Can a laptop make a man infertile?
Mobile phones, "gender-bending" plastics and even laptops have all been blamed for reducing men's fertility.
A new study from Argentina, published in the Fertility and Sterility journal, has suggested that Wi-Fi radio waves can adversely affect sperm motility and inflict DNA damage. With many men confused about how best to protect their sperm, our guide sorts the science from the myths about infertility.
Scientists now believe the quality and quantity of sperm fall as men get older, with male fertility declining steadily after the age of 50.
Whether the age of the father is linked to problems such as learning difficulties in the child is uncertain.
Alcohol affects the body's ability to absorb zinc, a nutrient vital for healthy sperm. But research suggests that moderate drinking (two to four units a day) has no harmful effects on sperm.
That said, heavy drinking can reduce sperm counts.
Bottom line: Moderation is the key
Fertility problems in men may be caused by "oxidative stress" -- linked to obesity, alcohol, diet, pollutants and smoking.
Studies have shown that men with fertility problems who take antioxidant supplements as well as zinc and fish oils increase the chance of conceiving.
Bottom line: If you have been trying unsuccessfully to conceive for more than a year, consider dietary supplements
In 2009, the Vatican published a report claiming male infertility had increased because of synthetic female hormones from the Pill. It argued that female hormones released into the sewage system find their way into the water supply. The report was viewed with scepticism by scientists who pointed out that the digestive system breaks down oestrogen, so it is unlikely to be released into the environment.
Bottom line: Case unproven
A healthy diet will maintain healthy sperm, but there is no truth in the claim that meat eaters are more virile.
"India has more than a billion people, 70pc of whom are vegetarian," says Dr Siladitya Bhattacharya, Professor of Reproductive Medicine at Aberdeen University. Chemicals called phytoestrogens, which are found in foods including soy, coffee and beer, have been linked to lower sperm counts, but the link is not proven.
Bottom line: Eat sensibly and ignore the fads
Physically fit men tend to have healthier sperm, but excessive exercise (especially in combination with the use of illicit bodybuilding steroids) can lower sperm counts.
Bottom line: Exercise regularly and stay off the steroids
More sex means the number of sperm in any given ejaculation declines. Intercourse every two or three days is thought to be the optimum for couples wishing to conceive. Having sex every day will probably decrease the chances of conception.
Bottom line: Go for quality over quantity
Chemicals present in plastic packaging, detergents and shampoos, paints, glues, coatings and construction materials are known to mimic the effects of oestrogen.
Many environmentalists believe that when these substances find their way into the water supply, they may subsequently affect sperm, but the link is not clear. But it is possible that oestrogen-mimics may have an effect on the developing foetus, in turn affecting fertility later in life.
Bottom line: A potential concern, but not a lot you can do about it
There is evidence keeping the testicles warm will reduce sperm counts. "Don't wear tight underpants," says Dr Pacey. Resting a laptop on the lap can impair a man's ability to conceive, because of the heat generated by computers.
Bottom line: Keep it cool
Untreated sexually transmitted infections are one of the main causes of male infertility.
Men who are exposed to chlamydia, which is symptomless in males, can have problems in the testicular vesicles. Gonorrhoea, too, can affect male fertility. Mumps can lead to damage to the testicles or even lead to male sterility.
Bottom line: Use a condom and get tested for chlamydia
MOBILE PHONES, WASHING MACHINES, WI-FI SIGNALS
Electronic devices emit low-energy, non-ionising radiation, and studies have looked at possible links between them and male fertility problems. To date, the evidence for any effect is lacking. "If you take sperm and irradiate them in a dish, you see changes, but I see no evidence that it affects fertility," says Dr Pacey. Mobile phones have been linked to lower sperm counts in some studies, but many scientists remain sceptical.
Bottom line: Probably no cause for concern
PESTICIDES AND OTHER POLLUTANTS
A host of chemicals have been linked to male fertility problems, but hard evidence is limited. Some studies have shown that regular exposure to pesticides can affect sperm, with agricultural workers having more problems.
Dr Pacey says men who work in construction may be at risk from glycol ether, a solvent found in some paints, adhesives and coatings, which has been found to double the risk of fertility problems.
Bottom line: Men working with chemicals need to wear appropriate protective clothing
Low-level ionising radiation is found in the natural environment and is harmless. But higher levels produced by uranium and plutonium, X-rays and radiotherapy, may damage the genetic material in cells and pose a risk. There is little evidence that frequent air travel or proximity to a nuclear power station has any effect on sperm.
Bottom line: Probably not a worry
Some studies suggest cannabis and cocaine can impair male fertility. Cannabis seems to have a dramatic effect on sperm, making them swim too fast and "burn out" before they reach the egg.
Bottom line: Stay clean
Men who smoke heavily are more likely to have abnormal sperm, but the effect on fertility is unclear. "The effects of smoking are controversial, but there are irrefutable effects on sperm quality," says Dr Pacey. There is evidence, he adds, that children whose fathers were heavy smokers may be more susceptible to leukaemia.
Bottom line: Don't smoke
Stress can cause hormone changes that may affect fertility, but it is far from proven. "I don't know of any studies showing that stress is directly linked to sperm production," says Dr Bhattacharya. Stress may affect how often you have sex.
Bottom line: Try not to worry
Being overweight has been linked in some studies to poor sperm quality -- but so has being underweight. Scientists think this happens because oestrogen, usually present at low levels in men, may be released from fat cells and affect male fertility. Low body weight may result from disease or poor diet, which could both affect fertility.
Bottom line: Watch your weight