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Friday, 21 August, 1998, 08:01 GMT 09:01 UK
Jetlag explanation for breast cancer
Air hostess
The initial research had caused widespread concern in the air industry
The higher incidence of breast cancer in some air hostesses may be linked to jetlag, according to the Lancet.

The journal published Finnish research three years ago that suggested the country's female flight attendants were almost twice as likely to get breast cancer than women in other jobs.

Several explanations had been put forward including exposure to radiation at high altitude.

Now, in a research letter, Dr Anthony Mawson from North Carolina, suggests jetlag, caused by the disrupted sleep patterns of air workers, may be to blame.

Melatonin link

He says the body's sleep-wake cycle is associated with the secretion of melatonin, a hormone also shown in experiments to slow the growth of breast-cancer cells.

Melatonin is released by the pineal gland in the middle of the brain between nine in the evening and eight in the morning.

Working at night and flying across time zones interferes with the body's natural rhythms, says Dr Mawson, who works with the Carolinas Healthcare System in Charlotte.

"Disruption of pineal-gland activity as a result of being awake during normal sleep time and attempting to sleep during normal waking time would, therefore, be expected to decrease secretion.

"Melatonin production is decreased by exposure to bright light during normal sleep time, whereas supplementary melatonin prevents the symptoms [of jetlag] and is thought to be the best available pharmacological treatment for jetlag."

Influential role

He says supplementary melatonin has had a protective effect against breast cancer in animals.

There is other evidence that the hormone plays an influential role in determining whether normal tissue in the breast becomes cancerous.

It also augments the well know anti-breast cancer drug Tamoxifen which can block runaway cell division.

Dr Mawson suggests how his hypothesis can be tested: "Flight attendants with breast cancer should have more work-associated exposure to jet-lag, and lower melatonin than those without breast cancer."

Professor Gordon McVie, director general at the UK's Cancer Research Campaign, says the hypothesis is interesting.

"The radiation theory hasn't gone away, but what I find difficult to explain with that is why there isn't an excess of leukaemia, because that is the prime cancer associated with radiation."

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