|Year : 2017 | Volume
| Issue : 3 | Page : 178-184
Serum testosterone and insulin resistance in type 2 male diabetics attending University of Calabar teaching hospital, Nigeria
Ayu Agbecha1, Chinyere AO Usoro2
1 Department of Chemical Pathology, Federal Medical Centre, Makurdi, Nigeria
2 Department of Medical Laboratory Science, Chemical Pathology Unit, University of Calabar, Calabar, Nigeria
|Date of Web Publication||17-Aug-2017|
Department of Chemical Pathology, Federal Medical Centre, Makurdi
Source of Support: None, Conflict of Interest: None
Background of Study: Besides reproductive and sexual function, testosterone is reported to regulate metabolism, cardiovascular health, body composition, and enhancement cognitive function.
Objective: The aim is to determine the impact of type 2 diabetes mellitus (T2DM) on serum testosterone, in a relationship with insulin resistance in men.
Materials and Methods: This was a case-control study comprised 63 male type 2 diabetics (T2Ds) and sixty anthropometrically matched nondiabetic controls that fulfilled the inclusion criteria. Type 2 diabetes was diagnosed based on history and the WHO criteria.
Results: There was a significantly lowered testosterone (P = 1 × 10-13) in the diabetics compared to the matched controls. A significantly elevated (P < 0.0005) fasting plasma glucose (FPG), glycated hemoglobin (HbA1c), and (P = 0.015) homeostatic model assessment of insulin resistance (HOMA IR) was observed in the diabetics compared with the matched controls. A significantly elevated (P = 0.001) testosterone and lowered (P = 0.009) HOMA-IR was observed in diabetics with good glycemic control compared to poor glycemic control. There was a significant (P < 0.05) inverse correlation (r = –0.421) between testosterone and connecting peptide (C peptide), testosterone and HOMA IR (r = –0.396), testosterone and HbA1c (r = –0.402), testosterone and FPG (r = –0.270) in male T2Ds.
Conclusions: In this study, the low testosterone observed is a consequence of T2DM. Testosterone production seems to be impaired by elevated insulin that accompanies insulin resistance. Normalization of testosterone in controlled diabetes points at diabetic control instead of testosterone replacement therapy in the management of hypogonadism in male T2Ds.
Keywords: Connecting peptide, diabetes, insulin resistance, testosterone
|How to cite this article:|
Agbecha A, Usoro CA. Serum testosterone and insulin resistance in type 2 male diabetics attending University of Calabar teaching hospital, Nigeria. J Med Soc 2017;31:178-84
|How to cite this URL:|
Agbecha A, Usoro CA. Serum testosterone and insulin resistance in type 2 male diabetics attending University of Calabar teaching hospital, Nigeria. J Med Soc [serial online] 2017 [cited 2019 Dec 5];31:178-84. Available from: http://www.jmedsoc.org/text.asp?2017/31/3/178/211106
| Introduction|| |
Diabetes is a growing epidemic, with 328 million people worldwide having the disease, with this number expected to increase to 592 million by the year 2035. Insulin resistance defined as impaired action of insulin in its target organs has been shown to be the mediator of type 2 diabetes mellitus (T2DM).
Principally testosterone is a hormone that enhances reproduction and sexual function. In mammals, testosterone is primarily biosynthesized by the Leydig cells of the testes and regulated through the hypothalamic–pituitary–gonadal (HPG) axis. Small amounts of this androgen are also produced by the adrenal cortex and the ovaries. Testosterone is reported to regulate body composition, enhancement of cognitive function, and cardiovascular health. The metabolic role of testosterone is supported by the association of low testosterone with components of the metabolic syndrome.
Observational studies consistently show that men with type 2 diabetes independent of age and obesity have lowered circulating testosterone levels., In a prospective study, the metabolic syndrome is reported to predict low testosterone. The American Diabetes Association reported a general increase in insulin resistance in patients with type 2 diabetes who have low total testosterone levels compared to type 2 diabetic (T2D) patients with normal total testosterone levels. A cross-sectional study revealed an inverse relationship between testosterone and fasting insulin levels in men independent of age, obesity, and body fat distribution. Another cross-sectional study showed that diabetic men had not only lower testosterone but also lower levels sex hormone-binding globulin (SHBG) when compared with nondiabetic men. Two studies demonstrated a positive relationship between total testosterone levels and insulin sensitivity in normal and diabetic men. Population studies have shown that reduced level of serum testosterone is an independent risk factor for diabetes, metabolic syndrome, poor quality of life, and an overall increase in mortality in men.
