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Arch Intern Med. 2008;168(19):2163-2164.

Telomere shortening has been considered an aging marker since it represents lifetime exposure to oxidative and inflammatory stress, and it has been shown to be negatively correlated with age, smoking, and mortality up to age 75 years.¹ A recent article in the Archives² reported that the benefits of leisure activity include an association with longer telomere length in middle-aged subjects, after adjusting for confounding factors such as body mass index, smoking, and socioeconomic status, sending a potentially powerful message that regular exercise has antiaging effects. We report a study in an elderly Chinese population 65 years and older that suggests that by age 70 years, this beneficial effect on telomere length is much attenuated.

Methods
Four thousand men and women 65 years and older living in the community participated in a health survey between 2001 and 2003. Information was collected regarding self-perceived ranking of social status in terms of income, education, and occupation; history of chronic diseases; smoking habit; and physical activity of all types using the Physical Activity Scale for the Elderly.³ Body mass index was measured. A venous blood specimen was also collected, and leukocyte DNA was extracted for determination of telomere length using quantitative polymerase chain reaction methods⁴ and calibrated against samples with telomere length determined by standard Southern blot analysis of terminal restriction fragments. Specimens were analyzed for the first 976 men and 1030 women in the cohort (mean [SD] age, 72.8 [5.0] and 72.0 [5.2] years, respectively). The association between telomere length and quartiles of physical activity level was examined using analysis of covariance adjusting for age and other potential confounding factors (body mass index, smoking, and self-perceived socioeconomic status). The statistical package used was SAS version 9.1 (SAS Institute Inc, Cary, North Carolina), and the association was also tested for linear trend using the General Linear Model.

Results
Table 1 gives the baseline characteristics of the subjects, including some comorbidities for which associations with telomere length have been observed previously. There was no significant difference in mean telomere length across quartiles of physical activity, adjusting for age and also body mass index, smoking, and self-perceived socioeconomic ranking for all subjects (Table 2). The results remained unchanged when analyzed separately for men and women.

View this table: [in this window] [in a new window] [as a PowerPoint slide]   Table 1. Characteristics of Subjectsa

View this table: [in this window] [in a new window] [as a PowerPoint slide]   Table 2. Estimated Mean (SE) of Telomere Length by Different Level of Physical Activity (Analysis of Covariance)

Comment
There are possible factors that may account for the lack of an association in this study. First, by the seventh decade of life, the role of physical activity may not play such a prominent role in telomere attrition since there may have been selection bias in including only elderly people in this study. Second, a different method of telomere measurement was used (quantitative polymerase chain reaction instead of Southern blot method). The comparison of the results from this study with the recent study on leisure activity² does not contradict the concept that the underlying mechanism for the association is psychological stress rather than the total amount of physical activity per se. It is uncertain how to measure psychological stress in the elderly retired population, and this could be a confounding factor that should be adjusted for in future studies.

AUTHOR INFORMATION
Correspondence: Dr Woo, Department of Medicine and Therapeutics, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, NT, Hong Kong (jeanwoowong{at}cuhk.edu.hk).

Author Contributions: Study concept and design: Woo and Tang. Acquisition of data: Woo. Analysis and interpretation of data: Leung. Drafting of the manuscript: Woo. Critical revision of the manuscript for important intellectual content: Tang and Leung. Statistical analysis: Leung. Administrative, technical, and material support: Tang. Study supervision: Woo.

Financial Disclosure: None reported.

REFERENCES
1. Aviv A. Telomeres and human somatic fitness. J Gerontol A Biol Sci Med Sci. 2006;61(8):871-873. FREE FULL TEXT 2. Cherkas LF, Hunkin JL, Kato BS; et al. The association between physical activity in leisure time and leukocyte telomere length. Arch Intern Med. 2008;168(2):154-158. FREE FULL TEXT 3. Washburn RA, Smith KW, Jette AM, Janney CA. The Physical Activity Scale for the Elderly (PASE): development and evaluation. J Clin Epidemiol. 1993;46(2):153-162. FULL TEXT | ISI | PUBMED 4. Gil ME, Coetzer TL. Real-time quantitative PCR of telomere length. Mol Biotechnol. 2004;27(2):169-172. FULL TEXT | ISI | PUBMED

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