Influence of Weather Conditions on the Incidence of SAH

Abstract

Introduction

Subarachnoid hemorrhage (SAH) is a clinical condition in which there is bleeding into the subarachnoid space, and it is known that there are modifiable risk factors, such as high blood pressure and smoking. However, specific meteorological conditions, such as temperature and atmospheric pressure, have also been observed to represent a higher risk for this condition.

Objective

The objective of this systematic review was to synthesize the current literature data on the relationship between meteorological factors and the occurrence of SAH.

Methodology

Following PRISMA guidelines, the review investigated the impact of meteorological conditions on the incidence of subarachnoid hemorrhage, with the guiding question: "What is the relationship between climate variations and SAH cases?" through comprehensive searches in academic sources with studies published between 2013 and 2023 in the PubMed and BVS (Virtual Health Library) databases.

Results

The main variables evaluated were daily average temperature, average atmospheric pressure, relative humidity, wind speed, influenza incidence, solar incidence, partial oxygen pressure, seasonal distribution, and seasons of the year.

Conclusion

The study highlighted the influence of meteorological conditions on the occurrence of subarachnoid hemorrhage (SAH), especially in cases of extreme climate variations and high atmospheric pressure.

 

MissingLinkText

Resumo

Introdução

A hemorragia subaracnóidea (HSA) é uma condição clínica em que ocorre sangramento para o espaço subaracnóideo, sabe-se que existem fatores de risco modificáveis, como hipertensão arterial e tabagismo. No entanto, também se observou que condições meteorológicas específicas, como temperatura e pressão atmosférica, representam um risco mais elevado para esta condição.

Objetivo

O objetivo desta revisão sistemática foi sintetizar os dados atuais da literatura sobre a relação entre fatores meteorológicos e a ocorrência de HSA.

Metodologia

Seguindo as diretrizes do PRISMA, a revisão investigou o impacto das condições meteorológicas na incidência de hemorragia subaracnóidea, tendo como questão norteadora: "Qual a relação entre as variações climáticas e os casos de HSA?" por meio de buscas abrangentes em fontes acadêmicas com estudos publicados entre 2013 e 2023 nas bases de dados PubMed e BVS (Biblioteca Virtual em Saúde).

Resultados

As principais variantes avaliadas foram a temperatura média diária, pressão atmosférica média, umidade relativa, velocidade do vento, incidência de influenza, incidência solar, pressão parcial de oxigênio, distribuição sazonal e estações do ano.

Conclusão

O estudo destacou a influência das condições meteorológicas na ocorrência de hemorragia subaracnóidea (HSA), principalmente em casos de variações climáticas extremas e elevada pressão atmosférica.

 

MissingLinkText

Keywords

subarachnoid hemorrhage - weather - seasons - climate

Palavras-chave

hemorragia subaracnóidea - tempo - estações do ano - clima

Introduction

Subarachnoid hemorrhage (SAH) is a clinical condition characterized by bleeding into the subarachnoid space, the area between the arachnoid and pia mater meninges, known as the subarachnoid space.[1] This condition is caused by the rupture of an aneurysm in more than 80% of cases,[2] affecting approximately 600 thousand individuals globally, and it has two distinct etiologies: traumatic or spontaneous.[1] The development of this condition involves some modifiable risk factors such as arterial hypertension, smoking, and alcoholism, as well as non-modifiable risk factors such as female gender, nationality – i.e., Japanese and Finnish – and genetic markers.[2]

Beyond those risk factors, the incidence of SAH has been linked to environmental variations, specifically meteorological factors such as atmospheric pressure, climate, temperature, air humidity, and the different seasons of the year.[3] Therefore, several studies were extended to explore the relationship between these factors and SAH.

Although some work supports that meteorological and seasonal changes are associated with an increase in the rate of SAH, results vary according to geographic location, climate, and sample size, so this relationship is not fully understood.[3]

Considering these complexities, a systematic review was conceived in order to synthesize the main studies correlating meteorological factors with the occurrence of SAH, with meticulous attention to relevance criteria, aiming to elucidate this nuanced relationship.

 

MissingLinkText

Methodology

Study Design

The present study is a systematic review based on the PRISMA methodology. We performed a systematic search of the PUBMED, SciELO, LILACS databases and the selected studies references. Articles published between 2013 and 2023 wich hypothesized a link between meteorological conditions on the occurrence of subarachnoid hemorrhages were all considered. The study was guided by the question: "What is the relationship between climatic variations and the incidence of SAH cases?"

Using the PubMed search tool, we selected the MeSH terms of the most relevant articles to create a new search for more publications that could be included in this review.