The relationship pattern between low testosterone and T2DM seems to be bidirectional, either low testosterone occurring as a consequence of T2DM or a risk factor of T2DM. The present study aims at determining the impact of T2DM on serum testosterone level, in a relationship with insulin resistance. This is the first study of serum testosterone level and its relationship with insulin resistance in male T2Ds in Calabar and South-South Nigeria.
| Materials and Methods|| |
This case–control study was carried out in the Department of Chemical Pathology, of a teaching hospital. Ethical clearance was sought and obtained from the ethical board of the teaching hospital to allow the participation of type 2 male diabetics attending the diabetic clinic.
Selection of subjects
The sample size was determined using the OpenEpi version 3.0.1 sample size calculator, developed by Dean et al., for open source Epidemiologic Statistics for Public Health. Thereafter, 63 male T2Ds and sixty male nondiabetics who fulfilled the inclusion criteria between March 2015 and May 2015 were selected for the study. The inclusion criteria for the test group comprised male T2D patients aged between 35 and 70 years attending the diabetic clinic that fulfilled the WHO criteria of diagnosing type 2 diabetes. This WHO criterion includes a fasting plasma glucose (FPG) levels >7.0 mmol/L on two or more occasions or a 2 h postprandial plasma glucose levels >11.1 mmol/L on two or more occasions. Inclusion criteria for the control group comprised sixty apparently healthy male nondiabetic individuals with anthropometric indices (blood pressure [BP], body mass index [BMI], waist circumference [WC], and age) matched with those of the diabetic test group. The exclusion criteria comprised patients with endocrine disorders other than type 2 diabetes, patients on testosterone replacement therapy, HIV/AIDS patients, patients with malignancy, and those unwilling to participate in the study were excluded from the study. A written informed consent was obtained from the participants by educating them on the need and relevance of the study. The participant's medical history was obtained by a clinician, followed by administration, answering and return of a structured questionnaire regarding lifestyle, treatments, sociodemographic, and personal data. Anthropometric parameters such as weight, height, WC, and BP were obtained by a research scientist after the patients were comfortably seated.
Fasting venous blood samples were collected from both diabetic patients and nondiabetic controls. Six milliliters of blood was drawn from each participant aseptically and dispensed as follows; a volume of 2 ml of whole blood into fluoride oxalate bottles and plasma extracted was used for estimation of FPG. Two milliliters of whole blood into ethylenediaminetetraacetic acid bottles for the estimation of glycated hemoglobin (HbA1c). Two milliliters of the whole blood was dispensed into plain tubes and centrifuged after clot retraction. The serum was extracted aseptically and stored at −20°C for estimation of serum connecting peptide (C-peptide) and testosterone.
The Emax microplate reader manufactured by Molecular Devices, Sunnyvale, USA, was used for immunoassay of testosterone and C-peptide, whereas a spectrophotometer OPTIMA SP 300 manufactured by OPTIMA Inc., Tokyo, Japan, was used for other biochemical analyses. The determination of HbA1c was based on Trivelli et al., column chromatographic cation exchange resin method. Barham and Trinder glucose oxidase method was used in the determination of plasma glucose. C-peptide was determined using the quantitative solid phase sandwich enzyme immunoassay method. The competitive binding enzyme immunoassay method was used in determining testosterone. Intra and inter-assay of low, normal, and high-concentrated control samples were used in the assessment of the accuracy of the test methods. Insulin resistance was determined using a standardized Microsoft Excel HOMA 2 calculator, using FPG and serum C-peptide values.
