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Neuroendocrinology Letters No.6 December Vol.26, 2005Copyright 2005 Neuroendocrinology Letters ISSN 0172780X www.nel.edu

Exercise intensity and its effects on thyroid hormones

Figen Ciloglu, Ismail Peker1, Aysel Pehlivan2, Kursat Karacabey 3, Nevin lhan4,Ozcan Saygin5 & Recep Ozmerdivenli3

GENLAB Medical Diagnostics and Research Laboratory,1 Marmara University, Engineering Faculty, Department o Chemical Engineering,2 Marmara University, School o Physical Education and Sports Istanbul,3 University o Gaziantep, Te School o Physical Education and Sports,4 Firat University Medicine Faculty Biochemistry Department,5 Mula University Te School o Physical Education and Sports, Mugla - urkey

Correspondence to: Yrd. Doc. Dr. Kursat Karacabey, PhDUniversity o Gaziantep, Te School o Physical Education

and Sports (Beden Egitimi ve Spor Y.O)R 27100, Gaziantep, URKEYFAX: +90 342 3600751

EL:+90 342 3601616 Ext:1412 / 1417EMAIL: kkaracabey@gmail.comkaracabey@gantep.edu.tr

Submitted: May 1, 2005 Accepted: May 13, 2005

Key words: exercise; thyroid hormone; thyroxine

Neuroendocrinol Lett 2005;26 (6):830834 PMID: 16380698 NEL260605A14 Neuroendocrinology Letterswww.nel.edu

Abstract BACKGROUND: Physical activity infuences energy metabolism in human subjectsby increasing activity-induced energy expenditure and resting metabolic rate orseveral hours a er exercise. E ects o exercise on circulating thyroid hormone values remain controversial. We have investigated the e ect o acute aerobicexercise on thyroid hormone values.MATERIALS/METHODS: Te e ect o di erent intensity levels o acute aerobicexercise on thyroid hormones was investigated in 60 male well-trained athletesby per orming bicycle ergometer at 45% (low intensity), 70% (moderate inten-sity), and 90% (high intensity). Tese intensities were selected according to theirmaximum heart rate (MHR). At each intensity level, heart rate, blood lactic acid,serum total thyroxine ( 4), ree thyroxine ( 4), total triiodothyronine ( 3),

ree triiodothyronine ( 3) and thyroid stimulating hormone ( SH) values weremeasured.RESULTS: Te results o this study show that exercise per ormed at the anaerobicthreshold (70% o maximum heart rate, lactate level 4.59 1.75 mmol/l) causedthe most prominent changes in the amount o any hormone values. While therate o 4, 4, and SH continued to rise at 90% o maximum heart rate, the rateo 3 and 3 started to all.CONCLUSIONS: Maximal aerobic exercise greatly a ects the level o circulatingthyroid hormones.

Introduction

It is a well-known act that exercise a ects theactivity o many glands and the production o theirhormones. One o the glands a ected is the thy-roid. hyroid gland secretes two separate amino

acid-iodine bound thyroid hormones known as 3-5-3 triiodothyronine ( 3) and 3-5-3-5 tetraiodo-thyronine ( 4, thyroxine) both o which are also

ound in the ree orm ( 4, 3), whose impor-

To cite this article:Neuroendocrinol Lett 2005;26 (6):830834

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Exercise intensity and its effects on thyroid hormones

tance on the regulation o general metabolism, growth,and tissue di erentiation as well as gene expression hasbeen known or a long time [7, 22]. It is also knownthat thyroid hormones act in atty acid oxidation andthermoregulation [9]. hyrotropin-releasing hormone( RH) secreted rom hypothalamus stimulates anteriorpituitary to release thyrotropin ( SH, thyroid stimulat-ing hormone) [9]. When exercise is repeated at certainintervals, there is a pituitary-thyroid reaction that isproperly coordinated by increasing turnover o thyroidhormones [3]. When thyroxine turnover and relatedhormonal action is increased, this would lead to hyper-thyroidism [9, 10]. However, there is no evidence thatsuch a case occurs in trained athletes. For example, intrained athletes the di erence between basal metabolicrate and body temperature is rarely abnormal [9]. hus,it appears that an increase in thyroxine turnover, whichoccurs with physical training, may have a di erentmechanism [10, 14].

raining disturbs the athletes energy homeostasis inan attempt to invoke bene icial adaptations. At the sametime, body weight and ood intake controlling systemssend the signal to save energy. Ignoring this processcan result in overtraining and a reduced sensitivity toanabolic hormones and other endocrine signaling [10,20, 21].

Research on marathon training women brings out very interesting results about thyroid turnover. When arelatively sedentary person starts to train and increasestraining to 48 km/week a moderate thyroid disorderdevelops re lected by increasing 3 and 4 levels [21].

he purpose o this study is to uncover the acute

e ect o increasing metabolic activity through exerciseon thyroid hormones, i an e ect is observed to seewhether it is related to the intensity o exercise and

which o the thyroid hormones are more intensely a ected.

