Effect of Yoga Therapy on Hypothyroidism: A Systematic Review

Abstract

Background

Hypothyroidism (HT) is the most prevalent endocrine disorder, affecting approximately one in 10 out of 35 adults, with a higher prevalence in females and the elderly.

Purpose

This systematic review (SR) aimed to discuss the effects of yoga on markers and comorbid conditions of HT.

Methods

The SR was registered with the PROSPERO (PROSPERO 2022 CRD42022312990). Google Scholar, PubMed, Cochrane, and EMBASE were searched for the relevant English language interventional studies published from 31 December 1947 to 31 December 2023 by using the keywords ‘meditation OR breath regulation OR yoga OR yoga nidra AND hypothyroidism OR hypothyreosis OR underactive thyroid OR low thyroid’. Of the 4078 screened studies, eight eligible studies (three RCTs, two pilot studies, two pre-post trials, and one case study) with 421 HT patients (392 females and 29 males) and three to six-month yoga interventions were included. Two independent review authors extracted study characteristics and synthesised them descriptively. RCTs and NRSIs were assessed for risk-of-bias (RoB) using Cochrane tools RoB2 and ROBINS-1.

Results

The findings suggest that yoga effectively improves the thyroid profile, lipid profile, heart rate variability, pulmonary functions, anxiety, depression, and quality of life among HT patients.

Conclusion

Yoga may be an inexpensive add-on preventive and therapeutic option for HT. The clinical and methodological heterogeneity among the studies did not allow for meta-analysis (MA). Well-designed MAs are warranted by including rigorous RCTs to draw valid conclusions and defined mechanisms regarding the efficacy of yoga practices/interventions on HT.

Introduction

Hypothyroidism (HT) is the most prevalent endocrine disorder, affecting approximately one in 10 out of 35 adults, showing its higher prevalence in females and the elderly.^{1, 2} In the USA, HT prevalence grew from 9.5% in 2012 to 11.7% in 2019. ³ In India, 11% of people have HT, compared to 2% in the UK and 4·6% in the USA. ⁴ Women are affected approximately six times more often than men with an underactive thyroid, ¹ which may be due to autoimmune disorders, nutritional deficiencies, or hormonal imbalances. HT is the under-secretion of thyroid hormones (THs) from thyroid glands/impaired resistance of peripheral tissues to the effects of THs, resulting in a hypometabolic clinical state. ⁵ The signs and symptoms of HT include fatigue, weakness, dry skin, feeling cold, rapid heartbeat, thinning hair, trouble focusing, lousy memory, constipation, obesity, weak appetite, menorrhagia, dyspnoea, hearing impairment, myxoedema, bradycardia, diffuse alopecia, and peripheral oedema. ⁶ If left untreated, it may lead to hypertension, dyslipidaemia, infertility, cognitive impairment, neuromuscular dysfunction,^{4, 6, 7} and comorbidities, such as coronary artery disease, obesity, osteoporosis, depression, and sleep apnoea ⁸ . The treatment of HT focuses mainly on substituting the deficient hormone, and over 78% of HT patients receive thyroxine (T₄) monotherapy—levothyroxine (LT₄) to reach a euthyroid state.^{3, 9, 10} Persistent intake of synthetic levothyroxine (levothyroxine, synthroid, and others) might make patients drug-dependent and induce adverse effects.^{3, 5} Patients need to switch to alternative therapies to control the overall impact of HT on their lives. ¹¹

Yoga is an ancient oriental practice that aims to purify the body, breath, bioenergy, cognition, and emotion to promote holistic wellness as an indispensable foundation for spiritual elevation.^{12, 13} Yoga includes an array of practices─cleansing technique (shatkarma), pose (asana), conscious breath regulation (pranayama), neuromuscular lock (bandha), seal (mudra), sensory withdrawal (pratyahara), concentration/mindfulness (dharana), and meditation (dhyana).^{14, 15} Yoga improves psychosomatic health by optimising psycho-neuroendocrine interactions, musculoskeletal health, immune system, cardiopulmonary functions, metabolic processes, bioenergy, and worldly outlook. Yoga is also a psychosomatic intervention for thyroid disorders that can be practised by all age groups and genders with minor side effects. ¹⁶ Yoga is a cost-effective and easy option for several physical and mental ailments.^{17, 18} The American College of Sports Medicine (ACSM) and the American Heart Association (AHA) reported that moderate to low-intensity yoga exercises can mitigate underactive thyroid symptoms. ¹⁹ A study consistently showed that a 50-minute yoga session for 10 days significantly decreased body weight, body mass index (BMI), waist circumference, lipid profile, and thyroid-stimulating hormone (TSH) levels ²⁰ of underactive thyroid patients. The untested hypothesis asserts that yoga poses such as sarvangasana, bhujangasana, halasana, surya namaskar, marjariasana, and vipritkarani mitigate thyroid disorders, including HT by inducing mechanical effect and vascular supply on the thyroid. ²⁰ However, no systematic reviews (SRs) and meta-analyses (MAs) synthesise the reported results regarding the effectiveness of yoga interventions in improving primary/secondary markers and comorbid conditions of HT. Therefore, this SR aimed to discuss the impacts of yoga interventions on primary/secondary markers of HT by synthesising the reported effects in the eight interventional studies.

