Stress and other environmental factors affecting fertility in men and women: overview.

To understand how environmental factors contribute to fertility or infertility in humans, it is first necessary to define environment. A view that will guide this review is that environment represents the "external milieu," analogous to the well-defined concept of "internal milieu" first introduced by Claude Bernard. Within this context, the environment provides both positive and adverse influences on reproductive health and development. Environmental factors can then be classified into categories such as physical, chemical, biological, behavioral, and socioeconomic. In many circumstances, multiple environmental factors may contribute to adversely modify human health. It has been suspected and in some cases demonstrated that stress can adversely affect reproductive function. Both animal and human data support this contention; however, the human data are clear in extreme situations (e.g., inmates of concentration camps) but less so under less drastic conditions. In recent years many advances have been made concerning the neurochemical mechanisms that mediate the effects of stress on reproductive functions and on the identification of "stress hormones" that may not only be involved in the stress response but also serve as biochemical markers to identify and correlate stress with different fertility parameters. Nutrition also plays an important role in infertility, and undernutrition or nutrition disorders are associated with stress in infertility. Environmental factors are often invoked as contributing to many cases of unexplained infertility. However, the direct causal relationship between those factors and the ensuing infertility of the couple are seldom well established and remain largely anecdotal.(ABSTRACT TRUNCATED AT 250 WORDS)