The keywords used for were: “Subarachnoid Hemorrhage", "Weather”, “Seasons” and “Climate.”

After the removal of duplicates, two independent authors screened the title and abstracts for eligibility. Next, the authors screened full-text articles for inclusion. Disagreement was resolved by discussion with a third author.

Based on the PRISMA flowchart presented, a systematic search was conducted, identifying 216 records across multiple databases (PubMed/Medline: 183, Scielo: 2, and Lilacs: 31), along with 6 additional records from other sources. After removing 13 duplicates, a total of 209 unique records were screened. This initial screening led to the exclusion of 98 records, resulting in 111 full-text articles assessed for eligibility. Out of these, 89 articles were excluded, with 59 deemed unrelated to the subject and 30 lacking full-text availability. Ultimately, 22 studies were included in the qualitative synthesis, providing a curated selection of relevant literature for the systematic review. The PRISMA flow diagram illustrating the search and study selection strategy is presented in [Figure 1].

Fig. 1 Representative flowchart of the identification, screening, eligibility and inclusion and exclusion criteria of this systematic review.

 

MissingLinkText

Population

The study analyzed articles that demonstrate the correlation between the influence of climate and the incidence of SAH in adult and elderly patients. There were no limitations based on gender, sex, race, ethnicity, or socioeconomic status.

 

MissingLinkText

Inclusion Criteria

Inclusion criteria were the following: quantitative studies, such as randomized clinical trials and cohort studies, available in full in Portuguese, Spanish, or English, published in the last 10 years (2013–2023) related to the topic.

 

MissingLinkText

Exclusion Criteria

Articles whose studies weren't conducted on human subjects had no relation with the main subject, duplicated studies weren't available in full and case reports were excluded.

 

MissingLinkText

 

MissingLinkText

Results

A total of 22 articles, all of which met the predetermined inclusion and exclusion criteria, were analyzed and then organized in [Table 1], to specify the samples utilized and outcomes assessed in these studies.

