Telomere length and physical performance at older ages: an individual participant meta-analysis

Physical Performance and Telomere Length in Older Adults

BACKGROUND

The aging population prompts studying risk factors and markers to predict healthy aging. Telomere length is a promising candidate for assessing various age-related traits.

AIM OF THE STUDY

To investigate the association between physical performance and telomere length.

METHODS

We enrolled 323 older Mexican adults from the "Cohort of Obesity, Sarcopenia, and Frailty of Older Mexican Adults" affiliated with the Instituto Mexicano del Seguro Social and assessed their physical performance using the Short Physical Performance Battery, dividing participants into low (≤7) and high (>7) groups. Absolute telomere length was determined by qPCR, and individuals were classified into short (≤4.22 kb) and long (>4.22 kb) groups. We calculated the mean and adjusted mean, considering sex and age, among others, with 95% CI. We estimated the effect size between physical performance and telomere length using Cohen's d for unequal group sizes and calculated the odds ratio for physical performance based on telomere length.

RESULTS

Participants with low physical performance had significantly shorter telomeres (mean 4.14.44.7 kb, adjusted mean 3.54.04.5 kb, p <0.001), while those with high physical performance exhibited longer telomeres (mean 5.55.75.9 kb, adjusted mean 4.75.35.8 kb, p <0.001), with a medium-to-high telomere length effect size (d = 0.762). The odds of low physical activity increased 2.13.66.1-fold per kb of telomere attrition (adjOR 1.73.36.3, p <0.001).

CONCLUSION

Decreased physical function is associated with shorter telomere length. Absolute telomere length presents a promising biomarker for distinguishing between healthy and unhealthy aging, warranting further investigation.

Aging Processes Are Affected by Energy Balance: Focused on the Effects of Nutrition and Physical Activity on Telomere Length

PURPOSE OF REVIEW

The number and proportion of individuals aged 60 and over are increasing globally. The increase in the elderly population has important social and economic effects. Telomere length is an important marker for healthy aging. Here, we review the relevance between telomere length and energy balance by determining the effects of physical activity, nutrients, dietary patterns, and foods on healthy aging and telomere length with related studies.

RECENT FINDINGS

Evidence emphasizes the importance of telomere length and integrity for healthy aging. It also focuses on the importance of potential interventions such as physical activity and a healthy diet to improve this process. We suggest that ensuring energy balance with regular physical activity and healthy diets can contribute to the aging process by protecting telomere length. In addition, different methods in studies, short and inconsistent durations, different types of exercise, different diet patterns, and non-standard foods have led to conflicting results. More studies are needed to elucidate molecular-based mechanisms.

Telomere Length and Risk of Incident Fracture and Arthroplasty: Findings From UK Biobank

We investigated independent associations between telomere length and risk of fracture and arthroplasty in UK Biobank participants. Leukocyte telomere length (LTL) was measured in baseline samples using a validated polymerase chain reaction (PCR) method. We used, in men and women separately, Cox proportional hazards models to calculate the hazard ratio (HR) for incident fracture (any, osteoporotic) or arthroplasty (hip or knee) over 1,186,410 person-years of follow-up. Covariates included age, white cell count, ethnicity, smoking, alcohol, physical activity, and menopause (women). In further analyses we adjusted for either estimated bone mineral density (eBMD) from heel quantitative ultrasound, handgrip strength, gait speed, total fat mass (bioimpedance), or blood biomarkers, all measured at baseline (2006-2010). We studied 59,500 women and 51,895 men, mean ± standard deviation (SD) age 56.4 ± 8.0 and 57.0 ± 8.3 years, respectively. During follow-up there were 5619 fractures; 5285 hip and 4261 knee arthroplasties. In confounder-adjusted models, longer LTL was associated with reduced risk of incident knee arthroplasty in both men (HR/SD 0.93; 95% confidence interval [CI], 0.88-0.97) and women (0.92; 95% CI, 0.88-0.96), and hip arthroplasty in men (0.91; 95% CI, 0.87-0.95), but not women (0.98; 95% CI, 0.94-1.01). Longer LTL was weakly associated with reduced risk of any incident fracture in women (HR/SD 0.96; 95% CI, 0.93-1.00) with less evidence in men (0.98; 95% CI, 0.93-1.02). Associations with incident outcomes were not materially altered by adjustment for heel eBMD, grip strength, gait speed, fat mass, or blood biomarker measures. In this, the largest study to date, longer LTL was associated with lower risk of incident knee or hip arthroplasty, but only weakly associated with lower risk of fracture. The relative risks were low at a population level, but our findings suggest that common factors acting on the myeloid and musculoskeletal systems might influence later life musculoskeletal outcomes. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Development and Psychometric Evaluation of Family Caregivers' Hardiness Scale: A Sequential-Exploratory Mixed-Method Study

Objective

Caring for patients with Alzheimer's disease (AD) is a stressful situation and an overwhelming task for family caregivers. Therefore, these caregivers need to have their hardiness empowered to provide proper and appropriate care to these older adults. From the introduction of the concept of hardiness, few studies have been conducted to assess the hardiness of caregivers of patients with AD. Presumably, one reason for this knowledge gap is the lack of a proper scale to evaluate hardiness in this group. This study was conducted to develop a reliable and valid Family Caregivers' Hardiness Scale (FCHS) to measure this concept accurately among Iranian family caregivers sample.

