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Effects of testosterone replacement on glucose and lipid metabolism

Errazuriz, Isabel; Dube, Simmi; Basu, Ananda; Basu, Rita

Cardiovascular Endocrinology & Metabolism: September 2015 - Volume 4 - Issue 3 - p 95–99
doi: 10.1097/XCE.0000000000000061
Invited reviews
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Testosterone levels have become a much more available and frequent screening test in clinical practice. There is greater awareness of testosterone deficiency symptoms both among the medical community and among the patients themselves. Several studies have described the effects of testosterone on carbohydrate and lipid metabolism and the disturbances that occur in patients with hypogonadism. However, whether testosterone replacement reverts such alterations is less clear. In this article, we review the effects of testosterone replacement therapy on glucose and lipid metabolism.

aDepartment of Medicine, University of Desorralo, Santiago, Chile

bGandhi Medical College, Bhopal, MP, India

cEndocrine Research Unit, Division of Endocrinology, Diabetes, Metabolism, and Nutrition, Mayo College of Medicine, Rochester, Minnisota, USA

Correspondence to Rita Basu, MD, Medicine, Endocrine Research Unit, Division of Endocrinology, Diabetes, Metabolism, and Nutrition, Mayo College of Medicine, Joseph 5-194, Rochester, MN 55905, USA Tel: +1 507 255 4230; fax: +1 507 255 4828; e-mail: basu.rita@mayo.edu

Received May 6, 2015

Accepted July 1, 2015

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Introduction

Testosterone exerts various effects in different organs and it is involved in carbohydrate and fat metabolism. Testosterone concentrations decrease as men age, beginning at the fourth or the fifth decade of life 1,2. This decrease can be up to 2% per year in some cohorts 3,4. The actual prevalence of hypogonadism, defined as total testosterone less than 400 ng/dl, has been estimated to be 39% in men aged 45 years or older presenting to primary care offices in the USA 2.

With aging, glucose tolerance has also been shown to deteriorate 5,6 and, subsequently, the prevalence of type 2 diabetes mellitus (T2DM) increases as men grow older. The association of T2DM and low testosterone levels has long been described. T2DM has been proposed as a risk factor for hypogonadism in men because of a reduction in sex hormone-binding globulin levels induced by insulin resistance which, in turn, leads to a reduction in testosterone levels 7,8. It is estimated that 30–50% of men attending a diabetes clinic have low testosterone concentrations 4, being the highest among obese patients with T2DM 9. Furthermore, current guidelines published by the Endocrine Society in 2010 recommend measurement of morning total testosterone as an initial screening test for androgen deficiency in patients with T2DM 10.

Body composition is also affected by age. In the elderly, there is an increase in fat mass and BMI with redistribution of body fat and a decrease in bone mineral density, muscle mass, and muscle strength 11,12. Moreover, with age, an increase in the concentration of atherogenic LDL particles has been observed 13. These alterations have also been described in testosterone-deficient states 2. Various cross-sectional and prospective studies have reported that men with dyslipidemia have significantly lower levels of total testosterone and observed that testosterone is correlated positively with HDL and correlated negatively with total cholesterol, LDL, and triglycerides. 14–24. These observations of various investigators have led to speculations that the decrease in testosterone concentrations with age may cause or exacerbate abnormalities in lipid metabolism, contributing toward various metabolic and cardiovascular risks.

Testosterone replacement therapy (TRT) has, therefore, been proposed as a therapeutic approach to revert these metabolic disturbances.

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Effects of testosterone replacement therapy on glucose metabolism

Testosterone and development of type 2 diabetes mellitus

Epidemiological and clinical studies have supported the association between testosterone concentrations, insulin resistance, and T2DM. Furthermore, low testosterone concentrations have been shown to predict future risk of developing T2DM. Whether the association between testosterone and development of diabetes is dependent or not on BMI, weight, and visceral fat is less clear 4.

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Effects of testosterone replacement therapy on carbohydrate metabolism

In rats, testosterone replacement restores insulin action, increases islet insulin content, and enhances insulin secretion 25,26.

