Okay, let's be clear, smoking is still the leading preventable cause of death in the United States. Obesity, though, seems to be claiming much more attention from the media and the public health establishment -- perhaps because there has been recent controversy about exactly what the health effects of extra pounds might be. Two new studies published in the Journal of the American Medical Association (JAMA) should help put this question into perspective.
A couple years ago, researchers from the Centers for Disease Control and Prevention (CDC) presented data indicating that those who were "overweight," i.e., with a Body Mass Index of 25-30, actually had a decreased risk of death. These data referred only to mortality-from-any-cause, however. The latest studies present more information on what the specific risks of excess pounds might be.
The first study (Flegal, KM et al., JAMA 2007;298:2028-2037) examined causes of excess death from cardiovascular disease (CVD) and cancer, and from all other causes. Again the researchers found decreased excess deaths from non-cancer, non CVD causes for those in the overweight category but increased CVD death rates for those in the obese range of BMI. There were, however, increases in the death rates from diabetes and kidney disease in the combined overweight and obese categories. Further, obese individuals did have an increased risk of death from several cancers that are associated with obesity, such as cancers of the breast, colon, esophagus, uterus, ovary, kidney, and pancreas.
The second study (Alley, DE and Chang, VW, JAMA 2007;298:2020-2027) examined trends in disability as related to obesity. These researchers compared reports of functional limitations (such as difficulties in walking, stooping, lifting weights) and "activities of daily living" (ADL) (e.g., dressing, eating), between surveys from 1988-1994 and 1999-2004. They found that in the earlier survey obese people aged sixty years and older had a 78% increased risk of functional limitations compared to normal-weight individuals, and that this risk increased to 175% in the later survey. The ADL risk (as opposed to functional limitations) was not higher for the obese in the first survey but was greater in the second one.
Why the increase in disabilities over this timespan? The authors noted that obese people are living longer. Also, there is a trend towards a younger age of onset of obesity, and thus a longer time during which disabilities can develop.
So what's the bottom line? (First, to avoid premature death, the most important action to take is to quit or avoid smoking. But secondly:) Maintaining a normal body weight (BMI 18.5-25) can help prevent illnesses such as diabetes and kidney disease. For those who are overweight but not obese, it's important to avoid additional gains in body weight and to take other measures to promote health such as participating in regular physical activity.
While obesity may not cause premature death to the extent once feared, significant increases in functional disabilities suggest that the quality of life diminishes as obesity is prolonged. This is an important message that hasn't received nearly enough media play.