Background: 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.
Objective: 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.
Design: 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. PA was assessed with a validated self-report instrument. The combined associations between PA, BMI, and WC with mortality were examined with Cox proportional hazards models, stratified by center and age group, and adjusted for sex, education, smoking, and alcohol intake. Center-specific PAF associated with inactivity, body mass index (BMI; in kg/m2) (>30), and WC (≥102 cm for men, ≥88 cm for women) were calculated and combined in random-effects meta-analysis. Life-tables analyses were used to estimate gains in life expectancy for the exposures.
Results: Significant interactions (PA × BMI and PA × WC) were observed, so HRs 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% (95% CI: 5.88%, 8.83%). Corresponding estimates for avoiding obesity (BMI >30) were 3.66% (95% CI: 2.30%, 5.01%). The estimates for avoiding high WC were similar to those for physical inactivity.
Conclusion: 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.
Alex’s Notes: Physical inactivity is a well-known determinant of mortality in its own right, and while some may argue that this stems from an interaction with weight and fat mass, current evidence suggests that this is not the case. But just how strong is the association between physical activity and all-cause mortality?
To answer this, the current study analyzed data from 334,161 persons for whom measured height, weight, and waist circumference were available. These people came from the European Prospective Investigation into Cancer and Nutrition Study (EPIC) cohort that comprises 519,978 volunteers aged 25-70 years from 23 centers in ten European countries. In other words, this is a huge and diverse sample size. None of the subjects in the current analysis had a history a heart disease, stroke, or cancer, and none were missing data on physical activity.
Speaking of which, data for physical activity was obtained through in-person interviews or self-administered standardized questionnaires in the EPIC study. Total physical activity (PA) was divided into occupational, recreational, and household PA, and participants were classified as active, moderately active, moderately inactive, and inactive based upon their combined occupational and recreational PA using the Cambridge Index of Physical Activity.
Leisure time physical activity
(Duration of sport and cycling in hours/week)
|None||≤ 3.5||>3.5 and ≤ 7.0||> 7.0|
|Sedentary or non-worker||Inactive||Moderately inactive||Moderately active||Active|
|Standing||Moderately inactive||Moderately active||Active||Active|
What was found?
The average follow-up duration was 11.1 years, corresponding to over 4.15 million person-years. About 50% of men and 60% of women were either inactive or moderately inactive. Interestingly, there was a huge discrepancy between male and female activity levels in Italy, Spain, and Greece whereby the number of moderately inactive and moderately active men and women were similar, but the number of active males was three times greater than females, while inactive males were three times less than that of females. Moreover, a shout-out must be given to the Netherlands and Denmark, where the number of inactive men and women were 10% or less while the number of active men and women were in the 30-40% range.
Turning our attention to the fully adjusted (for sex, education, smoking, and alcohol) statistical models of all-cause mortality in relation to physical activity levels within strata of BMI, it is clear that every one-level difference in physical activity reduces mortality by 8-13%. However, the benefits are most pronounced in normal weight individuals and early on in activity. In fact, it is important to note that in obese persons, becoming active is just as good as becoming moderately inactive when compared to a baseline inactive classification. I summarized the relative risk reduction in the table below.
|BMI Category||Inactive||Moderately Inactive||Moderately Active||Active||Reduction of risk for every one-level difference in physical activity|
Similar findings appear for waist circumference.
|Abdominal Obesity?||Inactive||Moderately Inactive||Moderately Active||Active||Reduction of risk for every one-level difference in physical activity|
The above is in reference to overall physical activity, and analysis of its sub-components reveals that higher levels of recreational, but not occupational, physical activity was associated with lower risk of all-cause mortality independent of BMI and waist circumference.
The researchers estimate that if all inactive individuals were at least moderately inactive, all-cause mortality would be reduced by 7.35%. In comparison, if all obese people became non-obese, the reduction was estimated to be only 3.66%, which is still huge, don’t get me wrong, but it strongly suggests that physical inactivity is a larger health concern than a body mass to height ratio, per se. On the flip side, completely avoiding abdominal obesity as determined by waist circumference would result in a reduction similar to that of physical activity (6.53%).
Interestingly, when looking independently at the different countries, the elimination of inactivity was significant for all except Spain and hovered around the 5-10% mark. Except for Greece of course, which had an outstanding 16.54% reduction of death if everyone were at least moderately inactive. Similarly, France and Greece were both insignificant in the analyses for general (BMI) and abdominal (waist circumference) obesity.
Approximately 9.2 million deaths occurred in European men and women in 2008, which according to estimates of the current study, could be reduced by 676,000 or 337,000 if people were at least moderately inactive or not obese, respectively. Moving from one category to the next can be achieved by about 20 minutes of brisk walking per day, which is lower than the current ACSM physical activity guidelines.
I really cannot stress enough how the most pronounced risk reductions occurred early on when changing from inactive to moderately inactive (e.g., deciding to go for that 20 minute walk every night). I am surprised that the reductions were more pronounced in lean and normal weight persons compared to the obese, but this only supports the notion that being overweight has its own set of problems that may offset other benefits of lifestyle choices, such as being more active.
So really the bottom line is that being inactive is worse than being obese. However, even small increases in activity can have profound effects on health, and if combined with other lifestyle changes, can also lead to fat loss, which would then make the benefits of the physical activity habits you picked up even greater. So if you are inactive, just go walk for ~20 minutes at a brisk pace; make it a habit.