In humans, there is controversial evidence of the effects of testosterone on carbohydrate metabolism. Testosterone did not show any effect on insulin action in healthy young men 27. Centrally obese middle-aged men receiving testosterone showed an improvement in insulin sensitivity (by hyperinsulinemic/euglycemic clamp studies) and a lowering of serum insulin levels 28. Studies carried out by us and others, however, have shown that TRT, aiming at restoring physiological levels of testosterone in hypogonadal men, has no effect on glucose metabolism 29–31. Some of these differences may be partly explained by different study sample sizes, and different techniques and measurements as metabolic outcomes.

We conducted a 2-year placebo-controlled, randomized, double-blind trial in which men with relative testosterone deficiency underwent a mixed meal test and a frequently sampled intravenous glucose tolerance test before and after TRT or placebo. Fasting glucose, insulin, and C-peptide concentrations did not differ following 2 years of treatment with testosterone or placebo. Postprandial increments (i.e. area above basal) of glucose, insulin, and C-peptide concentrations also did not differ following treatment with testosterone or placebo. Fasting and postprandial glucose fluxes (endogenous glucose production, glucose disappearance, meal appearance) did not differ after treatment in either group (Fig. 1). Insulin action, glucose effectiveness, and hepatic insulin clearance measured with either the unlabeled oral or the unlabeled ‘oral’ or ‘intravenous’ glucose minimal models did not differ following 2 years of treatment with either testosterone or placebo. The change from basal in meal and intravenous glucose tolerance test insulin secretion indexes did not differ, which resulted in no difference in the change from baseline in either the meal or intravenous glucose disposition indexes in the testosterone and placebo groups 29.

Figure 1

Figure 1

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Testosterone replacement therapy in type 2 diabetes mellitus

The effects of TRT in patients with T2DM are just as controversial. There is evidence that testosterone can improve glycemic control, as measured by glycated hemoglobin, but study designs did not allow for body composition changes to be excluded as confounders 32,33. A recent systematic review and meta-analysis of five randomized-controlled trials on the metabolic effects of TRT on hypogonadal men with T2DM found that glycemic control was improved with testosterone. The meta-analysis for HbA1c% included 124 patients and found a mean decrease of 0.87% (P=0.0001) 7. The longest duration of testosterone intervention in these trials was 12 months and, as described previously, body composition changes were not taken into account when analyzing HbA1c difference.

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Effects of testosterone replacement therapy on body composition

Low levels of testosterone have long been associated with obesity 34–38. Testosterone affects body fat distribution. It has been shown that hypogonadal men store a greater proportion of both dietary fatty acids and free fatty acids (FFA) in lower body subcutaneous fat than eugonadal men 39. Moreover, weight reduction has been associated with increases in testosterone levels 37,40.

Some studies have proposed that TRT may reduce BMI and visceral fat in obese men 28,41–46. However, in a placebo-controlled, randomized, double-blind study carried out by our group, 2-year low-dose TRT in overweight men with low levels of bioavailable testosterone did not alter visceral or percentage body fat, although it resulted in a slight but statistically significant increase in fat-free mass 29,30. In contrast, a more recent double-blinded placebo-controlled study of men with metabolic syndrome and hypogonadism showed significant decreases in weight, BMI, and waist circumference following 30 weeks of testosterone replacement to the normal range 47.

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Effects of testosterone replacement therapy on fat metabolism

Lipid panel changes

Most of the studies investigating TRT in hypogonadal and eugonadal men have shown some beneficial effects on serum lipids. Significant reductions in total cholesterol and LDL were observed following TRT in hypogonadal men 48,49, with either a decrease 50 or an increase 33,44, or no change 32,51–54 in HDL cholesterol. The differences in these observations may be because of the differences in doses, routes of administration, and duration of TRT in these studies.

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Lipolysis

Testosterone supplementation in men has shown an increase in lipolysis and decrease in lipoprotein lipase activity and triglyceride turnover in abdominal fat, with no effect on femoral fat metabolism. These findings suggest a site-specific regulation of lipolysis following TRT, causing an increase in FFA concentrations 41,43,55. Freidreiksen et al.53 reported significant changes in body composition following TRT as a gel preparation, but did not observe significant changes in FFA concentrations. Moreover, following a 2-year patch-administered TRT, Koutsari et al.56 observed no change in post absorptive or whole-body lipolysis in elderly men. These differences in observations suggest that the route of testosterone administration for replacement therapy may play a role in the metabolic effects of TRT.

