Physical activity and telomere length in early stage breast cancer survivors

Latent pathway-based Bayesian models to identify intervenable factors of racial disparities in breast cancer stage at diagnosis

PURPOSE

We built Bayesian Network (BN) models to explain roles of different patient-specific factors affecting racial differences in breast cancer stage at diagnosis, and to identify healthcare related factors that can be intervened to reduce racial health disparities.

METHODS

We studied women age 67-74 with initial diagnosis of breast cancer during 2006-2014 in the National Cancer Institute's SEER-Medicare dataset. Our models included four measured variables (tumor grade, hormone receptor status, screening utilization and biopsy delay) expressed through two latent pathways-a tumor biology path, and health-care access/utilization path. We used various Bayesian model assessment tools to evaluate these two latent pathways as well as each of the four measured variables in explaining racial disparities in stage-at-diagnosis.

RESULTS

Among 3,010 Black non-Hispanic (NH) and 30,310 White NH breast cancer patients, respectively 70.2% vs 76.9% were initially diagnosed at local stage, 25.3% vs 20.3% with regional stage, and 4.56% vs 2.80% with distant stage-at-diagnosis. Overall, BN performed approximately 4.7 times better than Classification And Regression Tree (CART) (Breiman L, Friedman JH, Stone CJ, Olshen RA. Classification and regression trees. CRC press; 1984) in predicting stage-at-diagnosis. The utilization of screening mammography is the most prominent contributor to the accuracy of the BN model. Hormone receptor (HR) status and tumor grade are useful for explaining racial disparity in stage-at diagnosis, while log-delay in biopsy impeded good prediction.

CONCLUSIONS

Mammography utilization had a significant effect on racial differences in breast cancer stage-at-diagnosis, while tumor biology factors had less impact. Biopsy delay also aided in predicting local and regional stages-at-diagnosis for Black NH women but not for white NH women.

Role of Endorphins in Breast Cancer Pathogenesis and Recovery

Understanding the relationship between stress and breast cancer development is essential to preventing and alleviating the cancer. Recent research has shed light on the cognitive, physiological, cellular, and molecular underpinnings of how the endorphin pathway and stress pathway affect breast cancer. This chapter consists of two parts. Part 1 will discuss the role of endorphins in breast cancer development. This includes a discussion of three topics: (1) the neurophysiological effect of endorphins on breast tumor growth in vivo, along with further experiments that will deepen our knowledge of how β-endorphin affects breast cancer; (2) how both the opioid receptor and somatostatin receptor classes alter intracellular signaling in breast cancer cells; and (3) genetic alleles in the opioid signaling pathway that are correlated with increased breast cancer risk. Part 2 will discuss the role of endorphins in recovery from breast cancer. This includes a discussion of three topics: (1) the relationship between breast cancer diagnosis and depression; (2) the effectiveness of cognitive behavioral therapy in reducing stress in breast cancer patients; and (3) the effect of psychotherapy and exercise on preserving telomere length in breast cancer patients.

Role of telomere length in human carcinogenesis (Review)

Cancer is considered the most important clinical, social and economic issue regarding cause‑specific disability‑adjusted life years among all human pathologies. Exogenous, endogenous and individual factors, including genetic predisposition, participate in cancer triggering. Telomeres are specific DNA structures positioned at the end of chromosomes and consist of repetitive nucleotide sequences, which, together with shelterin proteins, facilitate the maintenance of chromosome stability, while protecting them from genomic erosion. Even though the connection between telomere status and carcinogenesis has been identified, the absence of a universal or even a cancer‑specific trend renders consent even more complex. It is indicative that both short and long telomere lengths have been associated with a high risk of cancer incidence. When evaluating risk associations between cancer and telomere length, a disparity appears to emerge. Even though shorter telomeres have been adopted as a marker of poorer health status and an older biological age, longer telomeres due to increased cell growth potential are associated with the acquirement of cancer‑initiating somatic mutations. Therefore, the present review aimed to comprehensively present the multifaceted pattern of telomere length and cancer incidence association.

The effects of exercise and diet on oxidative stress and telomere length in breast cancer survivors

PURPOSE

Cancer and its treatments accelerate biological aging. This analysis tested the hypothesis that exercise and diet reduce oxidative stress and prevent telomere shortening in breast cancer survivors.

