Staying out of the sun completely may increase your chances of developing cancer, say doctors.

For years, experts have advised people to cover up in the sun to protect themselves from skin cancer.

But a letter in this week's British Medical Journal warns people against taking this advice to the extreme.

Professor Cedric Garland from the University of California said a lack of sun can reduce levels of vitamin D, which may increase the risk of cancer.

The sun is a major source of vitamin D. Studies have suggested this vitamin can protect against colon, breast, prostate and other cancers.

Sun exposure

Professor Garland said people living in Britain should ensure they are get between 10 and 15 minutes of sun exposure each day, weather permitting.

"Residents of the UK should aim for 10 to 15 minutes a day in the sun when the weather allows, without sunscreen to allow adequate synthesis of vitamin D," he wrote.

He also suggested they should supplement their diets to ensure they are getting enough vitamin D, particularly during winter.

"Since the UK is located at northern latitudes supplementation of the diet with vitamin D would be helpful, in addition to encouraging moderate exposure to the sun," he wrote.

Professor Garland said a lack of sun during the winter months meant many Britons are deficient in this vitamin by December each year.

"People in the UK cannot synthesise vitamin D from November to the end of March," he said. "They become deficient by December."

He said that while avoiding the sun completely may reduce the risks of skin cancer, it could increase the chances of developing other cancers.

"Advice to avoid the sun would not be the best strategy for reducing overall incidence of cancer," he said.

However, cancer charities warned that even short spells in the sun could cause skin damage.

A spokeswoman for Macmillan Cancer Relief said: "Of course the sun has many qualities, however, it's best to be sensible about the amount of time spent sunbathing.

"Staying in the sun for 15 minutes a day, especially at midday, could cause skin damage for some types of people.

"For those who do want to sunbathe the best time to avoid the sun is between 11am and 3pm when the sun will be at its hottest and to use a high factor skin cream."

Healthy diet

Sara Hiom, information manager at Cancer Research UK, said: "It may be that vitamin D can help reduce the risk of certain cancers.

"People don't need to seek out the sun to get Vitamin D - they are most likely to get all they need from going out and about in their daily routine.

"Our diet is also an important source of Vitamin D - dairy products, some meats, eggs and fish oils all contain this important vitamin."

She added: "We do not advocate complete avoidance of the sun, but we caution against sun exposure that leads to tanning and burning, both of which are evidence of skin damage that can lead to skin cancer.

"There is no doubt that excessive UV radiation is the major cause of skin cancer."