Environment, lifestyle and male infertility.

Our understanding of the importance of environmental and lifestyle factors on sperm count and fertility is constrained by the extreme variation in sperm count between men and between ejaculates. The factors responsible for this variation provide a key to understanding what factors actually affect the sperm count. The relative importance of the various factors and the pathways via which they affect sperm count are discussed. The most important are Sertoli cell number, ejaculatory frequency, season, factors affecting scrotal heating (e.g. the time spent seated), a past history of reproductive tract disorders and ageing. The possible role of other environmental factors commonly supposed to affect sperm count (exposure to pesticides or endocrine disruptors) is discussed, although the evidence for a major influence of such factors is lacking. It is suggested that lifestyle changes, especially in the time spent seated, will exert an adverse effect on sperm production in a progressively larger group of men over the next decade.