University of Groningen
Affect and physical health
Schenk, Maria
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Publication date: 2017
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Schenk, M. (2017). Affect and physical health: Studies on the link between affect and physiological processes. Rijksuniversiteit Groningen.
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Emotions and affect
Emotions, and the ability to identify and describe them, is a hallmark of what makes us human1. Emotions can be defined as positive, when something makes us happy, grateful
or feel amazed, for example graduating, falling in love or becoming a parent. Similarly positive emotions are evident in the small things in life, such as a beautiful sunset, having a great moment with friends or drinking a glass of good wine. Emotions can also be defined as negative: “It’s just another manic Monday” from The Bangles expresses what every-body experiences every once in a while. Daily obstacles, stress and feelings of depres-sion can influence everyday life. In addition many people experience periods in which stress levels or feelings of depression increase or become overwhelming. Furthermore, an experience can be so unpleasant, and release such intense emotions, that it becomes a trauma2.
The experience of feeling, or nonreflective emotions is called affect3. Although the
terms ‘emotion’ and ‘affect’ are often used to point out the same thing, they are not com-pletely synonymous. Whereas emotions are usually directed at an object or person and can be feigned; affect is a non-conscious, but consciously accessible, neurophysiological state3. In psychology, affect is often measured using the Positive Affect Negative Affect
Scale (PANAS)4, a scale consisting of ten descriptors for positive affect (PA) for example
‘inspired’, ‘excited’ or ‘active’, and ten terms to describe negative affect (NA) for exam-ple ‘guilty,’ ‘scared,’ or ‘nervous.’
Affect is considered to have a physiological effect5. For example, when nervous, a
physiological response like sweating can occur. The increase of heart rate, blood pressure and skin temperature are also indicators of intense affective states. The anatomical link responsible for the physiological effect upon affect, is formed by the hypothalamic-pitui-tary-adrenal (HPA-) axis, the sympathetic nerve system (SNS) and the parasympathetic nerve system (PNS). Through this link, affect induces and provokes physical signs, a fortio-ri, affect influences processes on molecular level.
Affect and health
Mental wear and tear influences physical health6. A positive association between
ne-gative affect (NA) and somatic symptoms has been found in healthy individuals7–9. In
addition, mental disorders can function as precipitating and perpetuating factors in the development or presence of somatic symptoms10–12. Negative life events, stress, and NA
are all associated with poor health outcomes, including cardiovascular disease, diabetes, depression, and mortality13,14. This association may partly be due to harmful health
be-haviors, which are associated with NA, and mediate the association between psychologi-cal distress and poor health outcomes15,16. Nonetheless, the association between NA and
disease may also be due to dysregulation of glucocorticoid and downstream systems17,18.
Chapter 1
studies that have been undertaken show that patients who report higher levels of positive affect (PA) report lower severity of somatic symptoms19. Moreover, PA is associated with
a reduced risk of cardiovascular disease and mortality20–23. The influence of PA on health
outcomes might be explained by a positive influence on health behaviors. Individuals with higher levels of PA report more beneficial health behaviors, for example less smoking, more exercise and less alcohol intake24–26. However, positive attributes, such as optimism,
self-esteem and social status, and PA are inversely associated with metabolic syndrome and cardiometabolic risk, even after adjusting for health behaviors27–29. In addition,
se-veral studies show beneficial associations between PA and biological profiles30. Increased
levels of PA have been shown to correlate negatively with blood pressure31, and directly
decrease levels of cortisol32. The effects of NA and PA appear to be opposite, whereas
NA deteriorates health, PA seems to counteract this effect, and might even have a positive influence on health.
Affect and the neuroendocrine and immune system
The interaction and bidirectional role of affect and the neuroendocrine and immune sys-tem is receiving increasing attention in biopsychological research6,17,18,33. In contrast to
prolonged psychological stress and depression, the current paradigm argues that short-term stress is useful and enables the body to respond properly in a harmful situation and promotes survival. Prolonged stress and depression are associated with malfunction of the HPA-axis and low-grade inflammation, which lead to increased risk for (psycho-) pathology34,35. However, to date, the knowledge about the bidirectional association of
affect and the neuroendocrine and immune system is mainly focused on depression, nega-tive affect and pathological processes such as sickness behavior, somatic disease in men-tal disorders, or menmen-tal disorders in somatic disease. In addition, most studies available in biopsychological research have a cross-sectional design, which only disclose associations between individuals. Unraveling the bidirectional role of affect and the physiology in healthy individuals could enable us to gain a greater understanding about the link bet-ween affect and etiology of disease.
Between-individual versus within-individual
As mentioned, most studies available in biopsychological research have a cross-sectional design. Cross-sectional, between-subjects associations found in these studies have all too often been misconceived as indicating a causal effect, but this is not necessarily true. In fact, the association within-subject can be different in size or even sign from the associa-tion between subjects36. Increasing attention has been received by studies which focus on
the individual, so called idiographic studies37. Instead of focusing on for example whether
people who have more negative affect do report more somatic symptoms, idiographic studies explore whether within a person more negative affect leads to more or less soma-tic symptoms. By using time series analyses in data collected in a longitudinal idiographic observational study, one can learn about possible causalities, and biopsychological
pro-cesses within individuals.
