Testing hypothyroid without symptoms? This may explain why. *STUDY*

Credit goes to hypRgonad for locating and posting this study on DBT. I thought it may be relevant and useful for some folks here.

Exercise Intensity and its effects on Thyroid Hormone Levels

Figen Ciloglu, Ismail Peker

1, Aysel Pehlivan2, Kursat Karacabey3, Nevin İlhan4,Ozcan Saygin5 & Recep Ozmerdivenli3

GENLAB Medical Diagnostics and Research Laboratory,

1

Marmara University, Engineering Faculty, Department of Chemical Engineering,

2

Marmara University, School of Physical Education and Sports – Istanbul,

3

University of Gaziantep, The School of Physical Education and Sports,

4

Firat University Medicine Faculty Biochemistry Department,

5

Muğla University The School of Physical Education and Sports, Mugla - Turkey

Correspondence to:

Yrd. Doc. Dr. Kursat Karacabey, PhDUniversity of Gaziantep, The School of Physical Educationand Sports (Beden Egitimi ve Spor Y.O)TR 27100, Gaziantep, TURKEY

FAX

: +90 342 3600751

TEL

:+90 342 3601616 Ext:1412 / 1417

EMAIL

: [email protected]@gantep.edu.tr

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

exercise; thyroid hormone; thyroxine

Neuroendocrinol Lett 2005;

26(6):830–834 PMID: 16380698 NEL260605A14 © Neuroendocrinology Letters Neuroendocrinology Letters - Psychoneuroimmunology, Chronobiology, Peer-reviewed journal

Abstract

BACKGROUND

: Physical activity influences energy metabolism in human subjectsby increasing activity-induced energy expenditure and resting metabolic rate forseveral hours after exercise. Effects of exercise on circulating thyroid hormonevalues remain controversial. We have investigated the effect of acute aerobicexercise on thyroid hormone values.

MATERIALS/METHODS

: The effect of different intensity levels of acute aerobicexercise on thyroid hormones was investigated in 60 male well-trained athletesby performing bicycle ergometer at 45% (low intensity), 70% (moderate intensity),and 90% (high intensity). These intensities were selected according to theirmaximum heart rate (MHR). At each intensity level, heart rate, blood lactic acid,serum total thyroxine (T4), free thyroxine (fT4), total triiodothyronine (T3),free triiodothyronine (fT3) and thyroid stimulating hormone (TSH) values weremeasured.

RESULTS

: The results of this study show that exercise performed at the anaerobicthreshold (70% of maximum heart rate, lactate level 4.59 ± 1.75 mmol/l) causedthe most prominent changes in the amount of any hormone values. While therate of T4, fT4, and TSH continued to rise at 90% of maximum heart rate, the rateof T3 and fT3 started to fall.

CONCLUSIONS

: Maximal aerobic exercise greatly affects the level of circulatingthyroid hormones.

Introduction

It is a well-known fact that exercise affects theactivity of many glands and the production of theirhormones. One of the glands affected is the thyroid.Thyroid gland secretes two separate aminoacid-iodine bound thyroid hormones known as 3-5-3’ triiodothyronine (T3) and 3-5-3’-5’ tetraiodothyronine(T4, thyroxine) both of which are alsofound in the free form (fT4, fT3), whose impor-

To cite this article:

Neuroendocrinol Lett 2005; 26(6):830–834

Neuroendocrinology Letters No.6 December Vol.26, 2005 Copyright © Neuroendocrinology Letters ISSN 0172–780X

Neuroendocrinology Letters - Psychoneuroimmunology, Chronobiology, Peer-reviewed journal

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Exercise intensity and its effects on thyroid hormones

tance on the regulation of general metabolism, growth,and tissue differentiation as well as gene expression hasbeen known for a long time [7, 22]. It is also knownthat thyroid hormones act in fatty acid oxidation andthermoregulation [9]. Thyrotropin-releasing hormone(TRH) secreted from hypothalamus stimulates anteriorpituitary to release thyrotropin (TSH, thyroid stimulatinghormone) [9]. When exercise is repeated at certainintervals, there is a pituitary-thyroid reaction that isproperly coordinated by increasing turnover of thyroidhormones [3]. When thyroxine turnover and relatedhormonal action is increased, this would lead to hyperthyroidism[9, 10]. However, there is no evidence thatsuch a case occurs in trained athletes. For example, intrained athletes the difference between basal metabolicrate and body temperature is rarely abnormal [9]. Thus,it appears that an increase in thyroxine turnover, whichoccurs with physical training, may have a differentmechanism [10, 14].Training disturbs the athletes’ energy homeostasis inan attempt to invoke beneficial adaptations. At the sametime, body weight and food 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 outvery interesting results about thyroid turnover. When arelatively sedentary person starts to train and increasestraining to 48 km/week – a moderate thyroid disorderdevelops reflected by increasing T3 and T4 levels [21].The purpose of this study is to uncover the acuteeffect of increasing metabolic activity through exerciseon thyroid hormones, if an effect is observed – to seewhether it is related to the intensity of exercise andwhich of the thyroid hormones are more intenselyaffected.