Methods

This study is a cross-sectional study with a sequential-exploratory mixed-method approach. The concept of family caregivers' hardiness was clarified using deductive content analysis, and item pools were generated. In the psychometric step, the samples were 435 family caregivers with a mean age of 50.26 (SD ± 13.24), and the data were gathered via an online form questionnaire. In this step, the items of the FCHS were evaluated using face and content validity. Then, the factor structure was determined and confirmed using exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) followed by convergent and divergent validity, respectively. Finally, scale reliability, including stability, and internal consistency were evaluated.

Results

The finding revealed that FCHS consists of five factors, namely, "Religious Coping" (5 items), "Self-Management" (6 items), "Empathic Communication" (3 items), "Family Affective Commitment" (3 items), and "Purposeful Interaction" (4 items) that explained 58.72% of the total variance. The results of CFA showed a good model fit. Reliability showed acceptable internal consistency and stability.

Conclusion

Based on the results of the psychometric evaluation of the FCHS, turned out that the concept of hardiness in Iranian family caregivers is a multidimensional concept that is most focused on individual-cultural values, emotional family relationships, and social relationships. The designed scale also has acceptable validity and reliability features that can be used in future studies to measure this concept in family caregivers.

AI-Based Prediction and Prevention of Psychological and Behavioral Changes in Ex-COVID-19 Patients

The COVID-19 pandemic has adverse consequences on human psychology and behavior long after initial recovery from the virus. These COVID-19 health sequelae, if undetected and left untreated, may lead to more enduring mental health problems, and put vulnerable individuals at risk of developing more serious psychopathologies. Therefore, an early distinction of such vulnerable individuals from those who are more resilient is important to undertake timely preventive interventions. The main aim of this article is to present a comprehensive multimodal conceptual approach for addressing these potential psychological and behavioral mental health changes using state-of-the-art tools and means of artificial intelligence (AI). Mental health COVID-19 recovery programs at post-COVID clinics based on AI prediction and prevention strategies may significantly improve the global mental health of ex-COVID-19 patients. Most COVID-19 recovery programs currently involve specialists such as pulmonologists, cardiologists, and neurologists, but there is a lack of psychiatrist care. The focus of this article is on new tools which can enhance the current limited psychiatrist resources and capabilities in coping with the upcoming challenges related to widespread mental health disorders. Patients affected by COVID-19 are more vulnerable to psychological and behavioral changes than non-COVID populations and therefore they deserve careful clinical psychological screening in post-COVID clinics. However, despite significant advances in research, the pace of progress in prevention of psychiatric disorders in these patients is still insufficient. Current approaches for the diagnosis of psychiatric disorders largely rely on clinical rating scales, as well as self-rating questionnaires that are inadequate for comprehensive assessment of ex-COVID-19 patients' susceptibility to mental health deterioration. These limitations can presumably be overcome by applying state-of-the-art AI-based tools in diagnosis, prevention, and treatment of psychiatric disorders in acute phase of disease to prevent more chronic psychiatric consequences.

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.

Association between telomere length, frailty and death in older adults

Frailty is considered a clinical marker of functional ageing. Telomere length (TL) has been proposed as a biomarker of biological age but its role in human ageing is controversial. The main aim of the study was to evaluate the longitudinal association of TL with incident frailty and mortality in two cohorts of Spanish community-dwelling older adults. TL was determined at baseline in blood samples from older adults included in Toledo Study for Healthy Aging and ENRICA cohorts while frailty was determined by frailty phenotype (FP) at baseline and at follow-up (3.5 years). Deaths occurring during follow-up were also recorded. Associations of TL with frailty and mortality were analysed by logistic regression with progressive adjustment. Data were separately analysed in the two cohorts and in all subjects by performing a meta-analysis. TL was not different between frail and non-frail subjects. Longer telomeres were not associated with lower risk of prevalent frailty. Similarly, TL at baseline failed to predict incident frailty (OR: 1.04 [0.88-1.23]) or even the development of a new FP criterion (OR: 0.97 [0.90-1.05]) at follow-up. Lack of association was also observed when analysing the development of specific FP criteria. Finally, while frailty at baseline was significantly associated with higher risk of death at follow-up (OR: 4.08 [1.97-8.43], p < 0.001), TL did not significantly change the mortality risk (OR: 1.05 [0.94-1.16]). Results show that TL does not predict incident frailty or mortality in older adults. This suggests that TL is not a reliable biomarker of functional age.

