Men are not what they used to be, it seems. In fact, if some scientists are to be believed, the future for men may be bleak. The issue of falling sperm counts has raised concern for nearly a decade now, but the jury is still out on whether male semen production is truly less than it was in our grandfather's time.

The concern first emerged in 1992 when the subject was raised by a well-known Danish doctor, Niels Skakkebaek. Dr Skakkebaek decided to analyse the results of all the studies of sperm production that had been conducted since the 1930s. Such a study is known as a meta-analysis and is generally a good indicator of a genuine trend, allowing global data over a number of decades to be compared.

Writing in the 'British Medical Journal', he concluded that sperm counts had been falling by 1% a year since 1930. While many in the medical establishment reacted with scepticism, Skakkebaek's findings seemed to strike a chord with the general public.

Couples were increasingly finding that infertility difficulties hampered their chances of conceiving a child. In fact, the World Health Organisation confirmed the public suspicion by announcing that between 8 and 10% of couples of child-bearing age have some form of fertility problem.

This means that infertility affects at least 80 million people worldwide. According to the WHO, infertility is exclusively a female problem in around 30-40% of cases, while it is exclusively a male problem in 10-30% of cases. There can be many reasons why a woman might be infertile, but for men, infertility problems are attributed to a low sperm count or dysfunctional sperm.

During the 1990s, the explosion of clinics specialising in a variety of fertility treatments appeared to underline the Danish research that things were going wrong for men. The media began to suggest all manner of pseudo-scientific reasons why sperm counts might be falling, while at the same time the medical establishment seemed undecided about whether to believe Dr Skakkebaek's findings.

In Europe, researcher after researcher confirmed Skakkebaek's gloomy prognosis. For a while, it seemed that countries were trying to outdo each other in claiming which had the lowest sperm count. The nadir came when French scientists discovered in 1994 that 18% of French couples were suffering from fertility difficulties, twice the WHO estimate.

Pierre Jouannet of the Centre for the Study of Human Eggs and Sperm in Paris went on to examine the sperm levels of Parisian men. He looked at 1,351 sperm donors in Paris who had donated for artificial insemination. In 1973, the average sperm count was 89 million per millilitre, while men who donated sperm in 1992 had an average count of 60 million per millilitre, a fall of 33%.

In 1995, a prominent American reproductive scientist was the first to claim that sperm counts were not dropping at all - at least, not in the USA. Harry Fisch, the director of the Male Reproductive Center at Columbia Presbyterian Medical Center, New York, examined the sperm counts of over 1,200 men who had undergone vasectomies in LA, Minnesota and New York City.

Dr Fisch found that American sperm counts had actually risen by 14% between 1970 and 1994. As other American studies began to confirm Fisch's findings, he looked back to the earlier European research to find out why the results were conflicting. It transpired that most of the early sperm count studies had been conducted in New York, a centre for pioneering fertility research in the 1930s and 1940s. Later studies had been conducted worldwide, but especially in Europe.

What Skakkebaek had seen as falling sperm counts was in fact a geographical difference, not a chronological one. American sperm, it seems, was as healthy as ever, whereas European sperm did not bear up so well. The revelation that sperm counts varied with location increased rumours that the environment was having an impact on men's ability to procreate successfully.

So what, if anything, was affecting male fertility? Scientists, conspiracy theorists, feminists and environmentalists had a field day attempting to explain why some areas of the planet seemed to breed men with poorer sperm production than others. The reasons put forward for low sperm levels ranged from male insecurity to tight underwear, taking in all manner of bizarre explanations along the way.

Slowly, however, a consensus has developed that one particular cause may be to blame. The biology and physiology of the reproductive system is controlled by the endocrine system. Researchers observing bird populations in the Great Lakes area of the United States were the first to suggest that industrial pollutants seemed to have an affect on the endocrine system and hence the reproductive ability of males.

The birds had been affected by organo-chlorides like DDT, pesticides long since banned and rarely finding their way into the human food chain. So scientists began to look for other kinds of polluting substances that might be having a detrimental affect on the male reproductive system. Chemicals known as xeno-oestrogens, or oestrogen mimics, became the number one suspect.

Xeno-oestrogens were suspected because of their tendency to mimic the female hormone oestrogen, hence the alternative name. Found in shrink-wrap, pesticides, herbicides, solvents and some drugs, these substances were suspected because of the effects they had on animal reproductive systems.

Fish in polluted waters have been observed to behave physiologically like females, and alligators in Florida's xeno-oestrogen rich everglades have inexplicably become predominantly female. So far there is no direct evidence that xeno-oestrogens are to blame for the fall in human sperm counts and the simultaneous rise in penis abnormaility and testicular cancer in parts of the world, but the suspicion remains and research continues.

"The general impression is that sperm levels are falling, but the reports are conflicting and whether falling sperm counts are actually impacting on fertility is debatable", argues Ms Liz Butler, an embryologist with the J Marion Sims Clinic in Dublin.

"We are only able to judge this on the basis of large-scale studies. I would suggest that the ratio of men to women who are infertile is increasing. However, we may be seeing more cases because technology is now more successful at treating male factor infertility. The subject is in the public forum more these days and there are options for treating infertility that were not available even just a few years ago - so more men might be coming forward".

So, how can you ensure that your sperm remain healthy and fertile? Unless you have been medically tested, you can not be sure what your sperm count actually is.

The average European sperm count is in the region of 70 million per millilitre. While only one (or possibly two or three) sperm are required to fertilise an egg, a man needs a sperm count of 20 million per millilitre to be any way sure of success the natural way.

If your sperm count is high enough, you will want to keep it that way. You may have no intention of becoming a father just yet, but it is always best to prepare for the future. A diminishing sperm count is not reversible! Dr Simon Fishel of the Worldwide Infertility Network - which has both European and US bases - suggests six ways to maintain sufficient amounts of healthy sperm:

• Avoid hot baths - the testicles need to be cooler than the rest of the body.
• Wear loose underwear - boxers rather than Y-fronts.
• Stop smoking and refrain from all recreational drugs.
• Cut down on alcohol.
• Increase your intake of zinc, which can be found in grains, beans, milk and meat.
• Increase your intake of selenium.

For men with low sperm counts, but who are still fertile, there is no need to run to the nearest IVF clinic just yet. It is undoubtedly more pleasant to conceive a child in bed than in a clinic and clinics suggest that men try to increase their production of healthy sperm first, before undergoing expensive fertility treatments.

To increase your sperm count:

• Your diet should include the anti-oxidant vitamins C and E, which can be found in citrus fruits. Eating a variety of fresh fruits and vegetables is recommended anyway.
• Men are at their sexual peak in the morning, at this time more sperm is produced than in the evening.
• Reduce your caffeine intake. No coffee, tea or stimulant drinks.

If none of these precautions appear to be helping, it may be necessary for you and your partner to visit an assisted reproduction clinic to ascertain fertility levels. Many techniques are available to induce pregnancy using sperm from men with extremely low sperm counts, so there is no need to despair.

"Although you might have a high sperm count, many of them might not be functioning properly", explains Ms Butler. "Motility for most samples is around 50%. Then we examine how well they swim. We also look at the morphology - the shape of the sperm".

At the J Marion Sims Clinic, around 120 couples attended for infertility treatment last year. Of these, the difficulty was a male pattern infertility problem in 40% of cases. Two forms of fertility treatments are available for men suffering from low sperm counts in Ireland.