Nearly half of cancers linked to lifestyle factors, study finds

About 40 percent of new cancer cases among U.S. adults — and nearly half of all cancer deaths — are linked to lifestyle risk factors including smoking, obesity and alcohol consumption, according to a new study by the American Cancer Society.

The study points to the possibility that the daily choices people make can give them some control over their cancer risk. The exact cause of most cancers are unknown, and many are outside an individual’s control.

A list of lifestyle risk factors were identified in the study that put people at a greater risk of a cancer diagnosis in their lifetimes. Cigarette smoking was by far the leading risk factor, contributing to nearly 1 in 5 cancer cases and about a third of all cancer deaths. Excess body weight was next, contributing to nearly 8 percent of cancer cases, followed by alcohol consumption and excessive sun exposure, each linked to about 5 percent of cases. Physical inactivity was associated with 3 percent of cancer cases.

Researchers analyzed a total of 18 risk factors across 30 types of cancers. Other risk factors that contributed to cancer cases at a lesser degree include eating red and processed meat; low consumption of fruits and vegetables; and infections with Epstein-Barr virus (EBV) and human papillomavirus (HPV), according to researchers. The findings were published this month in the journal CA: A Cancer Journal for Clinicians.

In 2019, these lifestyle factors were linked to nearly 715,000 cancer cases and about 262,000 deaths.

Many questions remain

The findings are not exactly new, but they add to mounting research that shows many cancer cases — and as many as half the deaths — can be prevented with lifestyle changes.

“Despite considerable declines in smoking prevalence during the past few decades, the number of lung cancer deaths attributable to cigarette smoking in the United States is alarming. This finding underscores the importance of implementing comprehensive tobacco control policies in each state to promote smoking cessation, as well as heightened efforts to increase screening for early detection of lung cancer, when treatment could be more effective,” said Dr. Farhad Islami, senior scientific director of cancer disparity research at the American Cancer Society and lead author of the report.

In a news release, Islami said that intervention to help maintain a healthy body weight could lower the number of cases and deaths and is particularly important among young people with early onset cancers. Cancer cases in people under 50 have seen a sharp rise in recent years.

Despite the findings that people have more control than they think over their cancer risk, there are still many questions about who gets cancer and why.

About 10 percent of cancers are caused by factors that were inherited or genetic.

Colon cancer, which was once a more distant cause of cancer death in both men and women, is now a leading cause of cancer death for men and women under 50. Experts say risk factors including obesity and a lack of physical activity could be playing a role, but they still don’t know what’s causing the jump in cases among younger adults.

Links to risk factors

In this new ACS study, researchers used nationally representative data on cancer incidence and mortality and risk factor prevalence to estimate the proportion and number of cancer cases and deaths attributable to potentially modifiable risk factors overall for 30 cancer types. The study doesn’t include nonmelanoma skin cancers.

Some cancers have more of a direct link to risk factors than others, according to the study. For example, about 90 percent of melanoma cases are linked to ultraviolet radiation, and virtually every case of cervical cancer is linked to HPV infection, which can be prevented with an HPV vaccine, according to the study.

Lung cancer tops the list with the most number of cases associated with a modifiable risk factor — with the vast majority of cases linked to smoking, including current and former smoking habits as well as secondhand smoke.

Excess body weight was associated with 11 percent of breast cancer cases, 14 percent of stomach cancer cases and about half of endometrial cancer cases.

“These findings show there is a continued need to increase equitable access to preventive health care and awareness about preventive measures,” added Dr. Ahmedin Jemal, senior vice president, surveillance and health equity science at the American Cancer Society and senior author of the study.