The association of telomere length and telomerase activity with adverse outcomes in older patients with non-ST-elevation acute coronary syndrome

Background

Non-ST elevation acute coronary syndrome (NSTEACS) occurs more frequently in older patients with an increased occurrence of recurrent cardiac events following the index presentation. Telomeres are structures consisting of repeated DNA sequences as associated shelterin proteins at the ends of chromosomes. We aim to determine whether telomere length (TL) and telomerase activity (TA) predicted poor outcomes in older patients presenting with NSTEACS undergoing invasive care.

Method

Older patients undergoing invasive management for NSTEACS were recruited to the ICON-1 biomarker study (NCT01933581). Peripheral blood mononuclear cells (PBMC) were recovered on 153 patients. DNA was isolated and mean TL was measured by quantitative PCR expressed as relative T (telomere repeat copy number) to S (single copy gene number) ratio (T/S ratio), and a telomere repeat amplification assay was used to assess TA during index presentation with NSTEACS. Primary clinical outcomes consisted of death, myocardial infarction (MI), unplanned revascularisation, stroke and significant bleeding recorded at 1 year. TL and TA were divided into tertile groups for analysis. Cox proportional hazards regression was performed. Ordinal regression was performed to evaluate the relationship between TL and TA and traditional cardiovascular risk factors at baseline.

Results

298 patients were recruited in the ICON-1 study of which 153 had PBMC recovered. The mean age was 81.0 ± 4.0 years (64% male). Mean telomere length T/S ratio was 0.47 ± 0.25 and mean TA was 1.52 ± 0.61 units. The primary composite outcome occurred in 44 (28.8%) patients. There was no association between short TL or low TA and incidence of the primary composite outcome (Hazard Ratio [HR] 1.50, 95% Confidence Interval [CI] 0.68–3.34, p = 0.32 and HR 1.33, 95% CI 0.52–3.36, p = 0.51 respectively).

Conclusion

TL and TA are not found to be associated with the incidence of adverse outcomes in older patients presenting with NSTEACS undergoing invasive care.

Clinical trial registration

URL: https://www.clinicaltrials.gov Unique identifier: NCT01933581

Controlling for baseline telomere length biases estimates of the rate of telomere attrition

Longitudinal studies have sought to establish whether environmental exposures such as smoking accelerate the attrition of individuals' telomeres over time. These studies typically control for baseline telomere length (TL) by including it as a covariate in statistical models. However, baseline TL also differs between smokers and non-smokers, and telomere attrition is spuriously linked to baseline TL via measurement error and regression to the mean. Using simulated datasets, we show that controlling for baseline TL overestimates the true effect of smoking on telomere attrition. This bias increases with increasing telomere measurement error and increasing difference in baseline TL between smokers and non-smokers. Using a meta-analysis of longitudinal datasets, we show that as predicted, the estimated difference in telomere attrition between smokers and non-smokers is greater when statistical models control for baseline TL than when they do not, and the size of the discrepancy is positively correlated with measurement error. The bias we describe is not specific to smoking and also applies to other exposures. We conclude that to avoid invalid inference, models of telomere attrition should not control for baseline TL by including it as a covariate. Many claims of accelerated telomere attrition in individuals exposed to adversity need to be re-assessed.

Telomeres, Telomerase and Ageing

Telomeres are specialised structures at the end of linear chromosomes. They consist of tandem repeats of the hexanucleotide sequence TTAGGG, as well as a protein complex called shelterin. Together, they form a protective loop structure against chromosome fusion and degradation. Shortening or damage to telomeres and opening of the loop induce an uncapped state that triggers a DNA damage response resulting in senescence or apoptosis.Average telomere length, usually measured in human blood lymphocytes, was thought to be a biomarker for ageing, survival and mortality. However, it becomes obvious that regulation of telomere length is very complex and involves multiple processes. For example, the "end replication problem" during DNA replication as well as oxidative stress are responsible for the shortening of telomeres. In contrast, telomerase activity can potentially counteract telomere shortening when it is able to access and interact with telomeres. However, while highly active during development and in cancer cells, the enzyme is down-regulated in most human somatic cells with a few exceptions such as human lymphocytes. In addition, telomeres can be transcribed, and the transcription products called TERRA are involved in telomere length regulation.Thus, telomere length and their integrity are regulated at many different levels, and we only start to understand this process under conditions of increased oxidative stress, inflammation and during diseases as well as the ageing process.This chapter aims to describe our current state of knowledge on telomeres and telomerase and their regulation in order to better understand their role for the ageing process.

