The Cooper Institute
 

Founded in 1970 by the "Father of Aerobics"
Kenneth H. Cooper MD, MPH

 
 

Midlife Fitness Level is a Strong Predictor of Stroke: The Cooper Center Longitudinal Study

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Friday, Feb 16, 2018


Stroke is the leading cause of long-term disability and accounts for more than 140,000 deaths per year in the U.S. About 87% of the ~800,000 annual strokes in this country occur as a result of fatty plaques and blood clots accumulating within the arteries of the brain, while the remaining 13% occur as a result of brain arteries actually bursting. The former type is known as an ischemic stroke, while the latter type is known as a hemorrhagic stroke. While the majority of strokes occur in people over the age of 65, strokes can occur at any age. Besides age, other important risk factors for stroke include hypertension, obesity, diabetes, and atrial fibrillation.    

Over the past two decades, several studies have shown that cardiorespiratory fitness (CRF) is also strongly related to stroke risk, with substantially lower risk seen among individuals who are moderately to highly fit. While these studies have typically taken into account risk factors for stroke that were present at the time of the CRF measurement, they did not account for risk factors which may have arisen after the assessment of baseline CRF. Accordingly, Cooper Institute researchers sought to examine the relationship between midlife CRF and risk of stroke after the age of 65 years while taking all of these factors into account. A unique feature of this study was that it linked data from Cooper Clinic patient exams to stroke Medicare claims for these same patients. Previous studies had to rely on a medical history questionnaire where the patient self-reported whether or not they had experienced a previous stroke.

A total of 19,815 Cooper Clinic patients (15,683 men and 4,132 women) with an average age of ~50 years at baseline participated in the study. All were apparently healthy, with a relatively low risk of stroke at the time of their exam. An important component of the Clinic exam was a maximal treadmill exercise test to measure CRF. Based on their treadmill test performance, each individual was placed into 1 of 5 age and sex-specific quintiles of CRF. Quintile 1 was designated as low CRF, while quintiles 2-3 and 4-5 were designated as moderate and high CRF, respectively. There were a total of 129,436 person-years* of Medicare follow-up data, during which time 808 stroke hospitalizations occurred. Importantly, data regarding the presence of hypertension, diabetes, or atrial fibrillation at the time of the stroke that may not have been present at the time of the Clinic exam was also carefully considered in the analyses.   

Figure 1 below compares the risk of stroke hospitalization among patients with low, moderate, and high baseline CRF. Using the low fit group as the referent, patients with moderate and high CRF at midlife were 24% and 37% less likely to be hospitalized for stroke, respectively, during the period of Medicare follow-up. Importantly, these numbers were determined after taking baseline stroke risk factors into account, as well as stroke risk factors that were present at the time the stroke was diagnosed. So, independently of whether or not hypertension, diabetes, or atrial fibrillation was present at any time during the study, CRF remained a strong predictor of stroke hospitalization risk. A major strength of the study is that Medicare data was used to document stroke hospitalization rather than relying on the patient reporting a history of stroke from a written questionnaire. One limitation of this study is that ~98% of patients were white. Whether or not these findings apply to other ethnic groups is unknown.

To be clear, this study confirmed that age, hypertension, diabetes, and atrial fibrillation remain important risk factors for stroke. The important finding was that moderate to high levels of CRF provided protection against stroke even after taking those risk factors into consideration. These results show that having a higher level of CRF in midlife is a strong prevention strategy for strokes occurring after the age of 65. To help prevent stroke and other serious health outcomes, all adults are urged to meet current public health physical activity guidelines.**   

*In studies such as these, the term ‘person-years’ is used when describing follow-up. If one person is followed for one year, then we have 1 x 1 = 1 person-year of data. If 1000 people are followed for 10 years, then we have 1000 x 10 = 10,000 person-years of data.  
**accumulate a minimum of 150 minutes per week of moderate intensity aerobic activity or a minimum of 75 minutes per week of vigorous intensity aerobic activity. These numbers should be doubled for those who wish to lose significant amounts of weight and/or who wish to attain very high levels of CRF.  

Reference
Pandey, A., Patel, M., Willis, B., Gao, A., Leonard, D., Das, S., Defina, L., Berry, J. (2016). Association between midlife cardiorespiratory fitness and risk of stroke: the Cooper Center Longitudinal Study. Stroke, 47:1720-1726. Doi: 10.1161/STROKEAHA.115.011532/-/DC1.




Note: The Cooper Institute has recently published a state of the art textbook titled Principles of Health and Fitness for Fitness Professionals. This book is an absolute must for fitness leaders or anyone in the general population who wants to learn more about health and physical fitness. The book is also a great resource for anyone who is seeking to earn a nationally accredited personal trainer certification! Click on the links above to learn more.