Effect of sweet and caloric drinks on cardiac reactivity to slow-paced breathing in healthy adults

Cardiac reactivity is proposed to be a central indicator of autonomic functioning. While hyperglycemia plays a limited role in cardiac stress reactivity, it is unclear whether it may modulate cardiac reactivity in non-stressful situations. We investigated the effect of glucose on cardiac reactivity to a relaxing exercise, namely, slow-paced breathing (SPB). A total of 115 adults (age mean = 23.28 years, SD = 6.88; 76% female) either consumed a sweet & caloric, a sweet, a caloric drink, or pure water after baseline. Later, they performed a sustained attention test and SPB. Electrocardiography and impedance cardiography was obtained, and blood glucose and subjective relaxation were measured repeatedly. We analyzed changes in parasympathetic (root mean square of successive differences [RMSSD]) and sympathetic (pre-ejection period [PEP]) cardiac activity and subjective relaxation using growth curve models and performed correlational analyses. Hyperglycemia triggered cardiac PNS withdrawal and SNS activation. Despite this, SPB increased cardiac PNS activity and subjective relaxation and decreased cardiac SNS activity in all groups. Our results align with the autonomic space model and highlight the tight link between autonomic regulation and blood glucose homeostasis. Hyperglycemia might play a limited modulating role in cardiac reactivity to slow-paced breathing.