The aims of this study were to determine the prevalence of erectile dysfunction (ED) and its relationship with comorbidity in patients with diabetes. The study population comprised of 312 consecutive patients aged 20 years or over residing in the city of Hamadan in Iran in 2005. Depression was assessed by the modified version of the Beck Depression Inventory (BDI-II) and ED by the short form of the International Index of Erectile Function (IIEF-5) questionnaire. Potential confounding was controlled by stratification and by a logistic regression model. The prevalence of moderate or complete ED (IIEF score ⩽11) was 34% and that of moderate or severe depressive symptoms 30%. Each 1-year increment in diabetes duration was associated with a 10% higher risk of ED. The risk of ED was higher in men with depression (odds ratio (OR)=10.7, 95% CI 5.4–21.1) and in those with cardiovascular disease (CVD) (OR=2.0, 95% CI 1.1–3.6). CVD was associated with ED only in elderly men, whereas depression was related to ED in both young and older subjects. The risk of ED was higher in subjects with both depression and CVD (OR=17.2, 95% CI 6.8–43.1 compared with men free from both diseases). Subjects who consumed fruits weekly or seldom had a higher risk of ED (OR=3.2) compared with those who consumed daily. Our study shows a strong association between depressive symptoms and ED. The association is much stronger for older men. Depression and CVD may interact with one another in relation to a higher risk of ED. A diet rich in fruits may have a beneficial effect on erectile function.
Erectile dysfunction (ED) is more common in men with diabetes than in those free from it, with estimates ranging from two- to three-fold.1, 2, 3 Diabetes is one of the main systemic diseases causing ED and ED is an important cause of decreased quality of life in men with diabetes.3, 4
The inter-relationship among diabetes, depression and ED is complex. Epidemiological studies suggest that there is a bidirectional relation between diabetes and depression. Diabetes increases the risk of depression and men with depression are at greater risk for developing diabetes.5, 6, 7 Causes underlying the association between depression and diabetes are unclear. The chance of depression increases by increasing in the number of diabetes complications. Men with diabetes who have a history of depression are more likely to develop diabetic complications than those without depression. In addition, depression can lead to physical inactivity and noncompliance.8
There is also a bidirectional relationship between depression and ED.9, 10 Depressive symptoms cause ED, and depression is a consequence of ED. Both conditions have a negative effect on the quality of life of patients and their partners. Men suffering from ED may develop a reactive depression as a consequence of negative reaction from their partners related to loss of sexual functioning and psychosocial stress. These factors may cause men with ED to lose self-esteem and self-confidence, and experience depressive symptoms.11, 12 Recovery from depression after successful ED treatment supports reactive depression.13
Depression and ED may result from a common factor such as vascular diseases.14 There is evidence that depression predisposes men to an increased risk of developing vascular diseases such as coronary artery and cerebrovascular diseases.15, 16 In addition, chronic hyperglycemia is associated with an increased risk for vascular diseases in men with diabetes.17 Further a vasculogenic etiology is the most common cause of ED and the risk of ED increases with the number of vascular comorbidities.3
It is of interest to know the associations between comorbidities and ED in patients with diabetes and also interactions between them to identify subjects at a serious problem in treating ED. We conducted a study to estimate the prevalence of ED among Iranian men with diabetes and to assess its association with comorbidity.
Materials and methods
The population of this study comprised of 312 consecutive diabetic patients attending the Cina diabetes center and residing in the city of Hamadan in Iran in spring 2005. Cina diabetes center is the main specialized outpatient center for patients with diabetes in the city, which provides health care free of charge to the patients in the city and surrounding rural areas. All patients with type I or type II diabetes were considered eligible for this study, irrespective of age, duration of diabetes and treatment. The age of the study population ranged from 20 to 83 years. Of the study population, 308 men were married and four were single. A total of 252 men (80.8%) lived in the city and 60 (19.2%) in rural areas. There were 260 men with type II diabetes mellitus and 52 with type I. The study protocol was approved by the research review committee of the Hamadan University of Medical Sciences.
