A scatterplot presenting the association between baseline CRP and calculated bioavailable testosterone (A) and SHBG (B) at both visits. A constant and significant decrease in bioavailable testosterone was observed with increasing age, as well as increase of SHBG with age. Evaluation of the association between logCRP and testosterone was made through cross-sectional linear regression both at the first visit and in the longitudinal analyses. As measurement techniques changed during follow-up time, we compared similar age groups at both baseline and follow-up in order to estimate the change in concentration due to method change. Participants who did not participate in the second visit or had missing information on anthropometric measures, testosterone levels, sex hormone-binding globulin (SHBG), smoking, hypertension, leisure-time physical activity (LTPA), or diabetes were excluded, leaving a remainder of 641 men. The focus of this cohort study was the detection of early cardiometabolic disorders, and thus the age of participants ranged between 30 and 74, with oversampling of subjects between 30 and 50 years of age. This is a methodological challenge for all long-term observational studies investigating the changes in sex hormones. However, residual confounding cannot be excluded due to the observational nature of the study. This is a large cohort-based study of men, representative of the population in Sweden. This change in estimates was larger in the cross-sectional analyses than in the longitudinal ones (Table 3). In this prospective study, we observed a strong association between high levels of high-sensitive CRP and low concentrations of bioavailable testosterone in men in both cross-sectional and longitudinal analyses, independent of other relevant cardiometabolic and lifestyle factors. In conclusion, our study confirms an independent association between high levels of hsCRP and low bioavailable testosterone concentrations 10 years later, independent of cardiometabolic and lifestyle factors as well as baseline concentrations. Similarly, a cross-sectional study by Tsilidis et al., including data from the NHANES population (809 participants), found that men with low testosterone were at higher risk of having high CRP independent of total body weight, age, medication, or other comorbidities (23). In the BACH study (1559 male participants), a significant association was found between CRP and both total and free testosterone levels independent of age, obesity, and comorbidities (25). To the best of our knowledge, no study has earlier presented data confirming a longitudinal association between inflammation at baseline and a decrease in both levels of cBT and TT, defined as biochemical hypogonadism. However, when participants with biochemical hypogonadism at baseline were excluded, a total of 38 men (6.4%) were found to develop low testosterone levels during the observation period. Levels of TT remained almost constant until the age of 50, after which they declined somewhat more slowly compared to the decrease in cBT (Fig. 2A and B). Mean age at the first visit was 49.2 ± 11.6 and 58.9 ± 11.8 years at the second visit (Table 1). Testosterone was set as the dependent variable (TT and calculated bioavailable testosterone (cBT)) with logCRP as the independent variable. Characteristics of the study population were assessed using descriptive statistics to calculate means and confidence intervals. Calculation of bioavailable testosterone was done using the formula according to Vermuelen et al. (18). Blood pressure was measured in the supine position after 5 min of rest at baseline and follow-up. Non-fasting blood samples were collected close to waking time (median time since awakening 3 h 38 min) to control for diurnal variation in hormone levels. Interviews were completed with 63.3% of eligible subjects, resulting in a total sample of 5504 adults (2301 men, 3203 women, 1767 Black, 1877 Hispanic, 1859 White respondents). Detailed methods have been described elsewhere.9 In brief, BACH used a multi-stage stratified random sample to recruit approximately equal numbers of subjects according to age (30–39, 40–49, 50–59, 60–79 years), gender, and race/ethnic group (African American (Black), Hispanic, and Caucasian (White)). The BACH survey is a population-based epidemiologic survey of a broad range of urologic symptoms and risk factors in a randomly selected sample. A positive trend between estradiol (total and free) and CRP levels was not statistically significant. Over half of the analysis sample reported use of anti-inflammatory or other medications that could affect CRP levels. Analyses were conducted on a sample of 1,559 men with complete data on sex hormones and CRP. Serum testosterone (T) and sex hormone-binding globulin (SHBG) levels were measured by competitive electrochemiluminescence immunoassays on the 2010 Elecsys system (Roche Diagnostics, Indianapolis, IN). A robust, inverse dose-response correlation between testosterone and SHBG levels with CRP levels provides further evidence of a potential role of androgens in inflammatory processes. The association between CRP and sex hormone levels was assessed using multiple linear regression models. In contrast, a slight trend in increased CRP was observed with increasing E2 and FE2 levels. These figures show an inverse association of CRP levels with both TT and SHBG. Figure 1 presents scatterplots of CRP against sex hormone levels (TT, SHBG, and E2). Descriptive statistics for sex hormones and C-reactive protein (CRP) levels. Characteristics of the men included in the analysis are presented in Table 1 and descriptive statistics on sex hormones and CRP levels are included in Table 2. Multiple linear regression models were used to assess the association between sex hormones and CRP and to adjust for potential confounders. This antigen-antibody complex causes an increase in light scattering, which is detected spectrophotometrically, with the magnitude of the change being proportional to the concentration of CRP in the sample. However, comparison of sociodemographic and health-related variables from BACH with other large regional (Boston Behavioral Risk Factor Surveillance System) and national (National Health Interview Survey) surveys have shown that the BACH estimates are comparable to national trends on key health related variables. History of comorbid conditions was assessed by self-report with the potential for reporting and/or recall bias; however, previous research has demonstrated the reliability and validity of self-report for heart disease, diabetes, and hypertension.30 The BACH study was limited geographically to the Boston area. However, a full analysis of the potential influence of medication use in general on CRP levels is beyond the scope of this paper. Thus, we cannot exclude the alternative hypothesis that low androgen levels may be a consequence of inflammation. These associations remained statistically significant after adjusting for age, body mass index (BMI), comorbid conditions, and lifestyle factors. A multistage stratified design was used to recruit a random sample of 2,301 racially and ethnically diverse men age 30–79 years. Low-grade inflammation may be involved in the pathogenesis of subjective symptoms of androgen deficiency in ageing men.
