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Aerobic fitness in late adolescence and the risk of early death: a prospective cohort study of 1.3 million Swedish men
Umeå University, Faculty of Medicine, Department of Community Medicine and Rehabilitation, Geriatric Medicine. Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine.
Umeå University, Faculty of Medicine, Department of Community Medicine and Rehabilitation, Geriatric Medicine. Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine.
Umeå University, Faculty of Medicine, Department of Community Medicine and Rehabilitation, Geriatric Medicine.
2016 (English)In: International Journal of Epidemiology, ISSN 0300-5771, E-ISSN 1464-3685, Vol. 45, no 4, 1159-1168 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Fitness level and obesity have been associated with death in older populations. We investigated the relationship between aerobic fitness in late adolescence and early death, and whether a high fitness level can compensate the risk of being obese.

METHODS: The cohort comprised 1 317 713 Swedish men (mean age, 18 years) that conscripted between 1969 and 1996. Aerobic fitness was assessed by an electrically braked cycle test. All-cause and specific causes of death were tracked using national registers. Multivariable adjusted associations were tested using Cox regression models.

RESULTS: During a mean follow-up period of 29 years, 44 301 subjects died. Individuals in the highest fifth of aerobic fitness were at lower risk of death from any cause [hazard ratio (HR), 0.49; 95% confidence interval (CI), 0.47-0.51] in comparison with individuals in the lowest fifth, with the strongest association seen for death related to alcohol and narcotics abuse (HR, 0.20; 95% CI, 0.15-0.26). Similar risks were found for weight-adjusted aerobic fitness. Aerobic fitness was associated with a reduced risk of death from any cause in normal-weight and overweight individuals, whereas the benefits were reduced in obese individuals (P < 0.001 for interaction). Furthermore, unfit normal-weight individuals had 30% lower risk of death from any cause (HR, 0.70; 95% CI, 0.53-0.92) than did fit obese individuals.

CONCLUSIONS: Low aerobic fitness in late adolescence is associated with an increased risk of early death. Furthermore, the risk of early death was higher in fit obese individuals than in unfit normal-weight individuals.

Place, publisher, year, edition, pages
Oxford University Press, 2016. Vol. 45, no 4, 1159-1168 p.
Keyword [en]
Fitness, obesity, death
National Category
Geriatrics Environmental Health and Occupational Health
Identifiers
URN: urn:nbn:se:umu:diva-121364DOI: 10.1093/ije/dyv321ISI: 000393182000030PubMedID: 26686843OAI: oai:DiVA.org:umu-121364DiVA: diva2:932272
Available from: 2016-06-01 Created: 2016-06-01 Last updated: 2017-03-06Bibliographically approved
In thesis
1. Cardiovascular disease and all-cause mortality: influence of fitness, fatness and genetic factors
Open this publication in new window or tab >>Cardiovascular disease and all-cause mortality: influence of fitness, fatness and genetic factors
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background

Low aerobic fitness and obesity are associated with atherosclerosis, and thereforegreatly increase the risk of cardiovascular disease (CVD) and early death. It has long been known that atherosclerosis my begin early in life. Despite this fact, it remains unknown how obesity and aerobic fitness early in life influence the risks of atherosclerosis, CVD and death. Furthermore, it is unknown whether high aerobic fitness can compensate for the risks associated with obesity, and how genetic confounding affects the relationshipsof aerobic fitness with CVD and all-cause mortality. Thus, the main aims of this thesis were to investigate the associations of aerobic fitness in late adolescence with myocardial infarction (Study I), stroke (Study II) and all-cause mortality (Study III), and how genetic confounding influences the relationshipsof aerobic fitness with CVD, diabetes and death (Study IV).

Methods

The study population comprised up to1.3 million men who participated in mandatory Swedish military conscription. During conscription, all conscripts underwent highly standardized tests to assess aerobic fitness, body mass index, blood pressure and cognitive function. A physician also examined all conscripts. Data on subjects’ diagnoses, death and socioeconomic status during follow-up were retrieved using record linkage. Subjects were subsequently followed until the study endpoint, date of death or date of any outcome of interest. Associations between baseline variables and the risks of adverse outcomes were assessed using Cox’s proportional hazard models. Genetic confounding of the relationships between aerobic fitness and diabetes, CVD and death was assessed using a twin population and a paired logistic regression model.

Results

In Study I, low aerobic fitness at conscription was associated with an increased risk of myocardial infarction (MI) during follow-up (hazard ratio [HR] 0.82 per standard deviation increase). Similarly, in Study II, high aerobic fitness reduced the risk of stroke (HR 0.84 for ischemic stroke, HR 0.82 for hemorrhagic stroke; P < 0.001 for all), and obesity was associated with an increased risk of stroke (HR 1.15 for ischemic stroke, HR 1.18 for hemorrhagic stroke; P < 0.001 for all). In Study III, high aerobic fitness was also associated with reduced all-cause mortality later in life (HR 0.49, P < 0.001). High aerobic fitness exerted the strongest protection against death from substance and alcohol abuse, suicide and trauma (HRs 0.20, 0.41 and 0.52, respectively; P < 0.001 for all). Obese individuals with aerobic fitness were at higher risk of MI and all-cause mortality than were normal-weight individuals with low fitness (Studies I and III). In Study IV, fit twins had no reduced risk of CVD or death during follow-up compared with their unfit twin siblings (odds ratio 1.11, 95% confidence interval 0.88–1.40), regardless of how large the difference in fitness was. However, the fitter twins were protected against diabetes during follow-up.

Conclusions

Already early in life, aerobic fitness is a strong predictor of CVD and all-cause mortality later in life. In contrast to the “fat but fit” hypothesis, it seems that high aerobic fitness cannot fully compensate for the risks associated with obesity. The associationsof aerobic fitness with CVD and all-cause mortality appear to be mediated by genetic factors. Together, these findings have implications for the view of aerobic fitness as a causal risk factor for CVD and early death.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2017. 83 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1865
Keyword
all-cause mortality, aerobic fitness, obesity, cardiovascular disease, stroke, myocardial infarction
National Category
Public Health, Global Health, Social Medicine and Epidemiology Cardiac and Cardiovascular Systems
Research subject
Epidemiology; Population studies; Cardiology
Identifiers
urn:nbn:se:umu:diva-130312 (URN)978-91-7601-611-4 (ISBN)
Public defence
2017-02-10, Aulan, Vårdvetarhuset, Umeå universitet, Umeå, 09:00 (Swedish)
Opponent
Supervisors
Available from: 2017-01-20 Created: 2017-01-17 Last updated: 2017-01-27Bibliographically approved

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