Age plays an important role in helping to define the risk from obesity. The mortality rates due to being overweight decline with age. One study suggested, for example, that being over 65 and overweight but not obese (a BMI between 25 and 27) is not associated with any higher mortality rates. A BMI over 28, however, is dangerous in people at any age and is associated with an increased risk for death among people over 65.

In older women, being slightly overweight or even moderately obese may not be harmful and may offer some protection. Some excess fat in older women may produce some extra estrogen, nutritional reserve, and insulate bones from fall-related injuries. (It should be strongly noted, however, that when older overweight women lose weight they report improved vitality, physical function, and less pain.) The same positive effect of overweight does not appear to hold in older men.

Being severely underweight is also dangerous in both older women and men, possibly because of the relationship underweight older adults are likely to be smokers, which causes major health problems.