Methods

Registration

This SR followed Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines and was registered with the International Prospective Register of Systematic Reviews (PROSPERO) with registration number PROSPERO 2022 CRD42022312990.

Eligibility Criteria

In this SR, all the full-text interventional studies evaluating the effect of yoga on HT and published in the English language were included. The selection of studies was based on the Population Intervention Comparison Outcome (PICO) statement, as depicted in Table 1.

Table 1. PICO Statement.

P	Population/Patient	Patients of age group 18–55 years diagnosed with HT and TSH level >3.6 mlU/l
I	Intervention	Yoga practices: asanas, breathing techniques, locks, concentrations, mantra and meditations
C	Comparison	Passive/active controls, including standard care, diet, naturopathy, exercise, and behaviour moderation inputs)
O	Outcome	Primary outcomes: Thyroid profile (T3, T4, TSH and thyroxin medication—LT4): Secondary outcomes: Lipid profile: TG, TC, HDL, LDL, VLDL Anthropometric measures: height, weight, BMI, waist circumference, hip circumference, and waist/hip ratio Pulmonary functions: FEV1, FVC, FEV1/FVC, PEFR, MVV, and IC HRV: Mean RR, RMSSD, LF, HF, Total power, and LF/HF QoL: Physical domain, psychological domain, social domain, environmental domain, overall health and overall quality of life Mental health outcomes: Depression, anxiety, fatigue and stress

Note: BMI: Body Mass Index, BW: Body Weight, FEV1/FVCG: Forced Expiratory Volume/Forced Vital Capacity, FEV1: Forced Expiratory Volume in one second, FVCG: Forced Vital Capacity, HCG: Hip Circumference, HDL: High-Density Lipoprotein, HF: High-Frequency, hrs: Hours, HR: Heart Rate, HRV: Heart Rate Variability, ICG: Inspiratory Capacity, LDL: Low-Density Lipoprotein, LF: Low-Frequency, M: Male, MVV: Maximal Voluntary Ventilation, PEFR: Peak Expiratory Flow Rate, QoL: Quality of Life, RMSSD: Root Mean Squares of the Difference of Adjacent Intervals, T₃: Triidothyronine, T₄: Thyroxine, TCG: Total Cholesterol, TP: Total Power, TG: Triglyceride, TSH: Thyroid Stimulating Hormone, VLDL: Very Low-Density Lipoprotein, W/HR: Waist Hip Ratio, WCG: Waist Circumference.

Search Strategy

PubMed, Cochrane, EMBASE, and Google Scholar were searched to identify the relevant studies published from 31 December 1947 to 31 December 2023. Meditation OR breath regulation OR yoga OR yoga Nidra AND hypothyroidism OR hypothyreosis OR low thyroid were used as search keywords. Only articles in the English language were included in the studies. The search was limited and filtered by selecting only interventional studies that mainly assessed the effect of yoga therapy on HT. The detailed search strategy is depicted in Table 2.

Table 2. Detailed Search Strategy.

Databases	Search Details	No of Articles
PubMed	(meditation OR breath regulation OR yoga OR yoga nidra [Title/Abstract] AND (hypothyroidism[Title/Abstract] OR underactive thyroid[Title/Abstract] OR low thyroid[Title/Abstract] OR hypothyreosis [Title/Abstract]))	8
EMBASE	meditation OR breath regulation OR yoga OR yoga nidra:ti,ab,kw AND (hypothyroidism:ti,ab,kw OR ’underactive thyroid’:ti,ab,kw OR ’low thyroid’:ti,ab,kw OR hypothyreosis:ti,ab,kw)	16
Cochrane Library	(meditation OR breath regulation OR yoga OR yoga nidra):ti,ab,kw AND (HTOR underactive thyroid OR low thyroid OR hypothyreosis):ti,ab,kw	37
Google Scholar	meditation OR breath regulation OR yoga OR yoga nidra AND (hypothyroidism OR underactive thyroid OR low thyroid OR hypothyreosis)	4030

Study Selection and Data Extraction

The studies were searched from the above-stated databases, and the search engine was exported to the citation manager, Mendley version 1.19.8. The duplicates were filtered and removed. The retrieved articles were screened individually for titles and abstracts by two independent review authors to verify their eligibility for inclusion. The study characteristics, including author, publication year, country, study design, sample characteristics, intervention, comparator, measures, outcome variables, results, and findings, were extracted from each study and condensed into tabular form.

