Is sex as good for you as men like to claim it is? Well yes ... if you're a man. One study looked at 1,222 men aged 45-59 in Caerphilly and five of the villages around it. The men were assessed according to blood pressure, cholesterol, smoking etc and how much sex they claimed to have. Of the 918 who said how often they had sex, one in four fell into the "high" category (twice a week or more), just over half were "medium" (less than twice a week, but more than once a month), and one in five were "low" (less than once a month). The men who had the most sex were non-manual workers with slightly higher cholesterol levels than the once-a-monthers.
Over the following 10 years, 150 of the men died; 67 from heart disease and 83 from other causes. But the more sex a man said he had per week, the less likely he was to die. The high sex group had half the risk of dying of the low sex group. Don't use this for emotional blackmail. You may not get the answer you want, especially if you are married to a teacher. As a profession, teachers often complain that they can be too exhausted for sex during term, although it may be another matter in the holidays.
Whether it's sex or fantasy that's good for men is unclear. All the men in the study were married, which we know is good for a man's health too, and it seems that some men claimed to have sex twice a week despite being married for 10 years. However, the study didn't specify who they had sex with. Other studies have found that just thinking and fantasising about sex is good for you.
For women, it's quality rather than quantity. Sexual dissatisfaction may even be a risk factor for a heart attack. Studies suggest that women most value foreplay, foreplay and more foreplay.
But maybe we need to lower expectations here. The calorie counts for different acts have now been worked out. Putting a condom on an erect penis uses up just three calories. Trying to put one on Mr Floppy burns off 12,674.
A real orgasm uses up only 96 calories, but a fake one is 62,856. All that huffing, puffing and pretending can be a really good aerobic workout. So even bad sex can be good for you. That's my excuse, anyway.
Or why not go solo? One study found that 100 orgasms a year reduces your risk of death by 30 per cent. Now I'm not a mathematician, but I've worked out: a little DIY each day and you're immortal. Happy Valentine's Day.
Dr Phil Hammond is a GP and author of Medicine Balls.