METHODS

In a 2 × 2 factorial design, 342 breast cancer survivors who were insufficiently physically active and had overweight or obesity at enrollment were randomized to one of four treatment groups for 52 weeks: control, exercise alone, diet alone, or exercise plus diet. The endpoints of this analysis were the change from baseline to week 52 in 8-iso-prostaglandin F2α (8-iso-PGF2α) and lymphocyte telomere length.

RESULTS

Baseline telomere length was shorter than age-adjusted normative values (median difference: - 1.8 kilobases; 95% CI - 2.4, - 1.1); equivalent to 21 years (95% CI 17, 25) of accelerated chronological aging. Compared to control, exercise alone did not change 8-iso-PGF2α [9.9%; 95% confidence interval (CI) - 1.0, 20.8] or telomere length (13.8%; 95% CI - 15.6, 43.3). Compared to control, diet alone was associated with reduced 8-iso-PGF2α (- 10.5%; 95% CI - 19.5, - 1.5) but did not change telomere length (12.1%; 95% CI - 17.2, 41.3). Compared to control, exercise plus diet was associated with reduced 8-iso-PGF2α (- 9.8%; 95% CI - 18.7, - 0.9) but did not change telomere length (- 8.5%; 95% CI - 32.1, 15.2). Change in 8-iso-PGF2α did not correlate with change in telomere length (r = 0.07; 95% CI - 0.07, 0.20).

CONCLUSION

In breast cancer survivors, diet alone or exercise plus diet were associated with reduced oxidative stress but did not change telomere length. This analysis may inform future trials that aim to optimize healthy aging in cancer survivors.

Physical Activity and Breast Cancer Survival-Epidemiologic Evidence and Potential Biologic Mechanisms

PURPOSE OF REVIEW

To review the biologic mechanisms that may be operative between physical activity and survival after breast cancer.

RECENT FINDINGS

Physical activity decreases risk of mortality from breast cancer by up to 40%. Several biologic mechanisms have been hypothesized to explain this association. Previous cohort studies and randomized trials have examined the primary mechanisms that appear to be operative, which involve a decrease in sex hormone levels, insulin resistance, and inflammation. The evidence is still inconsistent and several limitations in the existing literature exist. Understanding the biologic mechanisms involved in the association of physical activity and breast cancer survival will provide more precision to physical activity guidelines for cancer survival. To achieve this objective, future research should include direct measurements of physical activity, sedentary behaviour, and health-related fitness to provide a more comprehensive assessment of these factors and their association with biomarkers and survival after breast cancer.

Association between Physical Activity and Telomere Length in Women with Breast Cancer: A Systematic Review

The association between physical activity and telomere length (TL) has been continuously reported. However, the interplay of physical activity and TL among women with breast cancer has not been elucidated. Thus, the purpose of this systematic review was to synthesize the evidence for the association of physical activity with TL in women with breast cancer. Systematic searches were conducted to identify quantified studies using MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Web of Science, and Clinical Trials.gov. Five studies were included in this systematic review. Three of the five studies reported that physical activity has a significant relationship in delaying TL shortening, but others observed no association between physical activity and TL in breast cancer survivors. Although the heterogeneous studies acted as limitations in drawing clear conclusions, physical activity strategies show encouraging impacts in delaying TL shortening. To understand the effects of physical activity on TL shortening in breast cancer survivors, further studies are needed considering the tissue site, treatments for breast cancer, DNA extraction methods, and tools for measuring physical activity.

Multicomponent Physical Exercise Training in Multimorbid and Palliative Oldest Adults

Exercise counteracts aging and pathology symptoms, but there is still scarce research on exercise programs for multimorbid and/or palliative old patients (MPO-Ps). In order to analyze whether the multicomponent physical-cognitive training is beneficial for this population, 17 MPO-Ps (81.59 ± 5.63 years) completed a >26 weeks home-based intervention (20-50 min/session, three sessions/week). Twenty-eight supervised and thirty-two autonomous sessions were gradually distributed along three phases: supervised training (ST), reduced supervision training (RST), and autonomous training (AT). Physical function (gait speed, hand grip and lower-limb strength, balance, and agility), mental status (MMSE), and autonomy in daily living (the Barthel Index) were assessed. Categorical analyses regarding the changes in the walking aids used in the test were added to improve the assessment of strength and agility along the intervention. Despite important study limitations, such as the small sample size and lack of a control group, and despite the MPO-Ps' very low baseline fitness and initial exercise intolerance, they benefited from the dual-tasking approach, especially in autonomy, lower-limb strength, and balance. Agility improvements were shown only by categorical analyses. As expected, most benefits increased the supervision (ST phase). Gait speed and cognitive status maintained despite the total autonomy in training in the last phase. Further research with larger samples should confirm if multicomponent physical-cognitive exercise, individualized and tailored on daily-basis, together with technical assistance and medical supervision, benefits this MPO-Ps population, and if it can be prescribed to them with security, in spite some of them already being palliative patients.

