Associations of Body Mass Index and Waist Circumference with 3-Year All-Cause Mortality Among the Oldest Old: Evidence from a Chinese Community-Based Prospective Cohort Study.
Yue-Bin Lv, Simin Liu, Zhao-Xue Yin and 9 others
PMID 29807748WHAT IT FOUND
Among Chinese oldest old, higher body mass index and waist circumference were linked to better 3-year survival.
Underweight participants had the highest mortality. This does not prove extra weight helps.
Key findings
01After full adjustment, each 1 kg/m2 higher BMI was associated with a 5.0% lower 3-year all-cause mortality in men and a 4.0% lower mortality in women.
02After full adjustment, each 1 cm higher waist circumference was associated with a 1.4% lower 3-year all-cause mortality in men and a 1.3% lower mortality in women.
03Compared with underweight participants, normal weight and overweight or obese participants had lower mortality risk, with hazard ratios 0.71 and 0.60 in men and 0.80 and 0.79 in women.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
This was an observational cohort, not a treatment trial, so it cannot show that changing BMI or waist circumference changes mortality. The authors say reverse causation, selection bias, and survival bias may explain the associations. BMI and waist circumference were measured only once at baseline, so changes over time were not captured. Height loss may have overestimated BMI. Cause of death data were not collected. Only 139 (3.2%) participants had BMI above 28 kg/m2, so the obese group was merged with the overweight group. 229 participants were lost to follow-up. Findings are from Chinese oldest old and may not apply to other ethnic and age groups.
Declared interests
Research support is listed as NIH extramural and non-U.S. government; the supplied text does not report author conflicts of interest.
The easy way to misread this
Do not conclude that telling oldest old to gain weight or reduce waist circumference will lower mortality. This is an association in a cohort, and the authors discuss reverse causation, selection bias, and survival bias as possible explanations.