Methods

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

Subjects.

Sixty healthy and well-trained male athletes participatedin this study. Their ages were between 20–26(23 ± 3) years; average heights were 176 ± 7,7 cm, andweights were 72 ± 7,8 kg. All subjects were informedabout the purpose and procedures of the study.All subjects were volunteers and selected randomly.They had a medical examination and completed ahealth status questionnaire.

Study Design.

A total of 9 minutes of exercise was applied to thesubjects with a gradually increasing intensity every 3minutes. Each subject performed in different intensitiesusing bicycle ergometer at the 45%, 70%, and 90%.These rates were calculated of maximum heart rates(MHR). Carvonen method was used for selectingintensity of exercises [1].Capillary blood was taken from the ear lobe fordetermination of lactate at the ergometer tests and duringthe training cycle.

Laboratory analysis.

At the end of each three minutes, they wereinterrupted for 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 adultvalues*

45% 70% 90%

Lactate (mmol/l)

2.86 ± 0.658 4.59 ± 1.75 8.25 ± 2.74

TSH (

μIU/ml) 0.5–8.9 1.69 ± 0.55 1.78 ± 0.60 1.89 ± 0.74T3 (ng/ml) 0.8–2.1 1.47 ± 0.23 1.78 ± 0.42 1.48 ± 0.26Free T3 (pmol/l) 3.4–7.2 5.30 ± 1.20 6.46 ± 1.62 6.17 ± 1.29T4 (ng/ml) 42–120 71.10 ± 19.02 84.35 ± 24.86 86.35 ± 28.36Free T4 (pmol/l) 11–24 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 intensities

45%–70%of max heart rate45%–90%of max heart rate70%–90%of max heart rateTSH (

μIU/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

832

Neuroendocrinology Letters No.6 December Vol.26, 2005 Copyright © Neuroendocrinology Letters ISSN 0172–780X Neuroendocrinology Letters - Psychoneuroimmunology, Chronobiology, Peer-reviewed journal

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

Mannheim lactate kit, Boehringer Mannheim 4010spectrophotometer), T4 (Diatech Diagnostic enzymeimmunoassay test kit), T3 (Diatech Diagnostic enzymeimmunoassay test kit), free T4 (Amerlex brand RIA kit),free T3 (Amerlex brand RIA kit), and TSH (BiodataDiagnostic brand RIA kit) values were measured.

Statistical analysis.

Differences between values at different time pointswere tested with one-way ANOVA and Tukey HSD.The assumed level of significance for differences wasequal to or less than 0.05 for all tests.

Results

In this study, hormone values at all heart ratecategories were compatible with the values of healthyand euthyroid adults (Table 1). In all hormones, withthe exception of TSH, the maximum rate of increasewas observed at the anaerobic threshold level (70% ofmaximum heart rate, lactate level 4.59 ± 1.75 mmol/l).The rate of increase of TSH was similar, going from45% to 70% and from 70% to 90% of MHR (Fig. 1). Theincrease in TSH level going from 45% to 90% of MHRwas statistically significant (Table 2). T4, fT4 continuedto increase, going from 70% to 90% of MHR and thisrise was statistically significant when compared to thevalues seen at 45% MHR, but T3 and fT3 began todecrease and for T3 almost to the same level as wasseen at the 45% of the MHR (Fig. 2, Fig. 3, Table 2).

Discussion

Some studies performed on animals show thatthyroid hormones regulate the transcription of severalgenes expressed in skeletal muscle, such as the genecoding for Type I myosin heavy-chain (MHC), actinand the sarcoplasmic reticulum (SR) Ca21 ATPasepump [ 7, 8,11, 18 ]. Therefore, hypothyroidism andhyperthyroidism states might respectively reduce andincrease Ca

+2 uptakes by the SR [4, 5, 8]. As a result ofthe effects of thyroid hormones on MHC expressionand Ca+2 uptake mechanisms, the shortening velocityof skeletal muscles increases with increasing thyroidlevels [11]. On the other hand, the slow fibers exhibita greater sensitivity to thyroid hormones than the fast

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

Neuroendocrinology Letters No.6 December Vol.26, 2005 Copyright © Neuroendocrinology Letters ISSN 0172–780X

