Holden et al. BMC Public Health 2010, 10:96 http://www.biomedcentral.com/1471-2458/10/96 circumference and physical activity) were confirmed in our study. Such associations also extended to other reproductive health disorders, with multivariate logistic regression analysis revealing that a sedentary lifestyle was also an independent risk factor for pAD. The rela- tionship between physical inactivity and lower risk of PD was not explained by adjustment for other lifestyle factors and co-morbid conditions, such as via a relation- ship between obesity and lowered blood testosterone concentrations, and remains enigmatic [19]. In contrast to previous studies [7,20,21], the effects of obesity on reproductive health were diminished when adjusted for other lifestyle and co-morbid conditions, suggesting that other factors are confounding this effect. Sedentary life- style may be the predetermining factor, irrespective of obesity whereas previous studies have suggested that increased physical activity is associated with less adverse male reproductive health, including erectile dysfunction [22], prostate disease and lower urinary tract symptoms [19]. In contrast to our findings, obesity has been linked with more frequent benign [23] and malignant prostate disease [24,25]. Another interesting observation is the higher likelihood of adverse reproductive health status with being under- weight (BMI < 20 kg/m2), although in our study this represents a small group of men. This may be attributa- ble to lower weight as a consequence of serious underly- ing disease and/or possibly a reduced blood testosterone as suggested by an unanticipated protective role for pros- tate disease. Cheng et al [26] also identified a U-shaped relationship between BMI and ED with underweight men having a higher risk than men of normal weight but this was only evident in men who did not exercise. The novel associations of underweight and sedentary lifestyle with increased risks of ED and of pAD and a reduced risk of prostate disease warrant further analysis. Smoking was associated with reduced risk of PD which is consistent with several reports that smokers have fewer operations for benign prostatic hyperplasia (BPH) or report fewer symptoms of BPH [1,27]. Whether this is related to a genuine underlying biologi- cal mechanism such as that mediated by alteration in sex hormone metabolism in smokers [28], although others have found no association [29], or whether it reflects indirectly the operation of other unrecognised health factors influencing both smoking status and PD, remains to be clarified. In contrast, evidence to suggest that smoking [20,30] and alcohol consumption [8] increase the risk of ED were not confirmed in this study. Alcohol consumption appears to have no inde- pendent effect on the range of reproductive health dis- orders examined in this study. The strong association between ED and cardiovascular disease and diabetes supports several previous studies Page 6 of 9 suggesting that common mechanisms exist between reproductive problems and concurrent disease [3,31-33]. Associations with cerebrovascular disease and hyperten- sive disease identified in age-adjusted analyses have been shown in other studies [3,20], although in our study these associations were reduced in multivariate analysis. Similarly, strong associations between LUTS and cardio- vascular disease and treatment of hypertension have been demonstrated [34]. These associations again high- light that reproductive health problems co-exist, or may be considered as clinical markers, with other co-morbid disease. This study supports suggestions that assessment of erectile function in middle-aged and older men may provide a useful indicator to modify lifestyle factors and reduce the risk of other life-threatening conditions [10,35,36]. One striking finding in this study is the similarity of odds ratios for ED and pAD across virtually all variables. The risk factor similarities are difficult to explain in bio- logical terms as low blood testosterone levels are an uncommon primary cause of erectile failure but the lack of libido may be confused with ED [37]. Participants may report suffering from perceived androgen deficiency when confused with non-specific feelings of poorer health and/or confusion of declining sexual function with symptoms of androgen deficiency [4]. There are acknowledged difficulties with measuring androgen defi- ciency in a study of this type and instruments are known to have low specificity [38]. If an interpretation of poorer health and/or declining sexual function is applied, then the risk factor associations identified can be more clearly explained. It is well known that chronic diseases in general, including most common co-morbid conditions associated with ageing, have a non-specific effect to lower blood testosterone concentrations [39,40]. The observation also suggests that middle-aged Australian men in this study may identify androgen defi- ciency as synonymous with erectile failure. At the time the study was done there had been little legitimate effort to raise the awareness of the public (and medical profes- sion) about low testosterone and the symptoms or cir- cumstances that should raise concern. The observed semantic and biological confusion indicates that com- munity education is important both to clarify men’s understanding of their healthy ageing as well as to stem the tide of androgen over-prescribing which is escalating in some countries [41]. An important novel observation from this study is the strong association between depressive symptomatology and all reproductive health disorders assessed, which persisted when all other risk factors (age, lifestyle and biomedical determinants) were taken into consideration. While studies have demonstrated associations between ED and depression previously [42,43], this is the first