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 Cardiofitness and the Risk of Cardiovascular Disease and Death from All Causes  

Forrest H. Blanding,  CHE-CHE                                                                             

Draft to Internet at http://www.lifeahead.net                                                                                                       Jan 1,  2004

Reviews and Comments appreciated to forrestx@cox.net.                                                                  Updated  July 9, 2007       

Abstract:

The risks of Cardiovascular (CV) disease and death and death from all causes are related at high significance to an index  of cardiofitness called the CFR that can be measured using a treadmill. The CFR that formerly was named Heart Efficiency or HEF is an age and sex adjusted index of the usual measure of cardiofitness of VO2 Max in ml of oxygen/kg.min and that alternately can be identified as METS.   Cardiofitness that is alternately known as cardiovascular or cardiorespitory fitness varies from about 80 CFR for very unfit to 150 CFR for quite fit men and women.  A 47% reduction is risk of CV disease and CV death and a 37% reduction in death from all causes is associated with each improvement of 10 CFR in cardiofitness.  The cardiofitness of individuals is determined mostly by selected types and amounts of physical activity and exercise, but is in part determined by genetics.  Improvements in efficiency of the CV system and in potential coronary artery flow produced by the regular periodic increases in the blood flow from exercise provide a quantified explanation for most of the benefits of cardiofitness.  The benefits of the efficient CV exercise that produces improvements in cardiofitness appear to have been substantially underestimated by most research results on physical activity and exercise. Cardiofitness measured either as VO2 max adjusted for age and sex or by the CFR is a new independent health risk factor potentially larger in importance to US population risks than are those associated with serum cholesterol, blood pressure, or smoking.

Introduction

Many studies have shown significant relationships between various measures of physical activity and cardiovascular diseases and death, and death from all causes (3).  Most studies have attempted to relate estimates of physical calories of exercise to health risk.  An alternate theory long hypothesized is that cardiofitness provides a primary and more casual protection of health, and that physical activity benefits mostly to the extent that it improves this cardiofitness.  Most studies of physical activity or exercise have shown that those in populations that exercised usually obtained 30-50% lower risks of CV disease than did those that did not exercise (3).  But as will be shown, much larger differences in risks of disease and death than this are associated with differences in measured values of cardiofitness.

An accompanying paper introduced an index of physical fitness called the Cardiofitness Ratio (CFR) that is directly proportional to the usual measure of VO2 Max in ml of oxygen/(kg.min) but also provides a numerical scale of similar significance for men and women of all ages.(7)  The CFR of individuals can be determined by a simple treadmill test described.  It thus becomes of interest to explore the relationship between cardiofitness and the risk of cardiovascular disease and death and death from all causes determined in available population research. 

Problems Using Research on Physical Fitness and Disease.

Eleven studies relating risk of CV diseases or death from all causes were found that identified the physical fitness of groups studied by measured differences in cardiofitness that could be translated into a common basis. Although the studies used differing methods for measuring cardiofitness, results of the various cardiofitness measurements are translated approximately herein in Table 1 following to common values of VO2 Max and the CFR.

Each of the eleven studies was prospective, with cardiofitness of participants usually measured only at baseline, but with outcomes on included populations followed for periods ranging up to 17 years.  All studies showed the risks of disease were related at significance to differences in cardiofitness at study baselines.  But the studies conducted for shorter time periods measured much larger effects of risk of disease vs. baseline differences in cardiofitness than did the longer term studies.  The reason for this appears clear.  Cardiofitness is a physical state of the CV system that develops over a period of several months and that can be lost a few months after exercise is stopped. As for diet, individuals' habits of exercise are variable. Thus the actual cardiofitness of groups compared in these studies was different at the time of disease than that measured at baseline.  Risk of disease and mortality should be related most accurately to cardiofitness at actual time of event. (5,11)  Thus a key question needing answer is: “What differences in risk of cardiovascular disease and death from all causes is directly associated with differences in probable actual levels of cardiofitness?”

Prospective studies of cardiofitness and disease that could answer this question directly would monitor the actual cardiofitness of individuals at least each year, and preferably each 6 months. Such studies of the ten thousand men and women needed for good significance are unlikely to be achieved, and even if feasible results would be many years distant. Thus the only alternative for achieving a most probable answer to this important question is to obtain a best estimate of the cardiofitness of groups already studied at the time when events occurred.

Research data provide a useful if approximate answer to this problem. Leon showed that differences in leisure time physical activity (LPTA) of men in his study dropped from about 118 at baseline to about 40 after both 4 and 6 years, for a decline of 24% and 16% per year respectively.(15)  The exercise of those initially of lowest cardiofitness moved up, and that of those initially highest cardiofitness declined. Morris reported that about that about half of those doing vigorous exercise were still doing this about 7 years later. (22)

Movements in cardiofitness of population segments measured in the Cooper Institute studies showed similarly that less than half of the key unfit group remained unfit after 5 years into the study.(5)  Computations from these data suggest that a probable regression in cardiofitness differences of 15% per year occurred in this data set, with much of this due to those initially unfit becoming more fit.  And changes in risk of disease during this study were related to whether or not cardiofitness was maintained.  Similar changes in cardiofitness during the term of study were measured by Erikssen. (11)  Paffenbarger found that only about 10% of his population of Harvard graduates initially classed as “High activity” were still at this activity level 13 years later. (24)  Again a computation suggests an average regression in exercise differences of about 16% per year in this population group.

This usual decline of differences in cardiofitness of groups with age means that shorter-term studies would be expected to reveal larger effects of disease related to baseline cardiofitness than those measured in longer term studies. Smoothed plots of the cumulative survival curves from  coronary death reported by Hein for various study years and terminating at zero deaths at study start showed a clear fan of increasing deaths for each lower category of cardiofitness measured as VO2 Max.(12)  The high cardiofitness group had an indicated percentage risk of death from coronary disease vs. that of  the low cardiofitness group of 17% (or just 1/6th)  at year 3,  30% at year 7, but a much less favorable 63% over the full 17 years. Most actual disease events occurred during later years of the study when differences in cardiofitness probably were much lower than those at study baseline.  Sandvik noted that the CVD risk ratio for highest cardiofitness quartile vs. lowest was 21% at seven years, but dropped to 42% for full 16 years. (26)  These results from actual risks of populations also suggest that cardiofitness differences of groups usually declined at a rate of about 16% per year after baseline.

In summary, all of the above studies that reported results found that the amounts of exercise and cardiofitness differences of groups during most of their actual study periods probably were substantially lower than the values  measured at baseline.  It is of interest thus to compare risk of disease with both baseline differences in cardiofitness and with the more probable actual average differences in cardiofitness that existed during the times that  disease and death events were recorded.

Results of Research Relating Measured Cardiofitness to CV Disease and Death from all Causes.

Table 1 following includes the the results of all studies found wherein the measured cardiofitness of groups could be translated directly into common basis values of VO2 Max and CFR.  Estimated cardiofitness levels by group are shown for men (M) or women (W) for both VO2 Max and CFR at study baselines in columns 3 and 4.  A next column shows the probable average cardiofitness achieved within each group during the period of the study assuming that cardiofitness of groups regressed from that at baseline toward the mean at an average of 16% per year.  Other columns show the risk ratios of higher cardiofitness groups as a percentage of those of the lowest cardiofitness groups for cardiovascular diseases and all-cause death, certain characteristics about each study, and the method by which cardiofitness values were measured. 

                                                                             Table 1

   Risk Ratios of Cardiovascular Disease and Heart Attack and All-Cause Death vs. Measures of Cardiofitness