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U.S. NIH’s Obesity Guidelines Part 19: Risk of death
Tuesday, December 14, 2004 4:58 am Email this article
The risk of death increases modestly in people who are overweight (a BMI of 25 to 29.9), but increases substantially in someone obese (a BMI of 30 or more) according to the U.S. NIH's Obesity Guidelines (p. 21). Being obese increases the risk of death from all causes, especially cardiovascular disease
Being obese, that is having a BMI exceeding 30, increases the risk of death from all causes, especially from cardiovascular disease which is increased by 50 to 100 percent above that of persons with BMIs in the range of 20-25. (p. 1 and 23)
A very low BMI also increases the risk of death, some of which is accounted for by smoking and preexisting diseases
The risk of death is higher in people with low BMI—usually below 20—as well as in people with high BMI.
Smoking and preexisting illness accounts for some, but not all, increase in mortality at low BMI.
It is not clear whether increased mortality associated with low BMI is due to a some factor not accounted for, inadequate body fat and/or body protein due to unintentional weight loss, or genetic factors, however, there is no evidence that intentionally gaining weight reduces mortality. (p. 23)
BMI and the risk of death less associated in older adults
BMI is less associated with the risk of death in older adults, especially after age 75. (p. 23)
Here are some of the possible reasons.
- Older adults are more likely to have diseases that increase mortality and cause weight loss.
- Waist circumference tends to increase with age, which increases the risk of death even at lower BMIs.
- A person’s weight in middle age is related to their risk of death in old age.
- Smoking may increase mortality and decrease body weight more in older adults because of the cumulative health effects of smoking.
- BMI tends to underestimate the levels of body fat in older adults.
- Older people with an elevated BMI may be resistant to the health effects of obesity.
Lowest mortality in older adults with BMI 25 to 30
A 20-year study of U.S. adults ages 55- to 74- years-old found that after adjusting for smoking and preexisting illness the lowest mortality occurred at a BMI of 24.5 in white men, 26.5 in white women, 27.0 in black men, and 29.8 in black women. (p. 24)
Blacks: Mortality risk starts 1-3 BMI units higher than in Whites
Weight-related health risks start to increase 1 to 3 BMI units higher in blacks than in whites. (p. 24)
For example, in the National Health and Nutrition Examination Survey minimum mortality was associated with a BMI of 27.1 for black men and 26.8 for black women, compared with 24.8 for white men and 24.3 white men.
Weight loss and mortality
Without differentiating between intentional and unintentional, weight loss is associated with increased risk of death. (p. 25)
The results of two large studies involving a total of approximately 38,000 people suggest the following:
- Based on a patient’s recall of weight loss, heavier people are more likely to report intentional weight loss, and lean people are more likely to report unintentional weight loss.
- Roughly half of all weight loss is intentional and half is unintentional.
- Unintentional weight loss is more frequent in older people than younger people, and intentional weight loss is less frequent.
- Unintentional weight loss is more frequent in people with poor health, people who use medications for chronic health conditions, and people who smoke. (p. 25)
Intentional weight loss reduces mortality in those with obesity-related health problems
One study found that among patients who had been hospitalized for a heart attack, those who lost at least 1.1 pounds reduced their risk of overall mortality by 54 percent, and reduced their risk of a cardiac event by 50 percent compared to patients who lost less than 1.1 pounds. (p. 25)
Intentional weight loss reduces mortality 20% in women with obesity-related health problems
A 12-year study which analyzed data from 43,457 overweight white women, ages 40- to 64-years-old who had never smoked, found the following:
- In women with obesity-related comorbidities, intentional weight loss of any amount was associated with a 20 percent reduction in all-cause mortality, primarily due to a 40 to 50 percent reduction in mortality from obesity-related cancers.
- Intentional weight loss reduced diabetes-related mortality 30 to 40 percent. Preliminary evidence suggests this is also true in men.
- Intentional weight loss was generally unrelated to mortality in women without any comorbidities.
- Intentional weight loss of at least 20 pounds during the previous year was associated with a small to modest increase in mortality in women.
- The association between intentional weight loss and longevity in middle-age overweight women depends on health status concluded the authors of the study.
Weight loss surgery appears to reduce the risk of death
It also appears that weight loss surgery probably reduces the risk of death according to preliminary 2-year follow-up data from the 10-year on-going Swedish Obesity Study.
The study involves 1,006 people ages 37- to 57-years-old with an initial BMI of 34 in men and 38 in women.
Diabetes occurred in only 0.5 percent of patients who underwent surgery compared to 16 percent of controls; elevated triglycerides occurred in 6 percent of surgery patients versus 23 percent of controls; and low HDL levels occurred in 5 percent of surgery patients versus 16 percent of controls. (p. 26)
Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults : the evidence report / National Heart, Lung, and Blood Institute [Bethesda, Md.] : National Institutes of Health, National Heart, Lung, and Blood Institute, . NIH publication No. 98-4083.
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