The purpose of this study is to explore the association of neuroticism with the metabolic syndrome, separate components of the metabolic syndrome, and the number of components of metabolic syndrome an individual possesses. The purpose of this study is to examine also the extent to which any associations are accounted for by sociodemographic factors, health behaviors, and cognitive ability.
Neuroticism is a personality trait largely characterized by a tendency to experience low moods and emotional lability [1] and [2]. Neuroticism may be a marker of central nervous system (CNS) excitation, with higher levels leading to biological senescence, thus, increasing susceptibility to disease [3], [4] and [5]. As such, neuroticism is related to dysregulated hypothalamic–pituitary–adrenal (HPA) axis responses to stress and a reduced antibody response to vaccination [6] and is associated with the presence of symptoms and illnesses including headaches, ulcers, arthritis, and cardiovascular disease [7]. Similarly, individuals with diseases thought to have a psychosomatic component, such as peptic ulcer disease [8] and chronic pain [9], have been found to have high neuroticism scores. In a metaanalysis of studies of correlates of neuroticism characteristics, there was evidence of associations with various chronic diseases, particularly proneness to coronary heart disease [10]. Furthermore, in a recent large longitudinal study, higher neuroticism was associated with increased prevalence of musculoskeletal, neurological, gastrointestinal, and cardiovascular conditions 25 years later [11]. Neuroticism and related traits have also been linked to increased mortality [12], although in some studies, these associations appeared to be mediated, at least in part, by sociodemographic and health behavior variables [13] and [14].
Similarly, lower cognitive ability or intelligence (IQ) has been associated with shorter life spans [15], but research examining neuroticism, IQ, and mortality together has yielded mixed findings. A recent study found that not only did neuroticism and IQ independently predict mortality, but there was also an interaction, such that those with high neuroticism and low cognitive ability experienced the greatest risk of death [16]. It was suggested that this was due to more intelligent individuals having greater emotional or financial resources for dealing with the negative consequences of neuroticism. However, a prior study showed no link between neuroticism and mortality after adjusting for cognitive ability as a potential confounding variable [17]. As neuroticism and cognitive ability have shown a small negative correlation [18], it is important to consider the independent prediction by both variables and their possible interaction in the prediction of health outcomes.
To our knowledge, there are no published studies testing the association between neuroticism and specific syndromes strongly related to mortality, such as the metabolic syndrome. The metabolic syndrome is a cluster of symptoms that markedly increases the risk of cardiovascular and all-cause mortality [19]. It consists of obesity, high triglyceride levels, low levels of high-density lipoprotein (HDL) cholesterol, raised blood pressure, and high levels of fasting blood glucose or a diagnosis of diabetes. There are strong reasons to anticipate a link between neuroticism and the metabolic syndrome. First, neuroticism is positively associated with some of its components including obesity [20] and raised cholesterol levels [21] and [22]. Second, health behaviors, such as smoking and high levels of alcohol consumption, which are important risk factors for the metabolic syndrome [23] and [24], are related to higher neuroticism [25] and [26]. Given that low IQ may be a predictor of the metabolic syndrome, it is also the case that IQ may have an explanatory role in the neuroticism–metabolic syndrome relationship.
The present study examined the association between neuroticism and the metabolic syndrome in Vietnam war-era veterans, with and without adjustment for sociodemographic variables, health behaviors, and cognitive ability. This study also investigated the associations between neuroticism and the individual components of the metabolic syndrome and the number of components an individual possessed. It was hypothesized that higher neuroticism would be associated with increased prevalence of both the metabolic syndrome, its individual components, and the number of components an individual had. The study examined whether cognitive ability was a mediator and/or a moderator of any association between neuroticism and the metabolic syndrome.
