Energy Expenditure May Explain Why Coffee Drinkers Have Lower Mortality

The totality of evidence, including recent data from a multinational cohort study of 10 European countries, indicates that individuals who self-select for coffee drinking have a decreased risk of total mortality. ¹ The totality of evidence also indicates that individuals who have increased energy expenditure due to regular physical activity have reduced risks of death from cardiovascular disease as well as total mortality. Cardiovascular disease is and will remain the leading cause of mortality in developed countries and is rapidly becoming so in developing countries and, as a consequence, worldwide. ² Increased energy expenditure represents a therapeutic lifestyle change that is readily available worldwide, including developed countries, principally the United States where levels of regular physical activity are relatively low in the population as well as in developing countries where levels of regular physical activity are decreasing. We propose a novel and timely hypothesis that coffee ingestion is associated with increases in energy expenditure during physical activity, which in turn decreases risks of total mortality. In addition, we also provide an outline for testing this plausible, but unproven, hypothesis.

The interrelationships among human behaviors, such as habitual physical activity with overweight and obesity as well as diet with total as well as cause-specific mortality, are complex. There is, however, a robust totality of evidence that increased regular energy expenditure plays a major role in reducing mortality. Specifically, energy consumed in regular physical activity up to a total of approximately 3000 to 3500 kcal per week is associated with reduced risks of death from cardiovascular disease as well as total mortality. ³ Individuals who engage in daily brisk walking for only about 20 minutes, which burns about 700 kcal/week, have a 30% to 40% reduced risk of coronary heart disease. ⁴

Physical inactivity is a major public health problem in developed countries such as the United States, where lack of physical activity accounts for about 22% of coronary heart disease, 22% of colon cancer, 18% of osteoporotic fractures, 12% of diabetes and hypertension, and 5% of breast cancer. ⁵ In addition, worldwide, physical inactivity is responsible for global median population attributable fractions of 4.0% for coronary heart disease, 4.5% for stroke, 4.9% for type 2 diabetes, 7.1% for breast cancer, 7.0% for colon cancer, and 6.4% for all-cause mortality. ⁶ With respect to costs, this problem is even greater in developed countries such as the United States. In the United States, physical inactivity accounts for about 2.4% of health expenditures or approximately $24 billion a year. ⁷ Worldwide, the corresponding figures are 1% to 2% and $54 billion a year, respectively. ⁶ Perhaps surprising to many clinicians and their patients, the World Health Organization estimates that, globally, 31% of adults are insufficiently active and approximately 3.2 million deaths each year are attributable to insufficient physical activity. ⁸ In the United States, approximately 36% of adults do not engage in any leisure-time physical activity, despite the fact that walking may be comparable to more vigorous exercise in preventing a cardiovascular event. ⁹ Even in patients who survive an acute myocardial infarction and undergo cardiac rehabilitation, less than 15% actually participate in cardiac rehabilitation following discharge.

With respect to dietary constituents, coffee is one of the world’s most widely consumed beverages and about 75% of US adults drink coffee, 50% daily. ¹⁰ In a recent publication of over 500 000 individuals living in 10 different European nations, compared with nondrinkers, individuals in the highest quartile of coffee consumption had a statistically significant lower all-cause mortality. ¹ Others also have reported a reduced risk of death that was even greater in a subgroup of those who drank between 3 and 6 or more cups of coffee per day compared with those who drank less than 1 cup of coffee per day. ¹¹

In the United States, approximately 85% to 90% of coffee drinkers consume caffeinated coffee ¹² and about 64% of caffeine ingested derives from consumption of coffee. ¹³ Intake of caffeine or caffeinated coffee intake results in a dose-dependent increase in resting metabolism of at least 5% to 8%. ¹⁴ It is often overlooked that resting metabolism accounts for approximately 60% to 70% of total daily energy expenditure. ⁴ Accompanying the gradual decline in resting energy expenditure with age, is a progressive weight gain among adults in the United States and many European nations of about 0.5 to 1.3 kg of body weight per year. ⁴ Thus, from about 25 to 55 years of age, many adults become between 13 and 23 kg overweight. This rate of weight gain averages to an excess daily intake of only 10 to 30 kcal (about 40-125 kJ)—amounting to one bite of food or less per day—above daily energy expenditure. ⁴ The magnitude of increase in resting energy expenditure due to ingestion of caffeine or caffeinated coffee may be sufficient to cancel this excess and thereby help combat the increase in overweight and obesity that may be the leading avoidable cause of premature death worldwide. ² In addition, ingestion of caffeine, predominantly in coffee, has a number of effects associated with increased capacity for energy expenditure during physical activity. In moderate doses, comparable to those associated with a reduced risk of mortality, ^1,11 ingestion of caffeine or caffeinated coffee increases alertness and enjoyment of physical activity, reduces exertional perception of effort and discomfort, and increases the capacity to perform strenuous exercise. ^15,16 In combination, among coffee drinkers, these effects may promote more regular and higher intensity daily physical activity among a large majority. ¹⁷ Further, in one study, when smokers and individuals with chronic disease were excluded, there was a stronger inverse association between coffee drinking and mortality for persons reporting good or excellent health than for those reporting poor to fair health. ¹¹ Not surprisingly, individuals reporting good to excellent health are more likely to be more regularly as well as more strenuously physically active than those less healthy.

It is also intriguing to note that individuals who drink decaffeinated coffee in amounts similar to caffeinated coffee may also experience reductions in total mortality. ^1,11 These benefits are plausibly attributed to other constituents of coffee that produce decreases in systemic inflammation and insulin resistance. ¹ It has, however, been observed that regular consumption of decaffeinated coffee is closely associated with beneficial behaviors including regular participation in vigorous physical activity and healthy dietary habits. ¹⁸ It is therefore tempting to speculate that increased levels of regular energy expenditure is the key common feature linked with reduced mortality in regular drinkers of both caffeinated and decaffeinated coffee.

In light of all these aforementioned considerations, we propose a plausible but unproven hypothesis that individuals who self-select for coffee drinking have a lower risk of total mortality due, at least in part, to higher levels of regular caloric expenditure. Specifically, at present, the totality of evidence suggests that individuals who self-select for coffee drinking have a decrease in total mortality. Thus, it is tempting to speculate that those reporting good or very good to excellent health were habitually more physically active. This, in turn, contributes importantly relevant data to the hypothesis that caffeinated coffee provided an energy boost to increase the likelihood of exercising as well as the ability to expend more energy in physical activity due to caffeine’s well-known effects of increasing performance and decreasing the perception of effort during exercise. Thus, coffee may increase regular levels of energy expenditure which, in turn, may lower risk of total mortality. In addition, by decreasing overweight and obesity, increased regular energy expenditure also is likely to reduce the risk of mortality.

Nonetheless, this novel hypothesis merits testing in analytic epidemiological studies designed a priori to do so. ¹⁹ Specifically, a large-scale prospective cohort study with high follow-up rates that collects objective and reproducible data on the aforementioned variables should provide an adequate test of this important and timely hypothesis that will add to the existing totality of evidence on the beneficial effects of increased energy expenditure. This hypothesis, if true, has major clinical and public health implications for the United States and worldwide.