Dietary factors in erectile dysfunction

Abstract

The role of dietary factors in erectile dysfunction (ED) has never been addressed. In the present case–control study, we investigated the relation of the Mediterranean diet with ED. A total of 100 men with ED were compared with 100 age-matched men without ED. A scale indicating the degree of adherence to the Mediterranean diet was constructed: the total Mediterranean diet score ranged from 0 (minimal adherence to the Mediterranean diet) to 9 (maximal adherence). The percentage of physical inactivity was greater in the ED group (35 vs 19%, P=0.04), whereas the diet score was lower (4.7±0.5 vs 5.4±0.5, P<0.01), indicating a reduced adherence to the Mediterranean diet. In analyses adjusted for the prevalence of associated risk factors (hypertension, hypercholesterolemia), body mass index, waist, physical inactivity and total energy intake, the intake of fruits and nuts, and the ratio of monounsaturated lipids to saturated lipids remained the only individual measures associated with ED. In conclusion, the results of the present study show that dietary factors may be important in the development of ED: adoption of healthy diets would hopefully help preventing ED.

Introduction

A high prevalence of erectile dysfunction (ED) in patients with cardiovascular risk factors has been reported.1, 2, 3 Moreover, patients with ED have an increased prevalence of coronary heart disease (CHD) and peripheral vascular diseases.4 Kaiser et al.5 have shown that subjects with ED but without evidence of clinical cardiovascular disease and free of traditional cardiovascular risk factors present widespread abnormality of endothelial function as has been seen in patients with cardiovascular risk factors. According to a raising popular view, subjects with ED seem to have a vascular mechanism similar to that seen in atherosclerosis,6 and therefore a diagnosis of ED may be seen as a sentinel event that should prompt investigation for CHD in asymptomatic men.7

As ED and atherosclerosis may share some pathways,8 it seems reasonable to assume that dietary factors, which are so important in reducing the burden of CHD disease,9 may also play a role in reducing the occurrence of ED. For example, there are several observational studies associating the Mediterranean diet with a lower risk of CHD morbidity and mortality.10, 11, 12, 13 Moreover, some randomized clinical trials have shown a beneficial effect of this dietary pattern on secondary prevention of CHD.14, 15 The effect of the Mediterranean diet on CHD can be mediated through multiple biological pathways other than serum lipids, including reduction of oxidative stress and subclinical inflammation, amelioration of endothelial dysfunction and insulin sensitivity, mitigation of blood pressure, and thrombotic tendency.9, 16, 17

To the best of our knowledge, the role of dietary factors in ED has never been addressed. In the present case–control study, we investigated the relation of the Mediterranean diet with ED.

Subjects and methods

Men were recruited to the outpatient departments at the University of Naples SUN, Italy, after exclusion criteria have been verified with the aid of a personal health and medical history questionnaire, which served as a screening tool. Exclusion criteria were age less than 20 or higher than 80 years, diabetes mellitus (fasting plasma glucose higher than 126 mg/dl in at least two occasions), impaired renal function, pelvic trauma, prostatic disease, cardiovascular disease, psychiatric problems, use of drugs, or alcohol abuse (>500 g/week in the last year). All participants provided written informed consent and the study protocol was approved by the ethics committee of our institution.

Erectile function was assessed by completing the International Index of Erectile Function (IIEF)-5, which consists of items 5, 15, 4, 2, and 7 from the full-scale IIEF-15.18 A score of 21 or less indicates the presence of ED.

Usual dietary intake was assessed with a food frequency questionnaire listing approximately 140 foods and beverages commonly consumed in Italy. Portion size was calculated on the basis of information provided on household units and photographs of usual portion sizes, and was then used for estimation of consumed quantities. A total of 14 all-inclusive food groups or nutrients were considered: potatoes, vegetables, legumes, fruits and nuts, dairy products, cereals, meat, fish, eggs, monounsaturated lipids (mainly olive oil), polyunsaturated lipids (vegetable-seed oils), saturated lipids and margarines, sugar and sweets, and non-alcoholic beverages. Intake of each of the indicated groups in grams per day and total energy intake were calculated.

