Active Voice: Does Cardiorespiratory Fitness Level Trump LDL-Cholesterol Level for Predicting CHD Mortality?
By Steve Farrell, Ph.D.
Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.
Dr. Farrell is the science officer for the Division of Education at The Cooper Institute in Dallas. He and his colleagues have delivered health and fitness workshops around the globe for the past 30 years. His main area of research focuses on the associations among cardiorespiratory fitness, adiposity, and various health outcomes. This commentary presents Dr. Farrell’s views associated with the research article he and his colleagues published in the November issue of ACSM’s Medicine and Science in Sports and Exercise® (MSSE).
There is broad consensus that elevated levels of LDL cholesterol and low levels of cardiorespiratory fitness (CRF) are powerful independent risk factors for coronary heart disease (CHD). Is it possible that one might be a stronger predictor of CHD mortality than the other? My colleagues and I designed a study that would look at all possible combinations of CRF and LDL and the subsequent risk of CHD mortality. In this study, recently reported in MSSE, we followed 40,718 apparently healthy men who underwent a comprehensive baseline physical exam at the Cooper Clinic during 1978-2006. All men had a maximal treadmill stress test and blood work at the time of their exam. We divided the group into three categories of CRF:
Low fit: the bottom 20% (1st quintile) compared to other men in their age group.
Moderate fit: the next 40% (2nd and 3rd quintile) compared to other men in their age group.
High fit: the top 40% (4th and 5th quintile) compared to other men in their age group.
We also classified the men according to their LDL cholesterol level using the NCEP ATP-III criteria:
Optimal: LDL < 100 mg/dl,
Near-Optimal: LDL 100-129 mg/dl,
Borderline High: LDL 130-159 mg/dl,
High: LDL 160-189 mg/dl,
Very High: LDL >190 mg/dl.
The group was tracked for an average of 17 years. During that time, 557 men died from CHD. Not surprisingly, we found that both CRF and LDL were each very strong and independent predictors of CHD death. We then examined the risk of death in all 15 possible CRF-LDL combinations following adjustment for confounding variables. The novel finding was that within all 5 LDL categories, we saw the greatest risk of death in low fit men, while the risk was decreased in moderate fit men, and tended to be the lowest in high fit men. Interestingly, among all men with optimal levels of LDL, low fit men were nearly 3 times more likely to die from CHD than moderate or high fit men with optimal LDL levels.
Why is this important?
Billions of dollars are spent each year on medications which lower LDL cholesterol. While lowering LDL levels undeniably decreases the risk of CHD mortality, focusing only on LDL is clearly not enough. Health professionals need to do a better job promoting physical activity, and the public needs to do a better job following through on our advice. Regardless of LDL level, men need to achieve at least a moderate level of CRF in order to achieve the lowest risk of CHD mortality possible. Most men should be able to achieve moderate CRF by meeting the current ACSM public health guidelines for physical activity (at least 150 minutes per week of moderate aerobic activity or at least 75 minutes per week of vigorous aerobic activity).
Previous work with this Cooper Clinic cohort has shown again and again that CRF trumps fatness as a predictor of various health outcomes. Our current paper suggests that CRF also trumps LDL cholesterol level with respect to CHD mortality in men. As is so often stated, "If the benefits of regular physical activity could be put into a pill, it would be the most widely prescribed and most beneficial of all medications."