Hypothesis: Gonadal hormones act as confounders in epidemiological studiesof the associations between some behavioural risk factors and some pathological conditions

There are grounds for suspecting that, to varying degrees, smoking, alcohol consumption, oral contraceptive use, vasectomy and induced abortion are ma rkers for high steroid hormone levels. So in epidemiological studies, false inferences may be drawn that these markers (treated as risk factors) have causal or exacerbating effects on diseases which are truly partially caused by high levels of hormones (e.g. probably prostatic cancer and breast canc er). Analogously, such studies of conditions which are truly partially caus ed by low levels of hormones (e.g. bone fractures, poor sperm quality, and perhaps testicular cancer and rheumatoid arthritis) may yield spurious sugg estions of an ameliorative effect. The results of epidemiological studies o f the above five "risk factors" for the above six pathologies are-in many c ases-in striking disarray. I suggest that this is, at least partially, beca use of this form of confounding. The point may be tested by contrasting the hormone levels of people who self-select for smoking, vasectomy, etc., at, the time that self-selection is made with those of appropriately selected control subjects. (C) 2001 Academic Press.