A scale indicating the degree of adherence to the Mediterranean diet was constructed according to Trichopoulou et al.10 A value of 0 or 1 was assigned to each of nine indicated components with the use of the median as the cutoff. For beneficial components (vegetables, legumes, fruits and nuts, cereal and fish), persons whose consumption was below the median were assigned a value of 0 and persons whose consumption was at or above the median were assigned a value of 1. For components presumed to be detrimental (meat, poultry, and dairy products), persons whose consumption was below the median were assigned a value of 1 and persons whose consumption was at or above the median were assigned a value of 0. For ethanol, a value of 1 was assigned to men who consumed between 10 and 50 g/day. As in Italy monounsaturated lipids are used in much higher quantities than polyunsaturated lipids, we used the ratio of monounsaturated to saturated lipids rather than the ratio of polyunsaturated to saturated lipids. The total Mediterranean diet score ranged from 0 (minimal adherence to the Mediterranean diet) to 9 (maximal adherence).

Physical activity status of the subjects was evaluated through a modified version of a self-reported questionnaire provided by the American College of Sports Medicine,19 which assesses the frequency (times per week), duration (in minutes per time), and intensity of sports- or occupation-related physical activity. Participants who did not report any physical activities were defined as sedentary.

Current smokers were defined as those who smoked at least one cigarette per day or have stopped cigarette smoking during the past 12 months. Former smokers were defined as those who had stopped smoking more than 1 year before. The rest were defined never smokers.

Height and weight were measured to the nearest 0.5 cm and 100 g, respectively, with participants wearing lightweight clothing and no shoes. Body mass index (BMI) was calculated as weight in kilograms divided by height (in meters) squared.

Statistical analysis

Comparison of group difference in baseline characteristics was made by analysis of variance (ANOVA) for continuous variables and by χ2 test for categorical variables. Associations between normally distributed continuous variables and group of patients were evaluated through ANOVA, whereas the associations between skewed variables and groups of patients were evaluated through the Kruskal–Wallis test. Multivariate regression analysis tested the independent association of nutrient intake, BMI, waist, physical activity, and total energy intake with the dependent variable (IIEF score). A value of P<0.05 was considered significant. All analyses were conducted using SPSS version 9.0 (SPSS Inc., Chicago, IL, USA).

Results

The clinical characteristics of the study population are shown in Table 1. As age represents the main risk factor for ED, the two groups of subjects with or without ED were matched for age (±1 year). Compared to the group without ED, subjects with ED were slightly heavier and with a greater waist, and were more likely to be hypertensive and hypercholesterolemic although this did not reach the level of statistical significance (P=0.06). Current smoking was found to be similar in the two groups. Lifestyle characteristics were found to be different between groups: in particular, the percentage of physical inactivity was greater, whereas the diet score was lower, indicating a reduced adherence to the Mediterranean diet in the ED group.

Table 1 Lifestyle and clinical characteristics of subjects with and without ED

Table 2 shows the daily dietary intake of several food groups. As expected, high Mediterranean diet scores were characterized by high intakes of vegetables, legumes, fruits and nuts, cereals, fish, and olive oil, and relatively low intakes of dairy products and meat (data not shown). Positive associations with ED were found for selected food groups: in particular, the intake of vegetables, fruits and nuts, and the ratio of monounsaturated to saturated lipids were significantly lower in subjects with ED. In analyses adjusted for the prevalence of associated risk factors, BMI, waist, physical inactivity and total energy intake, the intake of fruits and nuts (P=0.02), and the ratio of monounsaturated lipids to saturated lipids (P=0.04) remained the only individual measures associated with ED.

Table 2 Daily dietary intake of several food groups in the two groups of subjects

Table 3 shows the distribution of subjects according to the Mediterranean diet score. There was a significant inverse association between the Mediterranean diet score and ED (P<0.01).

