Date of Award
Doctor of Philosophy in Health Sciences
Nutrition and Food Sciences
Nutrition and Food Sciences
Background: Oysters are an excellent source of iron and zinc but may be contaminated by heavy metals such as cadmium. The micronutrient and metal content of smoked, dried oysters as well as the impact of oyster consumption on iron, zinc, and cadmium concentrations in Ghana is unknown.
Objectives: Our objectives were to 1) determine the micronutrient and metal content and health risk of dried, smoked oysters, 2) determine the associations between dietary iron intake with hemoglobin or ferritin concentrations and anemia, 3) determine the associations between oyster consumption and iron, zinc and cadmium concentrations in Ghanaian women living near the Densu Estuary.
Methods: We purchased one package of dried smoked oysters from the Densu estuary in the Bortianor community in the Greater Accra Region of Ghana. Dried oysters selected from the package were analyzed in bulk by inductively coupled plasma-mass spectrometry for 12 micronutrients and 5 heavy metals. We calculated a total hazard quotient and hazard index (>1 may indicate potential health risks). We also enrolled women in the Bortianor/Tsokomey area in Ghana in a 6-month, longitudinal pilot study, with 66 women who consumed oysters during the open season (oyster group) and 70 women did non consume oysters (non-oyster group). We collected data at two time points: 1) March 2020 (end of closed season) and 2) August 2020 (5 months into the open season). We collected the amount and frequency of dietary iron intake and oyster consumption using a 30-day food frequency questionnaire. We analyzed hemoglobin (to determine anemia prevalence), ferritin (to determine iron deficiency), zinc, and cadmium (ug/g creatinine) concentrations and used paired t-tests to analyze the difference between seasons and used independent t-tests between groups. We also used a pathway analysis to understand the relationships between dietary iron intake or oyster consumption and zinc, cadmium, and serum ferritin or hemoglobin concentrations.
Results: The heavy metal contents of the dried oysters (mg/kg) were: Hg (8.96 ± 3.59), Cd (0.96 ± 0.26), As (4.46 ± 0.67), V (1.08 ± 0.32), and Pb (0.59 ± 0.11). The hazard index of dried oyster consumption was 44.62. At enrollment, mean±SD age was 34±8 y and BMI was 26±5 kg/m2. For women in the oyster group, Hb did not differ by season. The prevalence of anemia and iron deficiency (ID) in the oyster group was 78% and 54% in the closed season and 70% and 70% in the open season (anemia p=0.64, ID p=0.008). The prevalence of anemia and ID in the non-oyster group during the closed season was 83% and 44%, and 78% and 56% during the open season. For women in both the oyster and non-oyster group, zinc and ferritin concentrations were lower during the closed season compared to the open season and cadmium concentrations were higher during the open season compared to the closed season. There was no difference between groups in Hb, ferritin, zinc, cadmium and anemia prevalence during the closed or open season. Oyster consumption was not associated with zinc or cadmium concentrations in continuous models. Cadmium and zinc did not mediate the association between dietary iron intake or oyster consumption and ferritin or hemoglobin concentrations.
Conclusions: The dried oysters are an excellent source of iron and zinc but contaminated with cadmium, lead, arsenic, vanadium, and mercury, which may be increase health risks for consumers. We observed that during the open season women in the oyster and non-oyster group had lower ferritin and zinc and higher cadmium concentrations, indicating that there may be factors outside of oyster consumption and cadmium exposure contributing to iron deficiency in this population. The prevalence of anemia and iron deficiency anemia was high during both seasons in both groups of women. Iron deficiency anemia is of great concern in this population and it is necessary to identify and implement effective interventions to address anemia and iron deficiency at a community level. Based on low cadmium concentrations among women who consumed oysters, cadmium contamination of oysters may not be of great concern in this community and oysters may continue to serve as a valuable nutrition source for women of reproductive age in Ghana. However, future research should evaluate whether oyster consumption increases the risk of exposure to other heavy metals such as mercury, and the association with iron deficiency, which was high in this population.
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Abreu, Alyssa, "ASSOCIATIONS BETWEEN OYSTER CONSUMPTION AND IRON, ZINC, AND CADMIUM CONCENTRATIONS IN GHANAIAN WOMEN" (2023). Open Access Dissertations. Paper 1552.