It is widely known that coronary heart disease (CHD) is among the leading causes of death in most countries that have a reasonably high standard of living. CHD is characterized by accumulation of plaque within the coronary arteries, which are located in the heart muscle. This can result in the need for procedures such as coronary artery bypass surgery or balloon angioplasty with stent placement. CHD can also result in heart attack, which occurs ~1.25 million times in the U.S. annually.
There is broad agreement that elevated levels of LDL cholesterol (also known as the bad cholesterol) and low levels of cardiorespiratory fitness (CRF) are powerful risk factors for CHD. Since no one had done it previously, my colleagues and I decided to design a study that would look at various levels of CRF and LDL to determine their combined effect on risk of death from CHD. We studied 40,718 apparently healthy men who underwent a comprehensive physical exam at the Cooper Clinic between 1971 and 2006. All of the men had a maximal treadmill stress test and blood work at the time of their exam. Based on their treadmill test time and age, we divided them into 3 categories of categories of CRF:
Low fit: men who scored in the bottom 20% (1st quintile) compared to other men in their age group.
Moderate fit: men who scored in the next 40% (2nd and 3rd quintile) compared to other men in their age group.
High fit: men who scored in the top 40% (4th and 5th quintile) compared to other men in their age group.
We also divided the men according to their LDL cholesterol level as follows:
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 then 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 very strong and independent predictors of CHD death. We took it a step further and looked at the risk of death in all 15 possible CRF-LDL combinations; this is shown in the Figure below (just in case you are wondering, we took age, length of follow-up, family history, and smoking into consideration before doing the analyses). The different bars that you see in the Figure show the risk of CHD death within each CRF-LDL category; the higher the bar, the higher the risk of death. 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. As you can also see from the Figure, the lowest risk of CHD death was seen in men with optimal levels of LDL and moderate to high levels of CRF, while the highest risk was seen in men with high or very high levels of LDL and low levels of CRF. Interestingly, among all men with optimal levels of LDL, low fit men were ~3 times more likely to die from CHD than moderate or high fit men with optimal LDL levels!
Why is this important and what does it mean?
Billions of dollars are spent each year on medications which lower LDL cholesterol. While lowering LDL levels undeniably decreases the risk of CHD, focusing only on LDL is clearly not enough. Health professionals need to do a better job promoting physical activity. Recall from the Figure that men with optimal levels of LDL who were low fit were still 3 times more likely to die from CHD than men with similar LDL levels who were moderately or high fit! Therefore, regardless of LDL level men need to achieve at least a moderate level of CRF in order to achieve the lowest risk possible. Most men should be able to achieve a moderate level of CRF by meeting the current public health guidelines for physical activity: Adults should accumulate at least 150 minutes per week of moderate aerobic activity or at least 75 minutes per week of vigorous aerobic activity. If achieving significant weight loss or a high level of CRF is the goal, then as much as 300 minutes per week of moderate, or 150 minutes per week of vigorous aerobic activity may be necessary. Start slowly and gradually work up to these suggested levels of activity.
So guys, if you really want to minimize your risk of needing bypass surgery, a stent, or having a heart attack then work towards getting your LDL as low as possible and getting your cardiorespiratory fitness level to at least a moderate level, and preferably to a high level if your LDL is >160 mg/dl. Additional steps for minimizing CHD risk are listed below:
Farrell S.W., Finley C.E., Grundy S.M. (2012). Cardiorespiratory fitness, LDL-cholesterol, and coronary heart disease mortality in men. Medicine and Science in Sports and Exercise. July 6 (E-pub ahead of print).