The Impact of Environmental Humidity and Seasonal Changes on Blood Pressure and Major Health Complications: Myocardial Infarction, Stroke, Pulmonary Embolism, Syncope, and Mortality in Hypertensive Elderly Patients in the Eastern Mediterranean Region

Background: Relative humidity is an important meteorological factor that has received considerably less attention than temperature and atmospheric pressure regarding its effects on human health. This study investigated the association between environmental humidity, blood pressure, and major cardiovascular complications in well-controlled hypertensive patients. Methods: In this prospective study (which was analyzed retrospectively), 128 hypertensive patients aged 65–92 years were followed for five years in a primary care clinic. Clinical evaluations were performed every season, resulting in 20 seasonal observation periods. Relative humidity (RH) was measured during each patient visit. Poisson regression was used to evaluate the associations between humidity, season, age, and the occurrence of major clinical events, including myocardial infarction, stroke, pulmonary embolism, syncope, and death. A negative Binomial model was used to check for overdispersion; no evidence of overdispersion was detected. Repeated-measures multiple linear regression analysis was performed to assess the effect of humidity on systolic and diastolic blood pressure. Results: Relative humidity ranged from 49% to 89% during the study period. The highest number of major clinical events occurred in winter when RH was the highest (23 events), followed by summer (10), autumn (7) and spring (3). In the unadjusted analysis, higher humidity was significantly associated with an increased number of major complications. However, this association was no longer statistically significant after adjustment for age and season. Mean systolic and diastolic blood pressure values were significantly lower in men than in women (systolic: 145.1 vs. 148.7 mmHg, p < 0.001; diastolic: 75.0 vs. 79.5 mmHg, p < 0.001). After adjustment for season, age, and body mass index, increasing humidity was associated with a significant increase in both systolic and diastolic blood pressure in men (p < 0.001), whereas no significant effect on systolic blood pressure was observed in women. In contrast, diastolic blood pressure decreased significantly with increasing humidity in women (p < 0.001). Conclusions: Higher relative humidity was associated with a greater number of major clinical events in the unadjusted analysis; however, this association was no longer statistically significant after adjustment for season and other relevant covariates. Seasonal variation was more strongly associated with adverse clinical outcomes than RH considered as an isolated environmental factor. Closer monitoring of blood pressure during periods of high humidity, particularly in winter, may help reduce cardiovascular risk in elderly patients with hypertension.