Seasonal variation in cardiovascular disease risk factors in a subarctic population: the Tromsø Study 1979–2008
- Laila Arnesdatter Hopstock1,
- Adrian Gerard Barnett2,
- Kaare Harald Bønaa1,3,4,
- Jan Mannsverk1,5,
- Inger Njølstad1,
- Tom Wilsgaard1
- 1Department of Community Medicine, University of Tromsø, Tromsø, Norway
- 2Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia
- 3Unit of Applied Clinical Research, Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway
- 4Department of Heart Disease, St. Olavs University Hospital, Trondheim, Norway
- 5Department of Heart Disease, University Hospital of North Norway, Tromsø, Norway
- Correspondence to Laila Arnesdatter Hopstock, Department of Community Medicine, University of Tromsø, N-9037 Tromsø, Norway;
Contributors All authors fulfil the ICMJE criteria of authorship, and there is no one else who fulfil the criteria who has not been included as an author. LAH has contributed to conception and design, analysis and interpretation of data and drafted the manuscript. AGB has contributed to conception and design, analysis and interpretation of data. KHB has contributed to conception and design, acquisition of data and interpretation of data. JM has contributed to analysis and interpretation of data. IN has contributed to conception and design, acquisition of data and interpretation of data. All authors have revised the manuscript critically for important intellectual content and approved the final version of the manuscript to be published.
- Accepted 4 July 2012
- Published Online First 2 August 2012
Background Seasonal changes in cardiovascular disease (CVD) risk factors may be due to exposure to seasonal environmental variables like temperature and acute infections or seasonal behavioural patterns in physical activity and diet. Investigating the seasonal pattern of risk factors should help determine the causes of the seasonal pattern in CVD. Few studies have investigated the seasonal variation in risk factors using repeated measurements from the same individual, which is important as individual and population seasonal patterns may differ.
Methods The authors investigated the seasonal pattern in systolic and diastolic blood pressure, heart rate, body weight, total cholesterol, triglycerides, high-density lipoprotein cholesterol, C reactive protein and fibrinogen. Measurements came from 38 037 participants in the population-based cohort, the Tromsø Study, examined up to eight times from 1979 to 2008. Individual and population seasonal patterns were estimated using a cosinor in a mixed model.
Results All risk factors had a highly statistically significant seasonal pattern with a peak time in winter, except for triglycerides (peak in autumn), C reactive protein and fibrinogen (peak in spring). The sizes of the seasonal variations were clinically modest.
Conclusions Although the authors found highly statistically significant individual seasonal patterns for all risk factors, the sizes of the changes were modest, probably because this subarctic population is well adapted to a harsh climate. Better protection against seasonal risk factors like cold weather could help reduce the winter excess in CVD observed in milder climates.
Competing interests None.
Ethics approval Ethical approval was provided by the Regional Committee for Medical and Health Research Ethics, the Data Inspectorate and the Directorate of Health and Social Affairs in Norway.
Provenance and peer review Not commissioned; externally peer reviewed.