サルコペニアとインシュリン抵抗性

私がいつも拝見させていただいている「内科開業医のお勉強日記」に、「骨格筋減少は肥満有無に関わらず独立したインスリン抵抗性と関連する」というブログが掲載されていましたので、紹介させていただきます。

http://intmed.exblog.jp/10781668/

もとの論文は、下記の通りです。

Srikanthan P, Hevener AL, Karlamangla AS (2010) Sarcopenia Exacerbates Obesity-Associated Insulin Resistance and Dysglycemia: Findings from the National Health and Nutrition Examination Survey III. PLoS ONE 5(5): e10805. doi:10.1371/journal.pone.0010805

下記HPで全文読むことができます。

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0010805

結論としては、サルコペニア（ここでは加齢に伴う骨格筋減少という狭義の原発性サルコペニアです）は非肥満者、肥満者ともインシュリン抵抗性と関連するという結果です。

ただ、横断研究なので、因果関係に関しては何ともいえません。骨格筋から分泌されるmyokineが少なくなるから炎症やインシュリン抵抗性が悪化するのかもしれませんが。

少なくともSarcopenic Obesityに関しては特に要注意です。糖尿病の運動療法として、有酸素運動だけではなくレジスタンストレーニングの重要性が高まりつつありますが、それとも関連してくる内容です。

Abstract
Background
Sarcopenia often co-exists with obesity, and may have additive effects on insulin resistance. Sarcopenic obese individuals could be at increased risk for type 2 diabetes. We performed a study to determine whether sarcopenia is associated with impairment in insulin sensitivity and glucose homeostasis in obese and non-obese individuals.

Methodology
We performed a cross-sectional analysis of National Health and Nutrition Examination Survey III data utilizing subjects of 20 years or older, non-pregnant (N = 14,528). Sarcopenia was identified from bioelectrical impedance measurement of muscle mass. Obesity was identified from body mass index. Outcomes were homeostasis model assessment of insulin resistance (HOMA IR), glycosylated hemoglobin level (HbA1C), and prevalence of pre-diabetes (6.0≤ HbA1C<6.5 and not on medication) and type 2 diabetes. Covariates in multiple regression were age, educational level, ethnicity and sex.

Principal Findings
Sarcopenia was associated with insulin resistance in non-obese (HOMA IR ratio 1.39, 95% confidence interval (CI) 1.26 to 1.52) and obese individuals (HOMA-IR ratio 1.16, 95% CI 1.12 to 1.18). Sarcopenia was associated with dysglycemia in obese individuals (HbA1C ratio 1.021, 95% CI 1.011 to 1.043) but not in non-obese individuals. Associations were stronger in those under 60 years of age. We acknowledge that the cross-sectional study design limits our ability to draw causal inferences.

Conclusions
Sarcopenia, independent of obesity, is associated with adverse glucose metabolism, and the association is strongest in individuals under 60 years of age, which suggests that low muscle mass may be an early predictor of diabetes susceptibility. Given the increasing prevalence of obesity, further research is urgently needed to develop interventions to prevent sarcopenic obesity and its metabolic consequences.