If you're over 65, you might want to reconsider BMI

A new study published in the American Journal of Public Health [may ask for registration] seems to show that being too thin or too fat is dangerous for older women, but being "just right" will mean reconsidering the ideal BMI.

For BMI, the lowest mortality rates were in the range 24.6 to 29.8 kg/m2. The U-shaped relations were seen throughout the age ranges included in this study and were not attributable to smoking or measures of preexisting illness. Body composition measures were not better predictors of mortality than BMI or waist girth.
Conclusions: Our results do not support applying the National Institutes of Health categorization of BMI from 25 to 29.9 kg/m2 as overweight in older women, because women with BMIs in this range had the lowest mortality.