Almost everything we know about cold temperatures and cardiovascular system comes from temperate climate countries. Therefore, researchers lacked data about tropical regions where people rarely experience cold.
Now a groundbreaking Brazilian study published in PLOS Global Public Health fills this critical gap. It is the first study to compare ambient temperature and heart hospitalization risk in tropical and temperate cities within same country.
The Massive Study: 3 Million Hospitalizations Across 103 Brazilian Cities
Researchers from Universidade Federal do Paraná and Pontifícia Universidade Católica do Paraná in Curitiba led the study. They cross-referenced climate data with nearly 3 million cardiovascular hospitalizations over 14.5 years.
The team analyzed records from January 2010 to June 2024 using Brazil’s open-access DATASUS system. DATASUS is Department of Informatics of Unified Health System.
They included acute myocardial infarction, stroke, heart failure, and cardiac arrhythmia hospitalizations. Additionally, they matched hospitalizations with average daily temperatures from National Institute of Meteorology, INMET.
The analysis included 103 cities with complete climate data. Furthermore, researchers noted 20 million additional heart-related hospitalizations were excluded due to incomplete climate data nationally.
The Shocking Finding: 19°C Is The Danger Threshold From Manaus to Porto Alegre
The study found no statistically significant difference in heart hospitalization risk between tropical and temperate climates. Surprisingly, a threshold of 19°C applied across entire Brazil, from tropical Manaus to temperate Porto Alegre.
Temperatures below 19°C were associated with increased cardiovascular hospitalization risk in both regions. Moreover, risk increased progressively as temperatures dropped further.
At 18°C, relative risk was 1.01 (95% CI, 1.01-1.02). At 14°C, relative risk rose to 1.03 (95% CI, 1.02-1.04). At 9°C, relative risk reached 1.05 (95% CI, 1.01-1.09).
Between 19°C and 24°C, ambient temperature showed neutral association with hospitalization rates. Above 25°C, trend reversed, with heart hospitalization risk decreasing as temperatures rose. At 30°C, relative risk was 0.97 (95% CI, 0.93-1.02).
What Lead Cardiologist Says About Cold Observation
According to Bruna Dóris, MD, cardiologist and study’s first author, findings matched clinical observations. “We had already noticed many more hospitalizations during cold weather,” she said.
“Our question was whether this was just observational bias or actual association,” Dóris explained. Therefore, researchers designed this large-scale analysis to confirm real-world patterns.
However, Dóris cautioned about causation interpretation. “Since this is ecological and observational study, it is not possible to conclude low temperatures caused hospitalization increase,” she emphasized.
Analysis: Is Cold Really The Culprit? Experts Raise Important Questions
Temperature is only one factor affecting cardiovascular system during winter months. Speaking to Medscape Portuguese edition, Glaucia Maria Moraes de Oliveira, MD, PhD, noted multiple confounders.
Furthermore, effects of cold on cardiovascular system may persist for several weeks. However, this study’s distributed lag model evaluated temperature effects over maximum of 7 days only.
The study evaluated only ambient temperature. Humidity, dietary habits, and pollution were not included in analysis. In southern Brazil, Rio Grande do Sul had highest heart hospitalization rate nationally. Authors speculated regional dietary habits may contribute to higher rates, but study did not evaluate diet. In equatorial region with lowest hospitalization rates, high Amazon humidity might offer protective effect.
However, available data do not permit confirmation of either explanation. Moreover, body’s acclimatization to temperature range influences individual vulnerability significantly.
What Can We Do To Reduce Cold-Related Heart Risks?
During cold weather, Dóris recommended campaigns targeting people experiencing homelessness urgently. Additionally, programs should improve access to heating systems in socioeconomically disadvantaged areas.
Oliveira emphasized importance of vaccination for heart patients. “We need adequate immunization against RSV and influenza,” she said. Vaccines prevent respiratory infections that can trigger heart attack or stroke.
Above all, most important measure remains appropriate treatment for cardiovascular disease patients. “If patient receives appropriate pharmacological treatment following SBC guidelines, we will see fewer adverse effects,” Oliveira concluded.
Q&A
Q: At what temperature does heart hospitalization risk increase in Brazil?
A: Risk increases progressively below 19°C in both tropical and temperate Brazilian cities, according to PLOS study.
Q: How much does cold increase heart hospitalization risk?
A: Risk rises to 1.01 at 18°C, 1.03 at 14°C, and 1.05 at 9°C compared to neutral temperatures.
Q: Does heat protect against heart hospitalizations?
A: Above 25°C, study found decreasing heart hospitalization risk, with RR 0.97 at 30°C.
FAQ
1. Where was this cold and heart disease study published?
Study was published in PLOS Global Public Health by researchers from Federal University of Paraná and Catholic University of Paraná.
2. How many hospitalizations did researchers analyze?
Researchers analyzed nearly 3 million cardiovascular hospitalizations in 103 cities from January 2010 to June 2024.
3. Does living in tropical climate protect you from cold-related heart risks?
No. Study found no significant difference between tropical and temperate cities; 19°C threshold applied from Manaus to Porto Alegre.
4. Is this study proof that cold causes heart attacks?
No. Authors caution this is ecological observational study, so it shows association, not causation, between cold and hospitalizations.
5. What else besides temperature affects winter heart hospitalizations?
Pollution, socioeconomic conditions, age, respiratory infections, humidity, and dietary habits may influence winter heart risks concurrently.
Disclaimer; This article is for informational purposes only and does not constitute medical advice. We actively summarize peer-reviewed research published in PLOS Global Public Health for educational purposes. Always consult a qualified cardiologist or healthcare provider for personal medical advice regarding cardiovascular disease. Do not delay seeking treatment based on this article.
