Junkfood Science: What is the greatest risk factor for mobility limitations as we age?

December 07, 2007

What is the greatest risk factor for mobility limitations as we age?

It is widely reported that obesity is the biggest risk factor for disability as we age. A recent study published in the Journal of the American Geriatrics Society examined this hypothesis. The findings were not what some might have anticipated. Since this study didn’t make the news, let’s take a look.

Impairment of the lower extremities and mobility limitations typically occur before disability in aging people. Lower extremity performance (LEP) has also been shown to predict risks for subsequent falls, nursing home admission rates and greater need for healthcare. As these Italian researchers, led by Giuseppe Sergi, Ph.D., at the University of Padova in Italy, noted, there remains considerable debate, however, as to the relationship between physical impairment and body mass index, with few studies objectively measuring lower extremity performance and overweight and obesity.

For this study, they used the clinical examinations done on 2,600 seniors (65+ years, average age 73.2 years) at enrollment into the Italian Longitudinal Study on Aging in 1992. Of the 4,521 participants, they excluded 1,849 who were disabled from previous traumas, stokes or Parkinsons disease, with no difference in BMIs between the included and excluded groups. LEP was assessed using a Motor Performance Test (MPT), which entailed six specific tasks — rising from a chair, turning a half-circle, tandem walking, standing on one leg, rapid steps up, and walking 5 meters — and they created a scoring method tallying the scores from each task, ranging from 0 (worst) to 14 (best). They used various computer models to exhaustively look for correlations between LEP and BMI, adjusting for age, smoking status, weight loss, depression, dementia, pulmonary diseases, CHD, distal symmetric neuropathy, peripheral artery disease, diabetes mellitus and hypertension.

They found that across all weight ranges, advancing age was accompanied by similar weight losses, with only men below BMIs of 20 showing significantly more weight loss. But there were no tenable associations between LEP and being ‘overweight’ or class I ‘obesity’ among men or women at any age. As they concluded:

The current results further fuel the debate on BMI thresholds in elderly people, suggesting that higher BMI cutoffs may be more suitable for older adults. Being overweight in old age may be associated not only with higher survival rates, but also with less physical performance impairment.

A notable correlation between LEP and BMI only surfaced in the most extreme obesity range, with odds ratios of 3.45 in men and 3.16 in women compared to the ‘normal’ weight range. But several cautionary notes deserve mention. The actual differences in MPT scores between the fattest and thinnest groups was only 0.8 and 0.5, men and women respectively. Those with BMIs >35, only represented 2% and 7% of the men and women, respectively. And the average weight among the most obese men was 219 pounds, and 190 pounds among the women, suggesting issues other than weight may account for these correlations.

Among women, being slender (BMI<20) was associated with a greater probablility of impairment than ‘normal,’ ‘overweight,’ or ‘obese’ class I. Slenderness was associated with a more than 2.5-fold higher risk, even though those with BMIs <20 had no higher rates of recent weight loss than the fat women. And, as the authors noted, BMIs < 20 have also been shown to “have a negative effect on morbidity and mortality.”

But the story doesn’t end with BMI. Several other factors were found to be much more significant.

Dementia was associated with more than a 5-fold higher risk for LEP among the men, regardless of BMI. Interestingly, there was no dementia among the most extremely obese men (BMIs >35) in this cohort and it was only present among 1% of the heaviest women. ***

But one factor for lower extremity limitations outshadowed all others: Age.

At 75 years of age, risks increased 5.5-fold, unrelated to BMI.

At age 80+, the risks increased to 13 times as high among men and 14 times as high for women.

The bottom line is that advanced age is most associated with age-related impairments. Given there is no known way to change anyone’s age, anymore than safely and effectively change their BMIs, rather than just blaming fat, examining ways we can help seniors remain as active and independent as possible is a worthwhile goal for healthcare providers.

© 2007 Sandy Szwarc

*** This concurs with Obesity Paradox #9, of course.

But it also concurs with another just-published study led by Dr. Anna Rita Atti, M.D., at the Aging Research Center, Karolinska Institutet and Stockholm Gerontology Research Center in Stockholm, Sweden.

Following 1,255 elderly people (average age of 80), living at home and in institutions, enrolled in the Kungsholmen Project, a longitudinal study on aging and dementia. They measured BMI at enrollment and changes during the first three years of follow-up. Dementia was diagnosed according to the clinical criteria in Diagnostic and Statistical Manual of Mental Disorders, Third Edition. To rule out the development of dementia due to medical issues, they even excluded the cases that occurred during the first three years from their analysis. They also examined the relationship between BMI and mortality.

They found no association between underweight and the development of dementia. Among the overweight and obese elderly, however, there was a (25% to 34%) lower risk for developing dementia even after 9 years of follow-up.

For all the elderly, rapid loss of weight was associated with more than double the risk for developing dementia within the subsequent three years.

Because underweight was associated with 87% higher mortalities and could be missing diagnoses of dementia, they did a secondary analysis on the risks for developing dementia only among survivors. The underweight survivors had a 20% higher risk, whereas the risks among the overweight remained lower.

This study suggests a protective effect for high BMIs in late life, they concluded, and confirmed that weight loss is a “marker of impending dementia.”

“Being moderately overweight at older ages might be indicative of good health status,” wrote Dr. Atti and colleagues.

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