In the field of biopsychology, there are already some longitudinal studies performed in relation to the association between affect and biomarkers. However, interpretation of the results of these studies is limited for several reasons: 1) studies are mostly perfor-med in a laboratorial setting thus lacking ecological validity38, 2) they cover only a short
period of time in which the effect of one intense stressor is studied39,40, or 3) have long
time windows between assessments, hampering the study of causality of such dynamic processes. Therefore, an intensive day-to-day study in a daily environment is necessary to increase ecological validity of research in biopsychological studies.
Limitations of current assessment methods
The relationship between psychological factors and inflammatory and metabolic biomar-kers would be studied preferably at a high frequency, over a longer period of time, in a non-clinical, natural everyday environment. To date, however, physiological measures and biomarkers are generally measured using inconvenient devices or methods. For example in an everyday environment, collecting venous blood, to measure levels of biomarkers, in a repeated measurement would be far too invasive and unpractical. This challenges the field of biobehavioral research to find new approaches, using advanced technologies in intensive day-to-day measurements to collect samples and data. Fortunately, several bio-markers are also excreted and expressed in for example urine, hair and saliva, which can be obtained in a non-invasive way, diminishing the intensity of the research protocol. In addition, the emergence of wearables and smartwatches is making sensors a ubiquitous technology to measure daily rhythms in physiological measures, such as movement and heart rate. Therefore, a closer look should be taken into the possibilities of non-invasive data-collection and the application in biopsychological research.
Outline of this thesis
The primary question is whether and in what way affective states, which are experienced in daily life, influence biomarkers related to health and physiological processes. Therefo-re, this thesis has two main aims: 1) to explore the possibilities for measuring biomarkers in specimens which can be obtained non-invasively and combining existing technologies, such as Fitbit devices, or smartwatches with self-reported data in intensive day-to-day measurement, and 2) to examine the between-subject and within-subject associations be-tween both PA and NA, and subjective and objective physiological measures, obtained from the general population and healthy individuals.
Part 1: New methods in biobehavioral research
In part one of this thesis several approaches of non-invasive sampling of objective measu-res in different biomaterials are described. It is essential to realize when measuring the
Chapter 1
patterns of expression of biomarkers in biomaterials that it reflects distinct patterns of expression. Biomarkers in saliva cover a small time window, whereas levels of biomarkers in urine reflect an accumulation of expression of biomarkers of the previous few hours. Scalp hair grows slowly, and measuring biomarkers in scalp hair shows the expression over the last few weeks to months.
The feasibility of non-invasive sampling in a daily environment is explored in
chap-ter 2, using an intensive day-to-day study design in 10 healthy individuals, which
collec-ted 24-hour urine during a 63-day study period. Furthermore the presence and inter- and intra-individual differences were explored of immunological biomarkers in urinary samples, since intra-individual variability is a requirement for time series analysis.
Scalp hair is assumed to provide a historical time line of systemic secretion of cortisol and therefore of interest in biopsychological research and clinical practice41. In chapter 3
the correlation between two well-established measures of cortisol secretion, namely uri-nary cortisol and hair cortisol, are compared to see how well they correlated.
Brain-derived neurotrophic factor (BDNF) is a confirmed marker of brain plasticity and of interest for biobehavioral research and the etiology of psychiatric disorders42. The
possibility to measure brain-derived neurotrophic factor (BDNF) in saliva is explored in
chapter 4.
Integrating data from commercially available sensors and service providers into one unified format for use in Ecological Momentary Assessments (EMA) or Experience Sam-pling Methods (ESM), and Quantified Self (QS) can provide new insights into the inter-action of mental and physiological processes in daily life. The development of a new platform for researchers is described in chapter 5, namely ‘Physiqual.’
Part 2: Association between affect and physiology
In part two of this thesis, the between-subject and within-subject associations between PA, NA and subjective and objective physiological measures are presented. Data was obtained from Lifelines43, a study across the general population, and from healthy
indivi-duals in an idiographic study design.
In chapter 6 a study is described, using data from the project ‘HowNutsAreTheDutch’ (or hoegekis.nl in Dutch). ‘HowNutsAreTheDutch’ is an ongoing study on the mental state of the Dutch and Flemish population. It is an online platform which contains a diary stu-dy, an intensive day-to-day survey in which 43 items about affect, daily activity, sleep, and physical discomfort were included44. Using diary data, the between-individual and
within-individual associations between PA, NA and somatic symptoms is studied.
The association between PA and NA and objective biomarkers is explored in a large cohort, and presented in chapter 7. Data of the Lifelines study was used. In this study over 165,000 individuals from the north of the Netherlands are included. Levels of objective biomarkers were measured in blood samples obtained from the participants aged 18 years and older. The correlation between PA, NA and a selection of biomarkers was cal-culated and adjusted for sex, age, exercise, smoking, and alcohol use.
In chapter 8, the within-individual association between PA, NA and eight inflammatory markers is assessed in data obtained from a longitudinal idiographic observational study. Ten healthy volunteers completed the entire study period of 63 consecutive days. During this period, participants were asked to fill out an electronic diary in the morning and in the evening, before going to bed. The questionnaires contained items about affect, stres-sful events, sleep (duration, quality), amount of exercise, caffeine, alcohol and nicotine use. Additionally, participants were asked to collect urine over a period of 24 hours in two portions (morning and day). Excretion of eight inflammatory markers was obtained by measuring concentrations with a multiplex assay, in urine samples.
In this thesis the association between PA and NA and the expression of biomarkers in a cross-sectional and longitudinal study design, and the general question whether and in what way affective states which are experienced in daily life influence health and physiological processes are explored.
Chapter 1
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