in your lifetime? You only want to do the screening when the benefits of extending life by preventing cancer outweigh the risks of the screening itself. For most people, the right cutoff is age 75.

Unfortunately, it looks like a lot of older Americans are unnecessarily putting themselves at risk. A study published this week in JAMA Internal Medicine found that 32 percent of the colonoscopies performed in people ages 76 to 85 were probably inappropriate. It's one thing to get a colonoscopy when it is likely to be beneficial; it is entirely another matter to have one done when you don't need one.

It might seem like the more you get screened, the healthier you'll be. But that's just not true. Here are some of the latest screening recommendations to help you avoid getting over-tested:

• Cervical cancer: Pap test every three years for women between the ages of 21 and 65; no screening for women older than 65, unless they are at high risk for cervical cancer, or for women younger than 21.
• Prostate cancer: No PSA-based screening for prostate cancer at any age.
• Breast cancer: Mammogram every two years for women between the ages of 50 and 74. Screening based on risk factors and a conversation between doctor and woman for those younger than 50. Women 75 and older should also base screening decisions on a conversation with a doctor.
• No screening at all for testicular cancer, pancreatic cancer or ovarian cancer.

"Tell Me the Truth, Doctor" is a weekly column written by ABC News' chief health and medical editor Dr. Richard Besser. Look for Dr. Besser's book April 23.