体型・脂肪量で調整したサルコペニアと移動制限

体型と脂肪量で調整したサルコペニアは移動制限と関連するというフラミンガム研究からの論文を紹介します。

Alyssa B. Dufour, et al: Sarcopenia Definitions Considering Body Size and Fat Mass Are Associated With Mobility Limitations: The Framingham Study. J Gerontol A Biol Sci Med Sci (2012) doi: 10.1093/gerona/gls109 First published online: April 13, 2012

今回サルコペニアはDEXAで身体組成を評価した後に、2つの方法で定義されています。
①四肢骨格筋量÷身長÷身長 (ALM/ht2)
②身長と脂肪量で調整した四肢骨格筋量 (residuals)

肥満は体脂肪率が男性30%以上、女性40%の場合としています。移動制限は、1.5マイルの歩行が困難、階段昇降が困難、重作業の家事（雪おろしや窓ふきなど）が困難のいずれかに該当する場合と定義しています。

結果ですが、男性の16％、女性の30％に移動制限を認めました。男性では①、②のサルコペニアとも移動制限と有意な関連を認めました。サルコペニア肥満ではオッズ比はより高くなりましたが、相乗効果はありませんでした。一方、女性では②のサルコペニアのみ移動制限と有意な関連を認めました。

以上より、体型と脂肪量で調整したサルコペニアは移動制限と関連し、サルコペニアの定義では体型と脂肪量を考慮すべきと結論付けています。

筋肉量の補正には身長、体重、BMIなどがあります。身長と脂肪量でどのように調整したかは下記の文献を読まないとわかりません。補正の必要性は理解できますが、どのように補正すればサルコペニアの診断に最適なのかはまだわかりませんね。

Newman AB, et al: Sarcopenia: alternative definitions and associations with lower extremity function. J Am Geriatr Soc 2003;51:1602-1609.

Abstract
Background. Sarcopenia defined by lean mass has been inconsistently associated with disability in elders. Studies suggest that definitions should consider body size and additional influences of high fat mass (FM; sarcopenic-obesity). We examined sarcopenia accounting for body size, and sarcopenic-obesity, in relation to mobility limitations among 767 elderly men and women (mean age 79 years) from the Framingham Study.

Methods. Whole-body dual-energy x-ray absorptiometry measured appendicular lean mass (ALM) and total FM in 1992–1995. Sarcopenia was defined in two ways: ALM/height squared (ALM/ht2) and ALM adjusted for height and FM (residuals). Sarcopenic-obesity categories (referent, obese, sarcopenic, and sarcopenic-obese) were defined by cross-classifying ALM/ht2 and obesity (% body fat: more than 30 for men and more than 40 for women). Mobility limitation was defined as self-reported inability to walk one-half mile, climb stairs, or perform heavy housework. Sex-specific logistic regression calculated odds ratios (OR) and 95% confidence intervals (CI) for mobility limitation, adjusting for covariates.

Results. Sixteen percent of men and 30% of women had mobility limitation. Among men, both ALM/ht2 (OR = 6.3, 95% CI = 2.5–16.1) and residuals (OR = 4.6, 95% CI = 2.0–10.5) sarcopenia were associated with increased limitation. For sarcopenic-obesity, odds of limitation was higher in sarcopenic (OR = 6.1, 95% CI = 2.2–16.9) and sarcopenic-obese categories (OR = 3.5, 95% CI = 1.0–12.7) but suggested no synergistic effect. In women, only residuals sarcopenia was associated with higher odds of limitation (OR = 1.8, 95% CI = 1.2–2.9).

Conclusions. Low lean mass is associated with mobility limitations after accounting for body size and fat, and lean and FM have independent effects on mobility in elders. These findings support previous reports that sarcopenia definitions should consider body size and fat.