Jet lag, shift work and even late nights staring at your tablet or smartphone may be making you sick. That’s because the body’s internal clock is set for two 12-hour periods of light and darkness, and when this rhythm is thrown off, so is the immune system. One reason may be that the genes that set the body clock are intimately connected to the type of immune cells known as T cells, said a study by Lora Hooper, an immunologist at the University of Texas Southwestern Medical Center in Dallas. The finding in mice adds to a growing body of research showing that a healthy pattern of light and dark, sleeping and waking, is essential to keep the immune system in balance. Hooper notes that inflammation is the basis of many chronic disorders, such as heart disease, asthma, chronic pain, bursitis and dermatitis. Inflammatory conditions are more prevalent in developed countries, where people’s circadian rhythms are chronically disrupted. Even people who don’t work shifts still wake and sleep out of sync with light and darkness. “We all have screwed up light cycles. We stay up late, keep the lights on, look at our lit-up iPhones at 2 a.m.” Hooper advises that a good starting point is limiting your exposure to artificial light at night. ScienceNOW