4 Discussion
In this study, we discovered a relationship between ED and osteoporosis persisted after adjustment for potential confounding risk factors in total male population. To the best of our knowledge, this is the first large population-based cross-sectional study to investigate the association of ED and osteoporosis for the all-aged (18-87 years) male population. According to the results of this study, ED can be used as significantly assessing factor for the prevalence of osteoporosis in all-age adult male population. In addition, model with ED can significantly improve the diagnosis ability for prevalence osteoporosis in total population, which was further confirmed that the importance of ED for diagnosis osteoporosis. Early intervention is of great importance for osteoporosis, and the present findings might provide insights into ED for the prevention and early detection of osteoporosis.
Many researchers concluded that a significant association between ED and osteoporosis exists. In our study, ED was a significant risk factor associated with osteoporosis. Concordant with an observational cross-sectional study based on 119 recruited men with depressive, it is reported that a low BMD was significantly associated with ED[20]. Similar results were obtained in a population-based cohort study which included 4,696 elderly (60-74 years) Danish men, which revealed a higher risk of osteoporotic fracture risk in men with self-reported ED[21]. However, a study which included 76 men aged ≥50 demonstrated no association between ED and osteoporosis, which was conducted from one region with a small sample size (n=76), where the conclusion might not be completely applicable to our study. Our study firstly based on all-aged (18-87 years) male population to explore the relationship between ED and osteoporosis, and ED can be used as significantly assessing factor for the prevalence of osteoporosis.
Some biological hypotheses have been proposed for the mechanism which was responsible for the relationship between ED and osteoporosis. Firstly, androgens levels were lower in patients with ED than without ED, which plays an important role in the regulation of bone formation in men [22, 23]. Secondly, patients with ED have been highly associated with inflammation, and inflammatory cytokines may inhibit osteoblast growth, thus causing osteoporosis[24]. Thirdly, nitric oxide (NO) bioactivity is a possible pathogenic mechanism underlying the relationship between ED and osteoporosis. NO is crucial for penile engorgement and affect bone metabolism as well[25]. Fourth, the condition of endothelial function is indicative of early stage of atherosclerosis which is well established in both ED and osteoporosis, which potentially explains the relationship between ED and osteoporosis[26]. Furthermore, vitamin D which plays a major role in maintaining the bone health, has a negative association with the risk of ED by promoting endothelial dysfunction, which also might also play an important role in explaining the association between ED and osteoporosis[27]. Finally, traditional ED risk factors including diabetes mellitus, hypertension and dyslipidemia are known to be predictors of osteoporosis. We suggest that ED and osteoporosis share similar risk factors and a diagnosis of ED increases the risk of osteoporosis. However, these co-morbidities do not account for the complete relationship between ED and osteoporosis.
There were several limitations in this study which require consideration. (1) No causal inference can be drawn due to the cross-sectional design of the current study. Further prospective studies are needed to illustrate the precise relationship between ED and osteoporosis. (2) By including only Chinese subjects, the results of the present study might not be representative of other ethnic groups, especially those in developed or undeveloped countries. To some extent, however, the present study of the Chinese population was still a convenient sample and selection bias is inevitable. (3) Our assessment of ED was performed using interviews and not confirmed by a specialist. We are aware that conditions like ED are highly associated with social stigmas. As a result of this, it is likely that ED was under-reported by study participants. Furthermore, ED was evaluated only by asking ”the ability to get and keep an erection for satisfactory intercourse?” and the answers were categorical (no/yes) and International Index of Erectile Function-5 items (IIEF-5) was not used in this study. However, no IIEF-5 was used in some of studies and the self-reported with categorical (yes/no) has strong correlations with IIEF-5[28-30]. (4) Data on osteoporosis were obtained by ultrasound bone densitometer, as X-rays were harmful to the health of participants and were not part of this study. Ultrasound bone densitometer revealed a strong correlation compared to X-rays[31] and has been used mainly used to assess BMD in large epidemiology survey[32-34]. (5) No androgen tests were performed in this study, and we could not identify the prevalence of osteoporosis with the levels of androgen. However, studies had confirmed that androgen deficiency is strongly associated with ED [2, 35].