Risk of Bias in Individual Studies

The quality of studies included in the review was assessed using the Revised Cochrane risk-of-bias tools for randomised controlled trials (RoB2) and non-randomised studies of interventions (ROBINS-I).

Study Selection

A total of 4091 records with 13 duplicates identified from one search engine (Google Scholar = 4030) and three databases (Cochrane = 37, PubMed = 08, EMBASE = 16) were exported to a citation manager, Mendley version 1.19.8. The remaining 4078 records were then screened for irrelevant studies. The screening yielded 10 studies, which were further assessed for eligibility. Of the 10, two descriptive studies were excluded. Finally, eight studies were eligible for this review, as shown in Figure 1.

Figure 1. PRISMA Flow Diagram for Study Selection.

Study Characteristics

Eight studies (three RCTs, two pilot studies, two pre-post clinical trials, and one case study) were eligible to be included in this review. The studies had 421 participants (392 females and 29 males) diagnosed with HT. Yoga therapy for three to six months was the intervention. Table 3 provides a detailed description of the study characteristics.

Table 3. Characteristics of Included Studies.

Author, Year	Design	Sample Characteristics		Intervention	Comparator	Measures	Outcomes	Results			Findings
		Inclusion	Exclusion					OVs	Pre	Post
Akhtar, 2019 9	RCT	n = 60 EG = 30 CG = 30 Age Range: ≥18 yrs	Those patients who refused to participate in the study	Asana: Bhujanga, Kandhara, Vajra, Matsyasana, Halasana Pranayama: Anulom Viom, Kapalbhati, Bharahmari, Ujjyai, Bhastrika Bandh: Jalandharbandh Relaxation Technique: Shavasana Duration: 6 months Session Hrs.: 60 min Frequency/Week: 6 days	‘-’	WHO QoL BREF	QoL	Physical	EG:12.03 ± 1.02 CG: 11.56 ± 1.05	EG:14.17 ± 0.89***### CG: 11.70 ± 1.14	Yoga practices improved the physical and psychological aspects of QoL in the yoga group compared to the controls.
								Psychological	EG:11.97 ± 0.87 CG: 11.93 ± 1.11	EG:14.17 ± 0.89***### CG: 12.04 ± 1.06
								Social	EG:9.14 ± 0.79 CG: 9.00 ± 0.96	EG:9.10 ± 0.67 CG: 8.96 ± 0.94
								Environmental	EG:13.10 ± 0.90 CG: 11.93 ± 0.87	EG:13.31 ± 1 0.88 CG: 12.00 ± 0.88
Bhavanani, 2008 21	A case study	n = 1F Age = 36 yrs	‘-’	Asana: Pawanmukta,Vakra, Sarvanga, Suryanamaskar, Vipritkarani, Tricon Pranayam: Suryabhedi, Ujjyai, Pranav, and Bhrahmari Bandh: Jalandharbandh Duration: 6 months Session Hrs.: 60 min Frequency/week: 6 days	‘-’	Biochemistry analyser	TSH T4	TSH	9.39	2.66	After one year of therapy, yoga practices reduced TSH and normalised FT4.
								FT4	12.57	9.39
Chintala et al., 2019 22	RCT	n = 50 FEG = 25 CG = 25 Age = 18-30 yrs	Pregnant, breastfeeding, addicted to alcohol and drugs, pre-practitioner of pranayam	Asana: Loosning Series Pranayam: Chandrabhedi, Bhrahmari, Nadishudhi, Pranav Relaxation Technique: Shavasan Duration: 1 month Session Hrs.: 60 min Frequency/week: 3 days	‘-’	Biochemistry Analyser	HRV T3 T4 TSH	RR	EG: 937.31 ± 165.97 CG: 808.7 + 127.09	EG:880.87 ± 132.8# CG: 799.1 + 118.12	Yoga practices significantly reduced LFnu and improved HFnu in the Pranayama group compared to the control.
								RMSSD	EG: 64.06 ± 22.98 CG: 74.48 ± 12.45	EG:68.18 ± 18.08**# CG:75.45 ± 12.08*
								LF	EG: 74.4 ± 13.08 CG: 62.0 ± 13.98	EG:31.90 ± 12.96***### CG:44.80 ± 15.05**
								HF	EG: 25.65 ± 12.87 CG: 38.0 ± 10.54	EG:68.11 ± 21.97***### |CG:539.88 ± 111.9**
								TP	EG: 104.28 ± 276.09 CG: 891.99 ± 134.96	EG:130.76 ± 11.98***## CG: 539.88 ± 111.9**
								LF/HF	EG:2.90 + 0.53 CG:1.63 + 0.89	EG: 0.47 ± 0.11***### CG: 0.81 ± 0.29*
Nilakanthan et al., 2016 8	Pilot Study	n = 22 F Mean Age = 36.7 ± 3.2 yrs	Subjects with known cardiac disease, hypertension, history of recent surgery, and slip disc	Asana: Suryanamskar, Sukshm Vyam, Asana- Bhujanga, Kandhara, Vajra, Matsyasana, Halasana Pranayama: Anulom Viom, Kapalbhati, Bharahmari. Ujjayi, Bhastrika Bandh: Jalandharbandh Relaxation Technique: Shavasana Duration: 6 Months Session Hrs.: 60 min Frequency/Week: 4 Days	‘-’	Biochemistry Analyser	TL TR LDL HDL TSH Thyroxine	TL	206.5 ± 27.08	190.18 ± 24.70	Yoga practices significantly reduced TL, LDL and TGs and increased HDL with a non-significant reduction in TSH and a significant reduction in LT4 intake.
								TR	142.13 ± 46.72	131.86 ± 32.15
								HDL	51.72 ± 15.28	54.36 ± 13.35
