Meta-analysis of the effect of excluding early deaths on the estimated relationship between body mass index and mortality.
OBJECTIVE
Prospective cohort studies typically observe U- or J-shaped relationships between body mass index (BMI) (kg/m2) and mortality. However, some studies suggest that the elevated mortality at lower BMIs is due to confounding by pre-existing occult disease and recommend eliminating subjects who die during the first several (k) years of follow-up. This meta-analysis tests the effects of such early death exclusion on the BMI-mortality association.


METHODS
Studies identified from MEDLINE, review articles, ancestry analyses, and the "invisible college."


METHODS
1) measured relative body weight at baseline; 2) included at least 1000 subjects; 3) reported results with and without early-death exclusion, or relevant data; and 4) did not study exclusively diseased populations. Blank tables were mailed to 131 investigators covering 59 databases. Completed tables (n = 16 databases), electronic raw data (n = 7 databases), and original articles (n = 6 databases) provided final data. Meta-analytic regressions compared the BMI-mortality association with and without early death exclusion. The sample included 29 studies and 1,954,345 subjects.


RESULTS
The effect of eliminating early deaths was statistically significant but minuscule in magnitude. Implementation of early death exclusion was estimated to shift the BMI associated with minimum mortality only 0.4 units for men and 0.6 units for women at age 50. Even at a BMI 16, the estimated relative risk (compared to BMI 25) decreased only 0.008 units for men and 0.076 units for women at age 50.


CONCLUSIONS
Results indicate that either pre-existing disease does not confound the BMI-mortality association or eliminating early deaths is inefficient for reducing that confounding.
Allison
D B
DB
Obesity Research Center, St. Luke's/Roosevelt Hospital, Columbia University College of Physicians & Surgeons, New York, NY 10025, USA. dba8@columbia.edu
Faith
M S
MS
Heo
M
M
Townsend-Butterworth
D
D
Williamson
D F
DF
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D015992:Body Mass Index; D015331:Cohort Studies; D016206:Databases, Bibliographic; D005260:Female; D006801:Humans; D008875:Middle Aged; D009026:Mortality; D011446:Prospective Studies; D012044:Regression Analysis; D012307:Risk Factors; D012680:Sensitivity and Specificity; D012907:Smoking