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Fat oxidation and storage

Studies have observed decreased fat oxidation in androgen-deprived elderly men with prostate cancer or post orchiectomy 48,57,58. Short-term TRT in men with testosterone deficiency because of hypopituitarism have shown stimulation of whole-body fat oxidation 59, which was also observed in healthy elderly men following TRT of 6 months. In contrast, Koutsari et al.56 observed no change in meal fat oxidation following 2 years of TRT, although they found a partially restored meal fat storage pattern without affecting regional adiposity in elderly men.

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Implications of testosterone replacement therapy on cardiovascular disease

Patients with low testosterone levels are at an increased risk for cardiovascular disease. Epidemiological studies, androgen deprivation therapy studies, and TRT studies have shown that low testosterone is associated with higher cardiovascular risk factors and increased mortality 60. However, TRT has yielded controversial cardiovascular outcomes in men. Some studies have shown carotid intima media thickness reduction and improvement in blood pressure, whereas others have described an increase in cardiovascular adverse effects 2. Further studies are needed to clarify the cardiovascular effects of TRT, especially on patients who are at an already increased risk, such as those with T2DM and dyslipidemia.

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Conclusion

TRT has been shown to exert beneficial metabolic effects. Testosterone increases fat-free mass and improves the lipid panel; however, there is no strong evidence of glucose tolerance improvement nor a decrease in the incidence of T2DM. Cardiovascular safety continues to be a concern. Current evidence supports screening for hypoandrogenism in certain populations at risk for developing low testosterone levels, such as in T2DM patients. We agree with the recommendations of the Endocrine Society 2010 that TRT be reserved for men with symptomatic androgen deficiency aiming to induce and maintain secondary sex characteristics and to improve their sexual function, sense of well-being, muscle mass and strength, and bone mineral density. Until more evidence builds up, we do not support TRT as a treatment to improve carbohydrate or lipid metabolism.

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Acknowledgements

This study was funded by NIH (DK29953 and AG14383).

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Conflicts of interest

There are no conflicts of interest.