Regular, Intense Exercise Training as a Healthy Aging Lifestyle Strategy: Preventing DNA Damage, Telomere Shortening and Adverse DNA Methylation Changes Over a Lifetime

Exercise training is one of the few therapeutic interventions that improves health span by delaying the onset of age-related diseases and preventing early death. The length of telomeres, the 5'-TTAGGG n -3' tandem repeats at the ends of mammalian chromosomes, is one of the main indicators of biological age. Telomeres undergo shortening with each cellular division. This subsequently leads to alterations in the expression of several genes that encode vital proteins with critical functions in many tissues throughout the body, and ultimately impacts cardiovascular, immune and muscle physiology. The sub-telomeric DNA is comprised of heavily methylated, heterochromatin. Methylation and histone acetylation are two of the most well-studied examples of the epigenetic modifications that occur on histone proteins. DNA methylation is the type of epigenetic modification that alters gene expression without modifying gene sequence. Although diet, genetic predisposition and a healthy lifestyle seem to alter DNA methylation and telomere length (TL), recent evidence suggests that training status or physical fitness are some of the major factors that control DNA structural modifications. In fact, TL is positively associated with cardiorespiratory fitness, physical activity level (sedentary, active, moderately trained, or elite) and training intensity, but is shorter in over-trained athletes. Similarly, somatic cells are vulnerable to exercise-induced epigenetic modification, including DNA methylation. Exercise-training load, however, depends on intensity and volume (duration and frequency). Training load-dependent responses in genomic profiles could underpin the discordant physiological and physical responses to exercise. In the current review, we will discuss the role of various forms of exercise training in the regulation of DNA damage, TL and DNA methylation status in humans, to provide an update on the influence exercise training has on biological aging.

Mechanical suppression of osteolytic bone metastases in advanced breast cancer patients: a randomised controlled study protocol evaluating safety, feasibility and preliminary efficacy of exercise as a targeted medicine

BACKGROUND

Skeletal metastases present a major challenge for clinicians, representing an advanced and typically incurable stage of cancer. Bone is also the most common location for metastatic breast carcinoma, with skeletal lesions identified in over 80% of patients with advanced breast cancer. Preclinical models have demonstrated the ability of mechanical stimulation to suppress tumour formation and promote skeletal preservation at bone sites with osteolytic lesions, generating modulatory interference of tumour-driven bone remodelling. Preclinical studies have also demonstrated anti-cancer effects through exercise by minimising tumour hypoxia, normalising tumour vasculature and increasing tumoural blood perfusion. This study proposes to explore the promising role of targeted exercise to suppress tumour growth while concomitantly delivering broader health benefits in patients with advanced breast cancer with osteolytic bone metastases.

METHODS

This single-blinded, two-armed, randomised and controlled pilot study aims to establish the safety, feasibility and efficacy of an individually tailored, modular multi-modal exercise programme incorporating spinal isometric training (targeted muscle contraction) in 40 women with advanced breast cancer and stable osteolytic spinal metastases. Participants will be randomly assigned to exercise or usual medical care. The intervention arm will receive a 3-month clinically supervised exercise programme, which if proven to be safe and efficacious will be offered to the control-arm patients following study completion. Primary endpoints (programme feasibility, safety, tolerance and adherence) and secondary endpoints (tumour morphology, serum tumour biomarkers, bone metabolism, inflammation, anthropometry, body composition, bone pain, physical function and patient-reported outcomes) will be measured at baseline and following the intervention.

DISCUSSION

Exercise medicine may positively alter tumour biology through numerous mechanical and non-mechanical mechanisms. This randomised controlled pilot trial will explore the preliminary effects of targeted exercise on tumour morphology and circulating metastatic tumour biomarkers using an osteolytic skeletal metastases model in patients with breast cancer. The study is principally aimed at establishing feasibility and safety. If proven to be safe and feasible, results from this study could have important implications for the delivery of this exercise programme to patients with advanced cancer and sclerotic skeletal metastases or with skeletal lesions present in haematological cancers (such as osteolytic lesions in multiple myeloma), for which future research is recommended.