								LDL	128.81 ± 17.86	116.90 ± 19.46
								TSH	3.99 ± 1.53	3.43 ± 0.99
								Thyroxine	55.571 ± 27.09	55.571 ± 27.09
Rani et al., 2021 23	Pilot Study	n = 38 F Mean Age = 34.2 ± 4.7 yrs	History of psychiatric disorders, addictions, antipsychotic medications, thyroid cancer, abdominal surgery in the past one year; morbid obesity; pregnancy; regular yoga practice habit and change thyroxin dosage in the preceding three months	Asana: Loosening Practices, Surynamaskar Pranayam: Right Nostril Breathing, Ujjayi Breath with Antar Kumbhaka and Chandra Bhedi Meditation: Sun Meditation, Gayatri Mantra ChantingDuration: 3 months Frequency/week: 5 days Session Hrs.:: 60 min	‘-’	DASS-21 Biochemistry Analyser	TSH Thyroxine Lipid Profile BMI Anxiety Fatigue Stress	TSH	5.24 ± 2.2	3.29 ± 1.03**	Yoga practices significantly improved depression, TSH, BMI, anxiety, fatigue, lipid profile, and stress.
								Thyroxine	45.77 ± 25.61	35.00 ± 19.16**
								TG	117.34 ± 34.06	91.63 ± 19.95**
								TC	218.42 ± 29.88	199.85 ± 14.53**
								VLDL	23.52 ± 7.17	18.31 ± 4.00**
								LDL	148.91 ± 28.75	128.27 ± 14.10**
								HDL	46.35 ± 8.75	53.25 ± 5.39**
								BMI	26.44 ± 2.67	24.8 ± 2.23*
								Depression	13.37 ± 1.8	5.61 ± 1.3**
								Anxiety	12.89 ± 2.5	5.37 ± 2.2**
								Fatigue	46.37 ± 6.2	16.26 ± 4.4**
								Stress	16.26 ± 3.0	7.29 ± 2.9**
Shetty et al., 2020 24	RCT	n = 60 (29 M + 31 F) EG = 30 CG = 30 Mean Age = 42.4 ± 7.4 yrs	Patients suffering from any severe organ dysfunction	Naturopathy Hydrotherapy Mud Therapy Fasting Therapy Diet Modification Asana: Suryanamaskar, Halasana, Matsyasana, Vipritkarni Pranayama: Bhastrika, Kapalbhati, Nadishodhan and Relaxation Techniques Duration: 10 days Frequency/week: 6 days Session Hrs.:: 50 min	‘-’	Anthropometric Measures Biochemistry Analyser	Thyroid Profile Lipid Profile Anthropometric Variables BW BMI WC HC	T3	EG: 103.4 ± 26.4 CG:117.8 ± 20.5	EG:107.9 ± 21.3 CG:116 ± 14.5	Naturopathy and yoga practices significantly decreased BW, BMI, WC, TGs, LDL, and TSH and increased HDL in the EG compared to the CC, with no significant change in T3 and T4.
								T4	EG:6.4 ± 1 CG:6.7 ± 1.1	EG:6.5 ± 0.9 CG:7.1 ± 0.9
								TSH	EG:9.8 ± 2.8 CG:10.5 ± 2.2	EG:9.0 ± 2.5*# CG:10.2 ± 2
								TG	EG:205.3 ± 30.3 CG:199 ± 58.9	EG:185.3 ± 30.3*# CG:195.3 ± 55
								TC	EG:237.1 ± 29.2 CG:216.4 ± 32.6	EG: 206 .1 ± 29.2**## CG:225.6 ± 33.2
								VLDL	EG:21.3 ± 3.3 CG:30.9 ± 11.7	EG:22.27 ± 5.4 CG:28.2 ± 11
								LDL	EG:182.1 ± 28.9 CG:145.7 ± 35.7	EG:145.07 ± 30*# CG:158.9 ± 35.7
								HDL	EG:33.9 ± 5.1 CG:39.7 ± 7.2	EG:38.9 ± 5.3*# CG:38.5 ± 11.9
								BW	EG:87.5 ± 11.1 CG:85.3 ± 8.5	EG:81.7 ± 10.9**## CG:85.1 ± 8.2
								BMI	EG:32.9 ± 2.6 CG:31.6 ± 1.5	EG:30.7 ± 2.4**## CG:31.5 ± 1.4
								WC	EG:95.0 ± 10 CG:92.6 ± 8.2	EG:91.4 ± 9.1*# CG:91.1 ± 9
								HC	EG:106.1 ± 8.2 CG:104.8 ± 6.6	EG:103.7 ± 8.3 CG:103.6 ± 7.5
								W/HR	EG:0.89 ± 0 CG:0.9 ± 0.1	EG:0.88 ± 0 CG:0.9 ± 0.1
Singh et al., 2011 25	Pre-Post	n = 20 F Mean Age = 38.2 ± 3.7 yrs	Pregnant females, diabetics, severe CVD	Asana: Loosening Execises, Asan- Bhujanga, Kandhara,Vajra, Matsyasana, Pranayama: Anulom Viom, Kapalbhati, Bharahmari, Ujjyai, Bhastrika. Jalandharbandh, Shavasana. Duration: 1 month Frequency/week: 6 days Session Hrs.: 60 min	‘-’	WHOQOL-BREF	QoL	Physical	11.5 ± 1.80	14.0 ± 1.52**	Yoga practices significantly improved the QoL—physical health, psychological health, social relationships, and environmental adaptation.
								Psychological	11.25 ± 2.98	13.6 ± 2.42**
								Social	12.2 ± 2.23	13.9 ± 2.05**
								Environment	11.55 ± 2.58	13.2 ± 2.42**
								OPH	3.25 ± 0.69	3.25 ± 0.69
								QoL	3.1 ± 0.3	4.4 ± 0.58**
Swami et al., 2009 26	Pre- Post	n = 20 F Mean Age = 39.70 ± 8.27 yrs	Subjects with chronic diseases or with organ system dysfunction	Pranayam: Kapalbhati, Bhastrika, Ujjyai, Anulom Vilom, Bhrahmari, Om Chanting Duration: 6 Months Frequency/Week: 7 Session Hrs.: 45 min	‘-’	Spirometry	TSH FVC FEV1 FEV1/FVC PEFR MVV IC	TSH	13.67 ± 10.22	9.10 ± 8.57	Yoga practices significantly improved TSH, FVC, FEV1, FEV1/FVC, PEFR, MVV, and IC.
								FVC	2.26 ± 0.38	2.39 ± 0.43
								FEV1	1.89 ± 0.26	2.05 ± 0.26**
								FEV1/FVC	79.97 ± 4.43	81.32 ± 5.59
								PEFR	3.02 ± 1.07	3.73 ± 1.23**
								MVV	72.72 ± 3.20	77.09 ± 14.43**
								IC	1.80 ± 0.34	1.89 ± 0.35***

