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Muscle, Fat Predict Functional Status Better Than BMD in HIV+ 45- to 65-Year-Olds
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3rd International Workshop on HIV and Aging, November 5-6, 2012, Baltimore
Mark Mascolini
Skeletal muscle and percent body fat predicted functional status better than hip bone mineral density (BMD) in a case-control study of 45- to 65-year-olds responding well to antiretroviral therapy [1]. Even so, people with low functional status had significantly lower hip and spine BMD than people with good functional status.
Because low lean mass, high body fat, and low BMD are tied to disability and frailty in older adults, University of Colorado researchers analyzed the impact of several variables related to those body composition components in low-functioning and high-functioning 45- to 65-year-olds with a good response to antiretroviral therapy. They defined low function and high function by combining standard frailty criteria and results on the Short Physical Performance Battery.
This prospective study involved people with a viral load below 48 copies/mL who had taken antiretrovirals for more than 6 months. All study participants weighed less than 300 pounds. The investigators matched 30 low-functioning people to 48 high-functioning people by age, gender, and time since HIV diagnosis. All study participants had body composition measured by DEXA scan. Body composition variables recorded were (1) total hip and lumbar spine BMD, (2) total body lean mass and appendicular skeletal muscle index (ASMI), and (3) percent body fat, fat normalized to height, and trunk-to-limb fat ratio. The researchers included all of these factors in a logistic regression model, then selected the three best predictors from each group for the final model.
Age averaged 52.8 (+/- 0.5) overall and did not differ significantly between low-functioning cases and high-functioning controls (average 53.1 and 52.8). The low- and high-functioning groups did not differ much in antiretroviral duration (average 145 and 146 months), tenofovir use (odds ratio 1.43, 95% confidence interval 0.40 to 5.08), or current CD4 count (average 551 low-function and 628 high-function). Time since HIV diagnosis averaged more than 15 years in both groups. Almost half of study participants had sarcopenia (loss of muscle mass and strength). A significantly higher proportion in the low-function group currently smoked (50% versus 21%, P = 0.01). Three quarters of study participants (77%) were white, 17% Hispanic, and 21% women.
Compared with high-functioning people, the low-functioning group had significantly lower hip BMD (0.812 +/- 0.023 versus 0.91 +/- 0.0192 g/cm(2), P = 0.001) and spine BMD (0.917 +/- 0.026 versus 1.007 +/- 0.021 g/cm(2), P = 0.01). Body fat percentage was higher in low-functioning people (28.1 +/- 1.6% versus 24.7 +/- 1.4%), and this difference approached statistical significance (P = 0.07). Fat normalized to height and trunk-to-limb-fat ratio did not differ significantly between the two groups. Lean mass was significantly lower in the low-functioning group (46.8 +/- 1.7 kg versus 51.5 +/- 1.4 kg, P = 0.01), as was ASMI (6.8 +/- 0.2 versus 7.7 +/- 0.2, P = 0.002).
Statistical analysis adjusted for CD4 count below 350 and any use of didanosine, stavudine, or zidovudine determined that the high-functioning group had 10% higher odds of higher total body lean mass (odds ratio [OR] 1.1, 95% confidence interval [CI] 1.01 to 1.2, P = 0.03). The same type of analysis determined that the high-functioning group had 80% higher odds of higher (better) ASMI (OR 1.8, 95% CI 1.1 to 2.9, P = 0.01). Statistical analysis adjusted for nadir CD4 count, body mass index, tobacco use, and current tenofovir found that the higher-functioning group had about doubled odds of greater hip BMD (OR 2.4 per 0.1 g/m(2), 95% CI 1.1 to 5.6, P = 0.03) and greater lumbar spine BMD (OR 2.1 per 0.1 g/m(2), 95% CI 1.1 to 4.0, P = 0.02).
Logistic regression analysis pinpointed total hip BMD, ASMI, and percent body fat as the best predictors in the three body-composition groups. In the final logistic regression model, lower total hip BMD did not significantly predict function (OR 1.7, 95% CI 0.8 to 3.5, P = 0.16). But lower ASMI more than doubled the odds or poor function (OR 2.6, 95% CI 1.4 to 4.8, P = 0.003), while higher percent fat mass raised the odds modestly but significantly (OR 1.1, 95% CI 1.0 to 1.24, P = 0.01).
The University of Colorado team proposed that further studies "should investigate the benefit of maintained or increased muscle mass and avoidance of excess body fat on the functional independence of persons aging with HIV-1 infection."
Reference
1. Erlandson KM, Allshouse AA, Jankowski CM, et al. Lean and fat mass are stronger predictors of impaired functional status than bone. 3rd International Workshop on HIV and Aging. November 5-6, 2012, Baltimore. Abstract: O_09.
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