TRIAL REGISTRATION

anzctr.org.au , ACTRN-12616001368426 . Registered on 4 October 2016.

Exercise medicine for advanced prostate cancer

PURPOSE OF REVIEW

Exercise is a provocative medicine, known for its preventive, complimentary and rehabilitative role in the management of cancer. Impressively, exercise is also emerging as a synergistic and targeted medicine to enhance symptom control, modulate tumour biology and delay disease progression, with the potential to increase overall survival. Given the complex clinical presentation of advanced prostate cancer patients and their omnipresent comorbidities, this review describes the current and potential role of exercise medicine in advanced prostate cancer.

RECENT FINDINGS

Exercise has been shown to be safe, feasible and effective for advanced prostate cancer patients, inclusive of patients with bone metastases; a previously excluded population due to patient and clinician fear of adverse events. Preclinical data provide insight into the ability of exercise to modulate cancer-specific outcomes, may synergistically increase the potency of chemotherapy and radiotherapy and may endogenously and/or mechanically suppress tumour formation, growth and invasion in visceral and skeletal tissue. Epidemiological studies have also shown an association between physical activity and increased survival.

SUMMARY

Exercise oncology is rapidly evolving, with impressive possibilities that may directly improve patient outcomes in advanced prostate cancer. Research must focus on translating preclinical trials into human clinical trials and investigate the direct effect of exercise on overall survival.

Leukocyte Telomere Length and Pancreatic Cancer Risk: Updated Epidemiologic Review

Many risk factors have been firmly established for pancreatic cancer (PC), but the molecular processes by which known risk factors influence susceptibility to PC are not clear. There has been a recent upsurge of interest in the role of telomere length (TL), the protective DNA sequence repeats at chromosome ends, in pancreatic carcinogenesis. Given this heightened interest, we performed an in-depth, focused, and up-to-date review of the epidemiological evidence linking leukocyte TL (LTL) with PC risk. We searched MEDLINE, Embase, and the Cochrane Library databases for all published studies on LTL and PC risk, up to May 2017. Five studies were identified for review: 4 nested case-control studies and 1 retrospective case-control study. Two studies found opposite associations between LTL and PC risk: 1 found a dose-response positive association and the other found a dose-response inverse association. Two studies also found a "U-shaped" association, whereas another reported a weak nonlinear relationship. We offer potential reasons for the conflicting findings including variation in study design, biospecimen characteristics, and differences in interlaboratory measurements of TL. Future studies should carefully control for risk factors of PC that are associated also with telomere attrition and investigate the role of genetic variation in TL maintenance.

Telomeres, Aging and Exercise: Guilty by Association?

Telomeres are repetitive tandem DNA sequences that cap chromosomal ends protecting genomic DNA from enzymatic degradation. Telomeres progressively shorten with cellular replication and are therefore assumed to correlate with biological and chronological age. An expanding body of evidence suggests (i) a predictable inverse association between telomere length, aging and age-related diseases and (ii) a positive association between physical activity and telomere length. Both hypotheses have garnered tremendous research attention and broad consensus; however, the evidence for each proposition is inconsistent and equivocal at best. Telomere length does not meet the basic criteria for an aging biomarker and at least 50% of key studies fail to find associations with physical activity. In this review, we address the evidence in support and refutation of the putative associations between telomere length, aging and physical activity. We finish with a brief review of plausible mechanisms and potential future research directions.

Can exercise suppress tumour growth in advanced prostate cancer patients with sclerotic bone metastases? A randomised, controlled study protocol examining feasibility, safety and efficacy

INTRODUCTION

Exercise may positively alter tumour biology through numerous modulatory and regulatory mechanisms in response to a variety of modes and dosages, evidenced in preclinical models to date. Specifically, localised and systemic biochemical alterations produced during and following exercise may suppress tumour formation, growth and distribution by virtue of altered epigenetics and endocrine-paracrine activity. Given the impressive ability of targeted mechanical loading to interfere with metastasis-driven tumour formation in human osteolytic tumour cells, it is of equal interest to determine whether a similar effect is observed in sclerotic tumour cells. The study aims to (1) establish the feasibility and safety of a combined modular multimodal exercise programme with spinal isometric training in advanced prostate cancer patients with sclerotic bone metastases and (2) examine whether targeted and supervised exercise can suppress sclerotic tumour growth and activity in spinal metastases in humans.