The IBM, Armonk, New York, USA, Statistical package for the social sciences version 21 was used in analyzing the data generated. Descriptive statistics were used in determining the means and standard deviations of the parameters measured. The Student's t-test was used in comparing the means of parameters in T2DM and control groups. Pearson correlation analyses were used to determine the association between parameters measured in the T2DM patients. A two-tailed P < 0.05 was indicative of statistical significance.
| Results|| |
[Table 1] shows the BP, age, WC, BMI, testosterone, C-peptide, and homeostatic model assessment of insulin resistance (HOMA-IR), FPG, and HbA1c. There was no significant (P > 0.05) difference between the mean systolic BP, diastolic BP, age, WC, and BMI of diabetic and control subjects. There was a significantly lowered testosterone (P = 1× 10-13) in the diabetics compared to the matched controls. A significantly elevated (P = 0.02) FPG, HbA1c, and HOMA-IR was observed in the diabetics compared with the matched controls. A higher but no significant difference in C-peptide level was found in the diabetics compared with the controls. [Table 2] shows serum testosterone and HOMA-IR of good glycemic and poor glycemic-controlled diabetics. There was a significantly elevated (P = 0.001) testosterone and lowered (P = 0.009) HOMA-IR observed in diabetics with good glycemic control compared to poor glycemic control. [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], respectively, show the correlation between testosterone and C-peptide, testosterone and HOMA-IR, testosterone and HbA1c, testosterone and FPG, testosterone and age in male T2Ds. There was a significant (P = 0.001) inverse correlation between testosterone and C-peptide (r = −0.421), testosterone and HOMA-IR (r = −0.396), testosterone and HbA1c (r = −0.402), and testosterone and FPG (r = −0.270, P = 0.032) in male T2Ds. There was no significant (r = −0.079, P = 0.540) correlation between testosterone and age in male T2Ds.
|Table 1: Comparison of blood pressure, anthropometric parameters, testosterone, C-peptide, homeostatic model assessment of insulin resistance, fasting plasma glucose, and glycated hemoglobin in diabetics and controls|
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|Table 2: Comparison of testosterone, homeostatic model assessment of insulin resistance in good and poor glycemic diabetics|
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|Figure 1: Correlation of testosterone with connecting peptide in diabetic patients|
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|Figure 2: Correlation of testosterone with homeostatic model assessment of insulin resistance in diabetic patients|
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|Figure 3: Correlation of testosterone with glycated hemoglobin in diabetic patients|
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|Figure 4: Correlation of testosterone with fasting plasma glucose in diabetic patients|
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| Discussion|| |
The morbidity associated with T2DM is more disabling than the disease itself. Thus, the relationship between testosterone and diabetes is an important issue, given the fact that diabetes is becoming a fast-growing epidemic. Various studies have reported the increasing prevalence of hypogonadism in male T2D patients. However, it remains a dilemma whether low testosterone levels are a cause or a consequence of T2DM. A number of epidemiological studies have suggested an association of low serum testosterone with poor quality of life in type 2 diabetes. The study and several other studies adopted the measurement of C-peptide in place of the traditional insulin as a surrogate marker of insulin resistance due to its advantages of a relatively longer plasma half-life and noncross-reactivity with exogenous insulin during assays. In a bid to eliminate confounding factors of hypotestosteronemia, this study matched BP, age, BMI, and WC of male diabetics with those of nondiabetics. We took into cognizance the physiological effect of age on testosterone regarding the independence of our findings on age.
Our study observed low testosterone level in male T2Ds compared to nondiabetics. The results are consistent with the findings of Grossmann et al., Stanworth and Jones, and Svartberg et al., who also found low testosterone levels in T2D males compared to the nondiabetic male controls.,, This present study observed an inverse correlation between testosterone and C-peptide, testosterone and HOMA-IR, testosterone and HbA1c, and testosterone and FPG. The nonsignificant inverse correlation observed between testosterone and age in our diabetic patients rules out the possibility of a physiological influence of advanced age on testosterone reduction. The correlation result of our study is consistent with that of Tsai et al., who also observed an inverse relationship between testosterone and C-peptide in T2Ds. An inverse correlation was observed between testosterone and insulin levels independent of age, obesity, and body fat distribution., Grossmann et al., Andersson et al., and Tsai et al. reported an inverse correlation between testosterone level and insulin resistance.,, Our correlation results are consistent with the works of Brand et al., and Svartberg et al., who also showed an inverse relationship between testosterone and HbA1c., Our study found low testosterone and high c-peptide level in poorly controlled diabetics compared with well-controlled diabetics. This finding agrees with that of Kapoor et al., who also observed low testosterone in poorly controlled diabetics. The low C-peptide observed in this study agrees with Park et al., and Lindmark et al., who reported decreased fasting C-peptide level in T2Ds with good glycemic control compared to diabetic patients with poor glycemic control and nondiabetic subjects., Grossmann et al. observed that improved lifestyle factors or altered pharmacological management improved insulin sensitivity in T2DM.
