Like the sun, insulin levels rise and fall in a daily rhythm. Disrupting that cycle may contribute to obesity and diabetes, a new study suggests.
Many body systems follow a daily clock known as a circadian rhythm. Body temperature, blood pressure and the release of many hormones are on circadian timers. But until now, no one had shown that insulin — a hormone that helps control how the body uses sugars for energy — also has a daily cycle. Working with mice, researchers at Vanderbilt University in Nashville have found that rodents are more sensitive to insulin’s effects at certain times of day. Disrupting the animals’ circadian timers interferes with the hormone’s daily rise and fall and makes mice prone to obesity.
If the findings hold up in humans, they could help explain why people who work night shifts tend to be overweight and suffer health problems. The discovery may also tie the obesity epidemic in part to staying up late and eating at the wrong time.
Many people had thought that it was best for the body to maintain insulin at a relatively constant level, says Carl Johnson, a circadian biologist who led the new study. “But that’s not how organisms have adapted,” he says. Since the environment cycles through light and dark, body processes often coordinate with that rhythm.