Here in America, the rate of diagnosis of colorectal cancer in people in their early 40s is increasing more rapidly than in any other group. If you are the health-obsessed type, you might be taking vitamin supplements in the hope of keeping yourself out of this particular predicament. Speaking as a cancer doctor, my advice is that you do something else for your health.
Colorectal cancer is often preventable. First and foremost, get a colonoscopy when your doctor tells you to. But there is another thing you can do — get some exercise.
Unfortunately, most Americans do not follow this advice.
Only one in five of us meet U.S. Physical Activity Guidelines, and one in four have a colonoscopy or other screening test done when it is recommended.
Yet over half of Americans take dietary supplements, a habit that notably has not been shown to prevent cancer. If those vitamin poppers instead had a colonoscopy and began to exercise, we oncologists would have less work.
Most people know that exercise prevents heart disease, diabetes and obesity. But exercise’s ability to reduce death from colorectal cancer is just as well established by research.
Diseases of the sedentary often go together. In fact, a recent study of more than 2.5 million people found that having diabetes increases your risk of dying of colorectal cancer by 30 percent. Type 2 diabetes is strongly associated with obesity, and there is an 84 percent increased risk of death from colon cancer for the morbidly obese.
For all these risks, the antidote is exercise. In a well-known project called the Nurses’ Health Study, women who exercised the most had their risk of colon cancer drop almost by half. And, for people who were diagnosed with colorectal cancer and have survived, they are less likely to die of cancer if they begin to exercise.
Some of exercise’s protective effects may come from reducing fat around the midsection.
Exercisers and other people with less belly fat are at lower risk for developing diabetes. For this reason, weight loss through diet alone is not enough because muscle mass is lost. In contrast, exercisers lose more fat than dieters and decrease their burden of central adiposity. In layman’s terms, they are not as soft at the middle.
But what about those vitamins? Although vitamins can sometimes fix cancer in a petri dish, inside people they are far less effective. Ironically, vitamins A, C, E and beta-carotene all increase the risk of death and have no effect on preventing gastrointestinal cancer.
Vitamin D has garnered a lot of attention lately as a possible exception to its neighbors on the supplement aisle, partly because vitamin D levels in the blood are correlated with a lower rate of cancer. However, vitamin D may simply be a reporter of overall health.
For example, people who spend more time outdoors naturally have higher vitamin D levels, and low vitamin D is an indicator of obesity and diabetes. In a recent metaanalysis of many studies, the benefit of taking vitamin D for cancer was a paltry 1 percent.
So, while it is a good sign if you have healthy blood levels of vitamin D, taking supplements to get there may not do much to prevent cancer.
Compare these minimal benefits with a recent New England Journal of Medicine study showing that a screening colonoscopy cuts your risk of death from colorectal cancer by more than two-thirds.
So, be aware of which of your habits does genuine good. As food journalist Michael Pollan puts it, “Be the kind of person who takes supplements, then skip the supplements.”
To be that kind of person, get off the vitamins and onto the treadmill. And March is Colorectal Cancer Awareness Month, so schedule your colonoscopy when your doctor tells you to. That way, maybe I will see you at the gym and not in my clinic.
Dr. Rebecca Moss is an assistant professor in the gastrointestinal oncology program at the Rutgers Cancer Institute of New Jersey and serves on the medical advisory board of the Robert Wood Johnson Fitness & Wellness Center, both in New Brunswick.