Table 1 Selected studies assessing the influence of meteorological conditions

Author (year)	Study Type	Sample	Evaluated Weather Condition	Outcome
Helsper M, Agarwal A, Aker A, et al. 2021[4]	Retrospective Study	The approach of big data and deep learning enabled the simultaneous analysis of 13 different meteorological and climatic parameters and 1,271 cases of SAH over 6,334 days. The study group consisted of 422 (33.2%) male patients and 849 (66.8%) female patients, with a mean age of 55 years (range 19 to 94; SD ± 14).	Meteorological parameters were included: maximum daily wind speed (m/s), average daily wind speed (m/s), daily amount of precipitation in (mm), daily amount of sunshine (hours), daily amount of snowfall (cm), average daily vapor pressure (hPa), average daily atmospheric pressure (hPa), average daily humidity (%), average daily temperature (°C), maximum and minimum daily temperature at 2 m above ground level ( °C), minimum daily temperature at 5 cm above the ground (°C) and cloud cover.	During the data preprocessing stage, ictus dates and certain climate parameters showed some correlation. However, the applied deep-learning models were not able to reproduce or predict bleeding days, nor to detect a pattern in the influence of climate and weather as a whole or individually for each parameter. This provides evidence that the incidence of SAH has no relevant correlation with meteorological factors.
Kockler M, Schlattmann P, Walther M, et al. 2021[5]	Retrospective Case-Crossover Study	A total of 791 individuals were included, with 469 (63%) women and 295 (37%) men, admitted to three major hospitals in Germany for non-traumatic SAH with determinable onset of symptoms.	Effects of atmospheric pressure, relative humidity and ambient temperature	For an increase in relative air humidity of 17.6%, the risk of SAH increased in men by 39% (OR 1.39, 95% CI 1.05–1.86) with a latency time of one day and by 35% (OR 1.35, 95% CI 1.02–1.80) with a latency time of two days. In the general population, the risk of hypertension increased by 15% (OR 1.15, 95% confidence interval (CI) 1.01–1.30) for each increase in mean daily atmospheric pressure of 11.5 hPa, with a latency time of three days. Similarly, in subgroups, the risk of SAH increased by 41% (OR 1.41, 95% CI 1.08–1.82) in patients with aneurysms smaller than 7 mm. There was no association between the risk of SAH and 24-h changes in all three meteorological variables investigated at all latency times, except for the risk of SAH in patients with aneurysms smaller than 7 mm, whose risk increased by 4% (OR 1.04, 95% CI 1.007–1.74) two days after exposure to a 24-h increase in atmospheric pressure of 6.2 hPa.
Illy E, Gerss J, Fischer BR, Stummer W, Brokinkel B, Holling M. . 2020[6]	Retrospective Study	We examined all patients (N = 1,169) treated for subarachnoid hemorrhage (SAH; n = 484), intracerebral hemorrhage (ICH; n = 417), or chronic subdural hematoma (CSDH; n = 268) in the department over a 7-year period, between June 1, 2005, and May 31, 2012. Admission date was correlated with corresponding meteorological parameters.	Seasonal distribution	The incidence of SAH was highest in April (n = 49, 10.1 % of all SAH cases) and tended to peak in winter with a trough in summer. Although the data suggest seasonal variations in SAH, ICH, and CSDH, individual climatic parameters do not demonstrate causal relationships with the incidence of cerebrovascular events. For SAH, logistic regression analyses revealed increased risk associated with decreased barometric pressure (p = 0.021), confirming previously published results and suggesting a possible underlying relationship.
Van Donkelaar CE, Potgieser ARE, Groen H, et al. 2018[7]	Observational Cohort Study	Included 1,535 patients with spontaneous SAH admitted to the neurovascular center in northern Netherlands between 2000 and 2015. To compare the incidences of SAH throughout the year and test the association with meteorological conditions, incidence rate ratios (IRRs) with corresponding 95% confidence intervals (CI) were used, calculated by Poisson regression analyses.	Atmospheric Pressure and Seasons (Summer).	A 1-hPa change in atmospheric pressure was significantly associated with an increased risk of SAH 2 days later (IRR, 1.11; 95% CI, 1.03e1.19). Also, a change of 1 hPa in the third day before the ictus increases the risk of SAH (IRR, 1.08; 95% CI, 1.01e1.16). Combination of the results of the second and third day before SAH yielded the same significant association. Again, these results were mainly found in the subgroup of aneurysmal SAH. For nonaneurysmal SAH, there was no significant association between change in atmospheric pressure and SAH. A change of 1°C 1 day before the ictus decreases the risk of SAH with an IRR of 0.89 (95% CI, 0.82e0.98). The initial 2 days before the ictus combined yielded a similar significant association between change in temperature and SAH (IRR, 0.86; 95% CI, 0.77e0.97), which once more was a result of the subgroup analysis of aneurysmal SAH. The IRR of aneurysmal SAH in July remains significantly lower compared with other months (IRR, 0.67; 95% CI, 0.49e0.92). The variation in atmospheric pressure the second and third day before the ictus remained associated with higher incidence of aneurysmal SAH (IRR, 1.11; 95% CI, 1.00e1.23).
