factors that affect spermatogenesis
ANTIOXIDANTS AND SPERM
Vitamin C and Sperm
Dietary antioxidants are our main protection against free radical attack. Vitamin C is a water-soluble antioxidant that is actively secreted into semen to reach levels eight times higher than those found in the bloodstream.
Smoking generates massive amounts of free radicals, so smokers are especially vulnerable to sperm damage. They need at least twice as much dietary vitamin C as non-smokers. Men who smoke 20 or more cigarettes per day have blood vitamin C levels that are up to 40 per cent lower than non-smokers. They also have sperm counts that are 17 per cent lower, reduced sperm motility and a greater percentage of abnormal sperm.
The amount of sperm damage due to free radical attack in smokers has been assessed by measuring levels of a gene breakdown product in the semen. Smoking males were given a diet containing 250 mg vitamin C per day and their semen analysed. Their intake of vitamin C was then drastically reduced to only 5 mg per day. The level of the chemical resulting from DNA damage promptly doubled. It was not until intakes of vitamin C rose to 250 mg per day that the protective antioxidant effect returned.
This would indicate that a dietary intake of 250 mg vitamin C per day (the equivalent of four large oranges or kiwi fruit) is a good starting point for men wanting to protect their sperm from free radical attack.
It has been shown that smokers taking 200 mg vitamin C per day can improve their sperm counts by as much as 24 per cent, sperm motility by up to 18 per cent and the number of sperm still alive 24 hours after ejaculation by 23 per cent. Improvement seems to start within a week of increasing vitamin C intake.
Smokers taking massive doses of 1,000 mg vitamin C per day have been found to improve their sperm count by up to 34 per cent, sperm motility by 5 per cent and viability by 34 per cent. Sperm are also less likely to clump together, which is the other way in which vitamin C helps to improve sperm quality.
Semen contains a proteinvitamin E complex called non-specific sperm agglutinin (NSSA). NSSA exists in two forms, an oxidized form which can't bind to sperm, and an unoxidized (reduced) form which binds to sperm to act as a 'non-stick' coating. This prevents sperm clumping together and increases sperm motility.
When NSSA is oxidized and can't bind to sperm, the sperm stick to each other and clump together instead. This brings them to an instant halt and, if 20 per cent or more of sperm are clumped, subfertility occurs.
Vitamin C has an antioxidant effect on NSSA to keep it in its reduced form so it can bind to sperm and prevent them sticking together.
Studies show that men who are subfertile because of sperm clumping can be helped by vitamin C. Supplements of 500 mg vitamin C taken twice a day can reduce sperm clumping from 37 per cent to 14 per cent after just one week. After four weeks, sperm clumping can be reduced to as little as 11 per cent. Research shows that the overall quality of sperm including numbers of normal sperm present, motility and lifespan is also improved.
If taking vitamin C supplements, it is best to take other antioxidants such as vitamin E, betacarotene and zinc as well. They all work together to produce a synergistic effect.
Vitamin E and Sperm
Vitamin E is a fat-soluble antioxidant vitamin. It can penetrate cell membranes and body fats to protect them against oxidizing free radical attacks (see antioxidants and free radicals).
High-dose vitamin E has been tested as a treatment for subfertility in men. By mopping up superoxide free radicals, doses as high as 600 mg vitamin E per day have shown a significant benefit on sperm numbers. This leaves vitamin E in an inactive form which is rapidly reactivated by vitamin C. It is therefore important for men to obtain adequate dietary supplies of both vitamins.
Vitamin E is a component of the non-specific sperm agglutinin (NSSA) and, together with vitamin C, plays a role in preventing sperm clumping and promoting motility. It also has a beneficial effect on the flexibility of sperm cell walls.
Supplements containing up to 100 mg of vitamin E are useful for general sperm health. In subfertility, doses up to 600 mg may be suggested by an andrologist. Vitamin E is non-toxic and seems safe at doses of 1,000 mg per day or more.
