Looking over the day to day aspects of an ordinary life that an individual has control over, those with the greatest negative influence on long-term health are as follows: a diet that leads you to be overweight or obese for years, lack of regular exercise, and smoking. Studies suggest that these cause around the same level of harm, a loss of perhaps five years to a decade of life expectancy, and the addition of many more years spent in ill health rather than in good health. In the golden future ahead medicine will be capable of efficiently and effectively rescuing you from all the consequences of poor health practices, but we do not yet live in that future, and neglecting your health today reduces the odds of living to benefit from the impressive medical technologies of tomorrow.
There are of course strong correlations between diet, level of exercise, and excess weight, but that doesn't stop epidemiologists from peering deeply into the statistics of large population studies to try to pick apart the various contributions to shorter rather than than longer lives. This latest study of hundreds of thousands of people provides confirming evidence for a number of themes set out in past research. For example, it is fairly easy to establish sizable differences between the long term outcome for no exercise and the long term outcome for regular moderate exercise, but there is little to show that any greater benefits result from more exercise or different types of exercise. Obviously there are studies of elite athletes such as cyclists wherein these individuals live a decade longer than the rest of the population, but this is only correlation: are they long-lived because of the exercise, or is it instead because only the most robust individuals tend to become successful athletes? For everyone else there is no good study out there to say that twice as much exercise is twice as good. The big threshold is between none and some, and after that the data is increasingly nebulous.
Physical inactivity has been consistently associated with an increased risk of early death, as well as being associated with a greater risk of diseases such as heart disease and cancer. Although it may also contribute to an increased body mass index (BMI) and obesity, the association with early death is independent of an individual's BMI. To measure the link between physical inactivity and premature death, and its interaction with obesity, researchers analysed data from 334,161 men and women across Europe participating in the European Prospective Investigation into Cancer and Nutrition (EPIC) Study.
Using the most recent available data on deaths in Europe the researchers estimate that 337,000 of the 9.2 million deaths amongst European men and women were attributable to obesity (classed as a BMI greater than 30): however, double this number of deaths (676,000) could be attributed to physical inactivity. The researchers found that the greatest reduction in risk of premature death occurred in the comparison between inactive and moderately inactive groups. The authors estimate that doing exercise equivalent to just a 20 minute brisk walk each day - burning between 90 and 110 kcal ('calories') - would take an individual from the inactive to moderately inactive group and reduce their risk of premature death by between 16-30%. The impact was greatest amongst normal weight individuals, but even those with higher BMI saw a benefit.
The higher risk of death resulting from excess adiposity may be attenuated by physical activity (PA). However, the theoretical number of deaths reduced by eliminating physical inactivity compared with overall and abdominal obesity remains unclear. We examined whether overall and abdominal adiposity modified the association between PA and all-cause mortality and estimated the population attributable fraction (PAF) and the years of life gained for these exposures.
This was a cohort study in 334,161 European men and women. The mean follow-up time was 12.4 y, corresponding to 4,154,915 person-years. Height, weight, and waist circumference (WC) were measured in the clinic. Significant interactions (PA × BMI and PA × WC) were observed, so hazard ratios were estimated within BMI and WC strata. The hazards of all-cause mortality were reduced by 16-30% in moderately inactive individuals compared with those categorized as inactive in different strata of BMI and WC. Avoiding all inactivity would theoretically reduce all-cause mortality by 7.35%. Corresponding estimates for avoiding obesity (BMI of more than 30) were 3.66%.
The greatest reductions in mortality risk were observed between the 2 lowest activity groups across levels of general and abdominal adiposity, which suggests that efforts to encourage even small increases in activity in inactive individuals may be beneficial to public health.
The difference in projected mortality reductions from eliminating lack of exercise versus eliminating clinical obesity stems, I think, from the demographics: many more people live sedentary lives than are overweight to that level.