- Title
- Salt, sour, mood, and mind: relationships between salt and sour taste qualities, genetics, and depression, anxiety, and cognitive impairment
- Creator
- Ferraris, Celeste
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2024
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Genetic variability in taste receptors contributes to variations in taste perception, food liking, and ultimately dietary intake. Diet is a well-known modifier of increasingly prevalent mental health conditions such as depression, anxiety, and cognitive impairment. Ion channels that detect salt and sour taste have been implicated in the biology of these conditions. Changes in salt and sour taste perception, and variance in taste-related genes have also been found in depression, anxiety and cognitive impairment and are linked to dietary changes that contribute to poor health outcomes. Extra-oral expression of salt and sour taste receptors occurs in tissues that demonstrate biological or functional changes in mental health. Therefore, in addition to the potential influence on diet there may be non-gustatory functions for these taste receptors that impact on mental health and may be influenced by genetic variation. Recently, changes in taste have been studied as potential markers for identifying and managing groups at risk of poor mental health. However, there are research gaps in the current body of knowledge. Most of the studies examining changes in salt and sour taste have used solutions in laboratory settings so there is limited evidence of the relationships in real-life settings. There is some indirect evidence linking salt and sour taste genes (TRPV1 and KCNJ2 respectively) with mental health; however, the direct associations have not been examined. Furthermore, the role of diet, nutrient intakes, and markers of health common to both salt and sour taste and mental health have not been explored in these potential genetic relationships. Understanding the interactions and relationships between these factors may help to identify risk, improve outcomes for sufferers, and identify prophylactic and therapeutic diets and treatments. Therefore, this thesis aimed to further elucidate the relationships between salt and sour taste qualities, and depression and anxiety, in real-life settings. Secondly, the project aimed to determine if variations in genes associated with sour and salt taste receptors are correlated with these mental health conditions and with cognitive impairment, and to understand the role of diet, nutrient intake, and markers of health. The preliminary nature of the pre-existing evidence required the use of exploratory research methods to identify patterns and relationships, gain further insights, generate hypotheses, and identify potential avenues for future research. The study methods included surveys and secondary data analyses. An observational, cross-sectional survey gathered data on participants recalled ratings of liking and intensity of salt and sour index foods, and levels of indicative depression and anxiety through the validated Depression, Anxiety, and Stress Scale (DASS-21). As the survey was self-administered, cognitive impairment was not evaluated. In a series of secondary cross-sectional studies on data collected in the Retirement Health & Lifestyle Study (RHLS), the relationships between sour and salt taste genotypes, diet, nutrients, markers of metabolic health, and measures of depression, anxiety and cognitive impairment were characterised. Salt (TRPV1-rs8065080) and sour (KCNJ2-rs236514) taste single nucleotide polymorphisms (SNPs) were assayed in pre-existing RHLS samples and outcomes analysed by allele carriage. Salt taste key findings: In the survey study, recalled liking of salt index foods was higher in participants with DASS-21 scores indicative of severe depression and anxiety. However, in the RHLS cohort, the genetic influence of the salt taste-related genotype TRPV1-rs8065080, was only found in depression. There were no associations between the SNP and sodium-related markers of health (blood pressure, kidney function) which are also linked to depression. In addition, sodium intake and three diet quality indices did not moderate the relationship between TRPV1-rs8065080 and depression. Together this suggests the SNP is likely driving the association. The research revealed sex-differences in responses to salt liking in depression that may be attributable to sex-hormones, which could also extend to the effects of TRPV1-rs8065080 in depression. While cognitive impairment has been correlated with high sodium intake, no association was found with the salt taste-related SNP. Sour taste key findings: In the survey study, those with DASS-21 scores indicative of mild depression rated the sourness of index foods higher than those with normal scores. The KCNJ2-rs236514 SNP known to alter sour taste intensity was not associated with depression in the RHLS cohort. However, intakes of nutrients linked to depression such as total fat, monounsaturated fat, saturated fat, water, retinol, riboflavin, folate, calcium, and sodium were lower in people carrying the KCNJ2-rs236514 variant (A) allele. The KCNJ2-A allele was associated with cognitive impairment independently of overall diet quality scores. However, it is possible the SNP-related changes to intakes of the aforementioned individual nutrients are impacting on cognitive impairment. In the analyses of metabolic markers, KCNJ2-A allele carriers had lower blood GGT, AST, albumin, and fasting blood glucose, and there were no associations with body composition, blood lipids or hypertension. The body of work in this thesis has identified changes to salt liking and sour intensity in depression, and salt liking in anxiety. These findings expand on existing preliminary evidence and contribute new knowledge by using specific taste and mood measurement tools. The novel use of validated salt and sour index foods indicates these changes in taste likely occur in real-world settings whereas previous research had largely been in laboratory settings. The gene studies in this thesis are the first to find relationships between salt and sour taste genetics, and depression, anxiety, cognitive impairment, and metabolic health markers. We now know that the salt taste SNP TRPV1-rs8065080 is associated with depression and is likely driving the relationship independently of dietary and health factors. In addition, we know that the sour taste SNP KCNJ2-rs263514 is associated with cognitive impairment, intakes of certain nutrients, liver enzyme and blood glucose levels. As the relationship with cognitive impairment was independent of diet quality, the SNP’s association with lower intakes of nutrients indicates the diet-related pathway may be nutrient-specific. Both TRPV1 and KCNJ2 genes are expressed extra-orally in tissues showing biological or functional changes in depression and cognitive impairment respectively. Therefore, non-gustatory functions for these SNPs could be considered in future research. Differences in outcomes for females and males occur across the findings indicating a sex-specific approach may be useful when considering their application and design of future studies. The studies in this thesis add to the scientific knowledge on the associations between salt and sour taste, taste genetics and depression, anxiety, and cognitive impairment. With further research, there may be opportunities to translate the findings into more tailored dietary interventions and innovative preventative or therapeutic strategies (nutraceutical or pharmaceutical). At a time when the prevalence of mental health conditions is rapidly rising, this knowledge may help to improve the health and quality of life of those experiencing the associated challenges.
- Subject
- taste; salt; sour; cognition; depression; anxiety
- Identifier
- http://hdl.handle.net/1959.13/1511437
- Identifier
- uon:56497
- Rights
- Copyright 2024 Celeste Ferraris
- Language
- eng
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