METHODS AND ANALYSIS

A single-blinded, two-armed, randomised, controlled and explorative phase I clinical trial combining spinal isometric training with a modular multimodal exercise programme in 40 men with advanced prostate cancer and stable sclerotic spinal metastases. Participants will be randomly assigned to (1) the exercise intervention or (2) usual medical care. The intervention arm will receive a 3-month, supervised and individually tailored modular multimodal exercise programme with spinal isometric training. Primary endpoints (feasibility and safety) and secondary endpoints (tumour morphology; biomarker activity; anthropometry; musculoskeletal health; adiposity; physical function; quality of life; anxiety; distress; fatigue; insomnia; physical activity levels) will be measured at baseline and following the intervention. Statistical analyses will include descriptive characteristics, t-tests, effect sizes and two-way (group × time) repeated-measures analysis of variance (or analysis of covariance) to examine differences between groups over time. The data-set will be primarily examined using an intention-to-treat approach with multiple imputations, followed by a secondary sensitivity analysis to ensure data robustness using a complete cases approach.

ETHICS AND DISSEMINATION

Ethics approval was obtained from the Human Research Ethics Committee (HREC) of Edith Cowan University and the Sir Charles Gairdner and Osborne Park Health Care Group. If proven to be feasible and safe, this study will form the basis of future phase II and III trials in human patients with advanced cancer. To reach a maximum number of clinicians, practitioners, patients and scientists, outcomes will be disseminated through national and international clinical, conference and patient presentations, as well as publication in high-impact, peer-reviewed academic journals.

TRIAL REGISTRATION NUMBER

ACTRN 12616000179437.

Telomere Length and Breast Cancer Prognosis: A Systematic Review

Telomeres ensure genome integrity during replication. Loss of telomeric function leads to cell immortalization and accumulation of genetic alterations. The association of telomere length (TL) with breast cancer prognosis is examined through a systematic review. Electronic databases (MEDLINE, EMBASE, CENTRAL), from inception to December 2015, and relevant reviews were searched. Studies that evaluated TL (blood and/or tumor) in association with breast cancer survival or prognostic factor were included. Thirty-six studies met inclusion criteria. Overall risk of bias was critical. Eight studies reported survival outcomes. Overall, there was a trend toward an association of longer telomeres with better outcomes (tumor, not blood). Of the 33 studies reporting associations with prognostic factors, nine adjusted for potential confounders. Among the latter, shorter telomeres were associated with older age (blood, not tumor), higher local recurrence rates (normal tissue), higher tumor grade (tumor), and lower physical activity (blood), which were reported in one study each. TL was not associated with molecular subtype (blood, one study), family history (tumor, one study), chemotherapy (blood, three of four studies), and stress reduction interventions (blood, two of two studies). Although major methodologic differences preclude from drawing conclusive results, TL could be a valuable breast cancer prognostic marker. Cancer Epidemiol Biomarkers Prev; 26(1); 3-10. ©2016 AACR.

Association of Telomere Length with Breast Cancer Prognostic Factors

Introduction

Telomere length, a marker of cell aging, seems to be affected by the same factors thought to be associated with breast cancer prognosis.

Objective

To examine associations of peripheral blood cell-measured telomere length with traditional and potential prognostic factors in breast cancer patients.

Methods

We conducted a cross-sectional analysis of data collected before surgery from 162 breast cancer patients recruited consecutively between 01/2011 and 05/2012, at a breast cancer reference center. Data on the main lifestyle factors (smoking, alcohol consumption, physical activity) were collected using standardized questionnaires. Anthropometric factors were measured. Tumor biological characteristics were extracted from pathology reports. Telomere length was measured using a highly reproducible quantitative PCR method in peripheral white blood cells. Spearman partial rank-order correlations and multivariate general linear models were used to evaluate relationships between telomere length and prognostic factors.

Results

Telomere length was positively associated with total physical activity (r_s = 0.17, P = 0.033; P_trend= 0.069), occupational physical activity (r_s = 0.15, P = 0.054; P_trend= 0.054) and transportation-related physical activity (r_s = 0.19, P = 0.019; P = 0.005). Among post-menopausal women, telomere length remained positively associated with total physical activity (r_s = 0.27, P = 0.016; P_trend= 0.054) and occupational physical activity (r_s = 0.26, P = 0.021; P_trend= 0.056) and was only associated with transportation-related physical activity among pre-menopausal women (r_s = 0.27, P = 0.015; P = 0.004). No association was observed between telomere length and recreational or household activities, other lifestyle factors or traditional prognostic factors.

