Abstract
Objective: To investigate the relationship of testosterone and different glucose tolerance state, and its association with osteocalcin.
Methods: A cross-sectional study was conducted of 1176 males aged 60–97 years who were arranged for an annual regular checkup from March to May 2012 in Chinese PLA general hospital in Beijing.
Results: Individuals categorized as having prediabetes or diabetes were more likely to have lower osteocalcin, testosterone, and SHBG levels compared to those with normal glucose tolerance (p < .05 in males). In aging males, after adjusting for age, the negative association between osteocalcin and BMI, waist circumference, FPG, 2hPBG, or TG were significant. And serum TT was negatively associated with BMI, waist circumference, FPG, 2hPBG, or TG independent of age, ALP, Ca, P, VitD, and PTH.
Conclusions: It showed that serum osteocalcin and TT were closely related with BMI, blood glucose, and TG, which supported the hypothesis that regulation of bone remodeling, energy metabolism, and reproduction are linked.
Introduction
With the progressive aging of the world’s populations, the incidence of type 2 diabetes mellitus and pre-diabetes is rapidly increasing. Both cross-sectional and longitudinal studies have shown declines in testosterone levels with normal aging in men [Citation1,Citation2]. Epidemiological data suggest that low testosterone levels are linked with many age-related clinical findings and diseases, such as diabetes [Citation3], osteoporosis [Citation4], obesity [Citation5], hypertension [Citation6] and frailty [Citation7], dyslipidemia. There is a bidirectional relationship between testosterone and metabolic dysfunction. The impact of low testosterone on the progressive stages of diabetes has drawn interest. There is emerging evidence that testosterone therapy may ameliorate some of the age-related symptoms and signs in men over 50 years of age [Citation8].
Osteocalcin, which is produced by osteoblasts, is detectable in the circulation and is serving as a well-known marker of bone formation. Recent studies indicate that osteocalcin has extended roles in the regulation of whole body metabolism and reproduction. Osteocalcin can increase insulin production and secretion. Bone is a positive regulator of male fertility, and osteoblasts can enhance testosterone production by Leydig cells [Citation9].
Many studies support the hypothesis that regulation of bone remodeling, energy metabolism, and reproduction are linked [Citation9–11]. The relationship of estosterone and different glucose tolerance state, and its association with osteocalcin remains unclear. In this study, we analyzed the association among testosterone, osteocalcin, and different glucose tolerance state in aging male.
Methods
Ethics statement
This study was conducted according to the guidelines laid down in the Declaration of Helsinki and all procedures involving human subjects were approved by the ethics committee of Chinese PLA General Hospital. Written informed consent was obtained from all subjects.
Subjects
A cross-sectional study was conducted of 1176 males aged 60–97 years who were arranged for an annual regular checkup from March to May 2012 in Chinese PLA general hospital in Beijing. Participants were excluded if they received glucocorticoid, sex steroids, other androgen-related drugs, or anti-osteoporosis agents within one year, had severe liver or kidney insufficiency, or had overt hyperparathyroidism.
Assessments
A standard questionnaire was used by trained interviewers to collect information on age, sex, smoking, alcohol drinking and self-reported diabetes, hypertension, and dyslipidemia. Resting blood pressure was measured. Anthropometric measurements such as weight, height, and waist circumference were also taken. Body height was measured to the nearest 0.5 cm and body weight to the nearest 0.1 kg. The waist circumferences were measured with a circumference measurement tape. The waist was defined as the point midway between the iliac crest and the costal margin (lower rib). All measurements were conducted by trained staff.
