Why wearing socks in bed can cure a low libido: It's a problem that afflicts millions. But from poor circulation to a blocked nose, the causes of a bad sex life can be as surprising as the cures By Chloe Lambert Are you happy with your sex life? If the answer is no, you're not alone. Studies suggest that behind closed doors, millions of Britons are struggling to find the time or the inclination to make love. A recent survey suggests 40 per cent of couples think their sex life could be better. Libido varies hugely from person to person, but if you've noticed a change in desire, or sexual function, it's worth investigating because it could be a sign of a physical or mental health issues, says Dr Michael Perring, a GP specialising in sexual medicine. Sock hop: One way for women to boost their libido is to pop on a pair of socks Generally, if a person has a good sex life it's an indicator of good health. Low libido or erectile dysfunction can sometimes indicate an underlying condition such as diabetes. Here the experts reveal the most common passion killers - and advice on how to tackle them . . . Surprisingly, one simple way for women to boost their libido is to pop on a pair of socks. In a study at the University of Groningen in the Netherlands, researchers found that 80 per cent of women involved were able to achieve orgasm when they were given socks to wear, compared with 50 per cent when barefooted. According to Gert Holstege, who led the study, it's all connected with how safe and comfortable women feel. The regions of the brain responsible for anxiety and fear - the amygdala and prefrontal cortex - need to be deactivated for a woman to successfully reach climax. "A pleasant environment, which includes the room temperature, is an important part of making her feel safe, secure and comfortable," he says. Some men worry that baldness affects their attractiveness, but the treatment for it may leave them under-performing in the bedroom, says Dr Radha Modgil, an NHS GP in London who specialises in sexual health. Lots of men come and see me asking for finasteride, a drug that treats male pattern baldness. Mooted theory: There's no proof that men who are bald are more virile - and the treatment for baldness may leave them under-performing sexually But when I tell them this drug behaves by blocking the male hormone testosterone and can therefore have an effect on libido and erectile function, they tend to have a change of heart. Worryingly, the effect may not be instantly reversible. A study last year of 71 men, by Dr Michael Irwig at the University of Washington, found that finasteride can cause persistent sexual dysfunction lasting for an average of 40 months after stopping taking the drug. And although it's a much mooted theory, there's been no conclusive proof yet that men who go bald are more virile. A growing body of evidence is showing the importance of smell in libido, and our ability to attract and be attracted to people. Last year, a study at the University of Gothenburg in Sweden found that men with anosmia - no sense of smell - have significantly fewer sexual partners on average. The researchers said this could be because we subconsciously use smell to recognise others" emotional states. "A lot of social signals are transported through the olfactory channel, and they are probably missing them," said lead author Ilona Croy, a psychologist at the university. Smell is also important because of pheromones - scents given off by a partner's body through sweat. Brain scan studies by the Karolinska Institute in Sweden show that the smell of testosterone and oestrogen activates the hypothalamus - the area of the brain responsible for mood, sexual behaviour and hormones. This may help to explain why 83 per cent of people with allergies report that their condition affects their sex life, according to a recent study in Allergy and Asthma Proceedings. Couples who have a TV in their bedroom have sex half as often as those who don't, according to a 2006 study of 523 Italian couples. The study also found that what you watch can play a role in your sexual relationship: violent films and reality TV were the biggest passion killers. Passion killer: Couples who have a TV in their bedroom have sex half as often as those who don't Men with gum disease are three times more likely to suffer erectile dysfunction, according to research published in the Journal of Sexual Medicine in December last year. Researchers from Inonu University, Turkey, suggest that erectile dysfunction and gum disease are caused by similar risk factors, such as ageing, smoking, diabetes and cardiovascular disease. This doesn't mean that flossing will save your sex life - but if you have bleeding gums and impotence, it could be down to poor circulation, and your body's way of telling you to have a heart health check. Alcohol is well known to affect sexual performance, and part of the reason it does so is that it reduces skin sensitivity. "A very small amount of alcohol will lower inhibitions, but anything over a few pints or a couple or glasses of wine affects coordination and balance, and also causes skin analgesia," says Dr Perring. Furthermore, the way the body metabolises alcohol seems to reduce the amount of an enzyme needed for the testes to produce testosterone. One recent study published in the Journal of Sexual Medicine suggests binge drinking youngsters could be setting themselves up for long-term problems having sex. Most worryingly, the researchers found that the men studied continued to suffer problems even after abstaining for two years. This may be because it has a long-term effect on testosterone production, or because of alcohol's role in diseases. "Long-term alcohol use damages the heart and the liver, all of which we know can affect sexual function," says Dr Graham Jackson, a cardiologist and chairman of the Sexual Advice Association. There may be bad news for gin and tonic drinkers. Quinine, found in tonic, lowered sperm concentration and motility and testosterone in rats, according to studies at the University of Lagos in Nigeria. However, the amounts the rats were given were far in excess of those most people would consume normally. Golden age of sex: Your 60s and 70s can be a wonderful time for your sex life, but joint pain can be a huge barrier to a fulfilling sexual relationship Surprisingly, your 60s and 70s can be a golden age in a couple's sex life. "Generally, people have more confidence now than at any other time, and hopefully life has become a bit more relaxing," says Paula Hall, a psychotherapist at Relate, which specialises in relationship and sex advice. However, the joint pain associated with osteoarthritis can be a huge barrier to a couple's sex life, adds Angela Jacklin, an occupational therapist for the charity Arthritis Research UK. Sometimes it's too painful to