Sperm are easily damaged and need a carefully controlled environment to develop normally. Any factor that has an adverse effect on spermatogenesis will lower the sperm count and significantly affect fertility.
There are many simple things a man can do to optimize the quality and quantity of his sperm. This is particularly important in the six months before trying to conceive a child.
It takes around 100 days to make a sperm from start to finish:
• 74 days division and growth within the testis
• 20 days to pass through the epididymis
• 6 days travelling through the vas deferens before ejaculation.
That’s 100 days in which the sperm are vulnerable to many dietary and environmental factors.
A low ambient temperature is essential for normal spermatogenesis. Testicular temperature needs to be from 47°C cooler than core body temperature. This is why the testes are designed to drop out of the abdomen into the scrotal sac. Three mechanisms keep the scrotum cooler than the rest of the body:
1. scrotal skin is thin, so the testes easily lose heat into the surrounding environment
2. air circulating around the scrotum can cool the skin
3. the arteries bringing blood into the scrotum run alongside the veins taking blood away to form a sophisticated heat-exchange mechanism. Rather like a hot and cold water pipe running together, the hot arterial blood (coming from the abdomen) loses heat to the cooler venous blood (coming away from the testes), so blood is already partly cooled before entering the scrotum.
Even if the testes heat up by as little as 2°C, sperm formation is adversely affected. Sperm count will drop, the number of normal sperm will fall and the number of abnormal sperm will increase.
Semen quality is naturally lower in summer compared with winter. Although semen volume does not change significantly, the total sperm counts per ejaculation in 131 volunteers fell from 320 million in winter to 250 million during July and August. This is probably a temperature effect.
Even taking a hot bath (4345°C/110115°F) for half an hour per day can significantly lower sperm counts as can wearing tight underpants or athletic scrotal supports. This was shown in a recent experiment where the fit of a man’s underwear and its effect on spermatogenesis was investigated.
Two unmarried males in their middle thirties wore tight, bikini-type briefs that fitted snugly against the scrotum for three months. They then changed to loose boxer shorts that extended 14 cm/5.5 in beyond the scrotum for the next three months. This tightloose sequence was repeated once more, so that each man was investigated for one year.
Their semen was analysed regularly and showed that sperm count and sperm motility gradually declined during the periods when the men were wearing tight underpants, and gradually increased when they wore loose boxer shorts. Changes in sperm count and sperm motility were noticeable within two weeks of changing over to each new set of underwear.
|First male||Second male|
|Variable||Tight||Loose||% Change||Tight||Loose||% Change|
Source: Sanger & Friman 1990. Reproductive Toxicology. Vol. 4, pp. 229232.
Although sperm counts stayed well within fertile levels during this experiment, it is possible that the type of underwear chosen by a man with a low sperm count might make the difference between fertility and subfertility. Temperature effects are probably most important, but electrostatic elec- tricity plays a role too.
Tight underwear containing man-made fibres (e.g. polyester) generates electrostatic electricity from friction between the scrotal skin and the synthetic material. These create an electrostatic field across the scrotum, with the skin covering the lower scrotum acquiring a positive charge and the skin covering the upper scrotum acquiring a negative charge. The testes lie between these two electrical poles, and spermatogenesis is adversely affected.
Figure 12: Electrostatic field across scrotum
Several studies have looked at the electrostatic potentials generated across the scrotum from different materials. Men who wear underpants made from 100 per cent polyester generate the greatest electrostatic fields around their testes. Men wearing 50:50 per cent polyester:cotton mix underpants generate a field that is half as strong, while men wearing 100 per cent cotton pants remain free of any significant electrostatic potential. When volunteer males wore a particular type of underpants for 18 months:
• 4 out of 11 men wearing polyester underwear showed evidence of a significant reduction in sperm count plus testicular degeneration by the 14th month. These changes were reversible once the pants were discarded.
• only 1 out of 11 men wearing polyester-cotton mix underwear showed a lowered sperm count after 16 months. This change was also reversible.
• None of the 11 men wearing pure cotton underpants showed any significant change in sperm quality or quantity.
Investigation showed that these changes were directly related to the electrostatic fields generated, and no significant changes in testicular temperature or blood hormone levels were found.
Egyptian doctors have designed a male method of contraception based on the combined effects of raised scrotal temperature and electrostatic electricity.
A polyester scrotal sling nicknamed the Jockstrap was tailor-made to hug the testicles closely while allowing the penis to poke through. The sling was attached to a waist belt designed to pull the testicles up close to the abdomen. This automatically raised testicular temperature due to the effects of increased body warmth. Fourteen volunteer males wore the sling day and night for a year, only changing it when soiled.
During the experiment, sperm counts of all 14 volunteers dropped to an amazing zero, and remained at zero after wearing the sling for an average of 140 days. Their testicles decreased in size from an average of 22.2 ml to 18.6 ml and the volume of semen they produced fell significantly. Biopsies of the tes- ticles showed that after wearing the sling for 6 months, there was degeneration and loss of some of the germ cells lining the seminiferous tubules.
At the end of the 12-month experiment, the slings were discarded and the men’s sperm counts slowly climbed back up to their previously normal levels within an average of 157 days.
These experiments show the fertility dangers of wearing tight, polyester bikini-style briefs or athletic supports for prolonged periods of time.
As there may be a link between overheated testes, testicular degeneration and the eventual development of testicular cancer (as has been noted in undescended testicles), it might be sensible for all males to wear loose, boxer style underpants made from 100 per cent cotton rather then bikini-style briefs made from artificial fibres.
Researchers estimate that 40 per cent of sperm damage is due to collision with molecular fragments known as free radicals (see Chapter 21). Cells are most vulnerable to free radical damage during division, when the normal gene repair mechan- isms are switched off. As it takes around 380 cell divisions to produce a sperm, the spermatocytes and spermatogonia within the testicular tubules are constantly dividing. This makes them sitting ducks for free radical attack. Damage to the DNA at this time can result in genetic material being wrongly copied so that mutations arise. Sperm may contain a lethal genetic defect and die, or they may develop structural abnormalities such as two heads or two tails, lack an acrosome, or be incapable of forward propulsion. If a high percentage of sperm are affected, this can result in subfertility.
Sperm may, however, acquire only a minor genetic defect as a result of free radical attack. This may even be passed on to the future offspring if fertilization is successful, to produce problems such as an increased risk of childhood cancer. This has already been noticed among the children of men who smoke (see lifestyle factors: smoking).
There are several ways in which a man can protect himself against free radical attack. This is important for every man, not just those hoping to father a child. Free radicals are now known to be linked with coronary heart disease and cancer. By mopping up and neutralizing the free radicals, a man can increase the quality of his sperm, reduce his risk of coronary heart disease and significantly reduce his risk of cancer (see coronary heart disease: antioxidants and cancer prevention).