This study by Leonid Gavrilov suggests to me that the optimum BMI to reduce mortaility and disability is BMI 24-26 for men and BMI 22-24 for women.I reviewed an earlier study on BMI, Waist circumferance and Waist-Hip ratio here.
We used prospective data of 16,176 white adults of the Health and Retirement Survey (HRS).
Outcomes were years to live with and without ADL disability at age 55.
Mild obesity (BMI: 30–34.9) did not change total life expectancy (LE) but exchanged disabled for disability-free years. Mild obesity decreased disability-free LE with 2.7 (95% confidence limits 1.2; 3.2) year but increased LE with disability with 2.0 (0.6; 3.4) years among men.
Among women, BMI of 30 to 34.9 decreased disability-free LE with 3.6 (2.1; 5.1) year but increased LE with disability with 3.2 (1.6;4.8) years.
Overweight (BMI: 25–29.9) increases LE with disability for women only, by 2.1 (0.8; 3.3) years).
Figure 2 illustrates the differences in hazard ratios by BMI between both sexes, disability and mortality that generated the increased LE (Life Expectancy) with ADL (Activities of Daily Living) disability.
The shape of mortality and disability by BMI is remarkably different, disability being far more BMI dependent than mortality. Among men, mortality shows a broad U shape with increasing BMI, increasing at the extremes only, whereas disability shows a sharp V shape. A BMI with lower disability risks would be between 22 and 28.
Among women, mortality increases earlier (at around a BMI of 33) and higher, whereas a BMI with lower disability would be between 20 and 26, two points lower than men.
The BMI effect on disability was not different between smokers and nonsmokers. Among individuals reporting poor or fair health, BMI had little effect on disability and mortality; among individuals reporting good or excellent health, the correlation was higher