American Journal of Epidemiology Advance Access originally published online on April 12, 2006
American Journal of Epidemiology 2006 164(1):41-46; doi:10.1093/aje/kwj151
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Original Contribution |
Association of Anthropometric Measures with the Presence and Progression of Benign Prostatic Hyperplasia
1 Division of Epidemiology, Mayo Clinic, Rochester, MN
2 Department of Epidemiology, Merck Research Laboratories, West Point, PA
3 Division of Biostatistics, Mayo Clinic, Rochester, MN
4 Department of Medicine, Mayo Clinic, Rochester, MN
5 Department of Research and Evaluation, Southern California Permanente Medical Group, Pasadena, CA
Correspondence to Dr. Steven J. Jacobsen, Department of Research and Evaluation, Southern California Permanente Medical Group, Second Floor, 100 South Los Robles Avenue, Pasadena, CA 91101 (e-mail: steven.j.jacobsen{at}kp.org).
Received for publication September 28, 2005. Accepted for publication January 13, 2006.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The authors investigated the association of anthropometric measures with the presence and progression of components of benign prostatic hyperplasia (BPH) and a clinical outcome of BPH in a cohort of healthy, Caucasian men aged 40–79 years that was randomly selected from the Olmsted County, Minnesota, population beginning in 1990. Exclusionary criteria included prostate or bladder surgery, urethral surgery or stricture, or medical or other neurologic conditions that could affect normal urinary function. Height, weight, and waist and hip circumferences were measured. Components of BPH, including American Urological Association Symptom Index scores, peak urinary flow rate, and prostate volume, were assessed on a randomly selected subsample. Acute urinary retention was assessed through review of community medical records. There were few significant associations of anthropometric measures with the presence or progression of components of BPH or clinical outcome of BPH, and there were no instances where the point estimates for the BPH components suggested a dose-response effect. The authors conclude that anthropometric measures are not significantly associated with the presence or progression of BPH as measured by American Urological Association Symptom Index scores, peak urinary flow rate, prostate volume, or acute urinary retention. These data provide no evidence of a consistent significant relation between anthropometric measures and BPH.
anthropometry; prostatic hyperplasia; urinary retention
Abbreviations: AUASI, American Urological Association Symptom Index; BPH, benign prostatic hyperplasia; Pvol, prostate volume; Qmax, peak urinary flow rate
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Although there are a few established risk factors for benign prostatic hyperplasia (BPH), such as sex steroids and age (1
), there have been debate and a great deal of interest in the association between anthropometric measures and BPH. Obesity could affect the presence and progression of BPH by a number of pathways. Obesity has been associated with decreased levels of serum testosterone levels and increased estrogen levels in men (2), both associated with BPH (3, 4). In a study investigating the influence of age and endocrine factors on BPH volume, Partin et al. (5) reported that, after adjusting for age, men with larger BPH volumes have higher androgen and estrogen levels, suggesting that these may be factors in BPH development. It has also been shown that estrogen acts synergistically with dihydrotestosterone to stimulate prostatic growth in dogs (6), and it has been speculated that the elevated estrogen/testosterone ratio associated with obesity may increase the stromal/epithelial cell ratio in BPH tissue (4, 7) seen in men with BPH.
Previous studies have suggested a possible relation between adiposity and the likelihood of undergoing prostate surgery, although the results of all studies did not reach statistical significance (7–12). Men with greater abdominal adiposity were reported to be more likely to have surgery for BPH and more likely to have frequent obstructive urinary symptoms (7). Men with lower body mass index were also reported to be more likely to have a clinical diagnosis of BPH (8). In another study, men greater than 66 inches (1.68 meters) in height or greater than 150 pounds (68.04 kg) had a reduced risk of BPH surgery (9). In addition, men with a lower body mass index were found to be more likely to have a clinical diagnosis of BPH by digital rectal examination but not necessarily surgery for BPH (10). Finally, a higher waist/hip ratio was associated with an increased risk of BPH in men newly diagnosed and hospitalized for surgery in Shanghai, China (12). It has not been shown that anthropometric measures are consistently associated with components of BPH.
The lack of consistent findings of an association between anthropometric measures and BPH could be due to the limitations of previous studies, such as cross-sectional design, various definitions of BPH, and lack of measures of the components of BPH. The question of whether obesity affects the progression of BPH has not been addressed. If obesity does increase the progression of BPH, as well as the likelihood of its development, this would have profound public health implications on the prevalence and severity of BPH because of the epidemic of obesity in the population. In order to circumvent some of the limitations of previous studies, we examined the association of anthropometric measures with components of BPH and a clinical outcome of BPH in a prospective, population-based study of men in Olmsted County, Minnesota.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The Olmsted County Study of Urinary Symptoms and Health Status among Men was established in 1990 and has been described in detail in previous publications (13
, 14). Briefly, this age-stratified random sample was drawn from an enumeration of nearly all Caucasian male Olmsted County, Minnesota, residents between the ages of 40 and 79 years. Subjects were excluded if they had prior prostate surgery, prostate cancer, or any of a number of specified medical conditions that would affect normal urinary function (other than BPH). At baseline, participants in the community cohort (55 percent response rate) were visited in their own homes where subjects completed a previously validated self-administered questionnaire with a field research assistant present (15). A subset of 475 randomly selected men completed an initial clinical evaluation, including peak urinary flow rate assessment and transrectal ultrasonography (16). Men in the clinical cohort who dropped out were replaced.
