廃用性筋萎縮を緩和する栄養戦略

廃用性筋萎縮を緩和する栄養戦略に関するレビュー論文を紹介します。

Benjamin T Wall, Luc JC van Loon. Nutritional strategies to attenuate muscle disuse atrophy. Nutrition Reviews, Article first published online: 28 FEB 2013, DOI: 10.1111/nure.12019

廃用性筋萎縮では、1日0.5％程度の筋肉量が減少します。筋力低下は1日0.3～4.2%と幅が大きいですが、筋肉量以上に筋力のほうが低下するという報告が多いです。短期では筋蛋白分解も廃用性筋萎縮に貢献している可能性がありますが、10日以上では筋蛋白合成低下がメインです。

栄養戦略としては十分な蛋白質摂取、蛋白質・必須アミノ酸の投与が重要です。クレアチンやn-3脂肪酸が有用な可能性があります。ビタミンDは健常高齢者で血中濃度が正常な場合には筋力改善の効果はありませんが、欠乏時には有用です。

廃用性筋萎縮に対しては、無駄な安静臥床を避けることが一番の治療です。治療上どうしても安静臥床にせざるを得ない場合には、十分にエネルギー・蛋白質を投与して飢餓を合併させないことがさらなる筋萎縮予防のために重要と言えます。侵襲の異化期であればエネルギーはほどほどですが。

Abstract
Situations such as recovery from injury or illness require otherwise healthy humans to undergo periods of disuse, which lead to considerable losses of skeletal muscle mass and, subsequently, numerous negative health consequences. It has been established that prolonged disuse (>10 days) leads to a decline in basal and postprandial rates of muscle protein synthesis, without an apparent change in muscle protein breakdown. It also seems, however, that an early and transient (1–5 days) increase in basal muscle protein breakdown may also contribute to disuse atrophy. A period of disuse reduces energy requirements and appetite. Consequently, food intake generally declines, resulting in an inadequate dietary protein consumption to allow proper muscle mass maintenance. Evidence suggests that maintaining protein intake during a period of disuse attenuates disuse atrophy. Furthermore, supplementation with dietary protein and/or essential amino acids can be applied to further aid in muscle mass preservation during disuse. Such strategies are of particular relevance to the older patient at risk of developing sarcopenia. More work is required to elucidate the impact of disuse on basal and postprandial rates of muscle protein synthesis and breakdown. Such information will provide novel targets for nutritional interventions to further attenuate muscle disuse atrophy and, as such, support healthy aging.