Male Fertility

There are a number of possible issues that can affect the possibility of a man fathering his own children.

Firstly there are the most obvious, but normally necessary prerequisites of achieving an erection and then being able to ejaculate.

  • The failure to achieve an erection is called erectile dysfunction - ED or impotence. This can be caused by stress or other psychological disorders and is relatively common. It can also be caused in older men by atherosclerosis, where blood flow to the penis is inadequate. Viagra is used by many to counter this problem, although like many drugs this can have side effects, the most common being headache.
  • The failure to ejaculate, anejaculation can also be caused by stress, fatigue and of course lack of desire. This is more or less the same as male anorgasmia, the failure to orgasm.

Secondly there are problems with the sperm. These fall into 3 main categories:

  • Sperm morphology is abnormal. This means that the shape of the sperm is not normal and they are less likely to fertilise an egg properly or lead to a normal pregnancy. Measurement standards vary. The new WHO standard is that 4% of sperm have normal forms*. That is a surprisingly low figure to many, but if a clinic measures semen  parameters using the strict criteria, sometimes called the Krugar criteria, then it is as accurate a figure as those for motility and count given below. As such it is important to understand how morphology is assessed. For instance you may hear that 25% is a normal value, but this is not correct for measurements done using the modern strict criteria.
  • Sperm motility is low. This means that sperm can't reach the egg because their ability to swim is limited or non-existent. An adequate level is that 40% of sperm are motile*.
  • The sperm count is low. This means that the density of sperm in the ejaculate is below a reasonable level. An adequate count is 1.5*106/ml (15 million per millilitre)*.

* Please note that measurements of semen vary between different laboratories and normal values have been reassessed and changed over the years. When reading blogs or articles that state one level is normal or not be aware of this fact! I have used the latest World Health Organisation, WHO assessment c.2009 for the levels reported above1. The figures are based on men who have fathered children easily in the recent past. I have used figures that represent an assumed "adequate level". This is based on a level that 95% of these recent fathers scored above and 5% scored below.

In practice all the semen parameters have to be assessed together, along with other data, to get a clear picture of a man's fertility. Just being over or under the levels I mention above, or indeed other levels provided by laboratories does not provide complete proof or otherwise of potential fertility.

Thirdly there are issues that affect sperm quality.

  • A dilation of the veins that drain the testicles called varicocele can raise the temperature of the testicles, contributing to infertility2. This is essentially similar to varicose veins. It normally occurs on the left hand side and affects between 15-20% of men. It is most commonly diagnosed between the ages of 15 and 30 years.

Factors that may influence fertility.

There are a number of factors that affect male fertility. Smoking, drinking, drugs and hormone disrupting substances are some of them. Others are radiation and excessive scrotal temperatures. Having a good diet and taking certain supplements can make a large difference also.

Harmful chemicals and radiation.

Smoking derived chemicals:

Smoking is associated with lower sperm counts and a lower sperm motility score. It can also lead to impotence as blood flow to the penis becomes impaired.


Over consumption of alcoholic drinks is associated with decreased male fertility. The more you drink the worse it gets. It harms men by reducing their sperm count, sperm motility and number of normal shape sperms. This is in part due to toxic products of alcohol breakdown, and also to reduced zinc absorption from the gut. Alcohol also plays havoc with a man's hormones, effectively making him more feminine. Levels of oestradiol (an oestrogen) and FSH and LH go up while the male hormone testosterone often declines3. This imbalance between oestrogen and testosterone can lead to gynecomastia, otherwise known as "moobs" or "man boobs".

Prescription drugs:

The following drugs are associated with reduced fertility: Anabolic steroids, Antihypertensives, Allopurinol, Erythromycin, Chemotherapy, Cimetidine, Colchicine, Cyclosporine, Dilantin, Gentamycin, Nitrofurantoin, Tetracycline, Caffeine, Cannabis, Heroin and Methodone. The most commonly consumed of these drugs is caffeine. It is possibly the least dangerous in terms of male fertility, but nevertheless is associated with small declines in pregnancy rates. This is most likely due to long-term reduction in the percentage of motile sperm.

