A good night's sleep could protect people from developing cancer, a US scientist has claimed.
Lack of sleep could affect hormone levels
Professor David Spiegel, from Stanford University Medical Center, said sleep can alter the balance of hormones in the body.
Hormonal imbalances can influence whether a person develops cancer.
The hormones cortisol, melatonin and oestrogen were all cited as potentially playing a role in determining whether someone develops a tumour.
Professor Spiegel looked at the research which has been carried out into the relationship between sleep and cancer.
One study looked at cortisol, the body's major stress hormone. It helps regulate the immune system - including the cells that help the body fight cancer.
Levels usually peak at dawn and decline during the day.
Professor Spiegel looked at research which found women at high risk of breast cancer had a shifted cortisol cycle.
He said that a cortisol rhythm disrupted by problems sleeping could make a person more
Professor Spiegel has previously looked at women with breast cancer whose cortisol levels peaked in the afternoon rather than at dawn.
He found that they died earlier from the disease.
Professor Spiegel also looked at the role of melatonin which is produced during sleep and plays a role in the body's daily cycle.
He said it acted as an anti-oxidant, which can prevent the DNA damage that can lead to cancer, and slowed production of oestrogen, which can fuel the growth of breast and ovarian tumours.
Female shift workers who are up all night and produce less melatonin may therefore be more vulnerable to oestrogen.
Research has shown that female night shift workers had higher rates of breast cancer than women who slept normal hours.
Studies of mice have also shown that when their sleep rhythms were disrupted, they had far more rapid tumour
growth than normal mice.
Prof Spiegel said: "I'd like people to reconceptualise cancer as a biological event that triggers stress responses affecting how the disease progresses.
"Doctors should not just be fighting the tumour but helping the people with the disease to live with it.
"Although having cancer might be something to lose sleep over, we'd rather help people regain the sleep and lose the cancer."
The research is published in the journal Brain, Behaviour and Immunity.