Obesity is a known health risk. The number of epidemiological studies that have linked excess weight to cardiovascular disease, cancer, diabetes, other chronic conditions, and increased risk of death is staggering.1,2 In fact, the cutoff points for BMI into overweight and obese were created to reflect increased risk of disease and death due to excess fat.3
Then there is the “obesity paradox.” This is the term used to describe the opposite of the usual finding - there are certain groups of people, usually those with severe chronic diseases such as heart failure and kidney disease, in which a higher BMI seems to be associated with a decreased mortality risk.4,5
Elderly persons are another group in which an obesity paradox has been observed in some studies.6 However, this observation is not consistent – other studies have reported an increased risk with higher BMI in adults over age 70 or 75, similar to younger age groups, and others have shown no association at all.7-11 Overall, the relationship between BMI and mortality in the elderly has been unclear.
Several explanations have been proposed to explain the paradox – these are a few examples:
- BMI is not a true indicator of body fat – older persons tend to have more body fat at the same BMI as younger adults.3 One study found that greater waist circumference in the elderly was associated with increased mortality risk, but greater BMI was associated with decreased risk. In these individuals, greater BMI may reflect greater fat-free mass, rather than greater body fat. Waist circumference and fat-free mass may be more important indicators than BMI for obesity-associated health risks in the elderly.12,13
- Unintentional weight loss may be involved – many older persons in these studies who are at a low or normal BMI may be there because of disease-related weight loss. Weight loss in elderly has been shown to be associated with negative health outcomes, presumably for this reason.14 So a study of elderly persons that only takes one weight measurement and does not measure weight change over time is inherently flawed.
- Another issue with the length of studies is that weight gain late in life is probably less dangerous than weight gained earlier in life and then maintained for many years – being obese for 50 years results in more cumulative damage than being obese for 15 years. The earlier you become obese, the greater the risk of death.15,16 Therefore, long-term data (decades, not years) is needed to get an accurate picture of health risks in the elderly due to obesity.
New research has attempted to reconcile the contradictions in previous studies by using long-term data. Although the researchers used BMI rather than waist circumference, they used two weight measurements 17 years apart, and followed subjects for a total of 29 years – importantly, they only included subjects who maintained a similar weight over the first 17 years – this helped to remove any potential effects from late life weight gain or disease-related weight loss.
Men (age 75-99) who maintained a BMI greater than 22.3 had a shorter life expectancy by 3.7 years, and an 88% increased risk of death during the study period compared to men with a lower BMI. Men who maintained a BMI greater than 27.3 had double the risk of death compared to those with a BMI less than 22.3. Women in the same age group who maintained a BMI greater than 27.4 shortened their life expectancy by 2.1 years, and had a 41% increase in risk of death compared to women with a lower BMI.17,18
This new study leads us to conclude: no matter what your age, carrying excess weight for a significant length of time is dangerous – in fact, it can be deadly.
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18. Contrary to Earlier Findings, Excess Body Fat in Elderly Decreases Life Expectancy. 2011. ScienceDaily. http://www.sciencedaily.com/releases/2011/08/110811151325.htm. Accessed September 29, 2011.