Effect of Synchronization Between Millihertz Geomagnetic Field Variations and Human Heart Rate Oscillations During Strong Magnetic Storms

Protecting people with various diseases from the adverse effects of space weather factors requires an understanding of their effects on healthy people who participate in heliobiological research as a ‘control group’. This study aimed to investigate the effect of human heart-rate synchronization with variations in the geomagnetic field of the ULF frequency range (1–5 mHz) (“biogeosynchronization effect”). We analyzed 61 electrocardiogram recordings of 100 min that were obtained on 24–27 September 2023, 10–13 May 2024 and 10–13 October 2024 from two female volunteers in good health. The biogeosynchronization effect was observed in 69% of cases. The probability of its occurrence correlates with the Dst index (correlation coefficient Rs = 0.313, p = 0.014); there is no correlation with the amplitude of the ULF oscillations. It has been shown that biogeosynchronization is mainly manifested during the recovery phase of magnetic storms, provided that at this time, the geomagnetic ULF oscillations are in phase at large distances along the observation meridian (Rs = 0.531, p < 0.00001). These results confirm that geomagnetic variations in the ULF range serve as a rhythm sensor for a healthy body under normal conditions. Being a “case study”, our results require further verification on large volumes of data in different geomagnetic conditions.