Changes in sleeping and basal energy expenditure and substrate oxidation induced by short term thyroxin administration in man

Body Composition, Resting Energy Expenditure, and Metabolic Changes in Women Diagnosed with Differentiated Thyroid Carcinoma

Background: Thyroid hormones heavily impact energy expenditure, body mass, and body composition. Their role in the state of exogenous subclinical hyperthyroidism in differentiated thyroid carcinoma (DTC) patients, however, is less well defined. The first aim of this study was to assess changes in body weight, body composition, resting energy expenditure (REE), respiratory quotient (RQ), and metabolic parameters in female DTC patients, starting from the phase of a euthyroid state before total thyroidectomy through the subsequent year after thyrotropin (TSH) suppression. The second aim was to assess the relationship between these variables and thyroid function parameters. Methods: This observational case series analyzed changes in body composition, calorimetric, and metabolic parameters of 15 DTC female patients at 5 time points: (1) at initial DTC diagnosis (euthyroid state), (2) at 2-3 weeks after thyroidectomy (hypothyroid state), (3) at 2-3 months of levothyroxine (LT4) treatment (exogenous euthyroid state), (4) after 6-9 months, and (5) after 1 year of TSH suppressive LT4 therapy (exogenous subclinical hyperthyroid state). A generalized estimating equation (GEE) analysis was performed to estimate the longitudinal correlations of the total triiodothyronine (TT3)/free thyroxine (fT4) ratio (as an independent variable) with body composition, metabolic, and calorimetric parameter changes (as dependent variables). Results: REE, REE per kilogram of lean body mass (REE/LBM), pulse, and systolic and diastolic blood pressure were significantly higher after TSH suppressive LT4 therapy. The GEE analysis revealed longitudinal negative correlations between the TT3/fT4 ratio and systolic blood pressure, fasting blood glucose, body mass index, android (abdominal wall and visceral mesentery) fat distribution, trunk, and arm fat distribution, REE, and REE/LBM. There was a positive correlation with RQ. Conclusions: REE, REE/LBM, pulse, and systolic and diastolic blood pressure were significantly higher after thyroidectomy, radioiodine and TSH suppressive therapy in female DTC patients, while no changes were observed in body weight or body composition. A lower TT3/fT4 ratio longitudinally correlated with increases in REE, REE/LBM, abdominal fat distribution, systolic blood pressure, and fasting blood glucose, as well as with decreased RQ. These findings highlight the importance of judicial balancing of the benefits and detriments of TSH suppression with subsequent decreased TT3/fT4 ratios for female DTC patients.

Does the Risk of Metabolic Syndrome Increase in Thyroid Cancer Survivors?

BACKGROUND

The steep rise in thyroid cancer observed in recent decades has caused an increase in the population of long-term thyroid cancer survivors. Other than recurrences of cancer, the long-term health consequences of surviving thyroid cancer, particularly metabolic syndrome, have not yet been determined. The aim of this study was to estimate the risk of metabolic syndrome in thyroid cancer survivors.

MATERIALS AND METHODS

Population-based data from the Korean National Health and Nutrition Examination Survey (KNHANES) were used for the analysis. The data of KNHANES IV-VI from 2007-2014 were obtained. After excluding subjects who were under 19 years old, whose fasting interval was less than 8 hours, and whose data for predefined variables including metabolic syndrome components were incomplete, 34,347 subjects were analyzed. The incidence of metabolic syndrome and its components were evaluated in three groups: subjects with no history of thyroid cancer, subjects diagnosed with thyroid cancer within 3 years of the survey date, and subjects diagnosed more than 3 years before the survey date.

RESULTS

Thyroid cancer diagnoses were made within 3 years of the survey date for 95 subjects (group 1, short-term survivors) and more than 3 years earlier than the survey date for 60 subjects (group 2, long-term survivors). Metabolic syndrome was frequently observed with clinical significance (odds ratio [OR] 1.986 [95% confidence interval [CI] 1.0-3.70], p = 0.030) in short-term survivors compared with subjects with no thyroid cancer history. Risks for having high blood pressure and high fasting glucose were estimated to be higher in the short-term survivor group (OR 2.115 [CI 1.23-3.64], p = 0.006 and OR 1.792 [CI 1.03-3.11], p = 0.038, respectively). No significant associations were noticed in the long-term survivor group when compared with the group with no thyroid cancer history.

CONCLUSION

Risks for metabolic syndrome, especially high blood pressure and high fasting glucose, were increased in short-term survivors of thyroid cancer but not in long-term survivors when compared with subjects with no history of thyroid cancer.

Effects of Levothyroxine Replacement or Suppressive Therapy on Energy Expenditure and Body Composition

BACKGROUND

Thyrotropin (TSH)-suppressive doses of levothyroxine (LT4) have adverse effects on bone and cardiac function, but it is unclear whether metabolic function is also affected. The objective of this study was to determine whether women receiving TSH-suppressive LT4 doses have alterations in energy expenditure or body composition.

