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Type: Thesis
Title: Subjective wellbeing in healthy, community-dwelling, older adults: measurement operationalisations and examination of folate, vitamin B12, homocysteine and omega-3 polyunsaturated fatty acids as potential predictors.
Author: Edney, Laura Catherine
Issue Date: 2014
School/Discipline: School of Psychology
Abstract: Traditional psychological research is frequently preoccupied with disability and treatment; Positive Psychology seeks to complement this approach to help form whole model conceptualisations of mental health. This thesis sought to assess (1) the empirical measurement of one measure of positive functioning – Subjective Wellbeing, (2) whether certain nutritional components commonly associated with mental illness were also associated with positive mental health, and (3) whether we could alter the normative trajectory of positive mental health with a nutritional intervention. Nutrition offers a potentially preventative measure to ill-health and was therefore investigated as a departure from the traditional focus on treatment of disability. If nutrition can be identified as a risk factor for sub-optimal positive mental health then it offers a preventative measure that is modifiable, easy to implement at the population-level, relatively cheap, and available to all. Subjective Wellbeing (SWB) is a well-defined measure of positive mental health that has been studied extensively. It is composed of three components: Positive Affect (PA), Negative Affect (NA), and Life Satisfaction (LS). Despite this consensus on what the construct is, there is little uniformity in its measurement. Paper 1 sought to review theory and empirical evidence on the definition and measurement of SWB, compare and contrast four common methods used to measure SWB, and provide an example of how these different methods may influence study results. Results favoured one method of measuring SWB and we demonstrated that each of the four methods had the potential to differentially impact any subsequent conclusions drawn regarding SWB and its relationship to an external variable of interest. Papers 2 and 3 sought to assess the influence of aspects of nutrition on SWB, using the most appropriate method for measuring SWB as identified in Paper 1. In Paper 2 we examined the relationships between folate, vitamin B₁₂, homocysteine, and SWB. Folate and vitamin B₁₂ are two B-vitamins that have been consistently implicated in mental illness, either directly, or via their influence on homocysteine levels. Folate, vitamin B₁₂, and their interaction significantly predicted levels of PA 18 months later but had no impact on levels of NA, or LS. Cross-sectionally, homocysteine was related to PA but this relationship was completely attenuated in longitudinal analyses suggesting that homocysteine is merely a marker for folate and vitamin B₁₂ status. This is the first study to demonstrate a potential causal link between levels of folate and vitamin B₁₂ to PA in a large, non-clinical population. Paper 3 involved results from a double-blind placebo-controlled RCT to investigate whether omega-3 long-chain polyunsaturated fatty acid (n-3 LC PUFA) supplementation was able to predict any observed change in the trajectory of SWB over 18-months in older people. n-3 LC PUFAs have been implicated in several mood disorders; deficient levels have been found in psychiatric patients and several randomised controlled trials have observed an improvement in depression with n-3 LC PUFA supplement alone, or as an adjuvant treatment to existing therapies. Our results demonstrated little change in SWB across 18 months in either the treatment or placebo groups. Treatment group did not predict change in PA, NA or LS; however, initial levels of n-3 LC PUFAs (EPA+DHA) were associated with initial levels of PA, but were not associated with initial levels of NA or LS or with change in PA, NA or LS. Initial levels of n-3 PUFAs (EPA+DHA+DPA+ALA) did not predict initial levels of PA, NA, or LS; however, they were able to predict rate of change over 18 months in NA and LS. These results were consistent when gender was controlled for. Results thus provided some evidence for a cross-sectional association between n-3 LC PUFAs with PA, and suggest a potential role of n-3 PUFAs in reducing rate of increase in NA and of decline in LS in otherwise healthy, older individuals. Clarification of the theoretical and empirical differences between models of SWB used and the application of SWB to an area often dominated by investigation of disorder constitute the two main areas of original contribution provided by this thesis. Results of the three papers suggest that choice of measurement of SWB has an impact on conclusions drawn, that one model provides a superior measurement to the other three commonly reported in the literature, that folate and Vitamin B₁₂ may play a role in Positive Affect independently of homocysteine, and that n-3 PUFAs are associated with change in NA and LS over 18 months.
Advisor: Burns, Nicholas Ralph
Danthiir, Vanessa
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Psychology, 2014
Keywords: subjective wellbeing; vitamin B12; folate; omega-3; polyunsaturated fatty acids
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
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