The Cooper Institute
 

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

 
 
 

2020 Research Review by The Cooper Institute 

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Wednesday, Jan 20, 2021

A Look at Research Published by The Cooper Institute During 2020


Last year was a very productive time for research at The Cooper Institute. Our team worked hard in 2020 to discover more about the many health benefits of regular physical activity, as well as the benefits of obtaining at least a moderate level of cardiorespiratory fitness (CRF). 

Most of our research stems from the Cooper Center Longitudinal Study (CCLS), the largest and longest-running health study of its kind in the world with an objective measure of CRF. This widely cited database is the crown jewel of our research with over 113,000 participants spanning the last 50 years and providing over 3,000 variables to study. The CCLS continues to grow as patients examined by Cooper Clinic physicians are continually added to the database. 

The results of our 2020 research, published in some of the top medical journals in the country, will make an impact on healthcare #WELLintothefuture. Let’s take a look back at the research and what it means.
 

Journal of the American College of Cardiology.

Relevance of fitness to mortality risk in men receiving contemporary medical care.
 

In 1989, Dr. Steve Blair published a landmark study on more than 13,000 men and women who were examined at the Cooper Clinic. The study, published in the Journal of the American Medical Association showed for the first time that moderate to high levels of measured cardiorespiratory fitness provide substantial protection from all-cause mortality. Since that time, screening guidelines and treatments for cardiovascular disease and cancer have changed significantly. Therefore, we sought to compare the relationship between fitness and mortality risk during two different eras of medical care. The current study looked at nearly 48,000 men over a 50-year span who all completed baseline examinations, including a maximal treadmill exercise test at the Cooper Clinic. The men were divided into two chronological groups. Group 1 consisted of men who were examined between 1971 and 1991 and followed for mortality through 1992, while Group 2 was examined between 1992 and 2013 and followed for mortality through 2014.


Men from both groups were categorized as low fit, moderate fit or high fit based on their treadmill test results and age group. When compared against those with low fitness, men in both groups demonstrated that high and moderate fitness significantly decreases all-cause mortality risk:

  • Heart disease and cancer combined accounted for 70% and 63% of all deaths in groups 1 and 2, respectively.
  • High fitness reduced mortality by 47% in the group seen between 1970 and 1991; Moderate fitness reduced mortality by 40%.
  • High fitness reduced mortality by 48% in the group seen between 1992 and 2014; Moderate fitness reduced mortality by 24%.

 
Central Illustration
 The cardiorespiratory fitness level of each group (expressed in METs) is shown on the horizontal line of the graph (bottom side). The 10-year death rate from all causes is shown on the vertical line (left side). The blue line represents Group 1 and the dotted red line represents Group 2. On the left side where fitness levels are the lowest, we see that Group 1 has higher mortality than Group 2. As we travel across the graph, we see that mortality drops as fitness level increases. What is clear in this graph is that even though Group 2 starts with lower mortality, thanks to modern medicine, both groups see significant improvements in mortality as fitness levels increase. Fitness still matters!


Medicine and Science in Sports and Exercise.

Cardiorespiratory fitness, serum vitamin D, and prevalence of metabolic syndrome in men.
 

Metabolic syndrome (MetSyn) is a common condition among U.S. adults, and is strongly related to an increased risk of developing type 2 diabetes and other adverse health conditions. There are 5 components of MetSyn: Low HDL-cholesterol, elevated blood triglyceride level, elevated resting blood pressure, elevated fasting blood glucose level, and high waist circumference. Individuals with 3 or more of these 5 components are defined as having MetSyn.

Vitamin D deficiency and low levels of cardiorespiratory fitness (CRF) are also quite common in the U.S. population, and are each strongly related to a number of adverse health conditions as well. In this study, we systematically examined the relationship between CRF, blood vitamin D levels, and the risk of having MetSyn in adult men.


