[Fatigue].

Many patients with fatigue do not visit a physician. In patients who do consult the general practitioner, the cause of their fatigue is explained in about a quarter: 8 percent has a somatic cause while psychosocial causes explain 16 percent. In about three quarters the cause of fatigue remains unexplained.

Individual Heterogeneity in the Relations Between Sleep, Inflammation, and Somatic Symptoms.

Objective: Poor sleep is associated with the experience of more somatic symptoms and a proinflammatory state, whereas a proinflammatory state may also result in the experience of more somatic symptoms. However, existing studies ignore individual differences in these associations. We aimed to study relations between sleep, inflammatory markers, and somatic symptoms at a within-individual level.

[Fatigue].

Many patients with fatigue do not visit a physician. In patients who do consult the general practitioner, the cause of their fatigue is explained in about a quarter: 8 percent has a somatic cause while psychosocial causes explain 16 percent. In about three quarters the cause of fatigue remains unexplained.

Mass spectrometric quantification of urinary 6-sulfatoxymelatonin: age-dependent excretion and biological variation.

Objectives: Regulators of circadian rhythm, including melatonin, influence fundamental biological processes. Measuring the melatonin metabolite 6-sulfatoxymelatonin in urine can estimate melatonin production. 6-sulfatoxymelatonin is mainly analyzed by immunoassays, but these methods are hampered by cross-reactivity and poor reproducibility when used to analyze small molecules.

Using bundle embeddings to predict daily cortisol levels in human subjects.

Background: Many biological variables sampled from human subjects show a diurnal pattern, which poses special demands on the techniques used to analyze such data. Furthermore, most biological variables belong to nonlinear dynamical systems, which may make linear statistical techniques less suitable to analyze their dynamics. The current study investigates the usefulness of two analysis techniques based on nonlinear lagged vector embeddings: sequentially weighted global linear maps (SMAP), and bundle embeddings.

Effects of urinary cortisol levels and resting heart rate on the risk for fatal and nonfatal cardiovascular events.

Background And Aims: Higher cortisol levels are associated with cardiovascular mortality in the elderly. It is unclear whether this association also exists in a general population of younger adults and for non-fatal cardiovascular events. Likewise, resting heart rate is associated with cardiovascular mortality, but fewer studies have also considered non-fatal events.

Using State Space Methods to Reveal Dynamical Associations Between Cortisol and Depression.

Despite extensive research, the link between etiological factors and depression remains poorly understood. This may in part be due to a focus on strictly linear definitions of causality, derived at the group level. However, etiological relations in depression are likely to be dynamical, nonlinear and potentially unquantifiable with traditional statistics.

How to assess stress biomarkers for idiographic research?

Associations between stress-related biomarkers, like cortisol or catecholamines, and somatic or psychological symptoms have often been examined at the group level. Studies using this nomothetic approach reported equivocal findings, which may be due to high levels of intra-individual variance of stress biomarkers. More importantly, analyses at the group level provide information about the average patient, but do not necessarily have meaning for individual patients.

Age- and sex-specific associations between adverse life events and functional bodily symptoms in the general population.

Objective: To test age- and sex-specific associations between adverse life events and functional bodily symptoms (FBS) in the general population.

Methods: In a population-based cohort, 964 participants (mean age 55 years SD 11, 48% male) completed two measurements waves of the present study. Lifetime exposure to 12 adverse life events was assessed through a modified version of the List of Threatening Experiences.