Making love could be one of the few pleasures in life that is genuinely good for you, say researchers.Not only does a healthy sex life boost mood, but there is growing evidence to show it boosts your physical well-being, too - from increasing longevity to reducing the risk of erectile dysfunction and even heart attack.
Only last month, researchers at Nottingham University concluded that men who kept up a regular sex life in their 50s were also at lower risk of developing prostate cancer.
(Conversely, they found 'too much' sexual activity - more than 20 times a month - in the 20s and 30s could increase the risk.)
In fact, the research seems to suggest that men - particularly older men - benefit the most from healthy effects of sex. Feel-good hormones help explain some of the benefits, such as mood-boosting, but the explanation is not always obvious.
But one thing is clear, and this applies to both men and women: you need to be having sex regularly if you don't want to lose the ability.
'Use it or lose it' was the advice given to older men by Finnish scientists recently.
They had followed 1,000 men aged between 55 and 75 for five years and found that those who had sex less than once a week at the start of the study were twice as likely to develop erectile dysfunction (see below) as those who had it at least once a week.
Those who had sex three or more times a week lowered their risk fourfold.
As women get older their oestrogen levels drop, says Dr Peter Bowen-Simpkins, consultant gynaecologist at the London Women's Clinic and spokesperson for the Royal College of Obstetricians and Gynaecologists.
This hormone is key to a woman's sexual enjoyment - lower levels can make sex uncomfortable, he explains.
But American research found that menopausal women who had sex every week had oestrogen levels twice as high as their abstaining counterparts.
'Regular sex increases the production of oestrogen,' says Dr Bowen-Simkins. As long as other symptoms, such as dryness, are not a problem or have been treated, having more sex can decrease the risk of vaginal atrophy which can occur with age, he says.
So what else can a regular love life do for your health?
Heart
Sex can be good for your heart. The idea that men are more at risk of a heart attack during love-making is mostly misconception, say experts.
Professor Peter Weisberg, medical director of the British Heart Foundation, says there is no evidence that men who have sex regularly in their 40s, 50s and beyond are at an increased risk of heart attack.
'As far as the heart is concerned, sex is just another form of exercise,' says Dr Graham Jackson, consultant cardiologist at Guy's & St Thomas' Hospital and president of the Sexual Dysfunction Association.
'In fitness terms, it's equivalent is going for a mile-long walk or climbing up and down two flights of stairs.
'If you're physically fit enough for that, there should be no increased risk during sex.'
A study at Queens University in Belfast found that having sex three times a week could actually halve the risk of heart attack or stroke.
Prostate
Prostate cancer is the most common cancer in British men, affecting 35,000 a year.
Previous research suggested that greater sexual activity was linked to a higher risk of prostate cancer, but findings from Nottingham University (published in the British Journal Of Urology International) suggest the opposite is true: that increased activity is protective for older men.
This backs up the findings of a major study five years ago by the National Cancer Institute, published in the Journal of the American Medical Association.
Previous studies have suggested the reduced risk is due to the release of toxins from the prostate gland.
'We can't say for certain that having regular sex can protect older men from prostate cancer, because such studies don't prove the mechanism through which risk is reduced,' says Dr Geoffrey Hackett, consultant urologist at Good Hope Hospital, Sutton Coldfield, and former chairman of the British Society for Sexual Medicine.
'But many men who maintain a regular sex life are also likely to maintain a healthy lifestyle in terms of regular exercise and a better diet. That's likely playing a bigger part in their prostate cancer risk reduction.'
Bones
'Testosterone levels have been found to increase during and after sex,' says GP Dr Sarah Brewer. 'This may provide some protection against male osteoporosis.'
Sexual activity can also protect you against other unwanted changes. Some scientists have linked low levels of sexual activity to structural changes in the penis or testicles which appear to reduce them in size.
'We know that men who don't have regular ejaculations or sexual intercourse have lower levels of testosterone,' says Professor Pierre Bouloux, consultant endocrinologist at University College London and the Royal Free Hospital.
And if your testosterone levels fall and you don't get erections, there is some evidence that the penile tissues can lose some of their elasticity, which in turn could make them appear smaller.
Mood
The evidence suggests that the 'feelgood' effect of making love could be more about chemicals than sexual ability.
'During lovemaking and orgasm, a cocktail of endorphins (the body's natural mood-lifting opiates), neurotransmitters and hormones are released,' says Professor Nadir Farid, consultant endocrinologist and founder of the London Endocrine Clinic.
'Oxytocin, in particular, is a hormone released during and after sex that has been shown to make people more generous towards their partners and can also help induce calm and sleep,' he adds.
Oxytocin is called the 'cuddling' hormone because it's released after just 20 minutes of hugging. Women produce four times as much as men, for whom production is inhibited by the prevalence of the hormone testosterone, which drives libido.
Another key neurotransmitter is serotonin, says Professor Farid. 'Serotonin is the body's key antidepressant chemical and one of the major reasons people smile and feel happy and relaxed after sex.'
Sexually active women in longterm relationships were less likely to be depressed than women who went without sex, according to a study of nearly 300 women by American psychologist Gordon Gallup and published in the Archives Of Sexual Behaviour.
Gallup speculated that semen contains several hormones which may have a mood-boosting effect when they are absorbed through the vaginal wall into the bloodstream.
Immunity
Having more sex might increase immunity from colds and flu.
