We all know someone who has cancer or had it, and ask “why?” Is it genetic, environmental, or just random? It may a combination of these factors, but researchers are learning that a significant cause of many cancers is potentially modifiable risk factors.

The conclusion of recent studies is that more than 40% of new cancers and cancer death each year are caused by lifestyle factors. Some of them are obvious: smoking, alcohol, and exposure to other carcinogenic substances. Consistent with this, cigarette smoking was the most significant cause found in the studies, accounting for 19% of all cancers, with obesity and alcohol intake ranking as second and third.

These numbers likely underestimate the true magnitude of lifestyle factors’ impact on cancer risk, according to Farhad Isrami, MD, PhD, in an article published in CA: A Cancer Journal for Clinicians. Despite this new research, it is difficult to quantify the impact of all established risk factors, and many cannot yet be firmly established as causative.

For example, although tobacco use is considered the leading contributor to cancer death, it is necessary to consider all of the other factors that may correlate with smoking, including obesity, poor health habits, nutrition, physical inactivity, and alcohol consumption.

The study did not break new scientific ground, but reinforced the knowledge that prevention can play a major role in reducing the national cancer burden. One difficulty in further refining the statistics is that the sources of information about a particular cancer that is attributable to risk factors may be different for each type of cancer. According to Dr. Islami, “[we] didn’t have a comprehensive analysis of all the contemporary data, using the same methodology to make all the results comparable.” With advancing research techniques, it is hoped that more informed decisions can be made about establishing priorities for cancer prevention and control.