Conclusions

Telomeres are longer in more active breast cancer patients. Since white blood cells are involved in anticancer immune responses, these findings suggest that even regular low-intensity physical activity, such as that related to transportation or occupation, could be recommended to breast cancer patients.

Movement-Based Behaviors and Leukocyte Telomere Length among US Adults

INTRODUCTION

Short leukocyte telomere length (LTL) has become a hallmark characteristic of aging. Some, but not all, evidence suggests that physical activity (PA) may play an important role in attenuating age-related diseases and may provide a protective effect for telomeres. The purpose of this study was to examine the association between PA and LTL in a national sample of US adults from the National Health and Nutrition Examination Survey.

METHODS

National Health and Nutrition Examination Survey data from 1999 to 2002 (n = 6503; 20-84 yr) were used. Four self-report questions related to movement-based behaviors (MBB) were assessed. The four MBB included whether individuals participated in moderate-intensity PA, vigorous-intensity PA, walking/cycling for transportation, and muscle-strengthening activities. An MBB index variable was created by summing the number of MBB an individual engaged in (range, 0-4).

RESULTS

A clear dose-response relation was observed between MBB and LTL; across the LTL tertiles, respectively, the mean numbers of MBB were 1.18, 1.44, and 1.54 (Ptrend < 0.001). After adjustments (including age) and compared with those engaging in 0 MBB, those engaging in 1, 2, 3, and 4 MBB, respectively, had a 3% (P = 0.84), 24% (P = 0.02), 29% (P = 0.04), and 52% (P = 0.004) reduced odds of being in the lowest (vs highest) tertile of LTL; MBB was not associated with being in the middle (vs highest) tertile of LTL.

CONCLUSIONS

Greater engagement in MBB was associated with reduced odds of being in the lowest LTL tertile.

Development and validation of the Penn Arthralgia Aging Scale among breast cancer survivors

BACKGROUND

Breast cancer survivors on aromatase inhibitors often experience joint pain as a side effect of their treatment; qualitative investigations suggest that this arthralgia may cause women to feel that they are aging faster than they should be. To facilitate further study of this experience, the Penn Arthralgia Aging Scale (PAAS) was developed. This report describes the development and validation of the PAAS in a racially diverse sample of breast cancer survivors suffering from joint pain.

METHODS

The items of the scale were developed from a content analysis of interviews with patients. The scale was pilot-tested, and modifications were made on the basis of patient feedback. Subsequently, 596 breast cancer survivors who endorsed joint pain completed the 8-item PAAS. The factor structure (with exploratory factor analysis), the internal consistency, and the convergent, divergent, and incremental validity were examined.

RESULTS

The resulting scale had a 1-factor structure with strong internal consistency (Cronbach's α = .94) and demonstrated both convergent and divergent validity: the PAAS was significantly correlated with joint pain severity (rs = 0.55, P < .01) and had a small and nonsignificant correlation with actual age (rs  = -0.07, P = .10). The PAAS was also found to explain incremental variance in anxiety, depression, and pain interference outcomes.

CONCLUSIONS

These findings suggest that the PAAS produces reliable and valid scores that capture perceptions of aging due to arthralgia among breast cancer survivors. With further research, the PAAS may advance our understanding of how perceptions of aging may affect breast cancer survivors' emotional, behavioral, and clinical outcomes.

Effects of physical activity in telomere length: Systematic review and meta-analysis

The aim of this systematic review is to assess the effects of exercise on telomeres length. We searched the following databases: MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library), Scopus, LILACS, SPORTDiscus and Web of Science from inception to August 2014. All articles that assessed the effects of exercise in telomere length were included in this review. The search strategy used the following combinations of terms: telomere AND "motor activity" OR exercise OR "physical activity". Two reviewers, working independently, screened all titles and abstracts to identify studies that could meet inclusion criteria. Whenever possible, and if appropriate, we performed a random-effect meta-analysis of study outcomes. Thirty-seven original studies were included in this systematic review, including 41,230 participants. Twenty articles did not find statistically significant association, whereas 15 described a positive association. Two papers found an inverted "U" correlation. There is a tendency toward demonstrating an effect of exercise on telomere length. Few prospective studies were found, many studies did not reach statistical significance and there was an important methodological diversity. For this reason, a possible significant association between physical activity and telomere length remains an open question.