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Multiple studies have found Conscientiousness to be protective against dementia. The purpose of this study is to identify which specific aspects, or facets, of Conscientiousness are most protective against cognitive impairment and whether these associations are moderated by demographic factors and/or genetic risk.
Health and Retirement Study participants were selected for analysis if they completed the facets of Conscientiousness measure, scored in the range of normal cognitive functioning at the baseline personality assessment, and had at least one follow-up assessment of cognition over the up to 6-year follow-up (N = 11 181). Cox regression was used to test for risk of incident dementia and risk of incident cognitive impairment not dementia (CIND).
Over the follow-up, 278 participants developed dementia and 2186 participants developed CIND. The facet of responsibility had the strongest and most consistent association with dementia risk: every standard deviation increase in this facet was associated with a nearly 35% decreased risk of dementia; self-control and industriousness were also protective. Associations were generally similar when controlling for clinical, behavioral, and genetic risk factors. These three facets were also independent predictors of decreased risk of CIND.
The present research indicates that individuals who see themselves as responsible, able to control their behavior, and hard workers are less likely to develop CIND or dementia and that these associations persist after accounting for some common clinical, behavioral, and genetic risk factors.
Major depressive disorder (MDD) is moderately heritable, however genome-wide association studies (GWAS) for MDD, as well as for related continuous outcomes, have not shown consistent results. Attempts to elucidate the genetic basis of MDD may be hindered by heterogeneity in diagnosis. The Center for Epidemiological Studies Depression (CES-D) scale provides a widely used tool for measuring depressive symptoms clustered in four different domains which can be combined together into a total score but also can be analysed as separate symptom domains.
We performed a meta-analysis of GWAS of the CES-D symptom clusters. We recruited 12 cohorts with the 20- or 10-item CES-D scale (32 528 persons).
One single nucleotide polymorphism (SNP), rs713224, located near the brain-expressed melatonin receptor (MTNR1A) gene, was associated with the somatic complaints domain of depression symptoms, with borderline genome-wide significance (pdiscovery = 3.82 × 10−8). The SNP was analysed in an additional five cohorts comprising the replication sample (6813 persons). However, the association was not consistent among the replication sample (pdiscovery+replication = 1.10 × 10−6) with evidence of heterogeneity.
Despite the effort to harmonize the phenotypes across cohorts and participants, our study is still underpowered to detect consistent association for depression, even by means of symptom classification. On the contrary, the SNP-based heritability and co-heritability estimation results suggest that a very minor part of the variation could be captured by GWAS, explaining the reason of sparse findings.
Many studies have linked depression and obesity; few have more than two assessments of depressive symptoms and adiposity to address the potential bidirectional relationship between adiposity and depressive symptoms from young adulthood through old age. We tested whether baseline depressive symptoms are associated with changes in weight, whether baseline adiposity is associated with changes in depressive symptoms, and whether these associations vary by sex.
Participants (n=2251; 47% female) were from the Baltimore Longitudinal Study of Aging (BLSA). Using hierarchical linear modeling (HLM) on 30 years of data, the trajectory of adiposity and depressive symptoms over adulthood was estimated from >10 000 observations (mean=4.5 assessments per participant) of body mass index (BMI; kg/m2), waist circumference and hip circumference and >10 000 observations (mean=4.5 assessments per participant) of the Center for Epidemiological Studies Depression Scale (CES-D). Baseline depressive symptoms and adiposity were then tested as predictors of the trajectory of adiposity and depressive symptoms respectively. Additional analyses tested for sex-specific associations.
Sex moderated the association between depressive symptoms and weight gain such that women who experienced depressed affect had greater increases in BMI (binteraction=0.12, s.e.=0.04), waist (binteraction=0.22, s.e.=0.10) and hip circumference (binteraction=0.20, s.e.=0.07) across the adult lifespan, controlling for relevant demographic and behavioral covariates. Baseline adiposity was unrelated to the trajectory of depressive symptoms (median b=0.00) for both sexes.
Women who experience symptoms of depression tend to gain more weight across adulthood than men who experience such symptoms. Whether an individual was normal weight or overweight was unrelated to changes in depressive symptoms across adulthood.
High Neuroticism and low Conscientiousness are frequently implicated in health-risk behaviors, such as smoking and overeating, as well as health outcomes, including mortality. Their associations with physiological markers of morbidity and mortality, such as inflammation, are less well documented. The present research examines the association between the five major dimensions of personality and interleukin-6 (IL-6), a pro-inflammatory cytokine often elevated in patients with chronic morbidity and frailty.
A population-based sample (n=4923) from four towns in Sardinia, Italy, had their levels of IL-6 measured and completed a comprehensive personality questionnaire, the NEO-PI-R. Analyses controlled for factors known to have an effect on IL-6: age; sex; smoking; weight; aspirin use; disease burden.
High Neuroticism and low Conscientiousness were both associated with higher levels of IL-6. The findings remained significant after controlling for the relevant covariates. Similar results were found for C-reactive protein, a related marker of chronic inflammation. Further, smoking and weight partially mediated the association between impulsivity-related traits and higher IL-6 levels. Finally, logistic regressions revealed that participants either in the top 10% of the distribution of Neuroticism or the bottom 10% of conscientiousness had an approximately 40% greater risk of exceeding clinically relevant thresholds of IL-6.
Consistent with the literature on personality and self-reported health, individuals high on Neuroticism or low on Conscientiousness show elevated levels of this inflammatory cytokine. Identifying critical medical biomarkers associated with personality may help to elucidate the physiological mechanisms responsible for the observed connections between personality traits and physical health.
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