Gender threats
In 1992, Carlsen and colleagues published an influential analysis of more than 60 studies, which suggested that human sperm levels are declining alarmingly – the mean sperm count of healthy men had declined by 1 per cent per year over the previous 50 years. Controversy followed, with some studies confirming the finding and others not. A study of 7500 men in Aberdeen between 1989 and 2002, for example, showed a 29 per cent fall in the average sperm count.
Although the picture is not crystal clear, sperm counts do appear to be declining in some countries in the West, but there is much geographic variation and other parts of the world do not seem to be affected. It is not clear how serious the effect is or what the overall impact on fertility might be.
What about the fish? There have been increasing worries about abnormal wild animals, particularly fish, which show signs of feminisation (male fish taking on the features of females). These have been seen at sites of environmental pollution, but also more widely (e.g. in river estuaries in much of North Europe).
The cause seems to be a cocktail of industrial chemicals (such as plasticisers or pesticides), and natural and artificial hormones (e.g. from the contraceptive pill), which are excreted by the body. Many of these chemicals are biologically active, and mimic or block normal hormonal function.
These 'endocrine disruptors' can be found at low levels virtually everywhere - in air, water and soil. Laboratory studies indicate that they can affect fertility but it is not clear yet how serious the problem is in nature.
But does this apply to humans? Again, there are some disturbing trends:
- although once seen as a female condition, males now account for half of all cases of infertility
- the incidence of testicular cancer is rising and there are fears that genital defects in baby boys are on the increase.
At the moment it is not possible to say that endocrine disruptors are definitely affecting human reproductive health – the complexity of the human reproductive system, and of the possible environmental impacts on it, will make it difficult for any firm conclusions to be drawn. Laboratory studies (e.g. on animals) suggest an effect is possible, so it remains an area that needs careful monitoring.