Neuroendocrinology Letters - Psychoneuroimmunology, Chronobiology, Peer-reviewed journal

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Exercise intensity and its effects on thyroid hormones

ones. Within physiological limits, increased thyroidactivity might be associated with a higher efficiency ofthe mechanical work performed by exercising muscles[9, 16].Peripheral metabolism of thyroid hormones can bechanged significantly by a number of physiological andpathological conditions, which can alter the deiodinationpathway and lead to a change in the circulatinglevel of thyroid hormones. The biological effects ofshort-term changes in the thyroid hormone levels arenot currently completely understood but are potentiallyimportant in the body’s adjustment to stressful orcatabolic states [17]. Compelling evidence also suggeststhat, if exercise-related energy expenditure exceedscalories consumed, a low T3 syndrome may be induced.In female athletes, four days of low energy availabilityreduced T3, fT3, increased rT3, and slightly increasedT4. Since an adequate amount of the prohormone T4was available throughout the study, an alteration in theperipheral metabolism of T4 was likely. The increase inrT3 and decrease in T3 are consistent with a decreasedactivity of hepatic 5’-deiodinase activity, since thisenzyme is responsible for the production of T3 and theclearance of rT3. These alterations in thyroid hormonescould be prevented solely by increasing dietary caloricconsumption without any alteration in the quantity orintensity of exercise [2, 15].While the role of a hypo caloric diet in producingalterations in thyroid hormones has been demonstratedin several studies, the role of exercise in thyroid hormonemetabolism is not very clear. A connection isestablished between increasing training to 80 km/weekand elevated hormone levels [10, 16]. In another studylooking at men with six months of endurance training,while T4 and free T4 concentrations reduced a little,no change in thyrotropin was observed [16]. Koistinen

et al

.’s study on unacclimatized top class skiers showedthat training at moderate altitude for 12 days resultedin a significant decrease in serum total T3 levels and anincrease in fT3 levels with no significant change in TSH,T4, fT4 and reverse T3 (rT3) [14]. Another study doneby Deligiannis et. al. looking at the thyroid hormoneresponse to swimming for 30 minutes at varying watertemperatures showed that TSH and fT4 levels weresignificantly increased at 20°C as compared to 32°Cbut no significant effect was seen on T3 [ 6 ]. Pakerinen

et. al

. study on the effects of one week of very intensestrength training on the thyroid hormones of maleweight lifters showed a significant decrease in TSH, T3and T4 with unchanged fT4, rT3 and thyroid bindingglobulin (TBG) [19]. Baylor et al revealed that overtrained athletes show an impaired hormonal responseto insulin-induced hypoglycemia with recovery after4 weeks of rest indicating a hypothalamic dysfunction[2]. In a different study, untrained subjects experiencedreductions in cortisol and rT3 and an increase in T3after exercise. However, trained subjects had an increasein cortisol and rT3 and a decrease in T3 with exercise.Concentration of T4 was unchanged in both groups[6,19]. The confounding results of thyroid hormonelevels seen following exercise might be mediated byelevated cortisol levels however; additional research isrequired to establish this connection.José L. et al., examined the thyroid hormone levelsof professional cyclists during a 3-week stage competition,they concluded that serum T4, FT4 and FT3 levelsshowed a significant increase by the last week of competitionwhile concentrations of TSH and T3 remainedunchanged [13].Zarzeczny R, et al., studied effects of thyroid hormonedeficit, and triodothyronine (T3) treatment on exerciseperformance, blood lactate (LA) concentrations and LAthreshold (TLA) were studied in trained and untrainedrats. They found that T3 treatment markedly increasesmaximal and submaximal LA levels. This shows somesimilarities with our studies results [23].This current study shows that as compared to thethyroid hormone values during low-intensity exercise(45% max. heart rate), there is an increase in TSHvalues at moderate intensity (70% max. heart rate) andhigh intensity exercise levels (90% max. heart rate). Anincrease then a decrease is seen in T3 and fT3 levels atmoderate and high intensity exercise conditions respectivelyand an increase in fT4 and T4 values in moderateintensity with continued increase at high intensitylevels. These results partially agree with Schmid et al

findings of continuous TSH increase until 15 minutesafter the end of a sub maximal exercise period with anunchanged or slightly decreased T3, rT3 and fT4 [21].A possible cause for the increase of TSH levels maybe due to pituitary secretion and may serve to fulfillthe exercise induced increase in peripheral need forthyroid hormones [12]. But it should be kept in mindthat 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 of the organismserves to change the thyroid hormone levels. Thyroidfunction depends to a certain degree on the exerciseintensity and perhaps to other factors such as specificcharacteristics of the athletes.

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