Betacarotene and Sperm
Betacarotene is a fat-soluble antioxidant which is likely to protect sperm from free radical attack in a similar way to vitamins C and E.
Betacarotene is also a provitamin it is converted into vitamin A when stores are low. As too much vitamin A is poisonous, ensuring an adequate intake of betacarotene is the safest way to maintain an optimal supply.
Vitamin A is thought to be important for sperm maturation as they pass through the epididymis. Vitamin A can bind to sperm at special receptor sites and seems to enter the egg at fertilization. Sperm vitamin A may be important during the early stages of foetal development.
Zinc and Sperm
Zinc is an antioxidant mineral that is also important in protecting sperm against free radical attack. Semen is rich in zinc, with each ejaculate containing 5 mg one third of the recommended daily nutrient intake. This would imply that it plays an important role in sperm health. Three additional functions of zinc have been discovered apart from its important antioxidant one:
1. The genetic material (DNA chromatin) in the sperm nucleus is tightly wound with special proteins to form an insoluble, stable complex. This condensed structure is important for successful fertilization. Zinc is important for this structure and protects it from breaking down.
2. The high concentration of zinc in semen damps down sperm activity, keeping them in a relatively quiescent state. This lowers their consumption of oxygen and conserves sperm energy. Once within the female reproductive tract, which contains very little zinc, zinc concentrations are rapidly diluted. This causes a sudden increase in sperm activity, speeding them up and acting like a mineral turbo charge.
3. During fertilization, a sperm exposes enzymes in a sac at the sperm head to drill a hole in the outer egg shell through which the sperm can pass. This is known as the acrosome reaction. In many cases of subfertility it seems that large numbers of sperm discharge their enzymes spontaneously before or just after ejaculation. By the time they reach the egg they are no longer capable of penetrating it. This early discharge of the acrosome reaction is linked with a zinc deficiency.
High concentrations of zinc in semen helps to damp down the acrosome reaction in a reversible way. Once zinc concentrations become diluted within the female tract, the acrosome reaction can again occur.
Another recent finding is that zinc deficiency changes the sequence in which seminal secretions are ejaculated. The secretions from the seminal vesicle, which are usually ejaculated last, are released along with the sperm instead.
There are several theories why this happens. Lack of zinc may cause swelling of the prostate gland, which will slow sperm travelling up from the testes. This swelling will also slow the release of prostatic secretions, which are usually the first fluids to be ejaculated.
It is possible that this alteration in the ejaculatory sequence is a survival response to low concentrations of sperm zinc. By mixing the sperm and the relatively zinc-rich seminal vesicle secretions as early as possible, the protective effects of zinc (stabilization of sperm DNA; delaying of acrosome reaction; conservation of energy) are maximized.
Most men do not obtain enough dietary zinc. Those that are highly sexually active may be losing more zinc per day in their semen (5 mg per ejaculation) than they can keep up with in their diet. Men ideally need a minimum of 15 mg zinc from their diet per day (see zinc).
ALCOHOL AND SPERM
As much as 40 per cent of male subfertility has been blamed on moderate alcohol intake. Alcohol damps down testosterone secretion and also hastens its conversion to oestrogen in the liver. This can lead to lowered sperm counts and a decreased sex drive.
Research shows that refraining from alcohol brings sperm counts up to normal within three months in 50 per cent of men with subfertility. Sperm motility also improves.
In one study, 26 men out of 67 (39 per cent) attending a hospital infertility clinic had a low sperm count. All were extensively investigated and no cause for their subfertility was found. These 26 men were advised to stop drinking alcohol and the sperm counts of 13 of them rose to normal within three months. The number of motile sperm increased significantly and the numbers of abnormal forms also dropped. As a result, at least 10 men (78 per cent of those whose sperm counts responded) successfully fathered a child.
