There is a natural loss of fertility due to ageing in both sexes: the menopause in women and the more gradual reproductive decline in men. Ageing, as with all aspects of reproduction, has both its genetic and environmental components. This is particularly true for the menopause where a genetically influenced time frame is strongly modulated by the environment.

The ageing process in both males and females can be accelerated by the following influences.

• Cytotoxic agents and xenobiotics (that is, biologically foreign chemicals). For example, organophosphorus pesticides, certain anticancer drugs and components of cigarette smoke. Epidemiological evidence suggests that cigarette smoking has an anti-oestrogenic effect in women, perhaps as a result of increased adrenal stimulation. On the other hand, aromatic hydrocarbons in cigarette smoke may accelerate the ageing of oocytes.

• Occupational stress. For example noisy environments and the sterilizing effects of ionizing radiation.

• Nutritional stress. Nourishment is fundamental as it relates closely to the basic requirements of life and is closely correlated with fertility. Malnutrition increases the frequency, severity and duration of other stresses, such as infectious diseases.

• Disease. For example, gonorrhoea and the delayed effects of mumps on the reproductive system. It is often difficult to distinguish between the direct effects of disease and the consequences of drug treatment used to combat disease.

• Immunological disorders. For example, 3–8% of men produce antibodies to their own sperm. An autoimmune disorder resulting from antibody production against the gonadotrophin receptors has also been identified.

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