Testosterone production pattern could be affected by the functional changes in the Leydig cell either directly on the testis or through changes along the HPG axis. SHBG, a major transporter of sex steroids, could be implicated in the bioavailability of this androgen. The exact mechanism by which type 2 diabetes impairs testosterone biosynthesis remains poorly understood. Pro-inflammatory cytokines, estradiol, leptin, and insulin elevated in T2DM independent of obesity may inhibit the activity of the HPG axis at multiple levels. Leydig cell testosterone biosynthesis is primarily regulated by pulsatile secretion of luteinizing hormone (LH). Compelling evidence exists that Leydig cell steroidogenesis is further modulated locally by circulating hormones, growth factors, and cytokines. Therefore, it is possible that increased insulin resistance or hyperglycemia may result in reduced testosterone biogenesis due to decreased central stimulation. Serum testosterone levels reflect the integrity of the HPG axis, and low testosterone levels noted in cases of insulin resistance may indicate a defect at one or more functional levels of the HPG axis. In the insulin-resistant state, Leydig cell function may be impaired, particularly steroidogenesis, by changes in the production of hormones and cytokines. It is not fully clear how the HPG axis mediates the relationship between testosterone and insulin levels. Several observations have suggested that a relationship exists between insulin/glucose and LH/follicle-stimulating hormone (FSH) levels. Diabetic men often have reduced serum levels of FSH, LH, prolactin, and growth hormone consistent with secondary hypogonadism.
Pro-inflammatory cytokines have been shown to be elevated in T2DM. Hong et al. proposed that tumor necrosis factor (TNF)-α inhibits steroid biosynthesis in Leydig cells and proposed a molecular mechanism by which pro-inflammatory factors can contribute to the inhibition of androgen biosynthesis. TNF-α and interleukin-6 suppress hypothalamic production of a gonadotropin-releasing hormone that leads to decreased release of LH and FSH from the pituitary, hence leading to decreased gonadal stimulation. This could lead to decreased testosterone release, causing a state of hypogonadotropic hypogonadism.
Leptin production is tightly coupled to insulin resistance and may play a key role in steroid-biogenesis and reduced testosterone levels. The expression of leptin receptors in Leydig cells and the inhibition of testosterone secretion from rat Leydig cells by leptin suggest a role of this hormone in the biogenesis of testosterone. Leptin levels have been shown to be inversely correlated with serum testosterone levels, with increased circulating leptin proposed to be involved in the pathogenesis of Leydig cell dysfunction.
The previous research has demonstrated that hepatic production of SHBG is downregulated by insulin. SHBG, in turn, has been shown to influence the bioavailability of testosterone. Thus, low testosterone levels observed in T2DM could be as a result of hepatic impairment of SHBG synthesis induced by elevated insulin. Fasting insulin and insulin resistance were also found to be negatively associated with SHBG and testosterone in nondiabetic adult men.
Conditions associated with altered systemic insulin levels such as type 1 and type 2 diabetes have been shown to affect SHBG and testosterone metabolism., Observations of normal testosterone levels in type 1 diabetics usually with subnormal or deficient insulin confirm the negative effect of hyperinsulinemia in testosterone metabolism. Chandel et al. observed a normal testosterone level in type 1 diabetics compared to low testosterone level in T2Ds. Comparing the testosterone levels of type 1 diabetics and nondiabetics revealed higher testosterone in type 1 diabetic group.
Estradiol has been shown to be inversely associated with gonadotropins and testosterone levels. In the meta-analysis of Ding et al., estradiol levels were significantly higher in men with diabetes compared with nondiabetic controls, even after adjustment for BMI. The positive association of estradiol with diabetes has been confirmed in a cross-sectional and prospective study which remained significant after multivariate adjustment including WC.
| Conclusions|| |
The low testosterone observed in this study is a consequence of T2DM. The low testosterone seems to be caused by impairment of testosterone production by elevated insulin in the face of insulin resistance. The testosterone results obtained were independent of the physiologic influences of age but solely dependent on T2D disease. The effect of insulin resistance on testosterone metabolism was evidenced by normalization of testosterone in controlled diabetes. This study is limited in sample size and calls for a larger sample size in further observational studies. We encourage diabetic control instead of testosterone replacement therapy in the management of hypogonadism in male T2Ds.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2]