Several components of BPH were assessed. Participants completed a previously validated baseline questionnaire that assessed lower urinary tract symptom severity from questions similar to those in the American Urological Association Symptom Index (AUASI), and a composite AUASI score was estimated. Although no single component provides a definitive nonhistologic diagnosis of BPH, previous studies demonstrate that the AUASI score, peak urinary flow rate (Qmax), and prostate volume (Pvol) have adequate construct and predictive validity for BPH (17). Follow-up was performed biennially for 12 years and supplemented with the review of community medical records. At each biennial follow-up, study subjects completed a questionnaire that was similar to the baseline questionnaire. A clinical outcome of acute urinary retention based on review of medical records was also assessed (18).
Anthropometric measures included height, weight, and waist and hip circumferences. All anthropometric measures were performed according to standardized protocols by a trained researcher and were collected in the third round. Body mass index (weight (kg)/height (m)2) was calculated and stratified into three categories (<25, 25–29.9, 
30). Waist circumference and waist/hip ratio were stratified into quartiles. Anthropometric measures were available on 2,064 men.
Descriptive statistics for anthropometric measurements were calculated, and distributions were compared by use of a nonparametric ranked-sum test. Spearman's correlation coefficients were calculated to determine correlations between anthropometric measures and components of BPH. Logistic regression analyses were used to describe the relations adjusting for age. Dependent variables were dichotomized according to clinically accepted cutpoints. Increased Pvol was defined as greater than 30 ml. Symptomatic men were defined as having moderate to severe symptoms with an AUASI score of greater than 7. Depressed uroflow was defined as having a peak flow rate of less than 12 ml/second. Subjects were excluded from analyses only when missing data occurred. Because of the very limited number of significant associations identified in the age-adjusted analyses and the possibility of age-dependent associations, additional analyses were conducted by stratifying the study population by 10-year age groups (40–49, 50–59, 60–69, 70 years).
To estimate longitudinal changes in the AUASI score, Qmax, and Pvol, a least-squares regression line was estimated for each man by regressing the measurement on time from baseline (19). An estimate of the American Urological Association symptom, Qmax, and Pvol intercept and slope was obtained for each man with two or more observations before prostatic treatment or diagnosis of prostate cancer. Only measurements made before the initiation of treatment or diagnosis of cancer were included in the analyses. Because of skewed distributions, log transformation was applied to Qmax and Pvol measurements before analysis. Mixed-effects models were used to corroborate our estimates of slope.
An alternative set of analyses examined predictors of a rapid increase in AUASI score and Pvol, defined as the upper 20th percentile of annual changes, and predictors of a rapid decrease in Qmax, defined as the lower 20th percentile of annual changes. Multivariate logistic regression models were used to assess the association between anthropometric measures and BPH progression, with adjustment for age.
All analyses were conducted with SAS, version 8.2, statistical software (SAS Institute, Inc., Cary, North Carolina).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The mean, median, and first and third quartiles of demographic, anthropometric, and BPH components are presented in table 1. Table 2 includes a bivariate comparison of median anthropometric measures in those with and without BPH, as measured by its components and the clinical outcome of acute urinary retention, as well as age-adjusted correlations of anthropometric measures and components of BPH. Men with an AUASI score of more than 7 had a significantly increased waist/hip ratio (p = 0.0209). Those with a Qmax of less than 12 ml/second had a significantly higher median waist/hip ratio (p = 0.0258) and a significantly lower median body mass index (p = 0.0153) compared with those with a Qmax of 12 or more ml/second. No other significant bivariate associations were found. There were few significant correlations identified. Body mass index and waist circumference were both significantly positively correlated with Qmax and Pvol.
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Table 3 presents age-adjusted associations of anthropometric measures with components of BPH and acute urinary retention. Men with a body mass index of greater than or equal to 25 kg/m2 were significantly less likely to have a Qmax of less than 12 ml/second compared with those with a body mass index of less than 25 kg/m2. No other significant age-adjusted associations were found. In addition, along the categories of the anthropometric measures, there were no instances where the point estimates for the BPH outcomes suggested any kind of dose-response effect.