EXERCISE AND SPERM
It is well known that excessive exercise can affect the fertility of female athletes by stopping the normal menstrual cycle (a condition known as 'runners' amenorrhoea'). New research shows that overtraining can damp down fertility in males, too.
Fit males who routinely took part in endurance training (e.g. running, swimming, cycling) for more than four days per week were asked to double their average weekly mileage (i.e. to overtrain) for a two-week period.
Their semen and blood hormone levels were analysed for six months before the period of overtraining, again immediately afterwards, and three months later.
Immediately after overtraining, their sperm counts fell by as much as 43 per cent. After three months, sperm counts had dropped to 52 per cent lower than before they overtrained. The number of immature and non-viable sperm increased. All semen samples stayed within the accepted fertile range, however, and this would not be expected to interfere with fertility except where sperm counts were already low.
The blood levels of testosterone hormone also fell significantly by over a third (36 per cent) immediately after overtraining but returned to normal within three months. In contrast, blood levels of the steroid hormone, cortisol, increased by almost 50 per cent.
Cortisol is a steroid secreted in times of stress. It encourages breakdown of muscle and is linked with the muscle wasting that can occur with prolonged overtraining. Cortisol also damps down the secretion of testosterone by Leydig cells in the testis, and is the probable cause of this observed decrease in sperm count. This would also fit in with anecdotal findings that stressed people are less fertile. It is important to realize, however, that the overtraining only occurred for a two-week period in this particular study. The effects of long-term overtraining on male fertility are likely to be more profound.
ENVIRONMENTAL OESTROGENS AND SPERM
Recent research has linked exposure to increased levels of the female hormone, oestrogen, with the observed falling sperm counts.
This is based on the effects of a synthetic oestrogen (diethylstilboestrol) prescribed to millions of pregnant women between 1945 and 1971 to prevent a threatened miscarriage. The male offspring of these pregnancies, who were exposed to diethylstilboestrol in the womb, had an increased risk of undescended testicles, abnormal penis development and future testicular cancers. As adults, they also produced low semen volumes and low sperm counts.
Over the last 3050 years, these same birth defects have become more common in men who have not knowingly been exposed to synthetic oestrogens in the womb. At the same time, semen volume and sperm counts in adult males have fallen dramatically (see infertility). Scientists suggest that men are exposed to weak environmental oestrogens from many sources. These include:
• plant and fungal hormones (phytoestrogens) such as soya, rye extracts.
• use of anabolic oestrogens in livestock. This was banned in Europe in 1981, but was an important source of exposure in the 1950s1970s.
• increased intake of dairy products. Cows continue to lactate while pregnant, so their milk contains high amounts of oestrogen.
• Low-fibre diets, which encourage greater absorption of dietary oestrogens from the stomach and intestines.
• Body fat which can convert other steroid hormones into oestrogen. Forty-five per cent of British males are now overweight; 8 per cent are obese.
• Pollutants such as PCBs, dioxins, and dichloro-diphenyl trichloroethane. Exhaust gases from petrol engines.
• Traces of drugs (e.g. contraceptive pills; hormone replacement therapy) in drinking water.
These weak environmental oestrogens may have an effect on the developing male foetus and on the rapidly maturing testes at puberty. They are thought to inhibit the division of Sertoli cells in the testes and to inhibit the development of the tes-ticular Leydig cells (see Chapter 3).
Sertoli cells are essential for sperm maturation, but each one can only support a certain number of sperm. If there are less Sertoli cells, a lower sperm count is inevitable. Leydig cells manufacture testosterone, and less cells would mean less circulating levels of androgens. This would increase the risk of undescended testes and of future low sperm counts. The environmental oestrogen theory needs further investigation, but observation of animals in the wild seems to back it up. Recent research also suggests that men who drink more milk than usual and are therefore exposed to higher quantities of cow's oestrogen are at increased risk of developing testicular cancer.
· 1 decade ago