A total of 14353 men completed a comprehensive health examination at the Cooper Clinic, including CRF measurement based on a maximal treadmill test, as well as measures of blood vitamin D levels and MetSyn components. Participants were classified into groups of low (unfit), moderate, and high CRF by age group, as well as by standard cut points for blood vitamin D level and MetSyn. Our main findings were as follows:

  • Overall, about 22% of the men had MetSyn.  
  • Men with MetSyn had significantly lower levels of vitamin D than men without MetSyn.
  • When compared with unfit men, moderate and high fit men were 69% and 92% less likely to have MetSyn, respectively.
  • When compared with men who were vitamin D deficient, men with normal vitamin D levels were 71% less likely to have MetSyn.


In the Figure above, notice that among men who were vitamin D deficient, the rates of metabolic syndrome were about 70% and 30% in unfit and fit groups, respectively. Among men who were vitamin D insufficient, the rates were about 55% and 20%, respectively. Finally, among men with normal vitamin D levels, the rates of MetSyn were about 45% and 15% in unfit and fit men, respectively. In summary, among adult men, higher levels of CRF and blood vitamin D were strongly related to a decreased risk of having MetSyn. Furthermore, within each vitamin D category, fit men were significantly less likely to have MetSyn than unfit men. Based on these results we strongly recommend that all men undergo a measure or estimate of their fitness level as well as a measurement of their blood vitamin D level and each of the components of MetSyn listed above. Additionally, all men should follow the Physical Activity Guidelines for Americans with the goal of obtaining at least a moderate level of fitness.  


The American Journal of Medicine. 

Cardiorespiratory Fitness, Body Mass Index, and Markers of Insulin Resistance in Apparently Healthy Women and Men.


Insulin is a hormone produced by the pancreas that helps glucose (sugar) enter our cells from the bloodstream. Glucose is then used as an important source of energy by all of our cells. Many adults have a condition called insulin resistance, which means that the cells are resistant to the normal effects of insulin. As a result, instead of traveling into the cells, some of the glucose remains in the blood. This can lead to prediabetes, type 2 diabetes and poor health outcomes. Insulin resistance can be identified by having elevated levels of fasting blood glucose as well as elevated levels of blood triglycerides. Although obesity is a risk factor for insulin resistance, many obese adults do not have insulin resistance.

A moderate to high level of cardiorespiratory fitness may be protective against insulin resistance, but the association between fitness, weight, and insulin resistance has not been studied in a large population of healthy adults. This study examined the relationship between cardiorespiratory fitness, body mass index (BMI), and markers of insulin resistance (elevated fasting blood glucose and triglyceride levels). Study participants were enrolled at the Cooper Clinic in Dallas, Texas. The analysis included 19,263 women and 48,433 men with no history of diabetes or cardiovascular disease. Cardiorespiratory fitness was measured using a maximal treadmill exercise test. In keeping with previous CCLS papers, individuals who scored in the bottom 20% compared to others of their same age and sex were classified as unfit, while the remaining 80% were classified as fit. Among individuals with normal weight, being unfit showed a 2.2-fold higher risk of insulin resistance in women and 2.8-fold higher risk in men. The impact of fitness remained significant for overweight and obese individuals, with the highest risk group being the unfit obese. Among obese women, the risk for insulin resistance was 11.0-fold higher for fit women and 20.3-fold higher for unfit women. Among obese men, the risk for insulin resistance was 7.4-fold higher for fit men and 12.9-fold higher for unfit men. The authors concluded that independent of weight, poor fitness is associated with increased risk of insulin resistance. Thus, all men and women are urged to meet the recommendations contained in the 2018 Physical Activity Guidelines for Americans in order to decrease their risk of insulin resistance. Additionally, all men and women should strive to meet and maintain a reasonable body weight.   
 


Journal of Investigative Medicine.

Association between C-reactive protein and depression in a population of healthy adults: The Cooper Center Longitudinal Study.
 