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References

1. Kaufman JM, Vermeulen A. The decline of androgen levels in elderly men and its clinical and therapeutic implications. Endocr Rev 2005; 26:833–876.
2. Rivas AM, Mulkey Z, Lado-Abeal J, Yarbrough S. Diagnosing and managing low serum testosterone. Proc (Bayl Univ Med Cent) 2014; 27:321–324.
3. Feldman HA, Longcope C, Derby CA, Johannes CB, Araujo AB, Coviello AD, et al.. Age trends in the level of serum testosterone and other hormones in middle-aged men: longitudinal results from the Massachusetts male aging study. J Clin Endocrinol Metab 2002; 87:589–598.
4. Allan CA. Sex steroids and glucose metabolism. Asian J Androl 2014; 16:232–238.
5. Basu R, Dalla Man C, Campioni M, Basu A, Klee G, Toffolo G, et al.. Effects of age and sex on postprandial glucose metabolism: differences in glucose turnover, insulin secretion, insulin action, and hepatic insulin extraction. Diabetes 2006; 55:2001–2014.
6. Basu R, Breda E, Oberg AL, Powell CC, Dalla Man C, Basu A, et al.. Mechanisms of the age-associated deterioration in glucose tolerance: contribution of alterations in insulin secretion, action, and clearance. Diabetes 2003; 52:1738–1748.
7. Cai X, Tian Y, Wu T, Cao CX, Li H, Wang KJ. Metabolic effects of testosterone replacement therapy on hypogonadal men with type 2 diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials. Asian J Androl 2014; 16:146–152.
8. Simon D, Charles MA, Nahoul K, Orssaud G, Kremski J, Hully V, et al.. Association between plasma total testosterone and cardiovascular risk factors in healthy adult men: The Telecom Study. J Clin Endocrinol Metab 1997; 82:682–685.
9. Dandona P, Dhindsa S. Update: Hypogonadotropic hypogonadism in type 2 diabetes and obesity. J Clin Endocrinol Metab 2011; 96:2643–2651.
10. Bhasin S, Cunningham GR, Hayes FJ, Matsumoto AM, Snyder PJ, Swerdloff RS, Montori VM. Testosterone therapy in adult men with androgen deficiency syndromes: an endocrine society clinical practice guideline. J Clin Endocrinol Metab 2006; 91:1995–2010.
11. Vermeulen A, Goemaere S, Kaufman JM. Testosterone, body composition and aging. J Endocrinol Invest 1999; 22 (Suppl):110–116.
12. Vermeulen A. Ageing, hormones, body composition, metabolic effects. World J Urol 2002; 20:23–27.
13. Lemieux I, Pascot A, Tchernof A, Bergeron J, Prud’homme D, Bouchard C, Després JP. Visceral adipose tissue and low-density lipoprotein particle size in middle-aged versus young men. Metabolism 1999; 48:1322–1327.
14. Monroe AK, Dobs AS. The effect of androgens on lipids. Curr Opin Endocrinol Diabetes Obes 2013; 20:132–139.
15. Jiann BP, Hsieh JT, Liu SP, Hsu SH, Wu HC. Associations of endogenous testosterone and lipid profiles in middle-aged to older Taiwanese men. Int J Impot Res 2011; 23:62–69.
16. Zmuda JM, Cauley JA, Kriska A, Glynn NW, Gutai JP, Kuller LH. Longitudinal relation between endogenous testosterone and cardiovascular disease risk factors in middle-aged men. A 13-year follow-up of former Multiple Risk Factor Intervention Trial participants. Am J Epidemiol 1997; 146:609–617.
17. Agledahl I, Skjaerpe PA, Hansen JB, Svartberg J. Low serum testosterone in men is inversely associated with non-fasting serum triglycerides: the Tromsø study. Nutr Metab Cardiovasc Dis 2008; 18:256–262.
18. Haffner SM, Valdez RA. Endogenous sex hormones: impact on lipids, lipoproteins, and insulin. Am J Med 1995; 98 (1A):40S–47S.
19. Mäkinen JI, Perheentupa A, Irjala K, Pöllänen P, Mäkinen J, Huhtaniemi I, Raitakari OT. Endogenous testosterone and serum lipids in middle-aged men. Atherosclerosis 2008; 197:688–693.
20. Khaw KT, Barrett-Connor E. Endogenous sex hormones, high density lipoprotein cholesterol, and other lipoprotein fractions in men. Arterioscler Thromb 1991; 11:489–494.
21. Van Pottelbergh I, Braeckman L, De Bacquer D, De Backer G, Kaufman JM. Differential contribution of testosterone and estradiol in the determination of cholesterol and lipoprotein profile in healthy middle-aged men. Atherosclerosis 2003; 166:95–102.
22. Haffner SM, Mykkänen L, Valdez RA, Katz MS. Relationship of sex hormones to lipids and lipoproteins in nondiabetic men. J Clin Endocrinol Metab 1993; 77:1610–1615.
