The impact of vitamin D status on hepcidin and iron status in premenopausal females living in Auckland, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Nutrition and Dietetics, Massey University, Albany, New Zealand

Abstract

Background: Iron deficiency impacts female health, potentially leading to reduced immunity, cognitive function and physical performance. Hepcidin is a hormone that regulates iron homeostasis via the iron export channel ferroportin, subsequently controlling iron absorption, export and recycling. Supplementation of vitamin D has been demonstrated to reduce hepcidin concentration via direct transcription of the hepcidin gene (HAMP gene). However, the role of vitamin D and the impact on hepcidin and iron status has yet to be fully investigated. Aim: To investigate the associations between serum 25 hydroxyvitamin D (s-25(OH)D), hepcidin and iron status in premenopausal females living in Auckland New Zealand (NZ). The secondary aim is to investigate potential determinants of vitamin D status in premenopausal females. Methods: Pre-menopausal females aged 18-45 years, living in Auckland, New Zealand (NZ) participated in this cross-sectional study. Body composition was measured using bioelectrical impedance analysis and included: height, weight and body fat %. S-25(OH)D, inflammatory (CRP and IL-6), and iron biomarkers (serum ferritin, haemoglobin, soluble transferrin receptor and hepcidin) were measured from a venous blood sample. A series of questionnaires were completed to assess demographic and lifestyle factors, including: medical history, skin colour, sun exposure and dietary iron intake. Statistical analysis was undertaken using SPSS statistics 27 for windows (IBM). Results: Of the 160 participants included in the final analysis, 60 were NZ European, 67 South Asian and 33 from ‘other’ ethnicities. South Asians had significantly higher body fat % and IL-6 concentration (38.34% and 1.66 pg·mL⁻¹ respectively) compared to NZ Europeans, (27.49% and 0.63 pg·mL⁻¹ respectively, p<0.001). South Asians had significantly lower s-25(OH)D concentrations compared to NZ Europeans (33.59 nmol·L⁻¹ vs 74.84 nmol·L⁻¹, p<0.001). In NZ Europeans, higher s-25(OH)D concentrations were seen in those with lower (≤3.5nM) hepcidin concentration p=0.0046. Conversely, in South Asians, higher s-25(OH)D concentration was seen in those with higher (>3.5nM) hepcidin concentrations, p=0.038. There was no significant association in the ‘other’ ethnicities and no associations between s-25(OH)D and iron status/serum ferritin. Key determinants of s-25(OH)D were ethnicity, age and body fat %. Conclusion: The positive relationship between s-25(OH)D and hepcidin concentration in the South Asian women was unexpected, although possibly explained by higher IL-6 concentration, body fat % and lower s-25(OH)D concentration identified in the South Asian ethnic group, requiring further research.