Biochemistry
All biochemical analysis was conducted by the Clinical Diagnostic Laboratory of the Chinese PLA general hospital. Analyses for total cholesterol (TC), high density lipoprotein cholesterol (HDL-c), low density lipoprotein cholesterol (LDL-c) and triglycerides (TG) were performed using commercially available enzymatic methods. Blood glucose was measured using standard hexokinase enzymatic assays. Luteinizing hormone (LH), follicle stimulating hormone (FSH), total testosterone (TT) and estradiol (E2) were measured using chemiluminescence immune assays (ACS:180, Bayer). Sex hormone binding globulin (SHBG) was analyzed using ELISA. Parathyroid hormone (PTH), serum 25-hydroxyvitamin D [25(OH)D], osteocalcin, β-crosslinked C-telopeptide of type l collagen (CTX), and N-terminal procollagen of type l collagen (P1NP) were measured using an automated Roche electro-chemiluminescence system (Roche Diagnostic Gmbh, Germany). All of the intra- and inter-assay coefficients of variation were <10%. 75 g oral glucose tolerance test (OGTT) was administrated. Impaired glucose regulation (IGR) was diagnosed according to the American Diabetes Association (ADA) criteria of 2003 (The expert committee on the diagnosis and classification of diabetes mellitus, 2003).
Data analysis
Data were entered and analyzed using SPSS for Windows version 19.0 (Somers, NY). Categorical variables were presented as frequencies and percentages while quantitative variables were presented as mean ± standard deviation (SD) or 95% CI where appropriate. Differences between groups were analyzed using one way analysis of variance or independent samples t-test for continuous data and Chi-square test for categorical data. Spearman correlation analysis was performed between each one of osteocalcin, testosterone or SHBG and the other factors. Multivariate Linear regression analysis was performed to determine the associations between serum osteocalcin and body mass index (BMI), waist circumference, fasting plasma glucose (FPG), 2 h postprandial blood glucose (2hPBG), systolic blood pressure (SBP), diastolic blood pressure (DBP), TC, TG, HDL-c, and LDL-c, model 1 is adjusted for age and model 2 is adjusted for age, ALP, serum calcium (Ca), phosphate (P), alkaline phosphatase (ALP), VitD, and PTH. All p values were two-tailed, and p values <.05 were considered to indicate statistical significance.
Results
The clinical and laboratory characteristics of study participants are shown in . With the deterioration of glucose tolerance status, age, waist circumference, SBP, TG, serum calcium level, LH and FSH increased significantly (p < .05). Individuals categorized as having prediabetes or diabetes were more likely to have lower osteocalcin, testosterone, and SHBG levels compared to those with normal glucose tolerance (p < .05 in males) ().
Table 1. Characteristics of the study population by glucose tolerance status.
According to their serum TT concentration, the study subjects were divided into quartiles (). BMI, waist circumference, SBP, DBP, TG, FPG, 2hPBG, PINP, LH, and FSH varied inversely with the TT quartiles (p < .05). With the increasing of TT, osteocalcin, HDL-c, 25(OH)D, E2 and SHBG increased significantly (p < .05). There were no significant differences in the serum Ca, P, ALP, PTH, TC, or CTX according to the quartiles of TT.
Table 2. Characteristics of the study population by TT quartiles.
The correlation analysis among the studied variables
A correlation analysis was performed to assess the associations among the studied variables. The association between serum TT, osteocalcin or SHBG and other parameters were shown in . Serum osteocalcin was negatively associated with BMI, waist circumference, FPG, 2hPBG, and TG (p < .05). Serum TT was negatively associated with BMI, waist circumference, SBP, DBP, FPG, 2hPBG, and TG (p < .05). SHBG was negatively associated with BMI, waist circumference, DBP, FPG, and TG (p < .05). HDL-c was positively associated with serum osteocalcin, TT, and SHBG (p < .05). Serum osteocalcin was positively related with TT and SHBG (p < .01).
Table 3. Spearman’s correlation coefficients among the studied variables.
Multiple linear regression analysis was conducted to determine the association between osteocalcin with other variables. It showed that BMI, waist circumference, FPG, 2hPBG, TG, were inversely and significantly associated with serum osteocalcin level after adjustment for age. There was also a positive and significant association between HDL-c and serum osteocalcin. After adjustment for age, ALP, Ca, P, VitD, and PTH, the significance of the association still exist (p < .05) (). This suggested that the association between serum osteocalcin and these variables were independent of age, ALP, Ca, P, VitD, and PTH.
