虚弱高齢者の蛋白投与で身体機能改善

虚弱高齢者に対する蛋白投与は身体機能を改善するというRCTを紹介します。

Michael Tieland, et al: Protein Supplementation Improves Physical Performance in Frail Elderly People: A Randomized, Double-Blind, Placebo-Controlled Trial. Journal of the American Medical Directors Association, http://dx.doi.org/10.1016/j.jamda.2012.07.005

リサーチクエスチョンは以下の通りです。

P：虚弱高齢者に
I：朝食と昼食時に15gの蛋白質を補給すると
C：朝食と昼食時にプラセボを補給した場合と比較して
O：身体機能が改善する
D：ランダム化比較試験

筋肉量はDEXAで、身体機能はSPPBで評価しています。結果ですが、筋肉量には有意差なし、筋力は介入群で増加傾向、身体機能は介入群で有意に増加でした。これより虚弱高齢者に対する蛋白投与は、身体機能を改善させるが筋肉量は増加させないという結論です。

筋肉量と身体機能でどちらがより患者さんに切実なアウトカムかといえば当然、身体機能です。筋力や身体機能は改善したが筋肉量が改善しなかったという報告や、逆に筋肉量は増加したが筋力は改善しなかったという報告をみると、これらの関係は単純ではないと感じます。

高齢者に対して日本では蛋白質の摂取量を控えめにしがちです。しかし、虚弱高齢者やサルコペニアの場合には、むしろやや多めの蛋白質を投与したほうがよい可能性があります。

Abstract

Objectives

Protein supplementation has been proposed as an effective dietary strategy to increase skeletal muscle mass and improve physical performance in frail elderly people. Our objective was to assess the impact of 24 weeks of dietary protein supplementation on muscle mass, strength, and physical performance in frail elderly people.

Design/setting/participants

A total of 65 frail elderly subjects were included and randomly allocated to either daily protein or placebo supplementation (15 g protein at breakfast and lunch).

Measurements

Skeletal muscle mass (DXA), muscle fiber size (muscle biopsy), strength (1-RM), and physical performance (SPPB) were assessed at baseline, and after 12 and 24 weeks of dietary intervention.

Results

Skeletal muscle mass did not change in the protein- (from 45.8 ± 1.7 to 45.8 ± 1.7 kg) or placebo-supplemented group (from 46.7 ± 1.7 to 46.6 ± 1.7 kg) following 24 weeks of intervention (P > .05). In accordance, type I and II muscle fiber size did not change over time (P > .05). Muscle strength increased significantly in both groups (P < .01), with leg extension strength tending to increase to a greater extent in the protein (57 ± 5 to 68 ± 5 kg) compared with the placebo group (57 ± 5 to 63 ± 5 kg) (treatment × time interaction effect: P = .059). Physical performance improved significantly from 8.9 ± 0.6 to 10.0 ± 0.6 points in the protein group and did not change in the placebo group (from 7.8 ± 0.6 to 7.9 ± 0.6 points) (treatment × time interaction effect: P = .02).

Conclusion

Dietary protein supplementation improves physical performance, but does not increase skeletal muscle mass in frail elderly people.