Methods

he ethical consent to study on human subjectswas provided by he Ethical Committee o MarmaraUniversity according to he Declaration o Helsinki.

Subjects.Sixty healthy and well-trained male athletes par-

ticipated in this study. heir ages were between 2026(23 3) years; average heights were 176 7,7 cm, andweights were 72 7,8 kg. All subjects were in ormedabout the purpose and procedures o the study.

All subjects were volunteers and selected randomly.hey had a medical examination and completed a

health status questionnaire.

Study Design.

A total o 9 minutes o exercise was applied to thesubjects with a gradually increasing intensity every 3minutes. Each subject per ormed in di erent intensi-ties using bicycle ergometer at the 45%, 70%, and 90%.

hese rates were calculated o maximum heart rates(MHR). Carvonen method was used or selectingintensity o exercises [1].

Capillary blood was taken rom the ear lobe ordetermination o lactate at the ergometer tests and dur-ing the training cycle.

Laboratory analysis.

At the end o each three minutes, they wereinterrupted or 30 seconds and blood samples weretaken. From the blood samples, lactate (Boehringer

Table 1:Values during low, moderate and high exercise intensities (at 45%, 70%, 90% of maximum heart rates)

Percentage of maximum heart rate(Mean value standard deviation)

Euthyroid adult values* 45% 70% 90%

Lactate (mmol/l) 2.86 0.658 4.59 1.75 8.25 2.74 TSH (IU/ml) 0.58.9 1.69 0.55 1.78 0.60 1.89 0.74T3 (ng/ml) 0.82.1 1.47 0.23 1.78 0.42 1.48 0.26

Free T3 (pmol/l) 3.47.2 5.30 1.20 6.46 1.62 6.17 1.29T4 (ng/ml) 42120 71.10 19.02 84.35 24.86 86.35 28.36Free T4 (pmol/l) 1124 16.97 3.86 19.49 3.82 20.16 4.80

* Reference values of kits

Table 2: P-values of thyroid hormones changes in different exercise intensities45%70%

of max heart rate45%90%

of max heart rate70%90%

of max heart rate TSH (IU/ml) 0.200 0.045* 0.204T3 (ng/ml) 0.025* 0.086 0.021*

Free T3 (pmol/l) 0.047* 0.063 0.038T4 (ng/ml) 0.012* 0.008* 0.049Free T4 (pmol/l) 0.023* 0.027* 0.311

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832 Neuroendocrinology Letters No.6 December Vol.26, 2005 Copyright Neuroendocrinology Letters ISSN 0172780X www.nel.edu

Figen Ciloglu, Ismail Peker, Aysel Pehlivan, Kursat Karacabey Nevin lhan, Ozcan Saygin & Recep Ozmerdivenli

Mannheim lactate kit, Boehringer Mannheim 4010spectrophotometer), 4 (Diatech Diagnostic enzymeimmunoassay test kit), 3 (Diatech Diagnostic enzymeimmunoassay test kit), ree 4 (Amerlex brand RIA kit),

ree 3 (Amerlex brand RIA kit), and SH (BiodataDiagnostic brand RIA kit) values were measured.

Statistical analysis.Di erences between values at di erent time points

were tested with one-way ANOVA and ukey HSD.he assumed level o signi icance or di erences was

equal to or less than 0.05 or all tests.

Results

In this study, hormone values at all heart ratecategories were compatible with the values o healthy and euthyroid adults ( able 1). In all hormones, withthe exception o SH, the maximum rate o increasewas observed at the anaerobic threshold level (70% o maximum heart rate, lactate level 4.59 1.75 mmol/l).he rate o increase o SH was similar, going rom45% to 70% and rom 70% to 90% o MHR (Fig. 1). he

increase in SH level going rom 45% to 90% o MHR was statistically signi icant ( able 2). 4, 4 continuedto increase, going rom 70% to 90% o MHR and thisrise was statistically signi icant when compared to the values seen at 45% MHR, but 3 and 3 began todecrease and or 3 almost to the same level as wasseen at the 45% o the MHR (Fig. 2, Fig. 3, able 2).

Discussion

Some studies per ormed on animals show thatthyroid hormones regulate the transcription o severalgenes expressed in skeletal muscle, such as the genecoding or ype I myosin heavy-chain (MHC), actinand the sarcoplasmic reticulum (SR) Ca21 A Pasepump [ 7, 8,11, 18 ]. here ore, hypothyroidism andhyperthyroidism states might respectively reduce andincrease Ca+2 uptakes by the SR [4, 5, 8]. As a result o the e ects o thyroid hormones on MHC expressionand Ca +2 uptake mechanisms, the shortening velocity o skeletal muscles increases with increasing thyroidlevels [11]. On the other hand, the slow ibers exhibita greater sensitivity to thyroid hormones than the ast

Fig. 2. Change in T4 and T3 values with exercise intensity Fig. 3. Change in Free T4 and Free T3 values with exercise intensity

Fig. 1. Change in TSH values with exercise intensity

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Exercise intensity and its effects on thyroid hormones

ones. Within physiological limits, increased thyroidactivity might be associated with a higher e iciency o the mechanical work per ormed by exercising muscles[9, 16].