Information on sociodemographic status, lifestyle factors, chronic medical conditions and medications, diabetes complications and metabolic control was gathered by face to face interview, physical examination and reviewing the patients medical records. Detailed information on the disease duration, complications, medication use and the levels of microalbuminuria and glycosylated hemoglobin (HbA1c) was obtained by reviewing the patients' medical records.
Body mass index (BMI) was calculated for all subjects and overweight was defined as BMI value greater than or equal to 25 kg/m2. The subjects were defined as current smokers, if they smoked cigarettes, cigars or pipe at the time of interview; ex-smokers, if they had smoked at least 1 year in the past and were not current smokers; and never smokers, if they had never smoked cigarettes, cigars or pipe. For the analyses, age was classified into three groups, to allow sufficient number of subjects in each group. Men with either hypertension or heart disease were classified as having cardiovascular disease (CVD).
The presence and severity of depressive symptoms were assessed by the modified version of the Beck Depression Inventory (BDI-II).18 The 21 self-report items were summed up and the severity of depressive symptoms was estimated for each subject. The subjects with score 0–13 were classified as free from depression, those with score 14–19 as having mild depression, score 20–28 as moderate and men with score 29–63 as having severe depression.18, 19
The short form of the International Index of Erectile Function (IIEF-5) questionnaire was used for the assessment of subjects' erectile function and the severity of ED calculated by scoring the five questions as follows: no ED, score 22–25; mild ED, score 17–21; mild to moderate ED, score 12–16; moderate ED, score 8–11; and severe ED, score 5–7.20, 21, 22 ED was dichotomized as no/mild (score greater than or equal to 12) versus moderate/complete (score less than or equal to 11) for the analyses of its determinants.
A statistical significance (two-tailed P-value ⩽0.05) was assessed by χ2 test, and logistic regression model was used in the multivariable analyses. Confounding was controlled by a logistic regression model and by stratification. The final models were limited to age and the variables associated with ED at a P-value less than 0.10 in the age-adjusted models. Age, education, type and duration of diabetes, pulmonary disease, CVD, depression, fruits intake, smoking, drugs and substance use, microalbuminuria and HbA1c were used as covariates. For interaction analysis, depression was dichotomized into two groups, none/mild versus moderate/severe.
The mean age of the study population was 55.2 years (s.d.=13.4). The duration of diabetes ranged from 1 to 28 years with a mean of 7.6 years (s.d.=5.0). Overall, 94.6% of subjects had some degree of ED (Table 1). The prevalence of moderate or complete ED (IIEF score ⩽11) was 34.0%, and that of mild, moderate or severe depression was 16.7, 15.4 and 14.4%, respectively. However, only four men (1.3%) used medication for their ED and 17 (5.5%) for their depressive symptoms.
In age-adjusted analyses, ED was associated with education, pulmonary disease, depression, CVD, fruits intake, diabetes duration, microalbuminuria, HbA1c and a history of foot ulceration (Table 2). BMI was not associated with ED. A nonsignificant higher risk of ED was found in current smokers and in patients with type I diabetes.
In multivariable model after controlling for the effects of other covariates, ED was still more common in men with a high level of HbA1c and in those with microalbuminuria or pulmonary disease. However, the associations were not statistically significant. Each 1-year increment in patient age was associated with a 12% (95% CI 8–16%) higher risk of ED and each 1-year increment in diabetes duration with a 10% (95% CI 2–18%). The risk of ED was higher in men with CVD compared with those free from it. It was higher in subjects who consumed fruits weekly or seldom compared with those who consumed them daily (odds ratio (OR)=3.2).
The prevalence of moderate or complete ED was 10.2% in men free from any depression and 61.4% in those with mild to severe depression. The OR of ED adjusted for other covariates was 10.7 (95% CI 5.4–21.1) for men with depression compared with those free from it. The highest risk of ED was found for men with moderate depression (OR=16.4, 95% CI 6.4–42.7). However, difference in the risk of ED between moderate and severe depression was not statistically significant (P=0.06).
The prevalence of CVD increased with increment in depressive symptoms severity (P<0.001). An interaction was found between CVD and depression in relation to a higher risk of ED (Table 3). Compared with men free from depression and CVD, the risk of ED was higher in men with both depression and CVD (adjusted OR=17.2, 95% CI 6.8–43.1). CVD alone was associated with a higher risk of ED only among men aged 62 years or older (Figure 1).
