Body fat and fat-free mass and all-cause mortality.
OBJECTIVE
To investigate whether the association between BMI and all-cause mortality could be disentangled into opposite effects of body fat and fat-free mass (FFM).


METHODS
All-cause mortality was studied in the Danish follow-up study "Diet, Cancer and Health" with 27,178 men and 29,875 women 50 to 64 years old recruited from 1993 to 1997. By the end of year 2001, the median follow-up was 5.8 years, and 1851 had died. Body composition was assessed by bioelectrical impedance. Cox regression models were used to estimate the relationships among body fat mass index (body fat mass divided by height squared), FFM index (FFM divided by height squared), and mortality. All analyses were adjusted for smoking habits.


RESULTS
Men and women showed similar associations. J-shaped associations were found between body fat mass index and mortality adjusted for FFM and smoking. The mortality rate ratios in the upper part of body fat mass were 1.12 per kg/m2 (95% confidence interval: 1.07, 1.18) in men and 1.06 per kg/m2 (95% confidence interval: 1.02, 1.10) in women. Reversed J-shaped associations were found between FFM index and mortality with a tendency to level off for high values of FFM.


CONCLUSIONS
Our findings suggest that BMI represents joint but opposite associations of body fat and FFM with mortality. Both high body fat and low FFM are independent predictors of all-cause mortality.
Institute of Cancer Epidemiology, The Danish Cancer Society, Strandboulevarden 49, DK-2100 Copenhagen, Denmark. janne@cancer.dk
Janne
J
Bigaard
Kirsten
K
Frederiksen
Anne
A
Tjønneland
Birthe Lykke
BL
Thomsen
Kim
K
Overvad
Berit Lillienthal
BL
Heitmann
Thorkild I A
TI
Sørensen
D000273:Adipose Tissue; D000375:Aging; D001823:Body Composition; D015992:Body Mass Index; D002423:Cause of Death; D003718:Denmark / Q000453:epidemiology; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009026:Mortality; D011446:Prospective Studies; D012907:Smoking