A large new study from the American Cancer Society inventories the risk factors for various types of cancer. Those findings shed much-needed light on the proportion of cancers that could be prevented by making the necessary lifestyle changes.

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Smoking is the top risk factor for all cancer cases, according to new research.

The new research examined a total of 1,570,975 cancer cases, 587,521 of which resulted in death. During the analysis, 26 cancer types and 17 risk factors were analyzed.

These 17 risk factors are called “modifiable” because people can take active measures to change them. In the new study, such factors included:

  • alcohol intake
  • smoking (both first- and second-hand)
  • excess body weight
  • a low content of fiber in one’s diet
  • the consumption of processed red meat
  • a low intake of fruit and vegetables
  • ultraviolet (UV) radiation
  • low calcium
  • a lack of physical activity

Six infections that have already been linked with cancer were also included among the risk factors.

Dr. Farhad Islami, of the American Cancer Society (ACS), led the research, and the findings were published in the journal CA: A Cancer Journal for Clinicians.

In their analysis, Dr. Islami and his team used not only the prevalence of the risk factors, but also their “associated relative risk” — that is, the probability that said factors actually result in cancer. This information was obtained from “large-scale pooled analyses or meta-analyses.”

Data on the number of cancer cases and cancer-related deaths were gathered from the Centers for Disease Control and Prevention (CDC) and the National Cancer Institute (NCI).

Study co-author Dr. Otis W. Brawley, ACS chief medical officer, comments on the magnitude of the study, saying, “In 1981, Doll and Peto published what has become a classic paper on the causes of cancer.”

“Since then,” he explains, “volumes of data have been published that have clarified the association between several important risk factors and cancer. In this new report, ACS scientists provide a 21st-century calculation that will guide us in the years ahead.”

The study revealed that 42 percent of all cancers and over 45 percent of all cancer deaths were down to modifiable risk factors. The top three risk factors were smoking, excessive weight, and alcohol use.

Nineteen percent of all cancer cases and almost 29 percent of related deaths were attributable to cigarette smoking. Excess body weight accounted for 7.8 percent of cases and 6.5 percent of deaths, while 5.6 percent of cases and 4 percent of deaths were down to alcohol intake.

UV radiation was attributable to 4.7 percent of cancer cases and 1.5 percent of deaths, and lack of physical activity accounted for 2.9 percent of cancer cases and 2.2 percent of deaths.

Certain major cancers had a high portion of cases attributable to modifiable risk factors. Lung cancer was at the top, with 85.8 percent of cases down to such factors, 81.7 percent of which were attributable to smoking alone.

Over 70 percent of liver cancer cases, almost 55 percent of colorectal cancer cases, and nearly 29 percent of breast cancer cases could be attributed to modifiable risk factors.

Additional findings include the fact that UV radiation was linked to 96 percent of skin melanoma cases, and excess body weight to over 60 percent of uterine cancers.

Fifty percent of esophageal cancers were tied to smoking. Cigarettes were also associated with nearly 47 percent of bladder cancer cases. Finally, over 10 percent of colorectal cancers were associated with a low intake of dietary fiber.

“[T]hese findings underscore the vast potential for reducing cancer morbidity and mortality through broad and equitable implementation of known preventive measures,” conclude the authors.

The study authors remind the public of the four key factors that everyone can keep in check: body weight, alcohol consumption, diet, and physical activity.

The combined influence of these four factors made up nearly 14 percent of cancer risk in women and over 22 percent in men.

Dr. Islami and colleagues write:

Our findings emphasize the continued need for widespread implementation of known preventive measures in the country to reduce the morbidity and premature mortality from cancers associated with potentially modifiable risk factors.”

“Increasing access to preventive healthcare and awareness about preventive measures,” the authors conclude, “should be part of any comprehensive strategy for broad and equitable implementation of known interventions to accelerate progress against cancer.”