Protocol for a systematic review of the association between chronic stress during the life course and telomere length

BACKGROUND: The effects of stress on ill health have become evident in recent years. Under acute stress situations, a cascade of physiological events helps the body mount an appropriate adaptive response. However, under chronic stress situations, this physiological response may lead to wear and tear on the body that accelerates the decline in physiological functioning and increases the risk of chronic conditions. Recent evidence for social stress experienced during childhood suggests serious consequences many years later, even later life. Telomere length, a marker of cell aging, may provide a link between chronic social stress and age-associated physical and mental decline and risk of chronic conditions. This study examines whether chronic social stress is associated with telomere length throughout the life course. METHODS/DESIGN: We will perform a systematic review of the literature on the relationship between chronic social stress, for example, due to violence, extreme poverty, or caregiving of people with disabling conditions (exposure), and telomere length (outcome) by searching electronic databases in MEDLINE (PubMed interface), EMBASE (OVID interface), Cochrane Central (OVID interface) and gray literature from their start date onwards. We will limit the search to studies performed on human populations. Two reviewers will conduct standardized screening, eligibility assessment, data abstraction, and scientific quality assessment. All study designs investigating the association between chronic social stress and telomere length in healthy or diseased adults and children will be eligible for inclusion in the review. We will extract individual demographic and socioeconomic characteristics, research setting, method of measuring telomere length, reported outcome, and determinants of interest. Studies will also be stratified by 1) age into 3 groups: childhood (0 to 18 years), adulthood (19 to 64 years) and late life (65+); 2) cell type; 3) study design; and 4) telomere length assessment method. Where feasible, study results will be combined through meta-analyses to obtain a pooled measure of associations. Results will be reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement. DISCUSSION: This systematic review will provide knowledge on the existing evidence for chronic social stress and its association with telomere lengths throughout the life course.