Zinc intake, zinc status and expression of zinc transporter genes in younger and older Saudi adults

Abstract

Background: During ageing, there are changes in many physiological systems including the gastrointestinal tract which may result in decreased absorption of micronutrients such as zinc. Decreased dietary absorption efficiency and/or inadequate zinc intake are contributing factors to the decline in plasma zinc concentration that has been reported in older adults. This decline in plasma zinc concentration may have important implications for health, e.g. through reduced immune function. To date, there is limited information on the relationships between zinc intake and plasma zinc concentration during ageing among adults in Saudi Arabia or on the molecular mechanisms responsible for age-related effects. Thus, the aims of this study were to test the hypothesis that changes in expression of zinc transporters including ZnT1, ZnT5 and ZIP4 are associated with changes in zinc status in young and older Saudi adults. Methods: Two hundred and two young and older Saudi adults of both sexes were recruited from Jeddah city in the western region of Saudi Arabia. Intakes of zinc and of zinc absorption modifiers in diet were assessed using an FFQ (designed and validated for this purpose) while plasma zinc concentration was determined by ICP-OES. RNA was extracted from white blood cells and qPCR was used to quantitatively measure expression of the ZnT1, ZnT5 and ZIP4 genes at the mRNA level. Results: Intakes of zinc and of protein were significantly higher in males than in females (P<0.05). A substantial proportion of the participants appeared to have inadequate zinc intake with the risk of inadequacy being greatest for young males (15%) and young females (4%). Plasma zinc concentrations in older adults were significantly higher than in young adults (P<0.05). Older males had significantly higher ZIP4 expression compared with young adults (P<0.05). Although older adults had apparently higher ZnT1 and ZnT5 expression than young adults, these differences were statistically non-significant. Several age and sex-specific correlations between zinc intake, zinc status and expression of zinc transporters were observed. Young and older adults who had apple-shaped fat distribution pattern, had significantly higher expression of ZnT1, ZnT5 and ZIP4 and plasma zinc status compared with participants who had pear-shaped fat distribution pattern (P<0.05). Discussion: Despite the changes in food availability in Saudi Arabia over recent decades, the prevalence of low zinc intake remains substantial. Contrary to reports from elsewhere, the prevalence of low plasma II zinc concentrations was greater in younger than in older Saudi adults. This study also identified relationships between expression of zinc transporters and zinc intake, zinc status and abdominal fatness in Saudi adults.