AVAILABILITY OF DIETARY IRON AND INFLUENCE OF INHIBITORS AND/OR ENHANCERS ON IRON STATUS OF ADOLESCENTS

A Dissertation submitted in partial fulfillment of the requirement for the Degree of Doctor of Philosophy (Ph.D) in the Faculty of Basic Medical Sciences, College of Medicine, University of Ibadan, Ibadan, Nigeria.

The bio-availability of iron from diets consumed by 160 apparently healthy Nigerians adolescents (aged 11-18 years) resident in an institution was assessed. The level of enhancers (ascorbic iron) and inhibitors (phytic and tannic acids) of iron absorption were also determined. Dietary adequacy of eight of the nutrients (calories, protein, calcium, copper, zinc, iron, phosphorus and ascorbic acid) consumed by the adolescents was estimated from proximate analysis of the foods. The iron status of the subjects was subsequently evaluated by measurement of haemoglobin (HB) concentration, haematocrit (HCT), serum iron (SI) concentration, and total iron binding capacity (TIBC),transferrin saturation (TS), free erythrocyte protoporphyrin (PEP) and serum ferritin (SF) concentration, over a period of 18 months. The effect of midterm (6weeks) dietary supplementation with iron and ascorbic acid on HB and SF concentration was assessed in 100 adolescents. They were divided into four groups (designated I-IV). Groups I-III received supplementation consisting of 60mg iron, 100mg ascorbic acid or 60mg iron in combination with 100mg ascorbic acid, respectively, While group IV (placebo) received no dietary supplement. The results from the present study revealed that in vitro iron absorption from the foods ranged between 0.84 and 9.33%. The tannic and phytic acids content of the foods were low and had no effect on the bioavailability of iron from these foods. A strong correlation, however, existed between the levels of inhibitors (p<0.05) and iron content of the foods. Ascorbic acid enhanced iron absorption from the diets. Assessment of nutritional status from dietary intakes showed that with the exception of protein, iron, copper and phosphorus, the adolescents consumed suboptimal or marginal intakes of other nutrient. Older male subjects had significantly higher intakes of all nutrients (except ascorbic acid) than all other adolescents. Barcelino hematological data obtained from these adolescent revealed a low incidence of anemia (Hb<12g/d1). The longitudinal study also showed that for male subject aged 14 years, significant elevation in Hb concentration, Hct and TS values the 18 month experimental period occurred. A strong correlation also existed between Hb and TS ,and FEP, TS and FEP for subjects with low Hb concentration (-< 11.9g/d1). Parasitaemia and hookworm Infestation were not prevalent among the adolescents studied. All biochemical indices evaluated in particular iron strong (serum ferritin) were higher for males than female subjects. Ascorbic acid supplementation for 6 weeks failed to produce beneficial effect on erythropoiesis in these adolescents .Iron alone or in combination with ascorbic acid, however, produced significant increase in Hb, Hct TS and SF values. It is suggested that dual supplementation with multi-vitamins (especially ascorbic acid) and iron be incorporated Into dietary regimen of the Adolescents.