Table 4. Linear regression results on the association between the variables studied and serum osteocalcin.
When serum TT was analyzed as an independent predictor, multiple linear regression analysis demonstrates the association between serum TT and other variables were similar with the association between osteocalcin and those variables ().
Table 5. Linear regression results on the association between the variables studied and serum testosterone.
Discussion
Accumulating data have shown that low serum testosterone level is strongly associated with an increased likelihood of type 2 diabetes, and low SHBG and testosterone may constitute part of the prediabetic state in men [Citation12–16]. The present study demonstrated that in aging males, with the deterioration of glucose tolerance status, serum TT decreased significantly. Experimental studies showed that androgen receptor knockout mice developed significant insulin resistance [Citation17]. Testosterone treatment could decrease insulin resistance by increasing the number of beta-adrenoceptors and lipolysis in male rat adipocytes [Citation18]. Testosterone supplementation inhibits triglyceride uptake and lipoprotein lipase activity and causes a more rapid turnover of triglycerides in the subcutaneous abdominal adipose tissue in vivo in men [Citation19]. In the present study, we found that with the increasing of serum TT level, TG decreased significantly.
Recently, a 9-year follow up among elderly men in Finland showed that higher levels of testosterone and free testosterone independently predicted a reduced risk of type 2 diabetes [Citation20], whereas low testosterone is an independent risk factor for high fasting blood glucose, comparable to aging and obesity [Citation14,Citation21]. Serum testosterone improves insulin resistance by changing body composition and reducing body fat. However, obesity might also alter the metabolism of testosterone. In our study, we found that serum TT was negatively associated with BMI and waist circumference.
Besides its associations with diabetes and obesity, low serum testosterone level was also associated with high blood pressure. Our study showed that serum TT was also negatively associated with SBP and DBP. A clinical study of hypogonadal men with metabolic syndrome and type 2 diabetes showed that transdermal testosterone administration improved insulin sensitivity and reduced blood pressure [Citation22].
In the present study, with the deterioration of glucose tolerance status, serum osteocalcin decreased accordingly. This maybe the result of a deficient osteoblastic function in diabetes mellitus [Citation23]. This was also in agreement with many other studies, which also found that serum osteocalcin concentration was significantly lower in patients with diabetes mellitus than in healthy individuals [Citation24,Citation25].
Our study found that with the deterioration of glucose tolerance status, the change pattern of serum osteocalcin and serum TT was quite similar, and further analysis showed that serum osteocalcin was positively related with TT and SHBG in aging males. The association between osteocalcin and testosterone levels has been demonstrated in some studies.
In a cross-sectional study of 69 Japanese men with type 2 diabetes mellitus, the authors suggest for the first time that undercarboxylated osteocalcin (ucOC) is associated positively with free testosterone (FT) and negatively with LH [Citation26]. In another study of 91 Caucasian men, it showed that overweight and obese patients had lower total and FT, associated with lower ucOCN [Citation27]. Bone is a positive regulator of male fertility, and this interaction is mediated through osteocalcin, which binds to a specific receptor present on Leydig cells of the testis and favors testosterone biosynthesis [Citation9]. Our results support the hypothesis that regulation of bone remodeling, energy metabolism, and reproduction are linked.
In this population-based study, we analyzed the independent impact of serum osteocalcin or TT on different studied variables. In aging males, after adjusting for age, the negative association between osteocalcin and BMI, waist circumference, FPG, 2hPBG, or TG was significant. After further adjusting for ALP, Ca, P, VitD, and PTH, the association still exists. The present study also showed that serum TT was negatively associated with BMI, waist circumference, FPG, 2hPBG or TG independent of age, ALP, Ca, P, VitD and PTH. We suggest that low serum osteocalcin and TT are possible mechanism for the association of bone remodeling, energy metabolism, and reproduction.
Disclosure statement
No potential conflict of interest was reported by the authors.
Additional information
Funding
References
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