Smoking does not accelerate leucocyte telomere attrition: a meta-analysis of 18 longitudinal cohorts

Smoking is associated with shorter leucocyte telomere length (LTL), a biomarker of increased morbidity and reduced longevity. This association is widely interpreted as evidence that smoking causes accelerated LTL attrition in adulthood, but the evidence for this is inconsistent. We analysed the association between smoking and LTL dynamics in 18 longitudinal cohorts. The dataset included data from 12 579 adults (4678 current smokers and 7901 non-smokers) over a mean follow-up interval of 8.6 years. Meta-analysis confirmed a cross-sectional difference in LTL between smokers and non-smokers, with mean LTL 84.61 bp shorter in smokers (95% CI: 22.62 to 146.61). However, LTL attrition was only 0.51 bp yr-1 faster in smokers than in non-smokers (95% CI: -2.09 to 1.08), a difference that equates to only 1.32% of the estimated age-related loss of 38.33 bp yr-1. Assuming a linear effect of smoking, 167 years of smoking would be required to generate the observed cross-sectional difference in LTL. Therefore, the difference in LTL between smokers and non-smokers is extremely unlikely to be explained by a linear, causal effect of smoking. Selective adoption, whereby individuals with short telomeres are more likely to start smoking, needs to be considered as a more plausible explanation for the observed pattern of telomere dynamics.

Consequences of measurement error in qPCR telomere data: A simulation study

The qPCR method provides an inexpensive, rapid method for estimating relative telomere length across a set of biological samples. Like all laboratory methods, it involves some degree of measurement error. The estimation of relative telomere length is done subjecting the actual measurements made (the Cq values for telomere and a control gene) to non-linear transformations and combining them into a ratio (the TS ratio). Here, we use computer simulations, supported by mathematical analysis, to explore how errors in measurement affect qPCR estimates of relative telomere length, both in cross-sectional and longitudinal data. We show that errors introduced at the level of Cq values are magnified when the TS ratio is calculated. If the errors at the Cq level are normally distributed and independent of true telomere length, those in the TS ratio are positively skewed and proportional to true telomere length. The repeatability of the TS ratio declines sharply with increasing error in measurement of the Cq values for telomere and/or control gene. In simulated longitudinal data, measurement error alone can produce a pattern of low correlation between successive measures of relative telomere length, coupled with a strong negative dependency of the rate of change on initial relative telomere length. Our results illustrate the importance of reducing measurement error: a small increase in error in Cq values can have large consequences for the power and interpretability of qPCR estimates of relative telomere length. The findings also illustrate the importance of characterising the measurement error in each dataset-coefficients of variation are generally unhelpful, and researchers should report standard deviations of Cq values and/or repeatabilities of TS ratios-and allowing for the known effects of measurement error when interpreting patterns of TS ratio change over time.

Brain age and other bodily 'ages': implications for neuropsychiatry

As our brains age, we tend to experience cognitive decline and are at greater risk of neurodegenerative disease and dementia. Symptoms of chronic neuropsychiatric diseases are also exacerbated during ageing. However, the ageing process does not affect people uniformly; nor, in fact, does the ageing process appear to be uniform even within an individual. Here, we outline recent neuroimaging research into brain ageing and the use of other bodily ageing biomarkers, including telomere length, the epigenetic clock, and grip strength. Some of these techniques, using statistical approaches, have the ability to predict chronological age in healthy people. Moreover, they are now being applied to neurological and psychiatric disease groups to provide insights into how these diseases interact with the ageing process and to deliver individualised predictions about future brain and body health. We discuss the importance of integrating different types of biological measurements, from both the brain and the rest of the body, to build more comprehensive models of the biological ageing process. Finally, we propose seven steps for the field of brain-ageing research to take in coming years. This will help us reach the long-term goal of developing clinically applicable statistical models of biological processes to measure, track and predict brain and body health in ageing and disease.

Adiposity, Telomere Length, and Telomere Attrition in Midlife: the 1946 British Birth Cohort

Background

Obesity has been linked with shorter telomere length, both of which have been implicated in ageing, but the impact of early life adiposity on telomere length is unclear.

Methods

We included 2,479 participants from the MRC National Survey of Health and Development with measurements of body mass index, waist and hip circumference, and leukocyte telomere length (LTL) at age 53, of whom 1,000 had second measurements at ages 60-64. Relative LTL was measured with rt-PCR. Linear regression was performed to investigate associations between adiposity and LTL. Body mass index from childhood through adulthood was used to assess adiposity across the life course.

Results

We found no cross-sectional associations between adiposity measures and LTL at ages 53 or 60-64. Longitudinally, each unit gain in waist circumference weakly corresponded with a 0.06% (95% CI: -1.31 to 0.10) LTL decrease annually, with association approaching statistical significance (p = 0.09). Being overweight at ages 6 and 15 corresponded to a nonsignificant shorter LTL at age 53 and they were associated with 2.06% (95% CI: 0.05-4.08%) and 4.26% (1.98-6.54%) less LTL attrition in midlife, respectively, compared to those who were not overweight.

Conclusion

There is a weak indication that greater telomere loss was seen with greater concurrent body mass index gain. Adolescent overweight corresponded to shorter telomeres in midlife, albeit weakly, and with less subsequent attrition. Our findings point toward potential pathways which may link adiposity and ageing outcomes.