23. Vaidya D, Dobs A, Gapstur SM, Golden SH, Hankinson A, Liu K, Ouyang P. The association of endogenous sex hormones with lipoprotein subfraction profile in the Multi-Ethnic Study of Atherosclerosis. Metabolism 2008; 57:782–790.
24. Haring R, Baumeister SE, Völzke H, Dörr M, Felix SB, Kroemer HK, et al.. Prospective association of low total testosterone concentrations with an adverse lipid profile and increased incident dyslipidemia. Eur J Cardiovasc Prev Rehabil 2011; 18:86–96.
25. Holmäng A, Björntorp P. The effects of testosterone on insulin sensitivity in male rats. Acta Physiol Scand 1992; 146:505–510.
26. Morimoto S, Fernandez-Mejia C, Romero-Navarro G, Morales-Peza N, Díaz-Sánchez V. Testosterone effect on insulin content, messenger ribonucleic acid levels, promoter activity, and secretion in the rat. Endocrinology 2001; 142:1442–1447.
27. Byerley LO, Lee WNP, Swerdloff RS, Buena F, Nair KS, Buchanan TA, et al.. Effect of modulating serum testosterone levels in the normal male range on protein, glucose and lipid metabolism in men: implications for testosterone replacement therapy. Endocr J 1993; 1:253–262.
28. Mårin P, Holmäng S, Jönsson L, Sjöström L, Kvist H, Holm G, et al.. The effects of testosterone treatment on body composition and metabolism in middle-aged obese men. Int J Obes Relat Metab Disord 1992; 16:991–997.
29. Basu R, Dalla Man C, Campioni M, Basu A, Nair KS, Jensen MD, et al.. Effect of 2 years of testosterone replacement on insulin secretion, insulin action, glucose effectiveness, hepatic insulin clearance, and postprandial glucose turnover in elderly men. Diabetes Care 2007; 30:1972–1978.
30. Nair KS, Rizza RA, O’Brien P, Dhatariya K, Short KR, Nehra A, et al.. DHEA in elderly women and DHEA or testosterone in elderly men. N Engl J Med 2006; 355:1647–1659.
31. Jedrzejuk D, Medras M, Milewicz A, Demissie M. Dehydroepiandrosterone replacement in healthy men with age-related decline of DHEA-S: effects on fat distribution, insulin sensitivity and lipid metabolism. Aging Male 2003; 6:151–156.
32. Kapoor D, Goodwin E, Channer KS, Jones TH. Testosterone replacement therapy improves insulin resistance, glycaemic control, visceral adiposity and hypercholesterolaemia in hypogonadal men with type 2 diabetes. Eur J Endocrinol 2006; 154:899–906.
33. Heufelder AE, Saad F, Bunck MC, Gooren L. Fifty-two-week treatment with diet and exercise plus transdermal testosterone reverses the metabolic syndrome and improves glycemic control in men with newly diagnosed type 2 diabetes and subnormal plasma testosterone. J Androl 2009; 30:726–733.
34. Allan CA, McLachlan RI. Androgens and obesity. Curr Opin Endocrinol Diabetes Obes 2010; 17:224–232.
35. Field AE, Colditz GA, Willett WC, Longcope C, McKinlay JB. The relation of smoking, age, relative weight, and dietary intake to serum adrenal steroids, sex hormones, and sex hormone-binding globulin in middle-aged men. J Clin Endocrinol Metab 1994; 79:1310–1316.
36. Tajar A, Forti G, O'Neill TW, Lee DM, Silman AJ, Finn JD, et al.. EMAS Group. Characteristics of secondary, primary, and compensated hypogonadism in aging men: evidence from the European Male Ageing Study. J Clin Endocrinol Metab 2010; 95:1810–1818.
37. Camacho EM, Huhtaniemi IT, O'Neill TW, Finn JD, Pye SR, Lee DM, et al.. EMAS Group. Age-associated changes in hypothalamic-pituitary-testicular function in middle-aged and older men are modified by weight change and lifestyle factors: longitudinal results from the European Male Ageing Study. Eur J Endocrinol 2013; 168:445–455.
38. Yeap BB, Alfonso H, Chubb SA, Handelsman DJ, Hankey GJ, et al.. Reference ranges and determinants of testosterone, dihydrotestosterone, and estradiol levels measuredusing liquid chromatography-tandem mass spectrometry in a populationof older men. J Clin Endocrinol Metab 2012; 97:4030–4039.
39. Santosa S, Jensen MD. Effects of male hypogonadism on regional adipose tissue fatty acid storage and lipogenic proteins. PLoS One 2012; 7:e31473.
40. Corona G, Rastrelli G, Monami M, Saad F, Luconi M, Lucchese M, et al.. Body weight loss reverts obesity-associated hypogonadotropic hypogonadism: a systematic review and meta-analysis. Eur J Endocrinol 2013; 168:829–843.