METHODS

This study was a cross-sectional comparison between three groups of women: 26 women receiving chronic TSH-suppressive LT4 doses, 80 women receiving chronic replacement LT4 doses, and 16 untreated euthyroid control women. Subjects underwent measurements of resting energy expenditure (REE), substrate oxidation, and thermic effect of food by indirect calorimetry; physical activity energy expenditure by accelerometer; caloric intake by 24-hour diet recall; and body composition by dual X-ray absorptiometry.

RESULTS

REE per kilogram lean body mass in the LT4 euthyroid women was 6% lower than that of the LT4-suppressed group, and 4% lower than that of the healthy control group (p = 0.04). Free triiodothyronine (fT3) levels were directly correlated with REE, and were 10% lower in the LT4 euthyroid women compared with the other two groups (p = 0.007). The groups of subjects did not differ in other measures of energy expenditure, caloric intake, or body composition.

CONCLUSIONS

LT4 suppression therapy does not adversely affect energy expenditure or body composition in women. However, LT4 replacement therapy is associated with a lower REE, despite TSH levels within the reference range. This may be due to lower fT3 levels, suggesting relative tissue hypothyroidism may contribute to impaired energy expenditure in LT4 therapy.

Winter Is Coming: Seasonal Variation in Resting Metabolic Rate of the European Badger (Meles meles)

Resting metabolic rate (RMR) is a measure of the minimum energy requirements of an animal at rest, and can give an indication of the costs of somatic maintenance. We measured RMR of free-ranging European badgers (Meles meles) to determine whether differences were related to sex, age and season. Badgers were captured in live-traps and placed individually within a metabolic chamber maintained at 20 ± 1°C. Resting metabolic rate was determined using an open-circuit respirometry system. Season was significantly correlated with RMR, but no effects of age or sex were detected. Summer RMR values were significantly higher than winter values (mass-adjusted mean ± standard error: 2366 ± 70 kJ⋅d⁻¹; 1845 ± 109 kJ⋅d⁻¹, respectively), with the percentage difference being 24.7%. While under the influence of anaesthesia, RMR was estimated to be 25.5% lower than the combined average value before administration, and after recovery from anaesthesia. Resting metabolic rate during the autumn and winter was not significantly different to allometric predictions of basal metabolic rate for mustelid species weighing 1 kg or greater, but badgers measured in the summer had values that were higher than predicted. Results suggest that a seasonal reduction in RMR coincides with apparent reductions in physical activity and body temperature as part of the overwintering strategy (‘winter lethargy’) in badgers. This study contributes to an expanding dataset on the ecophysiology of medium-sized carnivores, and emphasises the importance of considering season when making predictions of metabolic rate.

Effect of short-term thyroxine administration on energy metabolism and mitochondrial efficiency in humans

The physiologic effects of triiodothyronine (T3) on metabolic rate are well-documented; however, the effects of thyroxine (T4) are less clear despite its wide-spread use to treat thyroid-related disorders and other non-thyroidal conditions. Here, we investigated the effects of acute (3-day) T4 supplementation on energy expenditure at rest and during incremental exercise. Furthermore, we used a combination of in situ and in vitro approaches to measure skeletal muscle metabolism before and after T4 treatment. Ten healthy, euthyroid males were given 200 µg T4 (levothyroxine) per day for 3 days. Energy expenditure was measured at rest and during exercise by indirect calorimetry, and skeletal muscle mitochondrial function was assessed by in situ ATP flux (³¹P MRS) and in vitro respiratory control ratio (RCR, state 3/state 4 rate of oxygen uptake using a Clark-type electrode) before and after acute T4 treatment. Thyroxine had a subtle effect on resting metabolic rate, increasing it by 4% (p = 0.059) without a change in resting ATP demand (i.e., ATP flux) of the vastus lateralis. Exercise efficiency did not change with T4 treatment. The maximal capacity to produce ATP (state 3 respiration) and the coupled state of the mitochondria (RCR) were reduced by approximately 30% with T4 (p = 0.057 and p = 0.04, respectively). Together, the results suggest that T4, although less metabolically active than T3, reduces skeletal muscle efficiency and modestly increases resting metabolism even after short-term supplementation. Our findings may be clinically relevant given the expanding application of T4 to treat non-thyroidal conditions such as obesity and weight loss.

Total energy expenditure and physical activity in children treated with home parenteral nutrition