Yao DX, Liu YB, Wu QM, Guo N, Pan F, Yu HL. 2020[8]	Retrospective Study	Data collected between January 2005 and September 2019 were analyzed, including 1,682 consecutive SAH patients from one hospital. Meteorological data during this period, including temperature, atmospheric pressure, and humidity, were obtained from the China Surface Meteorological Station.	Average Temperature.	Temperature decline was associated with increased risks of SAH: overall cumulative OR was 1.14 (95% CI: 1.05-1.23) for -1.1°C; 2.11 (95% CI: 1.37-3.25) for -6.2°C, as compared with a reference TCP of 0°C. Temperature decline on the day of SAH onset was significantly associated with SAH incidence days, ORs 1.34 (95% CI: 1.19-1.52). In addition, December, ORs 1.49 (95% CI: 1.17-1.90) in winter was the ictus peak in Rizhao throughout the year.
Launey Y, Le Gac G, Le Reste PJ, Gauvrit JY, Morandi X, Seguin P. 2020[9]	Retrospective Study	Included 295 adults with SAH admitted to the neurosurgery department and intensive care unit of the University Hospital of Rennes (France) between January 1, 2011, and December 31, 2012. Meteorological variables, their variations, lunar phases, and tidal coefficients were compared between days with and without SAH.	Average Temperature.	The mean minimum temperature was significantly lower on days with SAH (7.7 ± 4.7°C versus 8.3 ± 4.6°C; P = 0.039); the temperature variation between two consecutive days was significantly higher for days with SAH (8.6 ± 4.1°C versus 7.9 ± 3.8°C). Multivariate analysis showed that a temperature drop of 8°C or more over two days was associated with a 35% increased risk of SAH (odds ratio 1.35 [1.03-1.77]). There were no significant effects of other meteorological variables, lunar phase, or tidal coefficient on the occurrence of SAH.
Hr D, Praneeth K, Aggarwal A, Gupta SK, Sachdeva N. 2022[10]	Prospective Study and Literature Review	Included were 392 patients with SAH who underwent clipping. Meteorological parameters such as temperature, barometric pressure, humidity, and hours of sunshine were recorded for two consecutive days before the ictus and on the day of the ictus.	Average Temperature .	There was no significant difference in the incidence of SAH among the different seasons. Pre-ictus temperature drop leads to an increase in the number of cases. 241 patients (61.5%) reported were from geographical areas that experienced a temperature drop in the last 2 days, with an average temperature drop of 1.1 (SD 2.1) degrees Celsius. The incidence of patients with SAH in seasons with fewer hours of sunshine (1.13 patients/day) was significantly higher than in seasons with higher hours of sunshine (0.9 patients/day).
Vencloviene J, Radisauskas R, Kranciukaite-Butylkiniene D, Tamosiunas A, Vaiciulis V, Rastenyte D. 2021[11]	Retrospective Study	The study was conducted in Kaunas, Lithuania, from 2000 to 2010, and 4,038 cases (2,226 men and 1,812 women) of stroke were analyzed. Of these, 3,245 (80.4%) cases were ischemic strokes (IS), 533 (13.2%) cases were intracerebral hemorrhages (ICH), and 260 (6.4%) cases were SAH.	Barometric Pressure	An increased risk of SAH was associated with a change in daily average barometric pressure above 3.9 hPa (RR = 1.49, 95% CI 1.14-1.96), and a stronger El Niño event had a protective effect against SAH (RR = 0.34, 95% CI 0.16-0.69).
Li M, Hu S, Yu N, Zhang Y, Luo M. 2019[12]	Retrospective Study	Between January 1, 2015, and December 31, 2017, a total of 1,751 patients (1,062 women and 689 men) were included in the present analysis.	Average Temperature and Barometric Pressure	In this study, the incidence of SAH was higher in winter (January and February); lower in summer (July); and significantly higher during two periods, from 4:00 to 7:59 and from 16:00 to 19:59, than at other times of the day. Lower daily average, maximum, and minimum temperatures, and higher daily average barometric pressure were associated with an increased rate of SAH.
Huang Q, Lin SW, Hu WP, et al. 2019[13]	Multicenter Study	A total of 2,555 consecutive patients with SAH in Fuzhou were collected using a specialized stroke admission database from January 2013 to December 2017.	Average temperature, barometric pressure, and seasons (spring and winter).	Daily minimum temperature (IRR 0.976, 95% CI 0.958-0.996) and maximum pressure (IRR 1.022, 95% CI 1.001-1.042) were independently correlated with the onset of SAH. Low temperature (below 16°C) and excessive barometric pressure (above 1008 hPa) increased the risk of SAH. March in spring and December in winter are the predominant onset periods in Fuzhou.
Steiger, H.-J., Petridis, A. K., Tortora, A., Mijderwijk, H.-J. et al 2020[14]	Retrospective Study	During a 10-year period, from January 1, 2009, to December 31, 2018, a total of 1,569 patients with SAH were hospitalized. .	Average daily temperature (T D0), barometric pressure (QNH D0), and precipitation (Precip. D0), and also from the preceding days, were selected as primary parameters	Pearson's correlation matrix suggested a weak positive correlation of admissions for SAH with precipitation on the previous day, and weak inverse relations with the actual mean daily temperature, the temperature change from the previous days, and with barometric pressure on the index day and the day before. The deep learning algorithm with the feedforward network achieved a predictive accuracy of 53%. For comparison, analysis using the Logistic Regression Classifier (LRC) achieved a predictive accuracy of 62%. In other words, higher and increasing temperature and higher barometric pressure appear to protect against SAH and on the other hand, colder and decreasing temperature and rain on the previous day appear to increase the risk.
