Having more sex could not only make us feel good, it could provide far-reaching health benefits.
Unfortunately we are having less of it - on average we have sex fewer than five times a month, compared to six-and-a-half times 20 years ago, according to the National Survey of Sexual Attitudes and Lifestyles.
Yet studies have linked regular sexual activity to emotional well-being, reduced migraine pain and even a lower risk of prostate cancer.
A Canadian study last month found that half-an-hour of sexual activity could burn more calories than walking on a treadmill - the researchers claimed sexual activity could be considered significant exercise.
The study measured the sexual activity of 21 couples aged between 18 and 35 - they were monitored using an armband to calculate how many calories the wearer burned, and the intensity of the activity.
In a typical session lasting 25 minutes, the men burned an average of 100 calories, the women 69. The intensity of the activity was measured in METs (the Metabolic Equivalent of a Task); for men, the average reading was six METs, for women it was 6.6.
It's roughly the same as playing doubles tennis, or walking uphill, for 20 minutes, 33 minutes of golf on a driving range, 40 minutes of yoga or 19 minutes of light rowing.
The Canadian findings chime with past campaigns by the British Heart Foundation, which suggested that 30 minutes of daily sex is as good for you as walking the dog.
Indeed, research is now showing that sex provides a 'triple-whammy' of benefits by combining a workout for the heart and lungs, the release of hormones that could lower stress and the production of new brain cells. And - for women - the added plus is a toning effect on the muscles in the pelvic floor.
Graham Jackson, a consultant cardiologist and president of The Sexual Advice Association, says we've known for a long time that sex has health benefits, but it's only in the past decade that the taboo has been lifted from sex research in Britain.
'This has led to more studies in the area,' says Dr Jackson.
A BOOST FOR THE HEART, LUNGS AND BRAIN
Increasingly doctors view sex as 'an under-used resource in terms of physical and emotional well-being', says Dr Arun Ghosh, a private GP with a special interest in the health benefits of sex. 'Plus, it's not emphasised enough as a really good form of exercise.'
The Canadian research suggests it can be classed as a moderate intensity exercise - if you do enough of it, but more of that later.
And it's not just the heart and lungs that get a workout. Last week, scientists at the University of Maryland in the U.S. discovered that middle-aged rats made more brain cells after mating.
The process, called neurogenesis, is thought to restore brain function lost through ageing. In particular, the benefits were seen in the hippocampus, the region of the brain where new memories are formed.
The rats' brain function improved after long periods of sexual activity, specifically in this hippocampus area.
'A huge amount of brain stimulus occurs during intercourse,' comments Dr Ghosh. 'It's why we feel so overtaken when we orgasm,' he says. 'When researchers do MRI scans on people in orgasm, they observe both sides of the brain being stimulated, including parts of the brain we wouldn't normally use.'
Still, it's important to note the study was on rats and we still don't know if neurogenesis happens as significantly in humans, says Dr Simon Ridley, of the Alzheimer's Research Council.
'Plus, any improvements in brain power were lost once the animals' sexual activity stopped, so we can't assume any benefits to their brains will be long-term.'
Though the study showed the new cells remained, 'there's as yet still no compelling evidence to support the idea that regular sex can help stave off dementia or cognitive decline in humans', adds Dr Ridley.
However, there is no doubt that sex provides a substantial workout to women's pelvic floor muscles. As Andrew Hextall, a consultant who specialises in genito-urinary medicine at Spire Bushey Hospital, London, explains, a stronger pelvic floor can help reduce the risk of prolapse of the womb, which affects half of women over 50.
And a stronger pelvic floor also reduces the risk of stress incontinence, which affects one in four women over 40.
'During intercourse, the muscles in a woman's pelvic floor naturally contract and squeeze,' says Mr Hextall. 'This increases muscle tone in the area, as the pelvic floor is like any other muscle, it responds to use by getting stronger.'
Even if your sex sessions only last a short time it's likely you would still get the effects, he says.
'The recommendation for exercises to strengthen the pelvic floor are to squeeze the pelvic floor only eight times at any one time,' he explains. 'It's likely that during sex you will be contracting your pelvic floor at least that many times, so there's no need for prolonged sex sessions to get these benefits.'
IT LOWERS MEN'S CANCER RISK
The good news for men - for older men, anyway - is that regular sex may be linked to a lower risk of prostate cancer, according to a study from Nottingham University.
The researchers, who questioned 840 men about their sexual histories, found those who kept up a regular sex life in their 50s - ejaculating more than ten times a month - were at a lower risk of prostate cancer, the most common form of cancer in British men. One theory is that if men don't clear the sperm, it can be re-absorbed by the prostate gland.
