An article published in the prestigious journal Nature demonstrates that the development of the vast majority of cancers is strongly influenced by factors associated with lifestyle. It is therefore a good opportunity to remember that it is possible to prevent most cancers by simple changes to our habits..
Most people think of cancer as a bad game of chance that you can’t do anything about. According to this view, cancer is always caused by factors beyond our control, be it heredity, aging, stress or pollution. These false beliefs go completely against what research has identified as triggering factors for cancer.
Heredity, for example, does not play the predominant role that is often believed. There are indeed some defective genes that can be passed down through heredity, but these hereditary cancers are relatively uncommon. For example, a recent study carried out on more than 200,000 identical twins shows that the vast majority of cancers, in particular those which mainly affect the population of Western countries (lung, colorectal, breast and prostate), are not of hereditary.
Significant differences from one country to another
To better understand these factors, a team of American scientists rigorously analyzed several studies dealing with the worldwide distribution of cancers as well as some of their molecular characteristics. They first noticed that chance, heredity or even aging cannot explain the phenomenal differences that exist in the incidence of several types
of cancers worldwide. Breast cancer is up to 20 times more common in America than in Asia, for example, while Westerners are 10 times more affected by prostate cancer than the Japanese. These differences are completely canceled following the migration of Asians to the West, which underlines the contribution of lifestyle to the development of these cancers.
Cancer does not start overnight
Moreover, the analysis of the molecular composition of cancers also suggests a major contribution of extrinsic factors, linked to lifestyle. Thus, the mutations found in most cancers have a molecular signature typical of exposure to carcinogenic substances (UV rays, tobacco, poor diet) and not that associated with normal aging. Most cancers also require multiple mutations to reach a mature stage (nine mutations for breast cancer, 11 for colon cancer and 12 for prostate cancer) and the statistical calculation indicates that a cancerous cell cannot acquire just by chance all these mutated genes on the scale of a human life.
Taking these factors into account, the authors estimate that a minimum of 70% of cancers are caused by lifestyle factors, a contribution that reaches almost 100% for cancers such as colon and lung, two cancers with high mortality.
Lifestyle risk factors
Lifestyle can influence cancer risk, regardless of genetic predisposition. Thus, the risk of developing early breast cancer (before age 50) in women carrying defective BRCA genes has tripled in recent years (24 to 67%), an increase attributed to the increase in obesity, poor diet and reduced physical activity.
Apart from heredity, non-modifiable risk factors are also influenced by lifestyle: a recent population analysis showed that women who are at higher risk of breast cancer due to certain factors beyond their control ( family history, long period of fertility without pregnancy, large size) can reduce this risk by following the recommendations issued by the World Cancer Research Fund. Thus, these high-risk women who maintain a healthy weight and who avoid consuming too much alcohol have a 25% lower risk of developing breast cancer, the same protection as those who are not at high risk.
The simple gestures of prevention
The countless studies of recent years clearly show that the high incidence of the main cancers affecting our society (lung, colon, breast, prostate) is mainly caused by the Western way of life and that these cancers can be prevented by adopting healthy lifestyle habits: no smoking, plant-rich diet, maintenance of normal body weight, adequate sleep and regular physical activity. Taking care of your health in cancer prevention remains simple, in the end.
Mucci LA et al. Familial risk and heritability of cancer among twins in Nordic countries. JAMA 2016;315:68-76.
Wu S et al. Substantial contribution of extrinsic risk factors to cancer development. Nature. 2016; 529: 43-7.
Nkondjock A et al. Diet, lifestyle and BRCA-related breast cancer risk among French-Canadians. Breast Cancer Res Treat. 2006; 98: 285-294.
Nomura SJ et al. WCRF/AICR recommendation adherence and breast cancer incidence among postmenopausal women with and without non-modifiable risk factors. Int. J.Cancer.