The thereby affecting energy intake, and the glucose and

The correlation between BMI and the various thyroid hormones differed in both sexes. In women, there was a statistically significant association between BMI and TT3 and TT4, while in men BMI was positively associated with FT3 levels and negatively with TSH.It is widely accepted that hypothyroidism causes weight gain associated with a decrease in basal metabolic rate (BMR) and thermogenesis, and that there is a perceived association between thyroid hormones and body composition.This emanates from the function of the thyroid gland in the regulation of basal metabolism and thermogenesis, thereby affecting energy intake, and the glucose and lipid metabolism (Longhi e Radetti, 2013). The most common form of TH replacement therapy is synthetic T4 hormone, which is generally known as levothyroxine (LT4) and it is used to suppress TSH.FT4 has been closely associated with metabolic syndrome factors independently of insulin resistance. The serum FT4 (not TSH) was found to have a negative correlation with BMI. It was also negatively associated with total cholesterol and triglycerides and positively associated with HDL. The serum TSH levels were positively related only to triglycerides A. Roos,.The thyroid hormone-induced increase in thermogenesis is explained, among other things, by an increased need for ATP due to increased activity in most cells and reduced efficiency of ATP synthesis, but the specific mechanism has not been settled. Increases are observed for obligative, as well as facultative, thermogenesis.Even small differences in thyroid function with TSH variation within the normal laboratory range for patients on T4 substitution therapy are associated with measurable differences in resting energy expenditure (REE), but the impact on body mass index (BMI) remains unsettled (al Adsani H.);However, the association between small differences in thyroid hormone levels, as seen in the general population without thyroid dysfunction, and body weight or BMI has only been described in few previous studies.In a recent study of old participants, an association was found between serum TSH and BMI, but also subjects with overt thyroid dysfunction were included (Gussekloo J 2004). In a study of elderly subjects, a possible association between mild hypothyroidism and BMI was found among women (Lindeman RD 2003), however with the opposite tendency among men. In another recent study, no association was identified (Hak AE 2000).A study by Lee and collaborators (2014) demonstrated no significant change in weight following treatment with L-T4 in patients with primary hypothyroidism. The authors observed that 52% of the investigated patients lost weight, with a median weight loss of 3.8kg following treatment. However, taking into account all patients, the overall weight change was only – 0.1kg. An earlier clinical trial showed that in 18 hypothyroid patients, there was an initialweight loss within the first six months of treatment, but by 24 months, patients had reverted to their pre-treatment weight (Hoogwerf and Nuttall, 1984).Although L-T4 is considered the mainstay of primary hypothyroidism treatment, combination therapy adding liothyronine (L-T3) has been used in selected group of patients (Chakera and collaborators, 2012). The combined therapy was associated with more weight loss compared to monotherapy with L- T4 (Bente and collaborators, 2005). However, it had a TSH endpoint below the reference range, which is not recommended, as there is a linear correlation of suppressed TSH with cardiovascular dysfunction and decreased bone mineral density (Kostoglou-Athanassiou and Ntalles, 2010).The evidence suggests that such a relationship is in existence. High TSH levels were shown to be significantly associated with high BMIs, whilst FT4 was inversely associated with body mass. Increased leptin levels and insulin resistance accompanied this profile. This association has led to the unsubstantiated use of thyroid hormone in the treatment of obesity in euthyroid subjects. Experts  agree that  thyroid hormonal therapy should be reserved for obese patients with overt hypothyroidism.References:al Adsani H, Hoffer LJ, Silva JE 1997. Resting energy expenditure is sensitive to small dose changes in patients on chronic thyroid hormone replacement. J Clin Endocrinol Metab 82:1118–1125Gussekloo J, van Exel E, de Craen AJ, Meinders AE, Frolich M, Westendorp;RG 2004. Thyroid status, disability and cognitive function, and survival in old age. JAMA 292:2591–2599Lindeman RD, Romero LJ, Schade DS, Wayne S, Baumgartner RN, Garry PJ 2003; Impact of subclinical hypothyroidism on serum total homocysteine concentrations, the prevalence of coronary heart disease (CHD), and CHD risk factors in the New Mexico Elder Health Survey.Thyroid 13:595–600Hak AE, Pols HA, Visser TJ, Drexhage HA, Hofman A, Witteman JC 2000; Subclinical hypothyroidism is an independent risk factor for atherosclerosis and myocardial infarction in elderly women: the Rotterdam Study. Ann Intern Med 132:270- 2781-Biondi, B. Thyroid and Obesity: An Intriguing Relationship. The Journal of Clinical Endocrinology & Metabolism. Vol. 95. Núm. 8. p.3614-3617. 2010. Available at: (Accessed 23/01/2016)A. Roos, S. J. L. Bakker, T. P. Links, R. O. B. Gans, and B. H. R. Wolffenbuttel, “Thyroid function is associated with components of the metabolic syndrome in euthyroid subjects,” Journal of Clinical Endocrinology and Metabolism, vol. 92, no. 2, pp. 491–496, 2007M. I. Surks, E. Ortiz, G. H. Daniels et al., “Subclinical thyroid disease: scientific review and guidelines for diagnosis and management,” Journal of the American Medical Association, vol. 291, no. 2, pp. 228–238, 2004.C. G. P. Roberts and P. W. Ladenson, “Hypothyroidism,” The Lancet, vol. 363, no. 9411, pp. 793–803, 2004.D. Ross, “Subclinical hypothyroidism,” in Werner and Ingbar’s the Thyroid: A Fundamental and Clinical Text, L. E. Braverman and R. D. Utiger, Eds., pp. 1070–1078, Lippincott Williams & Wilkins, Philadelphia, Pa, USA, 2005.D. S. Cooper, “Subclinical thyroid disease: consensus or conundrum?” Clinical Endocrinology, vol. 60, no. 4, pp. 410–412, 2004.Johannsen DL., Galgani JE., Johannsen NM., Zhang Z., Covington JD., Ravussin E. 2012. Effect of short-term thyroxine administration on energy metabolism and mitochondrial efficiency in humans. PLoS One 7:e40837.Barbe P., Larrouy D., Boulanger C., Chevillotte E., Viguerie N., Thalamas C., Oliva Trastoy M., Roques M., Vidal H., Langin D. 2001. Triiodothyronine-mediated