People who skip breakfast tend to lose their virginity earlier, according to researchers in Japan.

In a study of 3000 people, those who did not regularly eat breakfast in their early teens said they lost their virginity at an average age of 17.5, versus an overall average age of 19 for all Japanese.

Those who had a morning meal when they were younger had their first sexual experience at 19.4 years.

The study, backed by Japan's health ministry, was aimed at finding ways to curb unwanted pregnancies. It concluded that a stable home life discouraged early sex.

"Those unhappy with their parents - such as for not preparing breakfast - may tend to find a way to release their frustration by having sex," said Kunio Kitamura, head of the Japan Family Planning Association who led the research.

"If children don't feel comfortable in their family environment, they tend to go out."

Young people who start having sex early tended to miss breakfast because they return home late, he said.

Japan has one of the world's lowest birthrates as more young people put off starting families, finding them a burden on their careers or lifestyles.

The survey also found that nearly 40 per cent of married couples had not had sex in more than a month.

Respondents said they were too tired because of work or found sex to be a pain, according to the study.