The epigenetic clock and telomere length are independently associated with chronological age and mortality

BACKGROUND

Telomere length and DNA methylation have been proposed as biological clock measures that track chronological age. Whether they change in tandem, or contribute independently to the prediction of chronological age, is not known.

METHODS

We address these points using data from two Scottish cohorts: the Lothian Birth Cohorts of 1921 (LBC1921) and 1936 (LBC1936). Telomere length and epigenetic clock estimates from DNA methylation were measured in 920 LBC1936 participants (ages 70, 73 and 76 years) and in 414 LBC1921 participants (ages 79, 87 and 90 years).

RESULTS

The epigenetic clock changed over time at roughly the same rate as chronological age in both cohorts. Telomere length decreased at 48-67 base pairs per year on average. Weak, non-significant correlations were found between epigenetic clock estimates and telomere length. Telomere length explained 6.6% of the variance in age in LBC1921, the epigenetic clock explained 10.0%, and combined they explained 17.3% (allP< 1 × 10-7). Corresponding figures for the LBC1936 cohort were 14.3%, 11.7% and 19.5% (allP< 1 × 10-12). In a combined cohorts analysis, the respective estimates were 2.8%, 28.5% and 29.5%. Also in a combined cohorts analysis, a one standard deviation increase in baseline epigenetic age was linked to a 22% increased mortality risk (P= 2.6 × 10-4) whereas, in the same model, a one standard deviation increase in baseline telomere length was independently linked to an 11% decreased mortality risk (P= 0.06).

CONCLUSIONS

These results suggest that telomere length and epigenetic clock estimates are independent predictors of chronological age and mortality risk.

Associations between Global DNA Methylation and Telomere Length in Healthy Adolescents

Emerging evidence suggests that epigenetics regulates telomere dynamics in adults. However, the relationship between these pathways in children and youth remains unknown. Thus, we examined this association in 542 healthy adolescents aged 14 to 18 years old (44.8% African Americans; 55.2% females). Global DNA methylation level (%5-mC) was quantified using ELISA method. Leukocyte telomere length (LTL) was defined as relative telomere to single copy gene (T/S) ratio. Multiple linear regression models, adjusted for age, gender, ethnicity, Tanner stage, BMI, PA, and batch effect, revealed that %5 mC was associated with LTL (adjusted β = 0.17, p < 0.01). %5 mC accounted for 5.0% of the variation for LTL. A significant gender interaction was identified (p < 0.01). There was an association between %5 mC and LTL in females (all ps < 0.01), but not in males. Further sensitivity analyses by race revealed similar associations in African Americans and whites (all ps < 0.03). The present study, for the first time, shows that lower levels of global DNA methylation are associated with shorter telomere lengths in youth, which may decrease genome stability and augment the susceptibility to diseases. Longitudinal studies are warranted to establish the effects of global DNA methylation on LTL maintenance over time.

The role of epigenetics in renal ageing

An ability to separate natural ageing processes from processes specific to morbidities is required to understand the heterogeneity of age-related organ dysfunction. Mechanistic insight into how epigenetic factors regulate ageing throughout the life course, linked to a decline in renal function with ageing, is already proving to be of value in the analyses of clinical and epidemiological cohorts. Noncoding RNAs provide epigenetic regulatory circuits within the kidney, which reciprocally interact with DNA methylation processes, histone modification and chromatin. These interactions have been demonstrated to reflect the biological age and function of renal allografts. Epigenetic factors control gene expression and activity in response to environmental perturbations. They also have roles in highly conserved signalling pathways that modulate ageing, including the mTOR and insulin/insulin-like growth factor signalling pathways, and regulation of sirtuin activity. Nutrition, the gut microbiota, inflammation and environmental factors, including psychosocial and lifestyle stresses, provide potential mechanistic links between the epigenetic landscape of ageing and renal dysfunction. Approaches to modify the renal epigenome via nutritional intervention, targeting the methylome or targeting chromatin seem eminently feasible, although caution is merited owing to the potential for intergenerational and transgenerational effects.

Biological Age Predictors

The search for reliable indicators of biological age, rather than chronological age, has been ongoing for over three decades, and until recently, largely without success. Advances in the fields of molecular biology have increased the variety of potential candidate biomarkers that may be considered as biological age predictors. In this review, we summarize current state-of-the-art findings considering six potential types of biological age predictors: epigenetic clocks, telomere length, transcriptomic predictors, proteomic predictors, metabolomics-based predictors, and composite biomarker predictors. Promising developments consider multiple combinations of these various types of predictors, which may shed light on the aging process and provide further understanding of what contributes to healthy aging. Thus far, the most promising, new biological age predictor is the epigenetic clock; however its true value as a biomarker of aging requires longitudinal confirmation.

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Telomere length is the most well studied biological age predictor, but many new predictors are emerging.

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The epigenetic clock is currently the best biological age predictor, as it correlates well with age and predicts mortality.

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The various biological age predictors tend to reflect different aspects of the aging process.