Notes: BMI: Body Mass Index, BW: Body Weight, CG: Control Group, DASS-21: Depression Anxiety And Stress Scale, EG: Experimental Group, F: Female, FEV1/FVCG: Forced Expiratory Volume/Forced Vital Capacity, FEV1: Forced Expiratory Volume in one second, FVCG: Forced Vital Capacity, HCG: Hip Circumference, HDL: High-Density Lipoprotein, HF: High-Frequency, HFnu: Normalised high-frequency power, hrs: Hours, HR: Heart Rate, HRV: Heart Rate Variability, ICG: Inspiratory Capacity, LDL: Low-Density Lipoprotein, LF: Low-Frequency, LFnu: Normalised low-frequency power, M: Male, MVV: Maximal Voluntary Ventilation, n: Sample Size, NA: Not Applicable, OPH: Overall Perception of Health, OVs: Outcome Variables, PEFR: Peak Expiratory Flow Rate, QoL: Quality of Life, RMSSD: Root Mean Squares of the Difference of Adjacent Intervals, SD: Standard Deviation, T₃: Triidothyronine, T₄: Thyroxine, TCG: Total Cholesterol. TP: Total Power, TG: Triglyceride, TSH: Thyroid Stimulating Hormone, VLDL: Very Low-Density Lipoprotein, W/HR: Waist Hip Ratio, WCG: Waist Circumference, yrs: Years, * and # indicate intra-group and inter-group comparison respectively, *p < .05, **p < .01, ***p < .001, #p < .05, ##p < .01, ###p < .001.