41. Rebuffé-Scrive M, Mårin P, Björntorp P. Effect of testosterone on abdominal adipose tissue in men. Int J Obes 1991; 15:791–795.
42. Mårin P, Krotkiewski M, Björntorp P. Androgen treatment of middle-aged, obese men: effects on metabolism, muscle and adipose tissues. Eur J Med 1992; 1:329–336.
43. Mårin P, Odén B, Björntorp P. Assimilation and mobilization of triglycerides in subcutaneous abdominal and femoral adipose tissue in vivo in men: effects of androgens. J Clin Endocrinol Metab 1995; 80:239–243.
44. Saad F, Gooren L, Haider A, Yassin A. An exploratory study of the effects of 12 month administration of the novel long-acting testosterone undecanoate on measures of sexual function and the metabolic syndrome. Arch Androl 2007; 53:353–357.
45. Saad F, Gooren LJ, Haider A, Yassin A. A dose–response study of testosterone on sexual dysfunction and features of the metabolic syndrome using testosterone gel and parenteral testosterone undecanoate. J Androl 2008; 29:102–105.
46. Agledahl I, Hansen JB, Svartberg J. Impact of testosterone treatment on postprandial triglyceride metabolism in elderly men with subnormal testosterone levels. Scand J Clin Lab Invest 2008; 68:641–648.
47. Kalinchenko SY, Tishova YA, Mskhalaya GJ, Gooren LJ, Giltay EJ, Saad F. Effects of testosterone supplementation on markers of the metabolic syndrome and inflammation in hypogonadal men with the metabolic syndrome: the double-blinded placebo-controlled Moscow study. Clin Endocrinol (Oxf) 2010; 73:602–612.
48. Kelly DM, Jones TH. Testosterone: a metabolic hormone in health and disease. J Endocrinol 2013; 217:R25–R45.
49. Whitsel EA, Boyko EJ, Matsumoto AM, Anawalt BD, Siscovick DS. Intramuscular testosterone esters and plasma lipids in hypogonadal men: a meta-analysis. Am J Med 2001; 111:261–269.
50. Bagatell CJ, Heiman JR, Matsumoto AM, Rivier JE, Bremner WJ. Metabolic and behavioral effects of high-dose, exogenous testosterone in healthy men. J Clin Endocrinol Metab 1994; 79:561–567.
51. Uyanik BS, Ari Z, Gümüs B, Yiğitoğlu MR, Arslan T. Beneficial effects of testosterone undecanoate on the lipoprotein profiles in healthy elderly men. A placebo controlled study. Jpn Heart J 1997; 38:73–82.
52. Boyanov MA, Boneva Z, Christov VG. Testosterone supplementation in men with type 2 diabetes, visceral obesity and partial androgen deficiency. Aging Male 2003; 6:1–7.
53. Frederiksen L, Højlund K, Hougaard DM, Brixen K, Andersen M. Testosterone therapy increased muscle mass and lipid oxidation in aging men. Age (Dordr) 2012; 34:145–156.
54. Zgliczynski S, Ossowski M, Slowinska-Srzednicka J, Brzezinska A, Zgliczynski W, Soszynski P, et al.. Effect of testosterone replacement therapy on lipids and lipoproteins in hypogonadal and elderly men. Atherosclerosis 1996; 121:35–43.
55. Kapoor D, Jones TH. Androgen deficiency as a predictor of metabolic syndrome in aging men: an opportunity for intervention? Drugs Aging 2008; 25:357–369.
56. Koutsari C, Ali AH, Nair KS, Rizza RA, O’Brien P, Khosla S, Jensen MD. Fatty acid metabolism in the elderly: effects of dehydroepiandrosterone and testosterone replacement in hormonally deficient men and women. J Clin Endocrinol Metab 2009; 94:3414–3423.
57. Mauras N, Hayes V, Welch S, Rini A, Helgeson K, Dokler M, et al.. Testosterone deficiency in young men: marked alterations in whole body protein kinetics, strength, and adiposity. J Clin Endocrinol Metab 1998; 83:1886–1892.
58. Reis C, Liberman S, Pompeo AC, Srougi M, Halpern A, Filho WJ. Body composition alterations, energy expenditure and fat oxidation in elderly males suffering from prostate cancer, pre and post orchiectomy. Clinics (Sao Paulo) 2009; 64:781–784.
59. Birzniece V, Meinhardt UJ, Handelsman DJ, Ho KK. Testosterone stimulates extra-hepatic but not hepatic fat oxidation (Fox): comparison of oral and transdermal testosterone administration in hypopituitary men. Clin Endocrinol (Oxf) 2009; 71:715–721.
60. Saad F. Androgen therapy in men with testosterone deficiency: can testosterone reduce the risk of cardiovascular disease? Diabetes Metab Res Rev 2012; 28 (Suppl 2):52–59.
Keywords:

carbohydrate metabolism; lipid effects; testosterone replacement

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