Associations of Leukocyte Telomere Length With Aerobic and Muscular Fitness in Young Adults

Decline in both telomere length and physical fitness over the life course may contribute to increased risk of several chronic diseases. The relationship between telomere length and aerobic and muscular fitness is not well characterized. We examined whether there are cross-sectional associations of mean relative leukocyte telomere length (LTL) with objective measures of aerobic fitness, muscle strength, and muscle endurance, using data on 31-year-old participants of the Northern Finland Birth Cohort 1966 (n = 4,952–5,205, varying by exposure-outcome analysis). Aerobic fitness was assessed by means of heart rate measurement following a standardized submaximal step test; muscular fitness was assessed by means of a maximal isometric handgrip strength test and a test of lower-back trunk muscle endurance. Longer LTL was associated with higher aerobic fitness and better trunk muscle endurance in models including adjustment for age, sex, body mass index, socioeconomic position, diet, smoking, alcohol consumption, physical activity level, and C-reactive protein. In a sex-stratified analysis, LTL was not associated with handgrip strength in either men or women. LTL may relate to aspects of physical fitness in young adulthood, but replication of these findings is required, along with further studies to help assess directions and causality in these associations.

Leukocyte and Skeletal Muscle Telomere Length and Body Composition in Monozygotic Twin Pairs Discordant for Long-term Hormone Replacement Therapy

Estrogen-based hormone replacement therapy (HRT) may be associated with deceleration of cellular aging. We investigated whether long-term HRT has effects on leukocyte (LTL) or mean and minimum skeletal muscle telomere length (SMTL) in a design that controls for genotype and childhood environment. Associations between telomeres, body composition, and physical performance were also examined. Eleven monozygotic twin pairs (age 57.6 ± 1.8 years) discordant for HRT were studied. Mean duration of HRT use was 7.3 ± 3.7 years in the user sister, while their co-twins had never used HRT. LTL was measured by qPCR and SMTLs by southern blot. Body and muscle composition were estimated by bioimpedance and computed tomography, respectively. Physical performance was measured by jumping height and grip strength. HRT users and non-users did not differ in LTL or mean or minimum SMTL. Within-pair correlations were high in LTL (r = 0.69, p = .020) and in mean (r = 0.74, p = .014) and minimum SMTL (r = 0.88, p = .001). Body composition and performance were better in users than non-users. In analyses of individuals, LTL was associated with BMI (r 2 = 0.30, p = .030), percentage total body (r 2 = 0.43, p = .014), and thigh (r 2 = 0.55, p = .004) fat, while minimum SMTL was associated with fat-free mass (r 2 = 0.27, p = .020) and thigh muscle area (r 2 = 0.42, p = .016). We found no associations between HRT use and telomere length. Longer LTLs were associated with lower total and regional fat, while longer minimum SMTLs were associated with higher fat-free mass and greater thigh muscle area. This suggests that telomeres measured from different tissues may have different associations with measures of body composition.

Resistance training and redox homeostasis: Correlation with age-associated genomic changes

Regular physical activity is effective as prevention and treatment for different chronic conditions related to the ageing processes. In fact, a sedentary lifestyle has been linked to a worsening of cellular ageing biomarkers such as telomere length (TL) and/or specific epigenetic changes (e.g. DNA methylation), with increase of the propensity to aging-related diseases and premature death. Extending our previous findings, we aimed to test the hypothesis that 12 weeks of low frequency, moderate intensity, explosive-type resistance training (EMRT) may attenuate age-associated genomic changes. To this aim, TL, global DNA methylation, TRF2, Ku80, SIRT1, SIRT2 and global protein acetylation, as well as other proteins involved in apoptotic pathway (Bcl-2, Bax and Caspase-3), antioxidant response (TrxR1 and MnSOD) and oxidative damage (myeloperoxidase) were evaluated before and after EMRT in whole blood or peripheral mononuclear cells (PBMCs) of elderly subjects. Our findings confirm the potential of EMRT to induce an adaptive change in the antioxidant protein systems at systemic level and suggest a putative role of resistance training in the reduction of global DNA methylation. Moreover, we observed that EMRT counteracts the telomeres' shortening in a manner that proved to be directly correlated with the amelioration of redox homeostasis and efficacy of training regime, evaluated as improvement of both muscle's power/strength and functional parameters.

Does telomere length predict decline in physical functioning in older twin sisters during an 11-year follow-up?

