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Type 2 Diabetes, Muscle Strength, and Impaired Physical Function

The tip of the iceberg?

From the Medical Research Council Epidemiology Resource Centre, University of Southampton, Southampton, U.K

Address correspondence and reprint requests to Dr. Avan Aihie Sayer, MRC Epidemiology Resource Centre, Southampton General Hospital, Southampton, SO16 6YD, U.K. E-mail: aas{at}mrc.soton.ac.uk

Abbreviations: IGT, impaired glucose tolerance

	INTRODUCTION

TOP INTRODUCTION RESEARCH DESIGN AND METHODS RESULTS CONCLUSIONS References

 
There is growing recognition that the complications associated with type 2 diabetes may translate into functional impairment in older people (1). This may reflect a link between the metabolic and mechanical functions of muscle. However, the possibility that the link between glucose tolerance and physical function extends to people without diabetes has not been previously considered. The objective of this study was to determine whether there is a relationship among glucose tolerance, muscle strength, and physical function in men and women with and without type 2 diabetes.

	RESEARCH DESIGN AND METHODS

TOP INTRODUCTION RESEARCH DESIGN AND METHODS RESULTS CONCLUSIONS References

 
A cross-sectional survey within a cohort study design was used. Information was obtained on self-reported diabetes status cross-checked with medication data, glucose, and insulin levels 2 h after an oral glucose tolerance test (for participants without a previous diagnosis of diabetes) (2), grip strength using a Jamar dynamometer (3), and physical function using the physical function component of the Medical Outcomes Study 36-item short form questionnaire. This is a measure of subjective health status widely validated in both men and women (4,5).

The population-based study sample consisted of 1,391 men and women aged between 60 and 70 years and living in the English county of Hertfordshire. Additional information was collected on medical and social history, physical activity, height, and weight. The study had ethical approval from the North and East Hertfordshire Local Research Ethics Committee, and all subjects gave written informed consent. The methods for the cohort study have been described previously (6). Descriptive statistics, ANOVA, and linear and logistic regression were used to analyze the data with the Stata 8.0 statistical package.

	RESULTS

TOP INTRODUCTION RESEARCH DESIGN AND METHODS RESULTS CONCLUSIONS References

 
Known diabetes status was associated with significantly lower grip strength, particularly in the men. Mean grip strength in diabetic men was 41.8 kg compared with 44.1 kg in men with impaired glucose tolerance (IGT) and 44.7 kg in men with normal glucose tolerance (P = 0.002). An SD increase in glucose concentration was associated with a significant reduction in grip strength after adjustment for weight (ß –0.97 kg, P < 0.001) or weight and height (ß –0.60 kg, P = 0.02), and a significant relationship remained when newly diagnosed diabetic men were excluded. There were similar trends when those with IGT were also excluded (Fig. 1). There was no consistent pattern of relationships between fasting insulin concentration and grip strength.

View larger version (51K): [in this window] [in a new window]   Figure 1— Relationship between weight-adjusted grip strength and diabetes status in men and women.

	CONCLUSIONS

TOP INTRODUCTION RESEARCH DESIGN AND METHODS RESULTS CONCLUSIONS References

 
We have demonstrated that known and newly diagnosed diabetic older men have significantly weaker muscle strength and higher odds of impaired physical function than those without diabetes. This is consistent with findings from previous studies. However, we have also shown for the first time that the relationship between raised glucose levels, weaker muscle strength, and impaired physical function includes those with IGT and also extends across the normal range of glucose concentration. The effect sizes in the women were smaller and less consistent and may reflect sex differences in body composition.

Lower levels of physical activity could explain the relationship between increased glucose level and reduced grip strength. However, the findings remained significant after adjustment for level of physical activity, suggesting that this was not the full explanation. We suggest that the observed associations may be causal. However, the study is cross-sectional, so the direction of the associations needs consideration. Weaker muscles tend to be smaller and therefore have potential for reduced glucose uptake and hyperglycemia. For example, transporter protein GLUT4 expression at the plasma membrane is related to fiber volume in human skeletal muscle fibers (7).

However, previous work suggests that glucose disposal is not directly associated with muscle mass (8), and our findings were robust to size adjustment. Furthermore, there is clinical evidence that the causal association lies in the opposite direction. For example, there is a temporal relationship between the diagnosis of diabetes and the subsequent development of muscle weakness associated with complications such as diabetic amyotrophy. This is consistent with raised glucose levels leading to reduced strength and impaired physical function, and in vitro and in vivo animal models provide evidence that hyperglycemia can affect contractile function and force generation in muscle (9).

Our findings suggest a graded association between increased glucose level, weaker muscle strength, and impaired physical function not only in older men with diabetes or IGT, but also in those without either diagnosis. The relationships in women were less clear. This work warrants replication because there are implications for considering population-based strategies to reduce glucose across the whole range in later life to improve physical function for older people.

	Acknowledgments

 
The Medical Research Council and the University of Southampton provided funding for this study.

	Footnotes

 
A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances.

Received for publication March 11, 2005. Accepted for publication June 27, 2005.

	References

TOP INTRODUCTION RESEARCH DESIGN AND METHODS RESULTS CONCLUSIONS References

 

1. De Rekeneire N, Resnick HE, Schwartz AV, Shorr RI, Kuller LH, Simonsick EM, Vellas B, Harris TB: Diabetes is associated with subclinical functional limitation in nondisabled older individuals: the Health, Aging, and Body Composition study. Diabetes Care 26:3257–3263, 2003[Abstract/Free Full Text]
   
2. World Health Organization: Definition, Diagnosis and Classification of Diabetes Mellitus and Its Complications: Report of a WHO Consultation. Part I: Diagnosis and Classification of Diabetes Mellitus. Geneva, World Health Org., 1999
   
3. Rantanen T, Era P, Heikkinen E: Maximal isometric strength and mobility among 75-year-old men and women. Age Ageing 23:132–137, 1994[Abstract/Free Full Text]
   
4. Ware JE, Kosinski M, Gandek B: SF-36 Health Survey: Manual and Interpretation Guide. Lincoln, RI, Quality Metric Incorporated, 2000
   
5. Brazier JE, Harper R, Jones NM, O’Cathain A, Thomas KJ, Usherwood T, Westlake L: Validating the SF-36 health survey questionnaire: new outcome measure for primary care. BMJ 305:160–164, 1992
   
6. Sayer AA, Syddall HE, Gilbody HJ, Dennison EM, Cooper C: Does sarcopenia originate in early life? Findings from the Hertfordshire Cohort Study. J Gerontol A Biol Sci Med Sci 59:M930–M934, 2004[Abstract/Free Full Text]
   
7. Gaster M, Vach W, Beck-Nielsen H, Schroder HD: GLUT4 expression at the plasma membrane is related to fibre volume in human skeletal muscle fibres. APMIS 110:611–619, 2002[Medline]
   
8. Kamel HK: Sarcopenia and aging. Nutr Rev 61:157–167, 2003[Medline]
   
9. Helander I, Westerblad H, Katz A: Effects of glucose on contractile function, [Ca2+]i, and glycogen in isolated mouse skeletal muscle. Am J Physiol Cell Physiol 282:C1306–C1312, 2002[Abstract/Free Full Text]
   

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This Article Extract Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sayer, A. A. Articles by Cooper, C. Search for Related Content PubMed PubMed Citation Articles by Sayer, A. A. Articles by Cooper, C. Social Bookmarking                What's this?