even turn over in bed, let alone have sex. The pain is also often worse at night or first thing in the morning. It's an area that can cause great distress, but in the medical field we too often overlook it. She says communication with your partner is important - you may need to plan your time to take advantage of days and times when the pain is less bad. Try the Arthritis Research UK website for further advice. Somewhat ironically, a number of studies have shown that the Pill is linked to a reduced sex drive in women. In 2010, researchers at the University of Heidelberg analysed data from 1,046 female students and found those who used hormonal contraceptives - such as the Pill or a contraceptive implant - were most at risk of female sexual dysfunction, an umbrella term which can include low desire and arousal and problems reaching orgasm. Dr Modgil says: "It may be the balance of hormones in the body getting out of kilter. There's no evidence as to how long it can take, but I find it happens after two to three months of starting or changing the Pill, and we do see the same effect with the implant. For women in their 40s and 50s, another big cause of a drop in sexual desire is under-active thyroid or hypothyroidism. "Thyroid hormone affects the rate at which our body works and our energy levels," explains Dr Modgil. So if the thyroid is under-active it causes tiredness, depression and a general lack of motivation, which will of course have an impact on someone's appetite for sex. It can usually be successfully treated with drugs to replace the missing thyroid hormone, thyroxine. Here's a motivating thought for when you're on the treadmill - keeping a healthy weight is crucial for a satisfying sex life. "Obesity changes the levels of testosterone in the body, which affects libido in both men and women," says Dr Modgil. It also reduces blood flow and energy levels - and it raises your risk of heart disease, which can affect sexual function in both men and women. Weight gain can put strain on the pelvic floor muscle, says physiotherapist Sammy Margo, which may be even more of a problem in women who have had children. A tight, strong, pelvic floor muscle seems to make it easier to achieve orgasm, possibly because it increases sensation in the nerves and blood flow to the area. The good news is that losing weight can give you a boost in the bedroom. Big love: Obesity changes the levels of testosterone in the body, affecting libido in both men and women Last year, St Vincent's University Hospital in Dublin published a study of 900 middle-aged men with diabetes, a third of whom were told to lose weight through diet and exercise, a third of whom were given the diabetes drug metformin and the rest a placebo. In the first group, the proportion with low testosterone fell from 20 per cent to 11 per cent within a year. They had a higher sperm count and reported a better sex drive and stronger erections. Certain blood pressure medications are known to affect peoples" sex lives. "If you take a tablet for your blood pressure and you stop being able to get erections within two to four weeks it's probably the drug, but if it's after a year or two it's more likely to be a circulation problem," says Dr Jackson. Diuretics tend to be the drugs that cause problems by decreasing the force of blood flow into the penis. But angiotensin receptor blockers, which are also taken for high blood pressure, actually help sex lives - women's as well as men's. They work in the same way as Viagra - they help the tissues to relax, allowing better blood flow. Antidepressants, particularly selective serotonin re-uptake inhibitors, can decrease sex drive too, says Lorraine Grover, a clinical nurse therapist in sexual wellbeing. It's thought to be down to the effect they have on the feel-good brain chemical dopamine - this blunts extreme emotions, which reduces depressive thinking, but also affects sexual desire. Less-than-happy pills: Antidepressants can decrease sex drive Antidepressants can cause sexual problems and you need to address them - don't put up with it. You may need to take them to feel better, and then manage the sexual difficulties or change drug. Dr Modgil adds: "It's important the patient is aware that it's the pills that may be causing it, so they don't panic that it's to do with their relationship. I often try to encourage patients to have other treatments like counselling, which is a longer-term strategy. One in three men with diabetes will suffer erectile dysfunction, and the risk is higher if your diabetes is poorly managed. "Diabetes itself damages the arteries, which affects blood supply," says Dr Jackson. But the high blood sugar levels also damage nerves in the sexual organs - causing a lack of sensation. So it's a real double whammy. The effect of diabetes on women's sex lives has been less well documented, but Dr Jackson says the lack of good blood flow will have an effect. Treatment for an enlarged prostate (a common problem that occurs with ageing) can affect sex. "Surgery to reduce the size of the prostate can lead to retrograde ejaculation - where the semen goes back into the bladder," says Ali Rooke, a specialist nurse at Prostate Cancer UK. The condition doesn't affect health and the man still experiences an orgasm. Drugs used to treat prostate enlargement, such as 5-alpha-reductase inhibitors, can cause impotence - although such side- effects are most common during the first year of treatment, and should improve once the course has been completed. One in eight men will develop prostate cancer in their lives and the average age of diagnosis is between 70 and 74. "If someone has surgery or radiotherapy for prostate cancer and the surrounding nerves are removed or damaged, a man may not be able to get an erection spontaneously," says Rooke. These patients can be helped, usually with a combination of treatments including Viagra, or another type of drug that causes muscles to relax and the penis to fill with blood - available in injection or pellet form - or a pump device, which creates a vacuum to encourage blood flow. Some prostate cancer patients are given hormone therapy with radiotherapy; if the disease is advanced they may take these drugs alone as a long-term treatment. However, these also induce impotence, says Rooke. Hormone therapy controls prostate cancer by stopping testosterone reaching the prostate cancer cells. So not only are these patients struggling to get an erection, they have a reduced desire for sex. A cluttered bedroom does not make for a romantic setting - and experts say it could kill the mood for women in particular. "Women, more so than men, are prone to cognitive distractions - thinking of other things in ways that interfere with sex," says Debby Herbenick, author of Because It Feels Good: A Woman's Guide to Sexual Pleasure and Satisfaction.