Leukocyte telomere length (LTL) is known to be associated with mortality, but its association with age-related decline in physical functioning and the development of disability is less clear. This study examined the associations between LTL and physical functioning, and investigated whether LTL predicts level of physical functioning over an 11-year follow-up. Older mono- (MZ) and dizygotic (DZ) twin sisters (n = 386) participated in the study. Relative LTL was measured by qPCR at baseline. Physical functioning was measured by 6-min walking distance and level of physical activity (PA). Walking distance was measured at baseline and at 3-year follow-up. PA was assessed by questionnaire at baseline and at 3- and 11-year follow-ups. The baseline analysis was performed with path models, adjusted with age and within-pair dependence of twin pairs. The longitudinal analysis was performed with a repeated measures linear model adjusted for age and longitudinal within-pair dependence. A nonrandom missing data analysis was utilized. At baseline, in all individuals, LTL was associated with PA (est. 0.14, SE 0.06, p = 0.011), but not with walking distance. Over the follow-up, a borderline significant association was observed between LTL and walking distance (est. 0.14, SE 0.07, p = 0.060) and a significant association between LTL and PA (est. 0.19, SE 0.06, p = 0.001). The results suggest that LTL is associated with PA and may, therefore, serve as a biomarker predicting the development of disability. Longitudinal associations between LTL and PA were observed only when nonrandom data missingness was taken into account in the analysis.

A Natural Product Telomerase Activator Lengthens Telomeres in Humans: A Randomized, Double Blind, and Placebo Controlled Study

TA-65 is a dietary supplement based on an improved formulation of a small molecule telomerase activator that was discovered in a systematic screening of natural product extracts from traditional Chinese medicines. This study summarizes the findings on telomere length (TL) changes from a randomized, double blind, placebo controlled study of TA-65 over a 1 year period. The study was conducted on 117 relatively healthy cytomegalovirus-positive subjects aged 53–87 years old. Subjects taking the low dose of TA-65 (250 U) significantly increased TL over the 12 months period (530 ± 180 bp; p = 0.005), whereas subjects in the placebo group significantly lost TL (290 ± 100 bp; p = 0.01). The high dose of TA-65 (1000 U) showed a trend of improvements in TL compared with that of the placebo group; however, the improvements did not reach statistical significance. TL changes in the low-dose group were similar for both median and 20th percentile TLs. The findings suggest that TA-65 can lengthen telomeres in a statistically and possibly clinically significant manner.

Systematic review of the association between chronic social stress and telomere length: A life course perspective

Our aim was to examine whether chronic social stress is associated with telomere length throughout the life course, following our protocol published in 2014. Structured searches were conducted in MEDLINE (PubMed interface), EMBASE (OVID interface), Cochrane Central (OVID interface) and grey from their start date onwards. Reference lists of retrieved citations were hand searched for relevant studies. Eighteen studies published until May 1, 2015 investigating the association between chronic social stress (as defined by poverty, exposure to violence, or family caregiving) and telomere length in healthy or diseased adults and children were independently selected by 2 reviewers. Sixteen of those studies were cross-sectional and two had a longitudinal design. Studies differed in type of stress exposure, method to measure telomere length and cell type. As meta-analysis could not be conducted, the data were synthesized as a narrative review. Based on this comprehensive review, chronic social stress accompanies telomere shortening in both early and adult exposures, with most eligible studies showing a significant relationship. We discuss the significance of chronic stress of social origin and the potential for social interventions through public policies and we recommend methodological improvements that would allow for future meta-analysis.

Longitudinal telomere length shortening and cognitive and physical decline in later life: The Lothian Birth Cohorts 1936 and 1921

Telomere length is hypothesised to be a biological marker of both cognitive and physical ageing. Here we measure telomere length, and cognitive and physical abilities at mean ages 70, 73 and 76 years in the Lothian Birth Cohort 1936 (LBC1936), and at mean ages 79, 87, 90 and 92 years in the Lothian Birth Cohort 1921 (LBC1921). We investigate whether telomere length change predicts change in cognitive and physical abilities. In LBC1936 telomere length decreased by an average of 65 base pairs per year and in LBC1921 by 69 base pairs per year. However, change in telomere length did not predict change in cognitive or physical abilities. This study shows that, although cognitive ability, walking speed, lung function and grip strength all decline with age, they do so independently of telomere length shortening.

Leukocyte telomere length is related to appendicular lean mass: cross-sectional data from the Berlin Aging Study II (BASE-II)

BACKGROUND

Age-related progressive loss of muscle mass is an increasing problem in our aging society, affecting physical ability, risk of falls, and need for health care. Telomere length has been recognized as a marker of biological age on the population level. The relation between muscle mass in advanced age and telomere length, however, has rarely been examined.

OBJECTIVE

We evaluated the relation between appendicular lean mass (ALM) and relative leukocyte telomere length (rLTL) in 1398 participants of the Berlin Aging Study II (mean ± SD age: 68.2 ± 3.7 y; 49.6% men).

DESIGN

rLTL was determined by real-time polymerase chain reaction. Lean mass was estimated by dual X-ray absorptiometry and examined as leg lean mass (LLM), ALM, and the ratio of ALM to body mass index (ALMBMI).

RESULTS

Weak, but highly significant (P < 0.001), correlations of rLTL with ALM (r = 0.248), ALMBMI (r = 0.254), and LLM (r = 0.263) were found. In the fully adjusted model that included age, BMI, low-grade inflammation, lifestyle factors, and morbidities as potential confounders, rLTL was associated with ALM (β = 1.11, SEM = 0.46, P = 0.017), LLM (β = 1.20, SEM = 0.36, P = 0.001), and ALMBMI (β = 0.04, SEM = 0.02, P = 0.013) in men and with LLM in women (β = 0.78, SEM = 0.35, P = 0.026).

