Effect of 12 Weeks Yoga Therapy on Heart 
Rate Variability and Baroreflex Sensitivity 
in Female Hypothyroid Patients: 
A Randomised Control Trial.

BACKGROUND

Thyroid hormones tend to regulate the metabolic rate of the body. The autonomic nervous system (ANS) is involved in the regulation of cardiovascular functions, and its dysfunction increases cardiovascular risk. About 65% of overt hypothyroid patients have autonomic dysfunction, which is due to sympathetic overactivity and parasympathetic withdrawal leading to a state of sympathovagal imbalance. Also, hypothyroidism is stated to be an independent risk factor for cardiovascular disease.

PURPOSE: Yoga practice helps in better modulation of the ANS and has been shown to improve autonomic function in diabetes and heart failure patients. Pranayama has been shown to improve cardiac autonomic function in hypothyroidism. Therefore, we aimed to assess the effect of three months of yoga therapy on autonomic functions in female hypothyroid patients on levothyroxine supplementation.

METHODS

In this randomised open-label study, 99 hypothyroid women between the age groups of 18-50 years were recruited from the Endocrinology OPD in JIPMER and were randomly allocated to two groups. The study group subjects (n = 51) were administered three months of yoga therapy in addition to levothyroxine supplementation and a control group subjects (n = 48) received levothyroxine supplementation only. Autonomic function test parameters such as heart rate variability (HRV) and baroreflex sensitivity (BRS) were recorded at the baseline and after three months of study period in all the participants, and the parameters were compared between the groups and within the groups. HRV was measured from RR tachogram using Biopac MP150 and BRS was assessed using Finapres.

RESULTS

After three months of yoga therapy in female hypothyroid patients on levothyroxine supplementation, HRV parameters showed a significant increase in parasympathetic tone (SDNN: p = .002, RMSSD: p = .021, NN50: p < .001, pNN50: p < .001, TP: p = .001, HF: p < .001, HFnu: p = .002) along with a decline in resting sympathetic activity (LF: p = .002, LFnu: p < .001, LF:HF ratio: p = .022) and a significant improvement in BRS (p < .001). Additionally, cardiovascular parameters also showed improvement in the yoga group (SBP: p < .001, DBP: p = .010, PP: p < .001, MAP: p < .001, RPP: p < .001) compared to the control group.

CONCLUSION

Three months of yoga practice in female hypothyroid patients in addition to routine levothyroxine therapy, it is effective in enhancing cardiac autonomic function with a shift towards parasympathetic predominance, and significant improvements in cardiovascular parameters. Yoga therapy may be suggested for hypothyroid patients to improve their cardiovascular health.