Good health means people are almost twice as likely to be interested in sex compared with those who are ill or in poorer health.

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They are also likely to have regular sex - once or more a week - and report better quality lovemaking, experts found.

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Researchers already know that regular sex can improve people's health and wellbeing.

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Now, two new US studies on more than 6,000 people have determined the impact of health on sex.

The results also revealed how many years of active sex people generally have left at different stages of their lives.

Aged 30, men have a sexually active life expectancy of nearly 35 years while women can expect another 31 years of sex.

Aged 55, men can hope for another 15 years while women generally have another 11 years of sexual activity.

Being married or having a partner makes this gender difference less obvious, the research, published online in the British Medical Journal (BMJ) found.

Nevertheless, it seems men overall are more interested in sex and report a good sex life than women.

The difference between the genders was most noticeable among the 75 to 85 age group, where 39% of men compared with 17% of women were sexually active.

A total of 71% of men compared with 51% of women who were sexually active at this age reported a good sex life, while 41% versus 11% of women were interested in sex.

At age 55, men in very good or excellent health on average gained five to seven years of sexually active life compared with their peers in poor or fair health.

Meanwhile, women in very good or excellent health gained three to six years compared with women in poor or fair health.

Stacy Tessler Lindau and Natalia Gavrilova, from the University of Chicago in the US, looked at data from one group of men and women aged 25 to 74 and another group aged 57 to 85.

People were interviewed and filled in questionnaires on their marital status, rated the quality of their sex lives as well as how often they had sex.

They also rated their health on a scale between poor and excellent.

In an accompanying editorial, Professor Patricia Goodson from Texas University, said: "More importantly, the study bears good news in the form of hope: given the manner in which "second adulthood" has been redefined in recent years, the availability of sexual performance enhancers, the widespread use of the internet for social support, as well as improvements in overall health and better access to care, the news that adults in the US can enjoy many years of sexual activity beyond age 55 is promising."