Phiri, Felix Pensulo
(2020)
Quantifying selenium deficiency and potential utilisation of urine as a biomarker for large scale selenium and zinc surveys in Malawi.
PhD thesis, University of Nottingham.
Abstract
Micronutrient deficiencies (MNDs), also referred to as hidden hunger, are of global concern with over 2 billion people being at risk. Although MNDs, including iodine (I), iron (Fe) and zinc (Zn), are recognised as being of public health concern especially in sub-Saharan Africa (SSA), there is growing interest in the public health importance of selenium (Se) deficiency, an essential micronutrient important for thyroid and antioxidant functions.
Currently, there is limited evidence on the prevalence of Se deficiency at population level in SSA, and there has been little research of potential interventions to address Se deficiency. Based on evidence from small-scale, localised studies, Se deficiency was raised as a potential issue in Malawi and measurement of Se status was included in the Malawi National Micronutrient Strategy of 2013, alongside Zn. This thesis reports how evidence on the Se status of the Malawi population was developed through the inclusion of blood plasma Se measurements from the nationally representative National Micronutrient Survey, as well as new evidence on utility of urine for assessing population Se and Zn status. The plasma Se study comprised >3000 people, including preschool children (PSC, aged 6–59 months, n=1500), women of reproductive age (WRA, aged 15–49 years, n=780), school-aged children (SAC, aged 5–14 years, n=700), and men (aged 20–54 years, n=228). The plasma data revealed long-range geospatial variation in Se deficiency risks being closely linked to soil characteristics, socio-economic status, and proximity to Lake Malawi and the Shire Valley. The geospatial patterns in urine Se concentration based on casual (spot) urine samples (n=1,406) taken from the same sample of WRA (n=741) and SAC (n=665) showed that between-cluster (enumeration area, EA) variation in urine Se concentration corresponded with variation in plasma Se concentration. Geospatial correlation was stronger between urine and plasma Se concentrations – at the EA scale – when urine Se concentration data were adjusted for individual hydration status (e.g. using specific gravity) compared with uncorrected urine.
It is concluded that Se deficiency is widespread in Malawi and status is largely driven by environmental factors including soil type. Urine Se concentration appears to be a viable and useful biomarker of Se status, and may be appropriate for population-level surveillance of Se status, being less intrusive than blood plasma sampling. The utility of urine Zn concentration as a biomarker for Zn status was found to be effective. Policy and research recommendations to support the Government of Malawi’s effort in ending the neglected hidden hunger of Se and Zn have been drawn.
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