Plastics and pesticides:

Fertility rates among men have declined across the modern world over tha last few decades. One of the reasons for this decline is probably to do with the large amount of plastics and pesticides which are part of modern-day life. There are a number of plastics that seem to disrupt hormone levels. Of particular note are Bisphenol A, pthalates and PDBEs. Bisphenol A is found for example in babies bottles, CD cases and drinks cartons. This plastic was studied recently and found to decrease sperm counts by 23%. Pthalates have been associated with decreased sperm motility4 and are found in kids toys as they make plastic more soft and flexible.  PDBEs are used as flame retardents and can be found in household furniture such as sofas, computers, carpets and TVs. They also reduce sperm counts. When it comes to pesticides, the organochlorines are particularly harmful to fertility. These include DDT, Dieldrin, endosulfan, atrazine, vinclozolin and methoxychlor, all of which have some evidence to show they can harm reproductive health in males. Some are still in regular use in the UK, such as the weedkiller, atrazine. Atrazine can leak into the water supply causing widespread exposure to the chemical.

There is an ongoing debate as to how much exposure to plastics and pesticides is needed to impact on fertility. My view is that there is enough evidence to make it likely that some effects are being felt.


Exposure to radiation is a normal part of life, but some radiations are more powerful and come in larger doses than the body can effectively cope with. Medical x-rays would be a potential example and regular air travel a potential lifestyle choice that could impact on fertility.

All the above can affect fertility, what is less clear is the degree of danger posed by each. My advice is to not smoke, reduce drinking to less than 6 units per week for men and avoid the listed prescription drugs altogether if possible. Drinking 1 cup of coffee per day may have little effect, but more than this could damage your chances. Plastics and pesticides and radiation are hard to avoid completely. It is not productive to stress about these too much, just be aware of the danger they pose, and reduce exposure if possible.

Inadequate nutrition and temperature.

Essential fats:

Essential fats are known as omega 3 and omega 6 fats. These fats which can't be made by our bodies are needed in the diet. Omega 6 is normally found in abundance in the foods we eat. Omega 3 fats are not. These omega 3 fats are found primarily in oily fish such as salmon, mackerel and trout. For men's fertility it is a good idea to ensure you get plenty of omega 3 fats as these contain DHA, docosahexanoic acid. DHA is associated with increased sperm counts and increased fertility generally.

Other supplements: 

A report from China showed good results for L-Carnitine supplementation (2g/day) in conjunction with vitamin E. It was not clear if the vitamin E contributed anything as this was used as the baseline placebo. The L-carnitine improved sperm motility and resulted in a ninefold rise in pregnancy rates (3.8 – 31%). I have personally come across a case where sperm motility started at 17%. After carnitine supplementation at 500mg/day for 3 months it rose to 43%. A further 3 months after introducing zinc supplements at the RDA level 10mg/day led to motility of 68%. More evidence to my mind of the potential efficacy of these supplements. It would be possible to supplement at greater doses than those mentioned above without ill effects, Zinc supplementation is associated with improved sperm counts and increased motility. If taken at more than double the recommended amount of 11mg per day, it should be taken with the advice of a qualified nutritional therapist as it can reduce absorption of copper and other minerals. Vitamin C supplementation can also prevent sperm agglutination and therefore effectively increase the sperm count. 

Scrotal temperature:

The testes are both where a man produces most of his testosterone (the hormone that produces male characteristics) and his sperm. The reason testes sit in a sac outside the main part of the body is to lower their temperature. In man the optimum temperature for sperm production is 2 degrees Celsius below core body temperature. Because of this well-known fact, much advice can be found advising men how to keep their testes cool. Avoidance of saunas, lap tops (on laps) and tight underwear are often mentioned as is cycling. As a competitive cyclist myself I though I'd look further into this particular claim.


Cycling could potentially cause fertility problems in at least two ways. Firstly by reducing a man's ability to have an erection. This can occur as a result of too much pressure on the perineum, the bone that you sit on. Secondly by overheating the testes and affecting the sperm that are currently developing there. There are a variety of studies that have been carried out. Some actually suggest that there could be a cooling effect on the testes when compared to sitting down. Others suggest that most sperm parameters remain normal, but that morphology can be affected5. It is hard to assess the exact impact of cycling as there are many factors involved. I would not advise that it is necessary to give up cycling however. When compared to the average population cyclists tend to be more virile and this is undoubtedly because they are physically active with healthy cardiovascular systems. Remember that many professional cyclists have families and these are people cycling for up to 6 hours per day, 7 days per week. The best advice would be to ensure you have a comfortable saddle and that your cycling position is a reasonable compromise between comfort and outright speed. There are saddles nowadays that are designed to take pressure off the perineum. An example is pictured, left. Other factors to consider are:

  • Avoidance of rough roads.
  • Amount of time spent in the saddle in one go.
  • Adequately cushioned cycling shorts.
  • Standing up occasionally to relieve pressure on the perineum. This is also a useful technique for ascending hills so will be worthwhile for your fitness anyway.
  • Avoiding cycling during the hottest parts of the day.