Determining total energy expenditure (TEE) and its components in children treated with home parenteral nutrition (CHPN) under free-living conditions is an important consideration in the assessment of energy requirements and the maintenance of health. The aim of this study was to assess TEE and physical activity in CHPN. Eleven CHPN (three girls and eight boys; median age, 6.0 y; range, 4.5-15.0 y) were compared with 11 healthy children (three girls and eight boys; median age, 6.0 y, range, 4.5-14.0 y) after pairing for sex, age, and weight. Underlying diseases included chronic intractable diarrhea (n = 5), short bowel syndrome (n = 3), and intestinal dysmotility (n = 3). None of these children had inflammatory disease or recent infection when studied. Fat-free mass (FFM), measured by body impedance analysis, fat mass (FM), measured by skinfold thickness, and energy intake were similar between the two groups, suggesting that CHPN had normal body composition and energy intake. Resting energy expenditure (REE), measured by indirect calorimetry, and TEE, assessed by a technique using 24-h heart-rate monitoring calibrated against indirect calorimetry and physical activity using a triaxial accelerometer, were simultaneously recorded and were also similar in the two groups. Sleeping energy expenditure (SEE), expressed per kilogram of FFM, was significantly greater in the CHPN group (median, 0.15; range, 0.10-0.23 kJ/min/kg FFM versus median, 0.12; range, 0.09-0.21 kJ/min/kg FFM for controls; p < 0.05, Wilcoxon rank test). These findings were explained by the high correlation between the energy flow infused by parenteral nutrition and sleeping energy expenditure (p < 0.05, Spearman test) and also-diet induced thermogenesis (p < 0.05 Spearman test). These results suggest that the energy requirements of children on long-term home parenteral nutrition programs do not differ from controls and that cyclic parenteral nutrition does not interfere with physical activity.

Assessing sleeping energy expenditure in children using heart-rate monitoring calibrated against open-circuit indirect calorimetry: a pilot study

Total energy expenditure (EE) can be assessed in children by the heart-rate (HR) monitoring technique calibrated against open-circuit indirect calorimetry (IC). In this technique, sleeping EE is usually estimated as the lowest value of a 30 min resting EE measurement x 0 x 90 to give an average for the total sleeping period. However, sleeping is a dynamic process in which sleeping EE is modulated by the effect of factors such as body movement and different sleep stages. The aim of the present study was to determine a new method to improve the sleeping EE measurement by taking into account body movements during sleep. Twenty-four non-obese children participated in the present study. All subjects passed through a calibration period. HR and EE measured by IC were simultaneously collected during resting, the postprandial period, and during different levels of activity. Different methods for computing sleeping EE (resting with different breakpoints ('flex point' HR with linear regression or 'inflection point' (IP) HR with the third order polynomial regression equation (P3)) were compared with EE measured for least 2.0 h in eight sleeping children. The best method of calculation was then tested in sixteen children undergoing HR monitoring and with a body movement detector. In a subset of eight children undergoing simultaneous sleeping EE measurement by IC and HR, the use of the equation resting when HR<IP and P3 when HR>IP during the sleeping period gave the lowest difference (1 (sd 5.4) %) compared with other methods (linear or polynomial regressions). The new formula was tested in an independent subset of sixteen other children. The difference between sleeping EE computed with the formula resting and sleeping EE computed with resting when HR<IP and the P3 equation when HR>IP during sleeping periods was significant (13 (sd 5.9) %) only for active sleeping subjects (n 6 of 16 subjects). The correlation between the difference in the results from the two methods of calculation and body movements was close (r 0.63, P<0.005, Spearman test) as well as computed sleeping EE (Spearman test, r 0.679, P<0.001), indicating that this new method is reliable for computing sleeping EE with HR monitoring if children are moving during sleep and improves the total EE assessment.

Effects of red blood cell transfusion on resting energy expenditure in adolescents with sickle cell anemia

BACKGROUND

Previous studies indicate that resting energy expenditure is elevated in children with sickle cell anemia, possibly caused in part by hemolysis and increased erythropoietic activity. The purpose of the present investigation was to determine whether erythrocyte transfusion normalizes resting energy expenditure in sickle cell anemia.

METHODS

Five adolescents with sickle cell anemia (12-16 years old; 4 boys, 1 girl) were studied before and 1 week after erythrocyte transfusion before elective surgery or at the initial transfusion for growth failure. Resting energy expenditure was measured by indirect calorimetry, and laboratory measures were determined by routine, validated methods. Data comparisons were by nonparametric analysis.

RESULTS

After erythrocyte transfusion, total hemoglobin levels increased (difference (D) = 15 g/l; p < 0.05), whereas hemoglobin S (D = -0.36; p < 0.05) and reticulocyte count (D = -0.12; p < 0.05) decreased. Mean pretransfusion resting energy expenditure was elevated to 124% above predicted levels (p < 0.05) and increased further to 134% above prediction (p < 0.05 vs. pretransfusion levels). Plasma triiodothyronine (T3) levels increased (D = 0.17 nmol/l; p < 0.05), reverse T3 (rT3) levels tended to decline (D = -0.04 nmol/l; p = 0.14), and rT3/T3 decreased (D = -0.03; p < 0.05). Plasma insulin-like growth factor-I (IGF-I) levels were low-normal before transfusion and did not change, despite the change in resting energy expenditure.

CONCLUSIONS

The results confirm that resting energy expenditure is elevated in patients with sickle cell anemia. However, resting energy expenditure further increased after transfusion, despite decreased erythropoietic activity. A posttransfusion decrease in rT3/T3 may contribute to the increased resting energy expenditure. That there was no change in IGF-I implies that the growth hormone-IGF system is not involved in posttransfusion regulation of resting energy expenditure. Therefore, our data are not consistent with the hypothesis that increased resting energy expenditure in sickle cell anemia is directly related to erythropoietic activity. The mechanisms by which resting energy expenditure increases after transfusion in sickle cell anemia require additional investigation.