Introduction: There are structural and functional links between autonomic nervous and endocrine systems. Derivatives of estrogens and gestagens applied in combined oral contraceptives (COC) reduce the production of endogenous sex steroids, but their effect on autonomic nervous system remains unknown.
Aim: To compare indices of heart rate variability (HRV) and baroreflex sensitivity (BRS) among young healthy women taking vs. non-taking COC.
Material and methods: We performed a cross-sectional study in a group of 53 healthy women (age: 23 +/- 3 years, BMI: 22.3 +/- 2.8 kg/m(2)) taking COC for > or = 3 months (COC-group) and in a group of 113 healthy women (age: 24 +/- 4 years, BMI: 22.0 +/- 3.1 kg/m(2)) not taking COC for > or = 3 months (n-COC-group). All examined women were between the 4th and the 8th day of menstrual (or pill-driven) cycle lasting from 21 to 35 days. Indices of autonomic balance was assessed based on the time- and frequency- domains of heart rate variability (HRV very low (VLF), low (LF), high (HF) frequencies and total HRV spectrum). BRS was evaluated using the sequence (BRS-Seq) and the controlled breathing (BRS-CtBr) methods.
Results: There were no differences in: age, weight, height, measures of adiposity and fat distribution, the menstrual (or pill-driven) cycle day on the day of examination, heart rate and HRV parameters between the two studied groups (all p > 0.1). BRS-CtBr was higher among n-COC-group as compared to COC-group (20.00 +/- 6.28 versus 18.07 +/- 6.57 ms/mmHg, p < 0.05). There was a trend towards higher BRS-Seq in the n-COC-group as compared to the COC-group (19.4 7 +/- 7.85 versus 16.95 +/- 5.76 ms/mmHg, p = 0.12). In the n-COC-group, BRS-CtBr and RMSSD were inversely related to age (r = -0.23, r = -0.19, p < 0.05). In the COC-group, SDNN was inversely related to waist circumference and WHR (respectively r = -0.34 and r = -0.35, both p < 0.05).
Conclusions: COC impair the reflex regulation of cardiovascular system based on baroreflex, which may indicate unfavorable influence of COC use on women health. The exact mechanism of BRS impairment caused by COC remains unknown, also in the context of the different composition of various COC. Thus, it needs to be studied further