Working night shifts can interfere with the body’s natural rhythms, which can cause the brain and digestive system to become completely out of whack. Researchers found that three consecutive night shifts had little effect on the body’s master clock in the brain, but it wreaked havoc on gut function, throwing off the natural cycle in question by a full 12 hours, according to The Guardian in the UK. The findings highlight the huge impact of night shifts on the different biological clocks that govern the natural rhythms (responsible for managing the body’s various organs and systems), the report said. The inconsistencies within the body regarding day and night may explain why people who work night shifts and are jet-lagged may experience stomach pain or other gastrointestinal problems. Once their bodies have had time to adjust, these symptoms disappear. Hans Van Dongen, director of the Sleep and Fitness Research Center at Washington State University, says, “One of the first symptoms people experience when traveling across time zones is gastrointestinal discomfort. This is because the synchronization between the gastrointestinal biological clock and the body’s central biological clock is disrupted at this time.” To conduct the study, Van Dongen invited 14 healthy volunteers (aged 22-34) into his lab and divided them into two groups. The first group simulated working a three-day day shift. Volunteers in this group were allowed to sleep from 10 p.m. to 6 a.m. the next day. The second group of volunteers stayed awake for three consecutive nights, and they could only sleep from 10 am to 6 pm. For the next 24 hours, the scientists collected blood samples from the volunteers every three hours and sent them to the University of Surrey in England for analysis. At the University of Surrey, the researchers measured levels of melatonin and cortisol. These two hormones increase and decrease according to the body’s master clock. The researchers also measured levels of metabolites related to digestion. The results showed that three consecutive night shifts shortened the brain’s master clock by an average of about two hours. But the biological clock of the digestive system was profoundly affected, with night shifts shortening it by 12 hours. People have a central master clock in their brains that controls when they wake up and go to sleep based on changes in the surrounding light, the report said. However, many other organs in the body, including the digestive system, have their own biological clocks. Night shifts also interfere with the rhythms of two metabolites linked to chronic kidney disease.