Cancer is caused by a variety of identified and unidentified factors – and many of them are linked to the lifestyle of a person. The most important established cause of cancer is tobacco smoking. Other important determinants of cancer risk include diet, alcohol and physical activity, infections, hormonal factors and radiation.
The relative importance of cancers as a cause of death is increasing, mostly because of the increasing proportion of people who are old, and also in part because of reductions in mortality from some other causes, especially infectious diseases.
The incidence of cancers of the lung, colon and rectum, breast and prostate generally increases in parallel with economic development, while the incidence of stomach cancer usually declines with development.
Lifestyle and diet play a key role in cancer prevention and survival. It is estimated that roughly 30 to 60% of all cancers are related to nutrition.
The incidence of lung cancer is highly correlated with smoking. The most consistent finding, over decades of research, is the strong association between tobacco use and cancers of many sites. Hundreds of epidemiological studies have confirmed this association.
Further support comes from the fact that lung cancer death rates in the United States have mirrored smoking patterns, with increases in smoking followed by dramatic increases in lung cancer death rates and, more recently, decreases in smoking followed by decreases in lung cancer death rates in men.
Lifestyle choices cause cancer: tobacco, diet, exercise, alcohol, tanning choices, and certain sexually transmitted diseases are the major risks. “Most cancers are related to known lifestyle factors.”
There is also a growing body of research that correlates cancer incidence with the lower levels of melatonin produced in the body when people spend more time in bright-light conditions, as happens typically in the well-lit nighttime environments of the more developed countries. This effect is compounded in people who sleep fewer hours and in people who work at night, two groups that are known to have higher cancer rates.