Sperm needs to be regularly flushed out to allow new cells to develop. It's a bit like cleaning out a pipe, it may help stop the build-up of old cells that might be more likely to turn cancerous,' says Dr Ghosh.
A previous study from the National Cancer Institute in the U.S. of more than 29,000 men found that those having the most orgasms had a third lower risk of prostate cancer.
However, the Nottingham University research, which was published in 2009 in The British Journal of Urology International, also found that ejaculating more than 20 times a month in their 20s and 30s could increase prostate cancer risk later in life. This is possibly because higher levels of sex hormones in some men, which may be responsible for a high sex drive, may also be linked to the development of prostate cancer later.
IT'S EVEN GOOD FOR HEADACHES
Sex may also have a positive effect on emotional well-being.
A study published in the Archives of Sexual Behaviour found young women felt more depressed the longer they hadn't had sex.
One theory is that vaginal absorption of hormones in semen such as prostaglandins, testosterone and luteinizing hormone could help improve the mood of women, says Stuart Brody, professor of psychology specialising in sexual behaviour at the University of the West of Scotland. orgasm also releases feel-good brain chemicals such as serotonin, adds Dr Ghosh.
'Routinely now, when our patients - male or female - are diagnosed with depression or anxiety we encourage them to maintain their sex lives because it's so beneficial for mental well-being'.
Research by Professor Brody and his team has confirmed that sex is a stress reliever.
They studied a group of German adults and found those who had sex at least once over two weeks were better able to manage the stress of public speaking and recorded lower blood pressure in response to stressful situations.
Meanwhile, in women, orgasm might help a headache, killing the age-old excuse for abstaining.
'Orgasm is associated with an upsurge of blood flow from the brain which could reduce headache,' says Dr Ghosh.
One study of 83 women with migraine found that more than half experienced relief after orgasm. The research, published in the journal Headache in 2001, found that 30 per cent reported some pain relief while 17.5 per cent said it had in the past relieved their symptoms altogether. Orgasm is also associated with a surge of the chemical oxytocin in men and women. This is often called the 'bonding' hormone because it induces feelings of fondness and affection.
'Anthropological research has found that for humans, quite aside from the pleasure we glean from sex, one of the main drivers behind our need for sexual activity is to bond with other humans,' says Dr Ghosh.
Last week, researchers found that oxytocin may help sustain feelings of love and commitment in long-term relationships.
The study gave 40 men oxytocin, then showed them pictures - one of their partners and one of a woman they'd never met.
Brain scans showed in the majority of the men the brain's reward systems lit up when they saw their partner's picture.
'Regular sex stimulates the brain's pleasure and reward system through the release of chemicals such as oxytocin and dopamine,' Dr Ghosh explains. 'It's one thing that keeps us going back to our partners for more.'
YOU HAVE TO KEEP GOING FOR 30 MINUTES
Dr Jackson says sex could form a part of an overall, varied exercise regimen - if you can make it last long enough. For most long-married couples, sex sessions last around 15 minutes rather than the 30 minutes achieved by the couples in the Canadian study.
He peak moments can lead to an increase in heart rate of around ten beats per minute and sometimes more, he explains.
Foreplay is equivalent in activity terms to running for a bus. 'A typical game of tennis or squash is around 40 minutes of sustained cardiovascular activity, so to compare these to sex in fitness benefits you would need to perform your peak periods of sex for around the same amount of time,' says Dr Jackson.
If you last 30 to 40 minutes 'quite vigorously', 'you could get a good cardiovascular workout during sex'. But a paper in the New England Journal of Medicine last year concluded the average bout of sexual activity was only six minutes, expending about 21 calories. 'Sexual activity is meant to compliment other more sustained forms of exercise,' says Dr Jackson. 'You can't say, "I have sex, I won't exercise".'
WHY ARE MEN SO SLEEPY AFTERWARDS?
Research in the journal Neuroscience and Behavioural Reviews in 2012 has explained the sleeping-pill like effect sex has on men. Brain scans showed the pre-frontal cortex, the area associated with consciousness, alertness and mental activity, 'switches off' after an orgasm.
Other research has shown that in men an orgasm's tension-relieving effects are like taking 2mg of diazepam (a sedative). 'This explains why men want to sleep after sex,' says Dr Ghosh. And hormones released in orgasm - melatonin, oxytocin and vasopressin - are also all associated with sleep.
Courtesy of Dailymail.co.uk