Article summary with The relationship between childhood psychosocial stressor level and telomere length: a meta-analysis by Hanssen & Schutte - 2017

What are the objectives of this study?

Maltreatment or neglect experienced during childhood are predictors of negative (mental) health outcomes across the life course. These negative childhood experiences are linked to the development of depression, substance abuse, post-traumatic stress disorder and bipolar disorder. Besides mental illness, child abuse is also linked to several physiological disorders including metabolic disorders and gastrointestinal disorder. These negative childhood experiences, or stressors may also have epigenetic effects and influence the functioning of the immune system and biomarkers. In previous studies high levels of experience of stressors during childhood are related to physiological, cellular and immune stress responses.  

Later health developments as a result of childhood maltreatment might be associated with telomere length. Telomere length is considered an important health biomarker. They are nucleoprotein complexes that preserve genetic information, but also regulate cellular activity and prevent end-to-end fusion. Also, they can lengthen and shorten over time. These changes in telomere length are associated with cardiovascular disease and obesity. In this study the relationship between childhood psychological stressors and telomerase length is examined. Also, moderating effects are studied, because evidence for the influence of maltreatment on telomere length is done using various variables. The main aim of the study is to determine the overall effect sizes of the relationship between childhood psychological stressors and telomere length.

What method was used?

Various web libraries of scientific articles were searched reporting on psychological stressors and telomere length. They found 2,122 potentially relevant studies of which 27 samples met the inclusion criteria. A meta-analysis is done over 27 samples and 16,238 participants.

What were the results of the meta-analysis?

The researchers found a significant relationship (0.08) between an elevated level of childhood stressors and a shorter telomerase length. The mean age across studies was 42.

Moderator analysis showed the trend in the direction of effect size. Effect sizes tend to be larger when there are shorter times between the stressor and measurement of telomerase. Also, studies that used a categorical method for assessing the stressor level of a child showed higher effect sizes. Studies comparing groups, so being abused or not, showed higher associations between telomere length and childhood stressor. In comparison to studies using the level of stress as a continuous variable, these studies showed lower effect sizes. Also, studies completed with qPCR reported higher effect sizes than studies using the Southern blot method.

No significant moderation was fount between the assay of leukocytes or buccal cells. There was also no moderation of the assessment of child stressor, this could be either memory-based recall or archival records, it did not make a difference. No significant moderator effect was found when controlled for age and sex either.

What was the conclusion of the study?

A significant, but small relationship between telomere length and childhood stressors was found, regardless if stressor level was measured based on recall or objective documentation. Stressors experienced during childhood can have a long-term effect on telomere length at a mean of 42 years of age.  Therefore, perceived stress and negative emotions are associated to telomere length. The results also provide a mediational explanation for the relationship between experiencing psychosocial stressors during childhood and poor mental -or physiological outcomes across the life span. For example, early trauma affects inflammation, which is associated with telomere length.

Negative psychological states, such as depression, anxiety and perceived stress are predicted by negative childhood experiences. These negative childhood experiences -or stressors can predict shorter telomeres which is the reason for increased anxiety levels and stress. Also, telomere functioning is dynamic, so when time passes after exposure to a stressor shorter telomere could recover. Therefore, it was predicted that time would moderate effect size. However, according to findings, childhood stressors were still significantly related to shorter telomeres much later. Childhood stressors probably have more impact on the telomere length, because it happens during a critical period of the development of biological systems.

Another finding was that in the comparison of extreme groups, a significantly greater effect size was found. This effect size was bigger than the comparison between groups reporting various levels of stressors. For example, when looking at the relationship between telomerase length and anxiety level, extreme groups showed much higher effect sized. This could mean that only extreme experiences cause long-term effects on telomere length.

What are the recommendations for further research?

The results obtained from the moderator studies can be considered a suggestion. This is because the moderator analysis only used 27 samples. The analysis thus had little statistical power to identify significant differences. Also, there were no randomly assigned participants or studies -and every examined study used a different research method. Therefore, the outcome of the influence of moderators could be varied when conservative one-tail tests controlling for alpha inflation are done. Therefore, future research should focus on the influence of childhood psychosocial stressors and discuss the role of characteristics of both the stressors and caused distress. This way, important predictors of resilience and vulnerability to the effects of childhood stressors can be discovered.

Summary:

• Besides mental illness, child abuse is also linked to several physiological disorders including metabolic disorders and gastrointestinal disorder. These negative childhood experiences, or stressors may also have epigenetic effects and influence the functioning of the immune system and biomarkers. In previous studies high levels of experience of stressors during childhood are related to physiological, cellular and immune stress responses.  
• A significant, but small relationship between telomere length and childhood stressors was found, regardless if stressor level was measured based on recall or objective documentation. Stressors experienced during childhood can have a long-term effect on telomere length at a mean of 42 years of age.  

Study note:

• In this study they look at the relationship between childhood stressors and telomerase. What is the importance of finding moderating effects on this relationship and what does this mean for the association between negative childhood experiences and (mental) health issues across the life span?
• Make sure you can explain the moderating influences on effect size found by this study. What are the outcomes of the meta-analysis and what does this mean for past -and future research