Results

RoB in Studies

All three RCTs were assessed with moderate overall RoB. All NRSIs were assessed with unclear overall RoB. Summary of RoBs regarding included RCTs and NRSIs are shown in Figures 2 and 3.

Figure 2. Summary of RoB for RCTs.

Figure 3. Summary of RoB for NRSIs.

Thyroid Profile and LT₄

Four studies^{8, 23, 24, 26} indicated that yoga interventions significantly improve HT by decreasing TSH levels and doses of LT₄ and increasing T₃ and T₄ levels. Two NRSIs with six-month yoga interventions showed significant effects on reducing doses of LT₄.^{8, 23}

Lipid Profile

Three studies^{8, 23, 24} reported a significant positive effect of yoga intervention incorporating yoga asanas with varied durations from 10 days ²⁴ to 6 months^{8, 23} in improving lipid profiles, TC, LDL, VLDL, TG and HDL compared to standard care.

Anthropometric Outcomes

Two studies^{23, 24} indicated the significant effect of yoga interventions on decreasing BMI, BW, WC, HC, and W/HR of underactive thyroid patients after intra and inter-group comparisons.

Pulmonary Functions

One study ²⁶ indicated the significant effect of a six-month yoga intervention on pulmonary functions by increasing FEV1, PEFR, MVV, and IC of underactive thyroid patients.

Heart Rate Variability

One study ²² showed the significant effect of yoga intervention on HRV by increasing RMSSD, HF, and total power and decreasing LF and LF/HF.

Quality of Life Outcomes

Two studies^{9, 25} indicated a significant effect of the yoga intervention to improve QoL (with an increase in physical, psychological, and environmental aspects but a slight decrease in social aspects). However, Singh et al.’s study ²⁵ showed a significant effect of yoga intervention in improving overall QoL with no difference in overall perception of health.

Mental Health Outcomes

One case study ²³ showed the significant positive effect of 6-month yoga intervention on the mental health (rated in terms of depression, anxiety, fatigue, and stress) of HT patients.

Discussion

This SR aimed to investigate the effects of yoga interventions on primary, secondary, and comorbid outcomes of HT. The synthesis of results reported in eight studies^{8, 9, 21–26} substantiated the beneficial effect of yoga practices in improving TSH, T₃, T₄, LT₄, lipid profile, anthropometric outcomes (BW, BMI, HC), pulmonary functions, HRV, QoL, and mental health outcomes (depression, anxiety, fatigue, and stress) of hypoactive thyroid patients without reporting their adverse effects.

The three RCTs in the SR suggest favourable effects of yoga interventions on thyroid profile and LT₄. Six-month yoga nidra practice significantly decreased TSH levels. ²³ The actual mechanism underlying these results remains unknown. Studies have shown that breathing exercises, relaxation techniques, and meditation can reduce stress and balance the hypothalamic-pituitary-adrenal axis (HPA axis). ²⁷ Yoga regulates the HPA system, lowers cortisol,^{28, 29} epinephrine, and norepinephrine, boost immunity (by increasing T cells, NK cells, and CD4 cells)^{30, 31}, increases HRV ³² , empowers pulmonary functions ³³ , strengthens glucose tolerance and reduces LDL.^{31, 34, 35} Regular yoga lowered IL-6, TNF-α ³⁶ , and CRP and increased NK cells, T cells, B cells, and CD4 ³⁷ as an indication of inexpensive add-on therapy for HT and comorbid psychological problems. Regularly practicing bhujangasana, sarvangasana, vipritkarani, and halasana may impact the hypothalamic-pituitary-thyroid (HPT) axis and reduce blood TSH. ³⁸ T₄ and T₃, which comprise just 20% of the circulating T₃ in the blood, are the two main hormones secreted by the thyroid gland. Ujjayi breathing increases the intrathoracic pressure due to a slight contraction of the thyroid gland, potentially resulting in the increased secretion of T₃ and T₄. ³⁹ The remainder of the T₃ is created by peripheral tissues, including skeletal muscle, activating enzymes of both types 1 and 2 of iodothyronine deiodinase –DIO1 and DIO2, which split an iodine atom from T₄. These yoga poses may affect skeletal muscle and peripheral tissue to activate DIO1 and DIO2, which split an iodine atom from T₄. Omkar meditation enhances the circadian rhythm, induces plasma melatonin ³³ , and may modulate serum TSH levels.