Kellogg M, Petrov D, Agarwal N, et al. 2017[15]	Retrospective Study	The study population consisted of 312 patients who presented at Newark University Hospital, New Jersey, between January 1, 2003, and December 31, 2008, with SAH.	Barometric Pressure, Average temperature	The peak number of bleed days per month was 33 in September and December, and the fewest number of bleed days was 20 in April and May. There was no statistically significant relationship between mean temperature and incidence of bleed, cluster, or multiple-bleed days; however, the mean temperature was consistently decreased on aSAH days. Multiple-bleed days had a mean atmospheric pressure of 1,018.51 millibars (mbars), and non–multiple-bleed days had a mean atmospheric pressure of 1,016.53 mbars.
Han MH, Yi HJ, Ko Y, Kim YS, Lee YJ. 2016[16]	Retrospective Study	Data from patients were retrospectively collected from the hospital's subarachnoid hemorrhage registry between January 1, 2004, and December 31, 2014, with 1477 cases included.	Average temperature, degree of sunshine, and air humidity.	There was no significant correlation between average temperature and SAH. Sunshine correlated positively with SAH in the younger age group, and humidity showed a negative correlation with SAH in the older age group.
Zheng Y, Wang X, Liu J, Zhao F, Zhang J, Feng H. 2016[17]	Case-Control Study	Over a 2-year period, 735 patients with hypertensive intracerebral hemorrhage (HIC) or subarachnoid hemorrhage (SAH) were included in the study in the Fularji district, Heilongjiang province, China.	Average Temperature	The daily average ambient temperature (TA) was statistically associated with the onset of primary hypertensive intracerebral hemorrhage (OR, 0.983) and SAH (OR, 0.984; P = 0.046). The incidence of SAH increased on days with lower temperatures.
Lee S, Guth M. 2017[18]	Cross-Sectional Cohort Study	During the nine-year study period, the total number of hospital admissions for SAH was 111,316 in 1,578 hospitals in Korea.	Average Temperature.	The increased risk of SAH was higher in the temperate zone. An increase above the heat threshold temperature and a decrease below the cold threshold temperature were correlated with an increased risk of SAH in susceptible populations.
Backes D, Rinkel GJ, Algra A, Vaartjes I, Donker GA, Vergouwen MD. 2016[19]	Prospective Observational Study	A national sample of 18,714 patients with SAH was associated with weekly temperature and influenza-like illness consultation data.	Average temperature and influenza incidence	The incidence of SAH increases during cold temperatures and influenza epidemics. The association between cold weather and SAH was confirmed in our analysis of 30 European population-based studies.
Tarnoki AD, Turker A, Tarnoki DL, et al. 2017[20]	Retrospective Study	During the 1,045-day study period, 937 cases of ischemic stroke occurred on 594 days, and 473 cases of subarachnoid hemorrhage occurred on 314 days.	Barometric Pressure	The increased incidence of SAH cases was consistent with both lower and higher daily barometric pressure (IRR 0.87and IRR 1.08) and higher air temperature (IRR 0.98). The presence of hurricanes and/or tropical storms did not influence the frequency of SAH. We found no relationship between the presence of fronts and hospitalizations for ischemic stroke or SAH.
Patrice T, Rozec B, Desal H, Blanloeil Y. 2017[21]	Case-Control Study	Seventy-one patients were consecutively recruited at a single center located 45 km from the Atlantic coast. Weather conditions were analyzed from 72 hours before subarachnoid hemorrhage until 24 hours after.	Barometric pressure, partial pressure of oxygen (pO2), and seasons (spring and autumn).	The risk of subarachnoid hemorrhage is higher during spring and autumn, lower between midnight and 6:00 a.m. The risk is higher after a period of barometric pressure above 1010 hPa (83%) and high pO2, and lower for barometric pressure below 990 hPa and pO2 below 20.6.
Lai PM, Dasenbrock H, Du R. 2014[22]	Retrospective Study	A total of 16,970 patients from 723 hospitals across 41 states in the US were analyzed over a 10-year period who presented with aneurysmal subarachnoid hemorrhage.	Degree of sunlight incidence and air humidity.	The decrease in daily sunlight and lower relative humidity were associated with an increase in the hospital admission rate for ruptured brain aneurysms, but they were not associated with differential mortality among hospitalized patients. Additionally, it was found that higher precipitation was associated with a significant reduction in hospital mortality afterward, but not with different admission rates for subarachnoid hemorrhage.
Rivera-Lara L, Kowalski RG, Schneider EB, Tamargo RJ, Nyquist P. 2015[23]	Retrospective Study	Between January 1, 1991, and March 31, 2009, 1,168 patients with acute SAH were admitted to our institution and included in the study.	Average temperature and seasons (summer).	Subarachnoid hemorrhage (SAH) was more likely to occur during the summer and on days with temperature fluctuations below 10°F (8% versus 4%; p = 0.002). During the warmer months of the year in the mid-Atlantic region, cooler daily maximum temperatures, lower heat loads above 70°F, and smaller intraday temperature fluctuations are associated with increased SAH admissions similar to the colder months.
Takumi I, Mishina M, Kominami S, et al. 2015[24]	Retrospective Study	A total of 4,310 patients hospitalized for hemorrhagic or ischemic stroke were included from January 2000 to December 2005.	Average temperature.	Daily admissions for hypertensive intracerebral hemorrhage (HIC), subarachnoid hemorrhage (SAH), acute ischemic stroke (AI), lacunar infarction (LI), and cerebral embolism (CE) increased when the mean temperature on the onset day was 1°C lower than that of the previous week. Decreases in minimum ambient temperature predicted an increase in the number of admissions for HIC and SAH.

