Only Substantial Obesity Is Associated with All-Cause Mortality

Summary and Comment |
January 17, 2013

Only Substantial Obesity Is Associated with All-Cause Mortality

  1. Thomas L. Schwenk, MD

In a meta-analysis, being modestly overweight was somewhat protective.

  1. Thomas L. Schwenk, MD

The reported relation of overweight or obesity to mortality for any given follow-up has been inconsistent, because studies have used varying definitions and categories of normal weight and obesity. In this meta-analysis, researchers identified 97 studies, mostly from the U.S., Europe, and Australia (2.88 million participants and >270,000 deaths), in which weight categories were standardized. Participants were categorized by body-mass index (BMI) as normal weight (18.5 to <25 kg/m2), overweight (25 to <30), grade 1 obese (30 to <35), grade 2 obese (35 to <40) and grade 3 obese (≥40).

Compared with normal-weight participants, all-cause mortality was significantly lower for overweight participants (hazard ratio, 0.94), was similar for grade 1 obesity (HR, 0.95), and was significantly higher for grade 2 and grade 3 obesity (HR, 1.29). Results were similar when analysis was limited to studies that were considered to be appropriately adjusted (neither overadjusted for possible causal pathways between obesity and mortality, nor underadjusted for age, sex, and smoking status).


These results call into question, as have prior data, the assumption that mild overweight or low-grade obesity are associated with early all-cause mortality. Editorialists note that BMI does not account for demographic, racial, and other differences in how fat is stored or for the independent association of cardiorespiratory fitness with mortality, regardless of weight. Healthcare advances might have traded mortality for substantial morbidity and lower quality of life in patients with mild obesity, which would not be captured by this study. Weight and BMI provide useful, but imperfect, data for counseling patients.


Reader Comments (4)

JW Scheier

I remind clients that weight is only one risk factor and that there is significant differences between being overweight and obese (and within each category). Waist circumference, activity level, lipid profile, glucose levels, BP etc. often seem secondary to body size . At the same time I am concerned for disordered eating and creation of eating disorders -esp in children. Good questions asked. Appreciate the thoughts.

Competing interests: None declared

Marilyn E Johnson, RPH

This is somewhat reassuring. It could be that BMI is not that accurate a predictor because it is often measured by height vs. weight-- and we "grow" shorter as we age! (From posture (wheelchair confinement makes it harder to stand up straight..) to vertebral fractures, etc. Doctor's I have seen won't use my college height--just my present one which is 2 inches shorter.

Competing interests: None declared

RR Logan

I never hear where the weight figures come from. Is it weight at the time of death? Many (most?) people lose weight before they die because of their disease or treatment. Smokers also tend to be lighter. Not to mention BMI puts athletic and fit people in the overweight and even obese category.

Competing interests: None declared

Carol Vassar, MD

Do these studies follow people over time or do they just give BMI at death? Since the average lifespan is late 70's, BMI at death shows little about the effect of an overweight BMI over a lifetime and age at death.

As pointed out by M.Johnson, RPH, the BMI should be calculated using height at maturity rather than current height which could be lowered by trauma with vertebral compression fractures, progressive scoliosis, kyphosis, osteoporotic fractures or just the disc degeneration that is normal with aging. Perhaps all of these causes of loss of height effect mortality, but not on the basis of body composition.

Competing interests: None declared

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