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The age-adjusted association of anthropometric measures with progression of BPH measured by the AUASI score, Qmax, and Pvol is presented in table 4. There were no significant associations found between anthropometric measures and progression of components of BPH. In addition, there were no instances where the point estimates for the BPH components suggested any kind of dose-response effect. When stratifying the population by 10-year age groups, we found a few other associations between anthropometric measures and progression of components of BPH, but these were sporadic and showed no dose-response relation (data not shown).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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This study examined the association of anthropometric measures with the presence and progression of components of BPH and acute urinary retention in a population-based sample of men in Olmsted County, Minnesota. There were few statistically significant associations identified. Although there were a number of significant correlations identified, most were not seen when the outcomes were stratified into clinically meaningful categories. In addition, associations were not consistent nor were dose-response relations seen across anthropometric categories or quartiles. This indicates that, in this Caucasian cohort, measures of obesity were not significantly related to the presence and progression of BPH.
The association between anthropometric measures and BPH has been inconsistent. Although some studies have identified a significant association, either positive or negative, other studies have found no significant associations of anthropometric measures and BPH. Among those that found a positive association was one in which participants in the Health Professionals Follow-up Study were examined (7). The main outcomes of this study were the incidence of prostatectomy for BPH and frequency and severity of symptoms of urinary obstruction. After adjustment for age, smoking, and body mass index, abdominal obesity was related to prostatectomy for those with a waist circumference of greater than or equal to 43 inches (109.22 cm) relative to those with a waist circumference of less than 43 inches. Body mass index, hip circumference, and waist/hip ratio were not significantly associated with BPH.
Hammarsten and Hogstedt (20) examined 250 men referred to the Urological Section, Department of Surgery, Central Hospital, Varberg, Sweden, with lower urinary tract symptoms with or without manifestations of the metabolic syndrome. This cross-sectional study examined risk factors for fast-growing BPH. The growth of BPH was based on the assumptions that the prostate growth rate is linear over time and that the prostate gland volume was 20 ml when the patient was 40 years of age, both of which assumptions could be questioned. Body mass index, waist circumference, hip measurement, and the waist/hip ratio were all significantly associated with an increased rate of growth for BPH.
Results from some studies indicated a significant inverse relation between anthropometric measures and BPH. One examined the association of history of weight and obesity through life and risk of BPH (21). In this hospital-based, case-control study, participants were histologically confirmed cases of BPH, while controls were men admitted to the same hospitals for a wide spectrum of acute conditions unrelated to the known or potential risk factors for BPH. The highest quartile of both body weight and waist/hip ratio was inversely related to BPH.
There are a few studies that did not find a significant association between anthropometric measures and BPH, including a community-based population of healthy aging men participating in the Massachusetts Male Aging Study (22). Men in this study who were examined for risk factors for BPH were considered to have BPH if they reported frequent or difficult urination and were told by a health professional that they had an enlarged or swollen prostate, or if they reported having surgery for BPH. Body mass index and the waist/hip ratio did not individually predict clinical BPH.
The inconsistency in the results of studies examining the association of anthropometric measures and BPH may be due to a number of reasons. One may be variations in the definition of BPH, with many studies examining only symptomatic BPH that would exclude individuals with less severe cases of BPH. A second may be the cross-sectional design of most studies. This would result in only a single measure of obesity and would not determine temporality of obesity and BPH outcome. A third may be the lack of anthropometric measures at the time when men may be developing BPH. Thus, these studies do not have data available to assess the real relation between obesity and BPH. With one exception (20), most studies have used anthropometric measures at one time point. Finally, variation in anthropometric measures throughout an individual's life may also result in inconsistent findings.
Several potential limitations should be noted in this study. We do not have serial anthropometric measures prior to study entry, and thus it is not possible to determine how long individuals were obese. In addition, anthropometric measures can vary significantly, and thus there is a potential for misclassification. Finally, men participating in the Olmsted County Study may not be representative of the US population, which may limit the generalizability of these data. However, there are a number of significant strengths of this study, including a population-based sample covering the spectrum of severity of BPH as well as the availability of serial measures of components of BPH. This enabled us to examine the effect of anthropometric measures on progression of BPH.
In summary, results from this study provide little indication of an association between anthropometric measures and the presence and progression of components of BPH, including the AUASI score, Qmax, or Pvol, or with the presence of acute urinary retention. This indicates that other factors may be important in the prevention of BPH in the population.
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ACKNOWLEDGMENTS |
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This study was funded, in part, by research grants from Merck Research Laboratories as part of the BPH Natural History Study Group and from the National Institutes of Health (AR30582).
The authors thank the Olmsted County Study personnel for their help in the study and Sondra Buehler for her assistance in preparation of this manuscript.
Conflict of interest: Thomas Rhodes and Cynthia J. Girman are employed by and own stock in Merck & Co., Inc., which manufactures products for the treatment of benign prostatic hyperplasia. C. J. G. also owns stock in Amgen and Genentech.
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