Contribution
of Overweight/Obesity 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 for all cause mortality associated with obesity
(BMI of 30 or more) is as follows:
Assume the prevalence
of obesity in SF is equal to that of US adults (Surgeon
General's Call to Action--epi): 27%
Assume the RR
for all cause mortality is between 1.5 and 2.0 (Surgeon
General's Call to Action--health risks), or 1.75 for this estimate.
PAF = P(RR-1)/[P(RR-1) + 1] = 0.27(1.75 - 1)/[0.27(1.75
- 1) + 1 = 0.2025/1.2025 = 0.169
= 17%
This is a burden
that may be greater than that of tobacco in San Francisco. (The relative
risk associated with smoking is larger, but the prevalence is smaller.)
Note, also, that there are great disparities in the prevalence of obesity
among ethnic groups.
Separate estimates
can be made for overweight (BMI 25-30) and for other health outcomes
(eg, osteoarthitis of the knee, type 2 diabetes, ischemic heart disease,
etc).
