For many of us, night has become day. We work, travel, shop, exercise and socialize in hours that used to be reserved for relaxation and sleep. Time is a limited resource and, to make full use of it, the night has been illuminated and occupied. Even when we do sleep, street lamps and security lights pierce the darkness.
But our freedom from the natural constraints of day and night may have come at a price. According to a growing band of scientists and doctors, many of us are no longer getting enough darkness in our lives. The theory is based on a simple premise. Our biological rhythms evolved in a time before artificial light, to take advantage of both bright days and dark nights. By succumbing to the temptations of 24-hour living, and ignoring or reducing our natural dark time, we could be putting our health at risk.
"A number of health and environmental problems are due to a loss of darkness," says Dr David Crawford, executive director of the International Dark-Sky Association, a group that campaigns against light pollution. "And it will get worse as we creep -- or rush -- to a 24/7 world. All of life, all of it, has evolved with a day/night cycle -- the circadian rhythm. It's essential to good health. Many studies are now showing that those who go without a true day/night cycle are adversely impacting their immune systems, and that's not good."
It's not good, but it's becoming the norm. In the UK for instance, more than 20 percent of the working population now work at least some of the time outside the 7am-7pm day. Global travel, the internet, job insecurity, 24-hour shopping and TV, and -- coming soon -- late-night pubs and bars, all help to push back the boundaries of the active day. To remain active at night we need light, with the result that the natural circadian cycle of day and night, light and dark, is becoming perilously unbalanced. We are creating a conflict between what we want to do, and what our internal timekeeper -- the body clock -- prepares us for.
"Our biological clock has been likened to the conductor of an orchestra, with the multiple rhythms of the body representing the various sections of that orchestra," says Russell Foster, professor of molecular neuroscience at Imperial College, London, which later this month hosts the first international sleep conference. "The body clock adapts us for the varying demands of activity and rest. It ensures our internal synchronicity: that our various internal systems -- temperature, alertness, blood pressure and so on -- are working together. And the body clock sets itself using the light/dark cycle. By moving to 24-hour living, and reducing or ignoring the dark bit, we are effectively throwing away the advantages of millions of years of evolution."
The effects of screwing up our body clocks are most readily observable in the growing army of night workers. Studies suggest that, even after years of night shifts, many workers never adjust to a regime that pitches them against our basic and hard-wired biology.
Instead, they head wearily home to bed just as the morning light is prompting their body clocks to prepare for activity, and back again when the gathering dusk tells them to prepare for rest.
Once at work, overriding the craving for dark and sleep comes at a price. "They activate the `fight or flight' stress mechanism," says Foster, "and we know that stress in turn can suppress the immune system." Bright lights, caffeine and nicotine artificially maintain stimulation. Perhaps unsurprisingly, studies show that nightshift workers are at increased risk of a range of health problems, from stress, constipation and stomach ulcers to depression, heart disease and cancer. For example, a 2001 study in Seattle, based on interviews with 800 women, found that females who worked the graveyard shift could face a 60 percent increase in the risk of breast cancer.