In the early stages of colorectal cancer, symptoms may be hard to identify. And because the symptoms don't often become apparent until the disease has progressed beyond the initial stages, regular screenings have always been recommended.

And now it appears that regular screenings are even more important than previously thought.

A large, long-term study from Harvard School of Public Health found that 40 percent of all colorectal cancers might be prevented if people underwent regular colonoscopy screening. The new research lends credence to existing guidelines recommending that people with an average risk of colorectal cancer have a colonoscopy every 10 years.

In the past, there has been some skepticism about whether regular colonoscopies actually help limit the prevalence of colorectal cancer. But this study -- which appears in the New England Journal of Medicine -- seems to indicate that the screenings are, indeed, beneficial.

"Colonoscopy is the most commonly used screening test in the U.S. but there was insufficient evidence on how much it reduces the risk of proximal colon cancer and how often people should undergo the procedure," said Shuji Ogino, co-senior author and associate professor at Harvard, in a press release.

Ogino said the study provides strong evidence that colonoscopy is effective at preventing cancers of both distal -- the lower body -- and proximal -- the upper body -- regions of the colorectum.

The researchers studied data from 88,902 participants in two long-term studies. These participants had to fill out questionnaires every two years between 1988 and 2008. They gathered information on colonoscopy procedures and documented 1,815 cases of colorectal cancers and 474 deaths from the disease.

They found that both colonoscopy and sigmoidoscopy -- which screens for tumors in the distal area -- were associated with decreased risk of either getting colorectal cancer or dying from it. More specifically, the researchers found that if all participants in the study had gotten colonoscopies, 40 percent of colorectal cancers would have been prevented.

Of course, screening won't actually prevent colon cancer from developing -- but it can catch it early, when it's still in the polyp stage, before it's progressed to a more advanced stage or spread beyond the colon.

According to the American Cancer Society, about 102,480 of new cases of colon cancer -- and 40,340 new cases of rectal cancer -- are diagnosed in the United States each year. About 50,830 people die from colorectal cancer.

Earlier this summer, a study found that taking aspirin regularly may reduce the risk of most types of colon cancer. In the study, people who took aspirin at least twice a week were 27 percent less likely to develop colon cancer over a 28-year period, compared with those who took aspirin less frequently, or not at all.

Earlier on HuffPost50:

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  • Before Your Appointment

    Gathering your health information and getting organized before your appointment are the key steps to ensuring a productive meeting with your doctor. This is especially important if you're seeing multiple doctors or are meeting with a new physician for the first time.

  • Get Your Test Results

    Make sure the doctor you're seeing has copies of your latest X-ray, MRI or any other test or lab results, including reports from other doctors that you've seen. In most cases, you'll need to do the legwork yourself, which may only require a phone call to your previous doctor's administrative staff, asking for it to be sent, or you may need to go pick it up and bring it to the new office yourself.

  • List Your Medications

    Make a list of all the medications you're taking (prescription drugs, over-the-counter medications, vitamins, minerals and herbal supplements) along with the dosages, and take it with you to your appointment. Or, just gather up all your pill bottles in a bag and bring them with you.

  • Gather Your Health History

    Your doctor also needs to know about any previous hospitalizations, as well as any current or past medical problems, even if they are not the reason you are going to the doctor this time. Genetics matter too, so having your family's health history can be helpful. The U.S. Surgeon General offers a free web-based tool called <a href="" target="_hplink">"My Family Health Portrait"</a> that can help you put one together.

  • Prepare A List Of Questions

    Make a written list of the top three or four issues you want to discuss with your doctor. Since most appointments last between 10 and 15 minutes, this can help you stay on track and ensure you address your most pressing concerns first. If you're in for a diagnostic visit, you should prepare a detailed description of your symptoms.

  • During Your Appointment

    The best advice when you meet with your doctor is to speak up. Don't wait to be asked. Be direct, honest and as specific as possible when recounting your symptoms or expressing your concerns. Many patients are reluctant or embarrassed to talk about their symptoms, which makes the doctor's job a lot harder to do. It's also a good idea to bring along a family member or friend to your appointment. They can help you ask questions, listen to what the doctor is telling you and give you support.