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Summer-winter differences in 24 h variability of heart rate
E Kristal-Boneh1, P Froom, G Harari
1Occupational Health and Rehabilitation Institute, Raanana, Israel.
Insights
Heart rate variability (HRV) in healthy men is lower in summer than in winter. These seasonal changes in HRV may contribute to increased cardiovascular disease mortality during winter months.
Area of Science:
- Cardiology and Environmental Health
- Physiology and Public Health
Background:
- Winter mortality from cardiovascular disease (CVD) is higher in many countries.
- Reduced heart rate variability (HRV) predicts cardiac death and may be influenced by seasons.
- HRV is an important indicator of cardiovascular health.
Purpose of the Study:
- To investigate seasonal variations in heart rate variability (HRV).
- To determine if HRV differs between summer and winter in healthy individuals.
Main Methods:
- Compared 24-hour HRV data from 120 healthy men in summer and winter.
- Utilized multivariate analyses with HRV indexes as dependent variables.
- Controlled for factors including age, cholesterol, smoking, BMI, and blood pressure.
Main Results:
- All HRV indexes were lower in summer compared to winter.
- No seasonal difference was observed in mean R-R interval.
- Multivariate analyses confirmed lower HRV in winter, even after adjustments.
Conclusions:
- HRV physiologically varies by season, with the lowest values in winter.
- Seasonal HRV changes are significant for individuals with CVD.
- The findings suggest a potential link between seasonal HRV and winter CVD mortality.
Objective:
To examine possible seasonal changes in heart rate variability (HRV).
Background:
Greater than normal mortality from cardiovascular disease (CVD) in the winter has been reported for many countries and might be partly explained by considering seasonal changes in CVD risk factors. Depression of HRV is an independent predictor of arrhythmic complications and of cardiac death, and it is also among the variables that may be affected by the season of the year.
Methods:
We compared pairs of 24 h HRV data of 120 healthy men who were examined once in the summer and once in the winter. Multivariate analyses were performed for each dependent variable (HRV indexes) in separate statistical models with age, resting heart rate, serum level of cholesterol, cigarette smoking, body mass index, sports habits, alcohol consumption, systolic blood pressure, physical activity at work, years of education, consumption of energy, and season as the independent variables.
Results:
Although there were no seasonal differences in mean R-R interval, all indexes of HRV were found to be lower in the summer than they were during winter. Differences and 95% confidence intervals were standard deviation (SD) of coupling intervals between normal beats 12 ms, 6-17 ms; SD of 5 min mean R-R intervals 14 ms, 8-20 ms; mean of all 5 min SD of R-R intervals 2.0 ms, 0.6-2.5 ms; proportion of adjacent R-R intervals differing by > 50 ms 1.5%, 0.6-2.5% and root mean square of the difference between successive normal intervals 3.1 ms, 1.5-4 ms. Multivariate analyses showed that HRV in the winter was less than that in the summer even after adjustment for age, serum level of cholesterol, systolic blood pressure, and body mass index.
Conclusions:
HRV indexes of healthy men vary physiologically by season, with lowest values obtained in the winter. Since low HRV is linked to pathologic conditions, the significance of seasonal changes for those suffering from CVD and their possible contribution to the greater mortality rates in winter have to be considered.