BMI and Obesity: What Role Do They Play in How Long You Live?

A high BMI and obesity have long been regarded as risk factors for a variety of health related problems such as hypertension, diabetes, cardiovascular disease, and certain forms of cancer. While this remains true, what affect does a high BMI and obesity play in overall mortality?

It was previously thought that a higher BMI was associated with an earlier, all cause mortality. Several studies done in the past have supported this idea. Some recent studies have called this conventional thinking on high BMI and obesity into question.

A few studies conducted on weight gain and obesity have shown that carrying around a few extra pounds may actually decrease mortality, particularly in the elderly. This may be partially due to the fact that elderly patients with lower BMI's may be more at risk for dying from a hip fracture due to their propensity towards osteoporosis and may be more susceptible to infectious disease due to their lower body weight.

It should be emphasized that this applies only to persons who are slightly overweight as opposed to those who are markedly obese. Being obese, particularly morbidly obese, seems to carry with it a higher all cause mortality rate across the board.

How is BMI measured to make the diagnosis of obesity? BMI or body-mass index is calculated by dividing your weight measured in kilograms by your height in meters squared. If your BMI is above 25, you are considered to be overweight. If above 30, you're classified as obese. Some recent studies have shown that elderly women with BMI's between 25 and 27 and elderly men with BMI's between 27 and 29 have the best chance for survival when compared to those with higher or lower BMI's.

Where does this conflicting information on BMI and obesity leave us as far as determining risk of mortality? This data would suggest that being very mildly overweight without any other underlying medical conditions probably doesn't significantly shorten lifespan and may even prolong it in the elderly population. Being obese or severely underweight may confer an increased risk of death, particularly in the elderly who are at risk for falls with resulting hip fractures.