Depression is a leading cause of disability in the world, and is associated with chronic illnesses characterized by ongoing inflammation, including cardiovascular disease, diabetes, and cancer. The relationship between depression and inflammation is currently a topic of much interest. Previous studies have produced mixed results regarding the association between depression and C-reactive protein (CRP), an inflammatory marker found in the blood. The aim of this study was to determine the relationship between CRP and depression in a large sample of healthy adults. A total of 26,638 healthy adults with an average age of 50 years and an average of 16 years of education underwent examinations at the Cooper Clinic between 2000 and 2018. Depression levels were measured using the 10-item Center for Epidemiologic Studies Depression Scale (CESD-10). After taking into account race, age, education, smoking history, alcohol use, menopausal status, and medication use, blood CRP level demonstrated a very modest positive relationship with depressive symptoms for both men and women. However, once body mass index (BMI) was taken into account, the relationship became insignificant. The authors concluded that levels of CRP were not associated with depression in a predominantly white, adult population of higher socioeconomic status. This finding suggests that associations between CRP and depression may be explained by obesity, which warrants further investigation into shared pathways between obesity and depression.


Journal of the American Academy of Dermatology.

Tanning bed use and depression in a preventive medicine cohort: The Cooper Center Longitudinal Study
 

This study sought to examine the relationship between tanning bed use and depressive symptoms. A total of 11,823 Cooper Clinic patients with an average age of 52 years were asked about tanning bed use on their medical history questionnaire. The patients also completed a commonly used depression questionnaire called CESD-10. A score of 10 or higher on the CES-D is indicative of depression. About 15% of the patients reported that they had used a tanning bed, while 85% reported that they had not used a tanning bed. The average number of uses per year among the tanning group was 4.2 (range from 1 to 200 times per year).

Men who reported using a tanning bed were about 1.9 times more likely to be identified with depressive symptoms from the CESD-10 when compared with men who were non-tanning bed users. Women who reported using a tanning bed were about 1.3 times more likely to be identified with depressive symptoms when compared with women who were non-tanning bed users. The frequency of tanning bed use among users was related to their CES-10 scores, those who were more frequent users tended to have higher depression scores than those who used less frequently.

The authors concluded that tanning bed users were more likely to score >10 on the CESD-10 than non-tanning bed users. The idea is not that the tanning causes depression, but rather people who are depressed often report that they feel better following a tanning session.  Health-care workers are encouraged to ask their patients about tanning bed use. Those who report tanning bed use should be screened for depressive symptoms.
 


Prostaglandins, Leukotrienes, and Essential Fatty Acids.

Higher omega-3 index is associated with more rapid heart rate recovery in healthy men and women.
 

It is well-established that cardiorespiratory fitness (CRF) is a strong predictor of many health outcomes such as cardiovascular disease, type 2 diabetes, and some cancers. The gold standard for measuring CRF is a maximal treadmill exercise test performed in a clinical setting. In recent years, heart rate recovery (HRR) from maximal exercise has also been identified as an important health metric. HRR is defined as the difference between maximal heart rate and the heart rate at a given time point following exercise. For example, if the heart rate obtained during maximal exercise is 185 beats/minute and the heart rate at the 1-minute mark of recovery is 160 beats/minute, then the HRR is 185 - 160 = 25 beats/minute. The more rapidly the heart rate decreases following exercise, the lower the risk for future cardiovascular events. Although there is a correlation between CRF and HRR, studies have shown that not everyone with high fitness has good/rapid heart rate recovery, and not everyone with low fitness has poor/slow heart rate recovery.


Omega-3 fatty acids, more commonly known as ‘fish oils’ are found in fatty fish as well as in supplement form, and have been shown to be beneficial to cardiovascular health. The Cooper Clinic has been measuring omega-3 fatty acid levels in the blood since 2007, using a method called the Omega-3 Index (O3I). The O3I is a measure of what percentage of fatty acids in red blood cells are omega-3’s. There are 3 categories for the O3I: low is <4%, normal is 4-8%, and optimal is >8%. The Omega-3 Index is an important marker of cardiovascular health.

In the current study, we examined the relationship between HRR at 1, 3, and 5- minutes post-maximal exercise with the Omega-3 Index in a group of 13,912 healthy men and women who were examined at the Cooper Clinic. Though the differences were relatively small, we did find a statistically significant relationship, even after controlling for CRF and other things that might potentially muddy the waters. The higher the Omega-3 Index, the better/more rapid the HRR. The authors concluded that higher O3I levels are related to a more rapid HRR in healthy men and women. These results reinforce recommendations from the American Heart Association to consume at least 2 servings of non-fried fatty fish per week.

 

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