The biological clock in our brain regulates the circadian rhythm of tissues and organs throughout the body. This is important for sleep as well as normal metabolic function. It is well established that shift work disrupts normal physiological function. For example, another study reported earlier this year by MedicalNewsToday, which simulated shift work in rats, found an association with increased incidence of non-small cell lung cancer. Now, some scholars have found that sleep disruption is associated with increased incidence of liver cancer. The American Cancer Society reports that 700,000 people worldwide are diagnosed with liver cancer each year. Men are more likely to get liver cancer than women. In the United States, experts estimate that more than 18,000 men and nearly 9,000 women die of liver cancer each year. Obesity is a major risk factor for hepatocellular liver cancer, which is the most common type of liver cancer. Excess fat in the liver can lead to nonalcoholic fatty liver disease (NAFLD), which occurs at a high rate in obese people. There has been speculation that NAFLD is the leading cause of hepatocellular liver cancer in the 21st century.