Diet and cancer: A dysfunction of the brain

Western diet, mental stress, and sleep disruption are important risk factors of obesity and carcinogenesis which result due to oxidative stress and inflammation. Diet and lifestyle factors also cause plasticity of the suprachiasmatic nucleus, circadian clock, cortex, hypothalamus, and other parts of the brain, resulting in adverse effects on physiology and metabolism, which may predispose to risk factors that predispose carcinogenesis. In previous studies, shift work has been linked to higher risk of chronic diseases, including certain types of cancers. Exposure to light at night suppresses the physiologic production of melatonin, a hormone that has antiproliferative effects on intestinal cancers which may worsen when functional foods are deficient in the diet. Epidemiological studies indicate that night shift work as well as mental stress may independently influence the function of the endocrine system, gastrointestinal system, and metabolism and circadian brain function. Sleep disruption enhances cortisol secretion and ghrelin release from the stomach and decreases melatonin and leptin which interfere with functioning of beta cells of the pancreas as well as other body systems. Apart from biological dysfunctions, behavioral changes (increased intake of refined carbohydrates, ω-6 fats and trans fats in the setting of lower intake of functional foods, low intake of ω-3 fats and flavonoids, physical inactivity, excess of tobacco use and alcoholism) may be common among night shift workers as well as among patients with psychosocial stress. Epidemiological studies indicate that sleep disruption may be associated with obesity and other chronic diseases, including cancers. Since electric light at night has adverse effects among night shift workers compared to day shift workers, it has been proposed that a portion of the high and rising risk of breast and prostate cancer worldwide may be because of night shift work in the setting of lower intake of functional foods. Suppression of nocturnal melatonin by exposure to light at night results in lack of protection by melatonin on cancer cell receptor sites which allows the uptake of linoleic acid (LA), which in turn enhances the growth of cancer cells. Melatonin is a protective, oncostatic hormone and potential antioxidant having evolved in all plants and animals over the millennia. Rotating night shift at least three nights per month for 15 or more years may increase the risk of colorectal cancer and other cancers.