Out of the 22 selected articles, 18 studies established an association between meteorological factors such as climate, the seasons of the year, barometric pressure, and air humidity levels with the incidence of SAH. However, 3 other studies reported either statistically insignificant relationships or findings contradicting the association between SAH occurrence and meteorological factors.

Of the meteorological factors analyzed, 16 articles addressed average temperature, 7 focused on barometric pressure, 4 discussed the seasons, 4 examined sunlight exposure and air quality, 1 covered partial oxygen pressure, 1 looked at influenza incidence, and 3 dealt with atmospheric pressure. All articles discussed more than one factor but with an emphasis on those mentioned.

 

MissingLinkText

Discussion

The interaction between climatic conditions and the incidence of subarachnoid hemorrhage (SAH) highlights the role of climate factors as potential contributors to cerebrovascular events. According to previous findings, climate can interfere with SAH incidence rates seasonally and periodically. Several observational analyses have explored these correlations using different parameters. Studies indicate that sudden climate changes, extreme temperatures, and atmospheric pressure fluctuations may actively impact SAH incidence.

Although these findings are significant, the exact temperature ranges capable of increasing SAH risk remain partially uncertain. Studies suggest that both minimum and maximum temperatures, when associated with adverse weather conditions, can elevate the risk of aneurysm rupture, particularly in predisposed individuals. Han et al. (2017)[16] demonstrated monthly variations in the incidence of subarachnoid hemorrhage and mortality correlated with climate and pollution, indicating that environmental factors may influence these outcomes. However, the variability in data collection methods and the lack of standardization in SAH diagnostic criteria can influence the results, making them less conclusive and hindering comparisons across studies.[4] [5] [7]

Temperature changes have been shown to predispose individuals to elevations in systolic blood pressure, one of the risk factors for SAH. Fluctuations in atmospheric pressure may indirectly impact SAH risk by affecting intracranial venous return. High atmospheric pressure can activate inflammatory responses, such as the release of IL-1β, which may weaken the aneurysm wall and lead to its rupture. The study by Steiger et al. (2020)[14] used a machine-learning approach to predict the probability of SAH patient admissions, reinforcing the idea that meteorological factors play an important role in the incidence of hemorrhagic events. Additionally, factors such as sympathetic nervous system activity, fibrinolytic function, and platelet aggregation may contribute to variations in systolic blood pressure. However, the lack of longitudinal data and the difficulty in controlling external variables that may influence these parameters make the findings less robust. This suggests that while data points to a relationship, further research is needed to solidify these connections and fully understand the underlying mechanisms.[10] [11] [22]

Low temperatures, especially those below 8°C, have been associated with an increase in the incidence of severe hemorrhagic strokes. The work by Kellogg et al. (2017)[15] demonstrated that meteorological variables influence the incidence of aneurysm rupture, reinforcing the vulnerability of populations exposed to adverse climatic conditions. Elderly patients, who often present comorbidities and blood pressure fluctuations, are particularly vulnerable to these temperature variations. During colder months, behavioral changes such as increased alcohol consumption and smoking may lead to blood pressure decompensation and cause vasoconstriction, thereby increasing the risk of SAH. Moreover, cold weather may be associated with influenza outbreaks, which some studies suggest are linked to higher rates of SAH. However, these studies often do not consider other risk factors, such as pre-existing cardiovascular diseases, which may confound the results and impact the observed relationship between climate and SAH incidence.[8] [13] [19]

While cold weather can increase sympathetic tone and catecholamine secretion—factors known to raise blood pressure and exacerbate aneurysm vulnerability, higher temperatures and high atmospheric pressure may, paradoxically, reduce SAH incidence. The research by Illy et al. (2020)[6] also discussed the influence of weather conditions on hemorrhage incidence, aligning with the hypothesis that climate may be an underlying factor in hemorrhagic events. Sun exposure, although associated with lower blood pressure and vasodilation, has a more pronounced effect on ischemic stroke rates than on SAH. However, high atmospheric pressure levels (above 1010 hPa) and low temperatures (below 16°C) during seasons with limited sunlight, such as autumn, winter, and spring, are cited as risk factors for SAH. High or low atmospheric pressure is recognized as a primary risk factor due to its role as a delayed trigger for SAH. Limitations of these studies include restricted sampling and the difficulty of generalizing results to broader populations, as demographic variables are not always adequately considered in analysis models.[9] [20]

