Exploring the relationships between microRNA expression, body composition and metabolic risk in healthy New Zealand women : a thesis completed as part of the requirements for Master of Science in Nutrition and Dietetics at Massey University, Albany Campus, Auckland, New Zealand

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Background: Excess adipose tissue is associated with metabolic risk and developing obesity related diseases. A significant amount of people are unknowingly metabolically unhealthy, having a high body fat percentage (BF%) despite normal body mass index (BMI) classification. Evidence of microRNAs (miRNA; miR) as potential biomarkers of metabolic risk has emerged and may prove useful in identifying those at metabolic risk where BMI classification may fail them. Objectives: To explore miRNAs expression levels in body composition of healthy New Zealand (NZ) women and its association with metabolic markers, dietary and physical activity factors. Methods: Cross - sectional design investigating healthy NZ women (n = 406) of three ethnicities (Māori, Pacific, European) aged 16 to 45 years. Body mass index and BF% defined body profile groups; “NN” group - normal BMI (≥18.5 and <25kg/m2) and normal BF% (≥18%, <30%); “NH” group - normal BMI (<25 kg/m2) and high BF% (≥30%); “HH” group – high BMI (≥25 kg/m2) and high BF% (≥30%), of which 382, met the criteria. Anthropometry, metabolic biomarkers, miRNA, dietary, and physical activity factors were evaluated. Results: 105 (27.5%), 70 (18.3%), and 207 (54.2%) participants were classified as having NN, NH, and HH body profile, respectively. The adjusted (age, deprivation index and other miRNAs) odds of having higher miR-222-3p were increased in NH (OR = 1.92, 95% CI 1.13-3.26) and HH (OR = 2.58, 95% CI 1.58-4.21) versus NN group. The adjusted odds of having higher miR-29b-3p decreased in HH (OR = 0.09, 95% CI 0.02-0.37) versus NN group. Higher miR-222-3p (1.084-14.438 AU) was associated with HH body profile (p = 0.002), higher leptin levels (p = 0.04) and sucrose intake (p = 0.025) and lower protein intake (p = 0.017). Higher miR-29b-3p (0.202-1.851 AU) was associated with lower HbA1c (p = 0.016), TNF-α (p = 0.001), IL-6 (p = 0.016), IL-10 (p = 0.021) and higher sucrose intake (p = 0.049), and higher miR-17-5p (0.103-0.806 AU) was associated with higher TNF-α (p = 0.014) and lower IL-6 (p = 0.001). Conclusion: Our findings for miR-222-3p strongly support previous research, making it the most promising biomarker for obesity of the selected miRNA analysed in this study. Our study identified a selection of specific metabolic (Leptin, HbA1c) and inflammatory markers (IL6, IL-10, TNF-α) as well as dietary factors (sucrose, carbohydrate, protein) and light physical activity, to be associated with miR-222-3p, miR-29b-3p, and miR-17-5p. These findings suggest that miRNAs are involved in metabolic processes and, with further research, may be used as biomarkers of metabolic risk.
Figures B.1 & B.2 are re-used with the respective publisher's permission.