Having sex once or twice a week has been linked with higher levels of immunoglobulin A, or IgA, a substance found in saliva and the nasal lining thought to help our immune systems fight colds and flu.
In one study, scientists asked 11 volunteers how often they had had sex over the previous month, then measured levels of IgA in their saliva.
Those who had sex once a week or less had a slight increase, compared with those who abstained; but those who made love more often had 30 per cent higher levels.
Professor Ron Eccles, director of the Common Cold Centre and Healthcare Clinical Trials at Cardiff School of Biosciences, is not convinced, though, that sex itself is the key.
Longevity
One of the largest studies on longevity and sex - conducted on Welsh men - found that those who had sex less than once a month had double the risk of dying prematurely than those who had sex twice a week.
'Sexual activity seems to have a protective effect on men's health,' says GP Dr Sarah Brewer. 'This may be linked with the effects of the master sex hormone, DHEA or dehydroepiandroterone, which is made in the adrenal glands and functions as a building block of other hormones such as oestrogen, testosterone and progesterone.
'DHEA levels rise just before orgasm and ejaculation to three times higher than normal, and some claim this is how regular sex can prolong your life.'
Fertility
For people trying to conceive, one of the biggest myths associated with fertility is that refraining from ejaculation boosts sperm mobility - the rate at which individual sperm can move forwards to penetrate an egg for fertilisation, says gynaecologist Dr Gillian Lockwood, medical director of Midlands Fertility Services.
'When sperm is hanging around in the epididymis, the long coiled tube in the back of the testes where sperm is stored, it dies off rapidly,' she says.
'Unless a man has a low sperm count, the more often he has sex, then the better the quality of his sperm.'
Preliminary results of a small study two years ago, by Australian researchers, found that in men whose sperm showed significant DNA damage, daily ejaculation reduced this damage by 12 per cent.
'When it comes to sex for fertility, having sex little and often - at least every other night - is far better than lots of it on infrequent occasions.'
And the bad news
Just when you thought you'd had the green light for more passion, the experts strike a cautionary note. Unbridled romping - particularly with a new partner and without protection - comes with bigger risks, especially for the 'Viagra generation'.
Rates of sexually transmitted infections (STIs) in the over 45s have doubled in the ten years since Viagra was launched, and STI rates are now rising faster in older people than they are in the young.
A study last year from University College London found that those in their late 30s and 40s were least likely to use condoms with new partners.
Other research has found that 12 per cent of sexually active over-50s did not use contraception while also not knowing their partner's sexual history.
'This is a generation that didn't have the open sex education that young people get today,' says Professor Janice Rymer, professor of obstetrics and gynaecology at St Thomas' Hospital London.
'Today's 50-somethings probably know less about sexual protection than many of today's teenagers.'
Most STIs are treatable with antibiotics, said Professor Rhymer, but it's important to be aware that some, such as human papilloma virus (HPV), have been strongly linked to cervical, mouth and other cancers.
How to cope when the mechanics let you down
MEN
ERECTILE DYSFUNCTION:
This affects 14 per cent of men in northern Europe and can be caused by underlying medical conditions such as high blood pressure, diabetes, smoking, high cholesterol, prostate surgery, or a psychological cause such as depression.
Repeated episodes of erectile dysfunction (ED) are a key indicator of undiagnosed early cardiovascular disease, warns Dr Graham Jackson.
'Two-thirds of men with erectile dysfunction have early onset coronary heart disease, in which no other symptoms - such as chest pain - are present.'
Studies have shown that erectile dysfunction could precede the onset of heart problems by three years. This is why men with ED should seek medical advice. 'The greatest risk to your heart comes with buying erectile-enhancing drugs without prescription on the black market,' said urologist Dr Geoffrey Hackett.
Treatments for erectile dysfunction include Viagra and Cialis, which have to be taken up to an hour before sex. These work by increasing blood flow by widening the blood vessels, but are effective in only 50 per cent of men. Cialis Once-A-Day, which is prescription-only, allows men to have sex whenever they want, and so restores the spontaneity lost with other treatments.
PREMATURE EJACULATION: Up to 30 per cent of Western men experience some form of this.
Treatments include condoms with numbing agents, anaesthetic sprays for the penis, antidepressant drugs to lower the anxiety that might cause the condition and pelvic floor exercise therapy.
WOMEN
FEMALE SEXUAL DYSFUNCTION: Up to 43 per cent of women are said to suffer from FSD, including low sex drive and inability to orgasm.
But medical experts question this figure, and the British Medical Journal has accused drug companies of medicalising the natural loss of libido that may come with age or relationship problems.
There are no drug treatments for FSD, though 25 are in development.
MENOPAUSE: The menopause causes a woman's ovaries to slow down and stop producing hormones, including testosterone, for sex drive, and oestrogen, which can reduce lubrication, making sex painful. 'KY Jelly can be effective,' says gynaecologist Dr Peter Bowen-Simpkins.
'Or we can prescribe estradiol, a weak oestrogen applied locally through pessaries or creams to help replace moisture and acidity'.
PAIN OR BLEEDING: 'Pain can be a sign of cysts, fibroids and, in very rare cases, ovarian cancer,' says Dr Gillian Lockwood, consultant gynaecologist. Bleeding is usually caused by benign cervical erosion and is easily treatable. Rarely, bleeding during sex can be a sign of cervical cancer. If it happens more than three times, see your GP.'