Socioeconomic and geographic factors also modify these climate-related risks. Individuals from lower socioeconomic backgrounds, particularly women under 75 years living in urban areas, are at increased risk, as demonstrated by hospitalization data during periods of low temperature. Male samples show a higher incidence among men over 75 years in rural areas during periods of high temperatures. This underscores the influence of environmental and demographic disparities on SAH outcomes, as well as the need for targeted approaches to prevention and treatment that consider these factors. However, many studies do not adequately control these socioeconomic factors, which may lead to an overestimation of the impact of climatic conditions.[17]

Conversely, some studies dispute the existence of a direct association between meteorological variations and SAH, arguing that current methods of climate and SAH tracking lack specificity, resulting in inconclusive outcomes. Lee and Guth (2017)[18] investigated associations between temperature and hospital admissions for SAH in Korea, highlighting the need for more in-depth data analysis. These studies suggest that the relationship between extreme weather variations and global warming may complicate studies on SAH incidence, emphasizing the need for more refined methodologies to effectively track these events. The lack of control for confounding variables and reliance on secondary data are also limiting factors in these studies, necessitating greater scientific rigor in future analyses.[1] [2]

In light of the findings linking climatic conditions to an increase in SAH incidence, some preventive measures can be suggested. Regular blood pressure monitoring is essential, especially in vulnerable populations, such as the elderly, during extreme temperature periods. Increased physical activity, where possible, and encouragement of vaccination against seasonal diseases, such as influenza, can be recommended to reduce SAH incidence, considering the correlation between infections and cerebrovascular complications.

 

MissingLinkText

Limitations

One of the main limitations of this study is the small total number of participants analyzed in the articles, which may represent a significant bias in the conclusions. Additionally, the meteorological factors were assessed in isolation, without accounting for the potential influence of various other elements, such as pre-existing comorbidities, ethnic factors, and genetic predispositions. This restricted approach may not adequately capture the complexity of the interactions among the studied factors, thus compromising the comprehensiveness of the obtained results.

 

MissingLinkText

Conclusion

From the identified studies, it can be concluded that, physiologically, it is possible to relate meteorological conditions to the occurrence of non-traumatic subarachnoid hemorrhage (SAH). As evidenced, these factors cannot be directly controlled, representing an inherent risk for the development of subarachnoid hemorrhagic events. Thus, protocols for evaluation and potential prevention may be developed in the future to reduce the rate of SAH in populations more exposed to these conditions. Furthermore, it is important to emphasize the need to foster the development of more research in this area, involving methodologies of greater technical and scientific rigor, as well as analysis of larger samples in major healthcare centers.

 

MissingLinkText

 

MissingLinkText

Conflict of Interest

All authors confirm that they have no affiliations with or involvement in any organization or entity that has a financial interest (including honoraria, educational grants, participation in speakers' bureaus, membership, employment, consultancies, stock ownership, or other equity interest, and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge, or beliefs) in the subject matter or materials discussed in this manuscript.