Our findings demonstrate that ED and depression are very common health problems among patients with diabetes. Depression was strongly associated with ED in both young and elderly men, whereas CVD was related to ED only in old men. The risk of ED in the presence of both depression and CVD was higher than their individual risks. A diet rich in fruits was related to a lower risk of ED.
The prevalence of ED in this study is within the range reported in other Asian countries. The prevalence of moderate or complete ED (IIEF score ⩽16) has been reported 78% among Saudi patients with diabetes,23 73% in the current study, 66% among Japanese patients24 and 64% among Chinese men with diabetes.25
Our findings consistent with previous studies1, 2, 9, 10, 13, 23 showed that ED is associated with age, duration of diabetes, CVD, depression and poor metabolic control. ED is often related to the severity and duration of diabetes. Patients with type II diabetes tend to report ED less frequently than patients with type I.1, 2 Multiple factors are involved in inducing ED among patients with diabetes including vascular disease, autonomic neuropathy, psychological problems and drug intake. However, the main cause of ED in patients with diabetes is unclear, but organic factors are more commonly cited.26 Poor metabolic control in patients with diabetes may lead to ED through causing vascular diseases.27
The inter-relationship among diabetes, depression, vascular disease and ED is complex. There is a spider web of interlocking causes (Figure 2). Endothelial dysfunction/atherosclerosis may play a major role in the development of ED and vascular disease in patients with diabetes,1, 28, 29 and depression may predispose these patients to an early development of atherosclerosis.15 In addition, ED may be a potential predictor of silent coronary artery disease in men with diabetes,28 or ED, vascular disease and depression may share common risk factors.
The vicious cycle among diabetes, vascular disease, depression and ED can be strongly weakened by the treatment of depression. Treating depression improves erectile function, ability to maintain good diabetes management, reduces the risk of vascular diseases and improves patient's interpersonal relationship and quality of life. However, it is difficult to eradicate economical deprivation underlying cause of depression in low-income patients. Despite the importance of treating depressive symptoms and ED in patients with diabetes, they often remain undiagnosed and untreated. In the current study, only 1.3% of patients with diabetes were treated for ED and 5.5% for depression. A significant recovery of either depression or ED improves other and diabetes. Sildenafil has been only moderately (49–59%) effective in patients with diabetes,30, 31, 32 which highlights the importance of treating depression before starting a treatment for ED. However, ED appears to be an early marker of silent coronary artery disease in men with diabetes.28 Therefore, low response to ED treatment in these patients may be related to severe atherosclerosis.
The present study has several limitations. Depression, CVD and ED are highly prevalent and frequently comorbid conditions in patients with diabetes; however, causality cannot be drawn from cross-sectional studies, because both exposure and outcome are assessed at the same point in time. This study cannot establish a temporal cause–effect relationship. However, it can confirm the association between comorbidity and ED in patients with diabetes. Therefore, it is unclear whether depression preceded ED or depression was the consequence of ED.
The study population comprised of men attending the diabetes health center for care free of charge. These patients were not randomly selected; therefore, they are probably not representative of the entire diabetic men. Patients seeking medical attention in a free program may have low income. They are less likely to have health insurance and more likely to be unemployed and have comorbidity and psychological problems.
We used the cutoff point of 13 to classify subjects with depression. It has been shown that subjects with BDI scores of less than 13 do not have depression.19 The cutoff of 13 seems most appropriate owing to the high sensitivity (100%) and specificity (99%). This cutoff point has a positive predictive value of 0.72 and a negative predictive value of 1. A clinically relevant ED (moderate or severe ED) was used to assess the association between comorbidity and ED because milder forms of the disease are common in patients with diabetes.
In summary, there is a strong association between depression and ED in patients with diabetes. The association is much stronger for older men. Depression and CVD may interact with one another in association with ED. A diet rich in fruits may have a beneficial effect on erectile function.
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Shiri, R., Ansari, M. & Falah Hassani, K. Association between comorbidity and erectile dysfunction in patients with diabetes. Int J Impot Res 18, 348–353 (2006). https://doi.org/10.1038/sj.ijir.3901432
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