Peripheral metabolism o thyroid hormones can bechanged signi icantly by a number o physiological andpathological conditions, which can alter the deiodin-ation pathway and lead to a change in the circulatinglevel o thyroid hormones. he biological e ects o short-term changes in the thyroid hormone levels arenot currently completely understood but are potentially important in the bodys adjustment to stress ul orcatabolic states [17]. Compelling evidence also suggeststhat, i exercise-related energy expenditure exceedscalories consumed, a low 3 syndrome may be induced.In emale athletes, our days o low energy availability reduced 3, 3, increased r 3, and slightly increased

4. Since an adequate amount o the prohormone 4was available throughout the study, an alteration in theperipheral metabolism o 4 was likely. he increase inr 3 and decrease in 3 are consistent with a decreasedactivity o hepatic 5-deiodinase activity, since thisenzyme is responsible or the production o 3 and theclearance o r 3. hese alterations in thyroid hormonescould be prevented solely by increasing dietary caloricconsumption without any alteration in the quantity orintensity o exercise [2, 15].

While the role o a hypo caloric diet in producingalterations in thyroid hormones has been demonstratedin several studies, the role o exercise in thyroid hor-mone metabolism is not very clear. A connection isestablished between increasing training to 80 km/week

and elevated hormone levels [10, 16]. In another study looking at men with six months o endurance training,while 4 and ree 4 concentrations reduced a little,no change in thyrotropin was observed [16]. Koistinenet al .s study on unacclimatized top class skiers showedthat training at moderate altitude or 12 days resultedin a signi icant decrease in serum total 3 levels and anincrease in 3 levels with no signi icant change in SH,

4, 4 and reverse 3 (r 3) [14]. Another study doneby Deligiannis et. al . looking at the thyroid hormoneresponse to swimming or 30 minutes at varying watertemperatures showed that SH and 4 levels weresigni icantly increased at 20C as compared to 32Cbut no signi icant e ect was seen on 3 [ 6 ]. Pakerinenet. al . study on the e ects o one week o very intensestrength training on the thyroid hormones o maleweight li ters showed a signi icant decrease in SH, 3and 4 with unchanged 4, r 3 and thyroid bindingglobulin ( BG) [19]. Baylor et al revealed that overtrained athletes show an impaired hormonal responseto insulin-induced hypoglycemia with recovery a ter4 weeks o rest indicating a hypothalamic dys unction[2]. In a di erent study, untrained subjects experiencedreductions in cortisol and r 3 and an increase in 3a ter exercise. However, trained subjects had an increase

in cortisol and r 3 and a decrease in 3 with exercise.Concentration o 4 was unchanged in both groups[6,19]. he con ounding results o thyroid hormonelevels seen ollowing exercise might be mediated by

elevated cortisol levels however; additional research isrequired to establish this connection.

Jos L. et al., examined the thyroid hormone levelso pro essional cyclists during a 3-week stage competi-tion, they concluded that serum 4, F 4 and F 3 levelsshowed a signi icant increase by the last week o com-petition while concentrations o SH and 3 remainedunchanged [13].

Zarzeczny R, et al., studied e ects o thyroid hormonede icit, and triodothyronine ( 3) treatment on exerciseper ormance, blood lactate (LA) concentrations and LAthreshold ( LA) were studied in trained and untrainedrats. hey ound that 3 treatment markedly increasesmaximal and submaximal LA levels. his shows somesimilarities with our studies results [23].

his current study shows that as compared to thethyroid hormone values during low-intensity exercise(45% max. heart rate), there is an increase in SH values at moderate intensity (70% max. heart rate) andhigh intensity exercise levels (90% max. heart rate). Anincrease then a decrease is seen in 3 and 3 levels atmoderate and high intensity exercise conditions respec-tively and an increase in 4 and 4 values in moderateintensity with continued increase at high intensity levels. hese results partially agree with Schmid et al

indings o continuous SH increase until 15 minutesa ter the end o a sub maximal exercise period with anunchanged or slightly decreased 3, r 3 and 4 [21].A possible cause or the increase o SH levels may be due to pituitary secretion and may serve to ul illthe exercise induced increase in peripheral need orthyroid hormones [12]. But it should be kept in mind

that in the current study all the observed changes arewithin the euthyroid levels and could be realized as aminor physiological response within normal levels. Asa conclusion it can be said that a rise in cell metabolismand changes in the internal medium o the organismserves to change the thyroid hormone levels. hyroid

unction depends to a certain degree on the exerciseintensity and perhaps to other actors such as speci iccharacteristics o the athletes.

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