Contribution
of Physical Inactivity to SF Burden of Disease
The
Population Attributable Fraction (PAF) for mortality is the proportional
reduction in a specific cause of death that would have been expected
if the population had no exposure to a specific determinant.
It is calculated from the relative risk from exposure (RR) to the determinant
and the prevalence of exposure to the determinant in the population
(P), expressed as PAF = P(RR-1)/[P(RR-1) + 1]. Though
it has limitations, PAF is an important measure for public health planning.
A reasonable first
estimate of the PAF associated with physical inactivity is as follows:
Standard minimal
guidelines for physical inactivity reduce all-cause mortality by about
25% (Lee
& Skerrett, 2001), so the relative risk (RR) of inactivity
risk is 1/0.75 = 1.33. Assuming that roughly 55% of Californians are
physically inactive (see UCSF
Physical Activity and Health Initiative page), the prevalence
of exposure (P) might be 0.55. (Note, however, that prevalence varies
widely with ethnicity and income.) In any case, assuming that P is
0.55,
PAF = P(RR-1)/[P(RR-1)
+ 1] = 0.55(1.33 - 1)/[
0.55(1.33 - 1)
+ 1]
= 15%
This suggests that
the contribution of physical inactivity to all cause mortality is comparable
to that of tobacco (the relative risk from smoking is larger, but its
prevalence is smaller).
See also, MEDLINE
strategies link on the right. The results of various studies might be
tabulated on a worksheet.
See also, slides
from a lecture by I-Min Lee, MD, ScD, Harvard Medical School & Harvard
School of Public Health, entitled "Population
Attributable Risk of No Physical Activity."