Table 3 Distribution (%) of subjects with or without ED across tertiles of the diet score

Discussion

The results of the present study demonstrate that men with ED show, as compared with age-matched men without ED, a difference in lifestyle attitudes that may play a role in the development and progression of ED. In particular, the prevalence of unhealthy dietary patterns and physical inactivity were significantly higher in men with ED.

We confirm here that weight is associated with ED, as BMI was significantly higher in men with ED as compared with men without ED. Prospective studies, such as the 9-year follow-up study of MMAS1 and the 25-year follow-up Rancho Bernardo Study,2 reported that body weight was an independent risk factor for ED, with a risk exceeding 90% of controls (OR between 1.93 and 1.96, respectively). In our study, visceral obesity, as measured with the waist circumference, was more pronounced in subjects with ED and was more strongly associated with ED than BMI. Although the relation between visceral obesity and ED may not be readily apparent, a growing body of evidence implicates central adiposity as a key regulator of inflammation.20 Among the various adipokines released by the visceral adipocytes, both tumor necrosis factor-α and interleukin-6 seem to play a major role, as they can depress endothelial function.21 As endothelial dysfunction is increasingly acknowledged as an early sign of generalized atherosclerosis and associates with ED,6 one possible mechanism linking visceral obesity to ED may be through the increased release of adipokines. We did not find significant association between the prevalence of hypertension and hypercholesterolemia and ED, although this might have been the result of the strict entry criteria, which excluded subjects with diabetes or drug users.

We have found that the intake of some foods was less represented in subjects with ED: in particular, the calculated intakes of vegetables, fruits and nuts, and the ratio of monounsaturated to saturated lipids were significantly lower in men with ED. Interestingly enough, each of these nutrients has been associated with a decreased risk of CHD, through an effect of improving endothelial dysfunction22 and decreasing inflammation.23 In general, the intake of foods that are more likely to be associated with increased CHD risk was higher in men with ED, whereas the intake of foods that are associated with decreased CVD risk was reduced. The concept of dietary patterns has recently attracted considerable interest in the field of nutritional epidemiology.24 In a subcohort of healthy men from the Health Professionals Follow-up Study, Fung et al.25 discerned two major dietary patterns: the prudent pattern characterized by higher intake of fruit, vegetables, whole grains, and poultry; and the Western pattern characterized by higher intake of red meat, high-fat dairy products, and refined grains. A positive correlation has been found between the Western dietary pattern and plasma biomarkers of obesity and cardiovascular disease risk, such as plasma concentrations of inflammatory (C-reactive protein) and endothelial dysfunction (ICAM-1, VCAM-1, P selectin) markers.26 Moreover, a dietary pattern that was high in sugar-sweetened soft drinks, refined grains, diet soft drinks, and processed meat, but low in wine, coffee, cruciferous vegetables and yellow vegetables was associated with an increased risk of diabetes and inflammatory markers in the Nurses' Healthy Study.27 As inflammation may play a causative role in ED,28 a reduced low-grade inflammation by healthy dietary patterns may be implicated in the association of increasing adherence to Mediterranean diet and reduced prevalence of ED.

In our study, we found that a dietary pattern that was high in fruit, vegetables, nuts, whole grains, and fish, but low in red and processed meat and refined grains was more represented in subjects without ED as compared with men with ED. This dietary pattern is quite similar to the traditional Mediterranean diet, which is characterized by a high intake of vegetables, legumes, fruits and nuts, and cereals, and a high intake of olive oil associated with a low intake of saturated fats, a moderate intake of fish, a low-to-moderate intake of dairy products, a low intake of meat and poultry, and a regular but moderate intake of ethanol, primarily in the form of wine and generally during meals.29

In conclusion, the results of the present study show that dietary factors may be important in the development of ED and claims for the widespread application of current nutritional guidelines, which insist upon increasing consumption of vegetables, fruit, nuts and healthy fats,30 whose intake is less represented in ED patients.

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Esposito, K., Giugliano, F., De Sio, M. et al. Dietary factors in erectile dysfunction. Int J Impot Res 18, 370–374 (2006). https://doi.org/10.1038/sj.ijir.3901438

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Keywords

  • healthy diet
  • erectile dysfunction
  • prevention

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