CONCLUSIONS

Our results suggest that short telomeres may be a risk factor for lower ALM, particularly for low LLM. To confirm the association between telomere attrition and loss of LLM and ALMBMI, which are highly relevant for physical ability, further research in a longitudinal context is needed. The medical portion of this trial was registered in the German Clinical Trials Registry (http://drks-neu.uniklinik-freiburg.de/drks_web/navigate.do?navigationId=start) as DRKS00009277.

Inflammation, telomere length, and grip strength: a 10-year longitudinal study

Telomere attrition has been associated with age-related diseases, although causality is unclear and controversial; low-grade systemic inflammation (inflammaging) has also been implicated in age-related pathogenesis. Unpicking the relationship between aging, telomere length (TL), and inflammaging is hence essential to the understanding of aging and management of age-related diseases. This longitudinal study explored whether telomere attrition is a cause or consequence of aging and whether inflammaging explains some of the associations between TL and one marker of aging, grip strength. We studied 253 Hertfordshire Ageing Study participants at baseline and 10-year follow-up (mean age at baseline 67.1 years). Participants completed a health questionnaire and had blood samples collected for immune-endocrine and telomere analysis at both time points. Physical aging was characterized at follow-up using grip strength. Faster telomere attrition was associated with lower grip strength at follow-up (β = 0.98, p = 0.035). This association was completely attenuated when adjusted for inflammaging burden (p = 0.86) over the same period. Similarly, greater inflammaging burden was associated with lower grip strength at follow-up (e.g., interleukin [IL]-1β: β = -2.18, p = 0.001). However, these associations were maintained when adjusted for telomere attrition (IL-1β, p = 0.006). We present evidence that inflammaging may be driving telomere attrition and in part explains the associations that have previously been reported between TL and grip strength. Thus, biomarkers of physical aging, such as inflammaging, may require greater exploration. Further work is now indicated.

Rate of telomere shortening and cardiovascular damage: a longitudinal study in the 1946 British Birth Cohort

Aim

Cross-sectional studies reported associations between short leucocyte telomere length (LTL) and measures of vascular and cardiac damage. However, the contribution of LTL dynamics to the age-related process of cardiovascular (CV) remodelling remains unknown. In this study, we explored whether the rate of LTL shortening can predict CV phenotypes over 10-year follow-up and the influence of established CV risk factors on this relationship.

Methods and results

All the participants from the MRC National Survey of Health and Development (NSHD) with measures of LTL and traditional CV risk factors at 53 and 60–64 years and common carotid intima-media thickness (cIMT), cardiac mass and left ventricular function at 60–64 years were included. LTL was measured by real-time polymerase chain reaction and available at both time points in 1033 individuals. While LTL at 53 years was not linked with any CV phenotype at 60–64 years, a negative association was found between LTL and cIMT at 60–64 years (β = −0.017, P = 0.015). However, the strongest association was found between rate of telomere shortening between 53 and 60–64 years and values of cIMT at 60–64 years (β = −0.020, P = 0.006). This association was not affected by adjustment for traditional CV risk factors. Cardiac measurements were not associated with cross-sectional or longitudinal measures of LTL.

Conclusion

These findings suggest that the rate of progression of cellular ageing in late midlife (reflected by the rate of LTL attrition) relates to vascular damage, independently from contribution of CV risk factor exposure.

A life-course approach to healthy ageing: maintaining physical capability

Research on healthy ageing lacks an agreed conceptual framework and has not adequately taken into account the growing evidence that social and biological factors from early life onwards affect later health. We conceptualise healthy ageing within a life-course framework, separating healthy biological ageing (in terms of optimal physical and cognitive functioning, delaying the onset of chronic diseases, and extending length of life for as long as possible) from changes in psychological and social wellbeing. We summarise the findings of a review of healthy ageing indicators, focusing on objective measures of physical capability, such as tests of grip strength, walking speed, chair rises and standing balance, which aim to capture physical functioning at the individual level, assessing the capacity to undertake the physical tasks of daily living. There is robust evidence that higher scores on these measures are associated with lower rates of mortality, and more limited evidence of lower risk of morbidity, and of age-related patterns of change. Drawing on a research collaboration of UK cohort studies, we summarise what is known about the influences on physical capability in terms of lifetime socioeconomic position, body size and lifestyle, and underlying physiology and genetics; the evidence to date supports a broad set of factors already identified as risk factors for chronic diseases. We identify a need for larger longitudinal studies to investigate age-related change and ethnic diversity in these objective measures, the dynamic relationships between them, and how they relate to other component measures of healthy ageing. Robust evidence across cohort studies, using standardised measures within a clear conceptual framework, will benefit policy and practice to promote healthy ageing.