The two included trials^{24, 40} showed positive effects of yoga interventions in reducing TG, TC, LDL, and VLDL of hypoactive thyroid patients. Yoga practice stimulates the thyroid gland to secrete THs—T3 and T4. Increased TH lowers plasma levels of phospholipids, TGs, and cholesterol. Conversely, decreased thyroid secretion significantly increases cholesterol, phospholipids, and triglyceride plasma concentrations. THs lower plasma cholesterol levels by several processes, one of which is a marked increase in bile secretion of cholesterol and the resulting loss of cholesterol in feces. THs may cause an increase in LDL receptors in the liver cells, which in turn causes the liver to quickly remove LDL from plasma and secrete cholesterol in these lipoproteins by the liver cells. The consequences are the same as Nilakanthan et al.’s study finding, which reported a significant decrease in lipid profile outcomes after 16 weeks of yoga intervention. ⁸ An RCT showed a significant reduction in lipid profile after five months of YT.^{22, 23} Increased postural activity may have contributed to a decrease in TGs, TC, LDL, and an increase in HDL.^{28, 41} The increase in hepatic lipase and lipoprotein lipase, which can enhance the absorption of TGs by adipose tissue and impact lipoprotein metabolism, may cause a change in lipid profile followed by yoga practice. ²⁰

Yoga interventions significantly improved anthropometric outcomes—BW, BMI, HC, WC, and W/HR-significantly. ²⁴ Another study has shown that bhujangasana (cobra pose), bhastrika (periodic breathing), and kapalabhati (deep breathing) pranayama stimulate metabolic rate and oxygen consumption ⁴² by reducing body weight. Various studies found that being overweight is associated with overstimulation of the HPA axis, which alters the diurnal cortisol secretion. ⁴³ Abnormal regulation of the HPA axis and perceived stress-dependent cortisol levels are strongly related to perturbations of the endocrine axis. ⁴⁴ Consistently, an SR and MA including 44 RCTs with a total of 3168 participants reported a significant effect of yoga on improving blood pressure, heart rate, breath rate, waist circumference, waist/hip ratio, total cholesterol, HDL, VLDL, TGs, glycosylated haemoglobin (HbA1c), and insulin resistance in the general population and high cardiovascular risk groups compared to usual care and no intervention. ⁴⁵

A study showed that yoga intervention significantly impacts pulmonary functions in hypothyroid patients. ²⁶ The three-month practice of Hatha yogic postures, pranayams (nadisodhan, bhastrika, bhramari, sheetali, and shitkari), and omkar meditation divided into two sessions—morning and evening, a day improved cardiorespiratory performance (heart rate, blood pressure, mean arterial pressure, respiratory rate, FVC, FEV1, FEV%, PEFR, and MVV), and psychologic profile (anxiety, depression, and well-being) along with an increase in plasma melatonin level. ³³ The improvement in pulmonary functions may be due to better respiratory muscle strength, improved thoracic mobility, and the balance between lung and chest elasticity, which yoga practitioners may have gained from regular yoga practice. ⁴⁶

A study indicated yoga intervention’s highly significant positive effect on HRV in hypothyroid patients. ²² The increased HRV at rest after practising pranayam indicated a stimulated parasympathetic tone that might reduce the risk of symptoms. ⁴⁷ Cyclic meditation/mindfulness followed by yoga poses consistently increased HRV by stimulating the parasympathetic tone.^{28, 32} HRV is decreased mainly because of a significant decrease in vagal activity. ⁴⁸ Some studies suggest that TSH stimulates sympathetic output from the central nervous system and acts as a neurotransmitter, critical in determining sympathovagal imbalance. ⁴⁹ Decreased vagal tone and increased sympathetic activity in HT have important clinical implications. Catecholamine receptor desensitisation decreases cardiac output, leading to a compensatory increase in norepinephrine release. ⁵⁰ Indeed, patients with low vagal tone are more susceptible to cardiovascular diseases such as myocardial infarction, rhythm disorders, and hypertension. ⁵¹ Pranayama appears to alter autonomic responses by breath-holding, increasing vagal tone, decreasing sympathetic discharge, and causing relaxation. ⁵² Various studies have found that slow breathing increases blood pressure oscillations and HRV amplitudes, particularly at a respiration rate of six breaths per minute (0.1 Hz).^{53, 54}

