In the present study, we have demonstrated that the relationship between T and the inflammatory markers (CRP and FER) is not independent of BMI, which suggests that this association is conditioned by body fat (Table 3). Bivariate correlations between age and inflammatory markers, lipid profile, and androgen profile and between BMI and inflammatory markers, lipid profile, and androgen profile. Simultaneously, age and BMI correlated positively with most of the inflammatory markers (CRP, AAG, FER, and IL-6) and the lipid profile variables (TC, LDL, non-HDL, and TG) and negatively with the androgen profile parameters (T, fT, and fT/C ratio) and HDL concentration. A direct association between BMI and hsCRP was observed across demographic variables such as age, sex, ethnicity, and education. Further evidence comes from studies involving individuals with schizophrenia, where BMI and hsCRP have been linked to abnormal lipid profiles (25). Among overweight or obese individuals and smokers, those who were constantly active also had a lower likelihood of elevated hsCRP levels compared to their physically inactive peers. BMI, body mass index; T, testosterone; fT, free testosterone; fT/C, free testosterone-to-cortisol ratio; CRP, C-reactive protein; AAG, alpha-1-acid glycoprotein; FER, ferritin; IL-6, interleukin-6; LDL, low-density lipoprotein; HDL, high-density lipoprotein; TG, triglycerides; β, standardized beta coefficient; p, significance value; aR2, adjusted coefficient of determination. The associations between fT and fT/C ratio and IL-6 concentration observed in the bivariate analysis (Figure 2) were no longer significant when controlling for other covariates (age, lipid profile, and BMI) (see Table 3). However, when adjustment for BMI was made (model 3), these associations stayed significant only for the androgen profile variables and the AAG concentrations (see Table 3). BMI, body mass index; CRP, C-reactive protein; AAG, alpha-1-acid glycoprotein; FER, ferritin; IL-6, interleukin-6; TC, total cholesterol; LDL, low-density lipoprotein; HDL, high-density lipoprotein; non-HDL, non-high-density lipoprotein; TG, triglycerides; T, testosterone; fT, free testosterone; fT/C, free testosterone-to-cortisol ratio. The only exceptions were a non-significant correlation between age and the AAG concentration and between age and the HDL concentration (see Table 2). In this study, the bivariate correlations were evaluated using Spearman’s correlation coefficient because of the non-normal distribution of the inflammatory and lipid profile variables and the time spent on physical activity. We wanted to verify the hypothesis that a higher androgen status is related to a better inflammatory profile independently of confounders such as age, BMI, and lipid profile. This concept has a strong scientific foundation since androgens have been shown to regulate the inflammatory response (6) by suppressing pro-inflammatory leukotriene biosynthesis (7), decreasing pro-inflammatory mediators, and increasing anti-inflammatory cytokines, leading to a state of reduced inflammation (8). We have concluded that a lowered serum T concentration may promote inflammatory processes independently of adipose tissue and age through a reduced inhibition of inflammatory cytokine synthesis, which leads to enhanced acute phase protein production. The negative relationship between testosterone and inflammatory cytokines has been reported for decades, although the exact mechanisms of their interactions are still not clear. Moreover, only one subject presented with T and fT concentrations slightly below the healthy adult male reference ranges, but even in this case, a late-onset hypogonadism (LOH) syndrome was not diagnosed because there were no symptoms suggestive of testosterone deficiency see, e.g., (13). Blood for serum CRP, AAG, FER, IL-6, total cholesterol (TC), triglycerides (TG), low- and high-density lipoproteins (LDL and HDL, respectively), total T, cortisol (C), and sex hormone-binding globulin (SHBG) concentrations was collected into plain tubes and left to clot for a minimum of 30 min at room temperature and then centrifuged at 4,000 rpm for 5 min. Studies concerning the relationship between androgens and inflammation have so far mainly focused on the inflammatory cytokines such as interleukin-1 (IL-1), IL-6, and TNF-α (4). What is interesting is that a heavy exercise training program is thought to unfavorably affect the T concentration (18) and the pro- and anti-inflammatory balance (19), whereas moderate training loads were linked to both enhanced gonadal androgen concentrations (20) and anti-inflammatory state (21). The possible influence of body fat content on the relationship between androgen and inflammatory status also indicates that the level of physical activity could be of paramount importance in this connection. One may speculate that a moderately higher level of physical activity affects positively both the testosterone and HDL concentrations, however, recent data have indicated that a more important risk factor for cardiovascular events is HDL cholesterol efflux capacity (63), which could be influenced by gonadal androgens (64). Taking into account that we have reported a significant positive correlation between the AAG concentration and BMI see Table 2 and "Results" in (11), one may suggest that a higher body fat stimulates AAG production by hepatocytes through the secretion of pro-inflammatory cytokines, mainly TNF-α and IL-6. The negative relationship between T concentration and fat mass has often been demonstrated (31, 32). The significant bivariate correlations between BMI and the markers of both androgen and inflammatory profiles (see Table 2) support such conclusions.
