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

The functioning of the autonomic nervous system is central to the maintenance of health. While glucose affects sympathetic and parasympathetic activity at rest, it is unclear whether it also affects cardiac reactivity. In this study, we investigated the effect of sweet and/or caloric drinks on cardiac reactivity to a relaxing exercise, namely, slow paced breathing (SPB).One hundred and fifteen healthy adults (age mean = 23.28 years, SD = 6.88 years; 75.65% female) took part in the study. After baseline, they consumed a drink that was either sweet & caloric, or sweet, or caloric, or pure water. Later, they performed a sustained attention test and SPB. Electrocardiography and impedance cardiography was obtained, blood glucose concentrations and subjective relaxation ratings were measured repeatedly throughout the session. We analyzed group differences in parasympathetic (root mean square of successive differences [RMSSD]) and sympathetic (pre-ejection period [PEP]) activity and subjective stress ratings using growth curve models and performed correlational analyses between RMSSD, PEP and blood glucose concentrations. The consumption of caloric drinks triggered PNS withdrawal and SNS activation. Despite this, SPB triggered a psychophysiological relaxation response by increasing PNS and subjective relaxation and decreasing SNS activity. This response was not modulated by the different drinks.Sweet and/or caloric drinks did not affect cardiac reactivity to SPB, but blood glucose increases triggered counterregulatory responses of the PNS and SNS. This highlights the tight connection between autonomic regulation and blood glucose homeostasis. Future research should determine modulating factors of cardiac reactivity to external demands.