There is also an increased risk of breast cancer. A Danish study of 7,000 women who worked nights found they were one-and-a half times more likely to be diagnosed with the disease.
Dr Graham Archard, a former night-shift veteran and a spokesman for the Royal College of GPs, is more optimistic. He says: If you do nothing but night work, there is no risk. Difficulties come when people swap between night and day. That stuffs you, as far as the biological clock is concerned.
He dismisses any link with cancer and heart disease but says such work does have adverse effects. It gets your hormones out of whack, he says. Often, women who work nights have delayed periods or missed periods. Sleeping patterns are disrupted, so the immune system is affected. People who work shifts are generally more prone to illness too, and evidence suggests it causes depression.
Even on the rare occasions when people who work late get eight hours sleep, they still feel terrible. They get spots and headaches, their eyes dry out and they become moody and anxious.
Stefan Chmelik, a Chinese medical physician at Londons Life Centre, is not surprised. The body wasnt made to work nights and, according to Chinese medicine, some functions can only be performed at night, he says. Between 1am and 3am, the liver uses this time to clean the blood, which it can only do if the body is resting. Failure to do so causes poor eyesight, a sallow complexion, and dry hair and skin. It can also cause irritability, anger and frustration.
There are measures you can take to make night working more bearable long term: Block out the world outside; have a pre-bed drinkwine, hot milk or water and just say no to drugs. Instead, have a hot bath. Also, routine is important and a good diet is a must.