An RCT showed significant improvement in the physical, physiological, social, and environmental domains of QoL ⁹ , like Cramer et al.’s findings. ¹⁶ Rani et al. (2021) reported a significant effect of yoga practices on comorbid psychological conditions of HT—depression, anxiety, fatigue, and stress, aligned with Streeter’s findings that assert a significant effect of yoga to increase thalamic GABA and improve anxiety. ⁵⁵ The two qualitative studies conducted by Cartwright et al. (2023) and Park et al. (2014) also consistently reported that yoga improved stress, mindfulness, emotional regulation, self-regulation, inclusiveness, social relation and spiritual pursuit.^{56, 57} Sudarshan kriya yoga (SKY) (including a set of breath regulatory practices ujjayi, bhastrika, pranav, and cyclical breathing) ⁵⁸ is found supportive of mitigating neuropsychiatric illnesses—depression, anxiety, and stress, by upregulating gene expression—cyclooxygenase-2 gene, antiapoptotic BCL-2 gene, heat shock protein 70, and telomerase reverse transcriptase (hTERT) resulting in robust immune functions ⁵⁹ ; decreased ACTH and cortisol^{28, 60}; and increased prolactin ⁶¹ and oxytocin. ⁶² SKY also elevates antioxidant markers—superoxide dismutase (SOD) ⁶³ and glutathione peroxidase. ⁵⁹ Carlson et al. (2004) also reported that a mindfulness-based stress reduction (MBSR) programme comprised of relaxation, meditation, gentle yoga poses, and daily home practice significantly improved overall QoL, stress, and sleep quality and reduced cortisol levels in breast and prostate cancer patients. ⁶⁴ Yogic breathing practices—ujjayi (breathing against airway resistance) and bhastrika (forceful nasal breathing), initiate adequate interhemispheric synchronisation and generate a dominant global brain rhythm with high-frequency cerebral activity and have been accepted for improving and maintaining physical and emotional health via down-regulation of the HPA axis resulting in enhanced autonomic and emotional control, cognitive functions and the QoL in all age groups.^{65, 66}

The mechanical and vascular effects developed on thyroid by the practice of yoga poses and locks (suryanamaskar, bhujanga, sarvanga, matsya, kandhra, vipritkarani, halasana, tricon, vakra, ardhamatsyendra, jalandharbandh); parasympathetic tone and immunomodulation induced by the practice of ujjayi, bhramari, chandrabhedi, solar meditation, om/Gayatri mantra chanting, and corpse pose; and improved cardiopulmonary function and weight reduction caused by the practice of bhastrika, kpalbhati, suryabhedi, loosening poses, and alternate nostril breathing may prevent and mitigate the HT. The mechanisms of yoga practices’ effects on HT are yet unclear and need to be explored and tested in further studies.

Conclusion

Duly designed yoga interventions, including yoga poses, breath regulations, locks, concentrations, and meditations, may improve thyroid profile, lipid profile, cardiopulmonary functions, anthropometric outcomes, quality of life, and mental health of hypothyroid patients as inexpensive add-on therapy with minimal risk. Definite yoga practices with a detailed mechanism of positive effects on thyroid disorders are still unclear, warranting the need for further explanatory research regarding specific yoga practices versus hypothyroidism.

Limitations and Recommendations

The included eight studies had considerable clinical and methodological heterogeneity. This created a fragile base to conclude the positive effects of yoga interventions on primary/secondary markers and comorbid conditions of hypothyroidism. Moreover, inclusion, discussion, and derived conclusions regarding the impact of yoga on hypothyroidism inferred from more NRSIs warrant the future conduct of more rigorously designed RCTs and their inclusion in SRs and MAs to reach more definite and valid conclusions regarding the effects of yoga interventions on hypothyroidism.

Authors’ Contribution

R.B.B.: Conceptualization, Supervision, Methodology, Writing-original draft, Writing-review and editing, Validation, Visualization, Project Administration. P. K. M.: Data Curation, Formal Analysis, Writing.

Statement of Ethics

Ethical permission was not applicable for this article, as this is a review article drafted from various research articles and not from patients directly.