The sex drive of women plummets sharply as they juggle the increasing demands of partners, children and careers, researchers said on Thursday.

One in 10 women questioned for a survey admitted losing interest in sex for at least six months in the past year.

"The next major problem was the inability to have an orgasm. That was reported by four percent of women," said Dr Catherine Mercer of University College London after a British study was made of over 11,000 men and women aged 16-44.

Married women were shown to be much more likely than single men or women to have sexual problems.

The survey showed that both sexes tend to suffer in silence when faced with sexual problems like lack of sex drive, premature ejaculation or erectile dysfunction.

Fifty-four percent of women and 35 percent of men have problems but fewer than 11 percent of men and 21 percent of women seek help, according to the survey published in the journal Sexually Transmitted Infections.

For both men and women, their first sexual encounter could be crucial to their future attitude to sex. The worse the experience, the more difficulty they may have in later life.

'Tired and exhausted'

Couples had sex on average four times a month and Mercer told Reuters: "People who had less than this were more likely to report sexual problems both short and long-term."

"Within a relationship, those less able to talk freely had more problems," she said, insisting that the findings had important implications for sex education and counseling services.

But the sex drive of women dropped sharply from those first heady months when they fell in love.

"Women were more likely to report problems if they had kids in the house under the age of five. That of course seems quite logical with the lack of sleep they are suffering," Mercer said.

The findings for men were in stark contrast.

"As Dr. John Gray said, men really are from Mars and women from Venus," said Dr David Goldmeier from the sexual function clinic at St Mary's Hospital in London ,

"Women want to hear, they want to tell you about their day. When men sit down and hear about the woman's exhaustion this is as likely as anything else to lead to sex," he told Reuters.

"There is nothing actually wrong with these women. Bringing up a family they are just tired and exhausted as opposed to the men who have 10 times the level of testosterone," he said.