Ambient Temperature and Stroke Occurrence: A Systematic Review and Meta-Analysis

Area of Science:

• Environmental Health
• Epidemiology
• Neurology

Background:

• Climatic conditions and stroke risk have plausible but inconsistent associations.
• Previous studies on ambient temperature and stroke occurrence show varied results.

Purpose of the Study:

• To systematically review and meta-analyze evidence on ambient temperature and stroke risk.
• To investigate associations by stroke type, age, sex, and temperature variation.

Main Methods:

• Systematic literature search across multiple databases (MEDLINE, Embase, etc.) up to October 2015.
• Inclusion of 21 population-based observational studies with 476,511 patients.
• Random effects meta-analysis to pool data and calculate Odds Ratios (OR) and 95% Confidence Intervals (CI).

Main Results:

• A significant association was found between a 1°C increase in ambient temperature and ICH risk (OR 0.97, 95% CI 0.94-1.00).
• No significant association was found for ischemic stroke (IS) or subarachnoid hemorrhage (SAH).
• Temperature changes over 24 hours were more critical than absolute temperature, particularly for ICH. Older individuals showed increased vulnerability to low temperatures.

Conclusions:

• Lower mean ambient temperature is significantly associated with increased risk of intracerebral hemorrhage.
• Ambient temperature does not appear to be significantly associated with ischemic stroke or subarachnoid hemorrhage.
• Significant temperature fluctuations increase stroke risk, especially in the elderly population.