• References

• 1 Rabelo NN, Rabelo NN, Brito JS. . Hipertensão intracraniana na Emergência. In: Sociedade Distância, v. 2). Brasileira de Clínica Médica; Lopes AC, Tallo FS, Lopes RD, Vendrame LS, organizadores. PROURGEM Programa de Atualização em Medicina de Urgência e Emergência: Ciclo 12. Porto Alegre: Artmed Panamericana; 2018. . p. 57–97. (Sistema de Educação Continuada a Distância, v. 2).
• 2 Neifert SN, Chapman EK, Martini ML. et al. Aneurysmal Subarachnoid Hemorrhage: the Last Decade. Transl Stroke Res 2021; 12 (03) 428-446
• 3 Kawai K, Nonaka K, Suzuki H, Kirino T, Tamura A. Differential effects of activity and climate on onset of subarachnoid hemorrhage. Neurol Med Chir (Tokyo) 2001; 41 (05) 229-236 , discussion 236–237
• 4 Helsper M, Agarwal A, Aker A. et al. The Subarachnoid Hemorrhage-Weather Myth: A Long-Term Big Data and Deep Learning Analysis. Front Neurol 2021; 12: 653483
• 5 Kockler M, Schlattmann P, Walther M. et al. Weather conditions associated with subarachnoid hemorrhage: a multicenter case-crossover study. BMC Neurol 2021; 21 (01) 283-292
• 6 Illy E, Gerss J, Fischer BR, Stummer W, Brokinkel B, Holling M. Influence of Meteorological Conditions on the Incidence of Chronic Subdural Haematoma, Subarachnoid and Intracerebral Haemorrhages - the “Bleeding Weather Hypothesis”. Turk Neurosurg 2020; 30 (06) 892-898
• 7 van Donkelaar CE, Potgieser ARE, Groen H. et al. Atmospheric Pressure Variation is a Delayed Trigger for Aneurysmal Subarachnoid Hemorrhage. World Neurosurg 2018; 112: e783-e790
• 8 Yao DX, Liu YB, Wu QM, Guo N, Pan F, Yu HL. Temperature decline is a trigger of subarachnoid hemorrhage: case-crossover study with distributed lag model. Eur Rev Med Pharmacol Sci 2020; 24 (10) 5633-5643
• 9 Launey Y, Le Gac G, Le Reste PJ, Gauvrit JY, Morandi X, Seguin P. Role of bioclimate conditions on cerebral aneurysm rupture in the Brittany region of France. Neurochirurgie 2020; 66 (01) 9-15
• 10 Hr D, Praneeth K, Aggarwal A, Gupta SK, Sachdeva N. Seasonal variation and Incidence of rupture of intracranial aneurysm : A prospective study and Literature review. Acta Neurol Taiwan 2022; 31 (03) 137-145
• 11 Vencloviene J, Radisauskas R, Kranciukaite-Butylkiniene D, Tamosiunas A, Vaiciulis V, Rastenyte D. Association between stroke occurrence and changes in atmospheric circulation. BMC Public Health 2021; 21 (01) 42-52
• 12 Li M, Hu S, Yu N, Zhang Y, Luo M. . Association Between Meteorological Factors and the Rupture of Intracranial Aneurysms. Available from: https://www.ahajournals.org/doi/suppl/10.1161/JAHA.119.012205
• 13 Huang Q, Lin SW, Hu WP. et al. Meteorological Variation Is a Predisposing Factor for Aneurismal Subarachnoid Hemorrhage: A 5-Year Multicenter Study in Fuzhou, China. World Neurosurg 2019; 132: e687-e695
• 14 Steiger HJ, Petridis AK, Tortora A. et al. Meteorological factors for subarachnoid hemorrhage in the greater Düsseldorf area revisited: a machine learning approach to predict the probability of admission of patients with subarachnoid hemorrhage. Acta Neurochir (Wien) 2020; 162 (01) 187-195
• 15 Kellogg M, Petrov D, Agarwal N. et al. Effects of Meteorological Variables on the Incidence of Rupture of Intracranial Aneurysms in Central New Jersey. J Neurol Surg A Cent Eur Neurosurg 2017; 78 (03) 238-244
• 16 Han MH, Yi HJ, Ko Y, Kim YS, Lee YJ. Association between hemorrhagic stroke occurrence and meteorological factors and pollutants. BMC Neurol 2016; 16 (01) 59
• 17 Zheng Y, Wang X, Liu J, Zhao F, Zhang J, Feng H. A Community-Based Study of the Correlation of Hemorrhagic Stroke Occurrence with Meteorologic Factors. J Stroke Cerebrovasc Dis 2016; 25 (10) 2323-2330
• 18 Lee S, Guth M. Associations between temperature and hospital admissions for subarachnoid hemorrhage in Korea. Int J Environ Res Public Health 2017; 14 (04) 449-460
• 19 Backes D, Rinkel GJE, Algra A, Vaartjes I, Donker GA, Vergouwen MDI. Increased incidence of subarachnoid hemorrhage during cold temperatures and influenza epidemics. J Neurosurg 2016; 125 (03) 737-745
• 20 Tarnoki AD, Türker A, Tarnoki DL. et al. Relationship between weather conditions and admissions for ischemic stroke and subarachnoid hemorrhage. Croat Med J 2017; 58 (01) 56-62
• 21 Patrice T, Rozec B, Desal H, Blanloeil Y. Oceanic Meteorological Conditions Influence Incidence of Aneurysmal Subarachnoid Hemorrhage. J Stroke Cerebrovasc Dis 2017; 26 (07) 1573-1581
• 22 Lai PMR, Dasenbrock H, Du R. The association between meteorological parameters and aneurysmal subarachnoid hemorrhage: a nationwide analysis. PLoS One 2014; 9 (11) e112961
• 23 Rivera-Lara L, Kowalski RG, Schneider EB, Tamargo RJ, Nyquist P. Elevated relative risk of aneurysmal subarachnoid hemorrhage with colder weather in the mid-Atlantic region. J Clin Neurosci 2015; 22 (10) 1582-1587
• 24 Takumi I, Mishina M, Kominami S. et al. Ambient Temperature Change Increases in Stroke Onset: Analyses Based on the Japanese Regional Metrological Measurements [Internet]. Available from: http://www.nms.ac.jp/jnms/

Publication History

Received: 08 April 2024

Accepted: 20 March 2025

Article published online:
16 July 2025