Research Indicates Nearly 50% of U.S. Cancer Cases Are Tied to Controllable Risk Factors

A large proportion of cancer cases and deaths among adults over 30 in the United States may be connected to modifiable risk factors such as smoking and excess body weight, according to a new study published by the American Cancer Society’s journal, CA: A Cancer Journal for Clinicians. 

Researchers analyzed how modifiable risk factors played a role in cases from 2019 involving every cancer except non-melanoma skin cancer. They also looked at 30 individual cancer types.

They found that of the 1,781,649 million cases, 713,340—or four in 10—were attributable to factors people could potentially control. About 44%, or 262,000, of the deaths resulted from these risk factors.

Though previous research has linked cancer to modifiable risk factors, lead study author Farhad Islami, MD, PhD, Senior Scientific Director of Cancer Disparity Research at the American Cancer Society, still found the number of cases and deaths connected to them “staggering.”

Here’s what you need to know about which modifiable risk factors are linked to the most cancer cases, why so many cancer cases are connected to habits often within our control, and what you can do to reduce your chances of developing cancer.

Smoking cigarettes was the leading contributor to cancer cases, the study revealed. Though cigarette-associated cancer has declined because fewer people are smoking, the study found that smoking still contributed to 19% of cancer cases and almost 29% of cancer-related deaths.

Excess body weight accounted for the second-highest proportion of cases, at almost 8%, followed by drinking alcohol (5%), exposure to ultraviolet (UV) rays (almost 5%), and physical inactivity (3%).

Unsurprisingly, lung cancer topped the list of cancers caused by smoking. The risk of lung cancer is about 25 times higher among smokers than those who’ve never smoked, according to the Centers for Disease Control and Prevention (CDC). But smoking is also connected to many other cancers, including urinary bladder, colorectal, and oral cavity cancer.

Excess body weight, meanwhile, contributed to more than 7% of both cases and deaths, while alcohol consumption contributed to 5% and 4%, respectively.

The study pointed to a particularly dangerous combination of risk factors: Having excess weight and drinking alcohol, being sedentary, and lacking a healthy diet were linked to 17% of cancer deaths.

The study found that a high proportion of cancers that occur among women—breast, endometrial, and cervical—are linked to those risk factors. The research showed that human papillomavirus (HPV) infections, which a vaccine can prevent, are also connected to those cancers.

Female breast cancer followed lung cancer as the disease with the most cases associated with elevated risk factors, which the study attributed to nearly 84,000 cases in 2019. Skin melanoma was next, with almost 83,000 cases, followed by colorectal cancer with over 78,000 cases.

A majority of people don’t realize that drinking alcohol, not getting enough exercise, and diet-related factors like not eating enough fiber can raise the risk of cancer, according to a 2019 survey from the American Institute for Cancer Research.

Many people are shocked when they learn that “energy imbalance”—when the amount of energy a person takes in from food doesn’t match the energy used—can cause cancer, said Otis Brawley, MD, an oncologist and epidemiologist at Johns Hopkins University.

“Energy imbalance, which incorporates obesity, bad diet, and a lack of exercise, is the second leading cause of cancer in the United States and will soon become the leading cause of cancer,” Brawley told Health. 'It is fair to say that the more obese people are, the worse their cancer risk is.”

Some factors that increase cancer risk are hard to get across to the public, Timothy Rebbeck, PhD, a professor at the Dana-Farber Cancer Institute who studies cancer risk, told Health. Examples include eating highly processed food like preserved meat, the importance of physical activity, and the risk of alcohol consumption, he added.

“It’s really clear that alcohol is associated with many cancers and that there is probably no safe level of alcohol consumption,” Rebbeck said. “But that’s a really hard message for a lot of people to hear.” 

To reduce your cancer risk, Islami recommended quitting smoking or not starting in the first place, maintaining a healthy body weight, following guidelines for healthy eating, and staying physically active.

The CDC generally advises 150 minutes of moderate aerobic activity per week, such as brisk walking or riding a bike on flat ground, and at least two days of muscle-strengthening activities per week. 

But even a tiny amount of exercise can have a positive impact, added Carolyn J. Heckman, PhD, co-leader of the Cancer Prevention and Control Research Program at Rutgers Cancer Institute and RWJBarnabas Health. Research suggests that short bursts of vigorous exercise throughout the day can cut cancer risk, with one study showing that as few as 11 minutes of daily exercise can reduce a person’s odds of developing some cancers.