title: Telomerase activity and its association with psychological stress, mental disorders, lifestyle factors and interventions: A systematic review.
abstract: OBJECTIVE
  To summarise and discuss the association between telomerase activity and psychological stress, mental disorders and lifestyle factors.
  
  
  METHODS
  A systematic review was carried out to identify prospective or retrospective studies and interventions published up to June 2015 that reported associations between telomerase activity and psychological stress, mental disorders and lifestyle factors. Electronic data bases of PubMed, ProQuest, CINAHL and Google Scholar were searched.
  
  
  RESULTS
  Twenty six studies on humans measured telomerase activity in peripheral blood mononuclear cells (PBMCs) or leukocytes and examined its association with psychological stress, mental disorders and lifestyle factors. Of those studies, three reported significantly decreased telomerase activity in individuals under chronic psychological stress. Interestingly, one of the three studies found that acute laboratory psychological stress significantly increased telomerase activity. Nine studies reported mixed results on association between mental disorders and telomerase activity. Of the nine studies, five reported that major depressive disorder (MDD) was associated with significantly increased telomerase activity. In thirteen out of fourteen studies on lifestyle factors, it was reported that physical exercise, diet micronutrient supplementation, mindfulness meditation, Qigong practice or yoga mediation resulted in increase in telomerase activity. In addition, two studies on animal models showed that depression-like behaviour was associated with decreased hippocampus telomerase activity. Five animal studies showed that physical exercise increased telomerase activity by cell-type-specific and genotype-specific manners.
  
  
  CONCLUSIONS
  Although multi-facet results were reported on the association between telomerase activity and psychological stress, mental disorders and lifestyle factors, there were some consistent findings in humans such as (1) decreased telomerase activity in individuals under chronic stress, (2) increased telomerase activity in individuals with MDD, and (3) increased telomerase activity in individuals under lifestyle interventions. Animal studies showed that physical exercise increased telomerase activity in specific cell-types. However, the exact mechanisms for the changes in telomerase activity have not been elucidated. We propose conglomerate models connecting chronic psychological stress, depression, mediation and physical exercise to telomerase activation. Several areas for future research are suggested.
authors.affiliation: School of Nursing, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: W
authors.initials: W
authors.lastname: Deng
authors.affiliation: School of Nursing, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: S T
authors.initials: ST
authors.lastname: Cheung
authors.affiliation: School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: S W
authors.initials: SW
authors.lastname: Tsao
authors.affiliation: School of Nursing, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: X M
authors.initials: XM
authors.lastname: Wang
authors.affiliation: School of Nursing, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China. Electronic address: afytiwar@hku.hk.
authors.forename: A F Y
authors.initials: AF
authors.lastname: Tiwari
mesh_terms: D004032:Diet; D015444:Exercise; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000201:enzymology; D008019:Life Style; D019122:Meditation; D001523:Mental Disorders / Q000201:enzymology*; D064906:Qigong; D013315:Stress, Psychological / Q000201:enzymology*; D019098:Telomerase / Q000378:metabolism*; D015013:Yoga
chemical_list: D019098:Telomerase
keywords: Intervention; Lifestyle factors; Mental disorders; Psychological stress; Systematic review; Telomerase activity