Using your cellphone before bed may stop you from getting a decent night's sleep.

A new study, funded by cellphone companies, suggests the radiation from mobile phones can cause insomnia, headaches and confusion.

Talking on the phone before bed caused people to take longer to reach the deeper stages of sleep and to spend less time in them, interfering with the body's ability to repair damage done during the day.

The study found children and teenagers were particularly vulnerable as they were most likely to use phones late at night and needed sleep the most.

Scientists from Sweden's Karolinska Institute and Wayne State University in the United States studied 35 men and 36 women aged between 18 and 45.

Some were exposed to the same levels of radiation emitted when using a cellphone, while others were given only "sham" exposure.

Those exposed to radiation took longer to enter the first of the deeper stages of sleep and spent less time in the deepest one.

The study suggested people use a landline if they needed to make a call before bed and not to sleep with mobile phones on their bedside table.

Christchurch sleep specialist Dr Mike Hlavac said it was an interesting study, but he would not be changing his advice to patients without further investigation.

"It's interesting that you can potentially manipulate sleep using mobile-phone signals. It would go with earlier research suggesting radiation might have an impact on sleep," he said.

The length of radiation exposure given to those in the study – three hours – was much longer than most people would talk on the phone, he said.

Hlavac recommended patients with insomnia kept a cellphone by the bed rather than an illuminated clock, which could keep them counting the hours.

(Agencies via China Daily February 4, 2008)