Tidal rhythms in human cardiovascular function

Objective: The objective for this study was to determine whether cardiovascular function, including heart rate and blood pressure, displays rhythms in synchrony with local daily tides. Hypothesis: Our laboratory has recently shown that sleep timing is synchronized with the lunar month phases, and a recent analysis suggests that the main predictor for sleep time changes is the gravitational pull exerted by the moon. We hypothesize that other physiological variables, including cardiovascular function, will also be synchronized with lunar gravity. Methods: Human participants gave informed consent to participate of the studies. We monitored continuous blood pressure (systolic and diastolic) and heart rate with a sample frequency of 1/30 minutes, during 7 consecutive days using a TM-2430 monitoring device (A mean age = 26.88 ±0.89 years; age range 14 – 60 y.o.; age range of 64%,18-24 y.o.). In our sleep studies, we could only study the association of daily sleep events with lunar-monthly changes in gravity. However, the sampling frequency of cardiovascular variables in our study allows us to study the association of cardiac outputs with diurnal (24.8 hours) and semidiurnal (12.4 hours) tides. Results: We screened for the presence of periodicities in all three variables using two independent methods. First, we used cosinor analysis with fittings to three preset sinusoidal periods (24 hours for daily rhythms, and 12.4 and 24.8 hours for semidiurnal and diurnal tides, respectively) to detect significant (p < 0.05) amplitudes within each individual. Second, we used the Lomb-Scargle periodogram to detect significant periodicities (p < 0.05) in periods that ranged between 10 and 26 hours. Table 1 shows that while some individuals only show tidal rhythmicity according to one or the other rhythm detection method, a large number of individuals showed tidal rhythmicity according to both methods for 12.4 hours (53%), 24.8 hours (75%) or both 12.4 and 24.8 hours (40%) for at least one of the cardiovascular variables under study. Conclusions: While the daily variation of cardiovascular function is well established, the possibility that it may change according to the local gravitational influence of the moon has not been explored. Both our sleep studies and recently published research on the synchronicity of the human menstrual cycle with the lunar month suggest that the gravitational pull of the moon may have direct impact on human physiology. Our study is the first to show that tidal periodicity is present in cardiovascular function. Additionally, it is the first study to show this periodicity in synchrony with diurnal and semidiurnal tides, and not simply with spring tides that occur twice every lunar month. Current analysis will determine the phase relationship between specific cardiovascular variables and local tides. Table: see text Funding source: The Bolashaq International Scholarship, R01HL162311. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.