Impaired bioavailability of vitamin A in adults and children with persistent diarrhoea in Zambia

Background: We have previously demonstrated a strong relationship between l ow serum retinol concentration and mortality in Zambian AIDS patients with diarrhoea, but were unable to detect any benefit from oral micronutrient su pplementation. Aim: To test the hypothesis that this is related to impaired availability o f vitamin A, we analysed serum retinol concentration changes over 6 h follo wing oral mega-dose therapy (60, 120 or 180 mg retinol). Methods: Twenty-four men without diarrhoea, 15 adults with persistent diarr hoea and 11 children (six girls, five boys) with persistent diarrhoea were studied. Results: Men with persistent diarrhoea had lower baseline serum retinol con centrations (median 0.39 mu mol/L, interquartile range 0.21-0.56) than cont rols (median 1.16 mu mol/L, interquartile range 0.84-1.47; P = 0.0003). Aft er 60 mg retinol, the rise in serum retinol in HIV seropositive controls (m edian 0.63 mu mol/L, interquartile range 0.35-0.77) did not differ signific antly from that observed in HIV seronegative controls (median 0.35 mu mol/L , interquartile range - 0.04-0.56; P = 0.20). Increasing the dose to 120 mg or 180 mg retinol did not enhance the increase in serum retinol concentrat ion. The increase in serum retinol was less in adults with persistent diarr hoea (median 0.25 mu mol/L, interquartile range 0.04-0.35) and in children (median 0.11 mu mol/L, interquartile range 0.04-0.46) than in men without d iarrhoea (median 0.44 mu mol/L, interquartile range 0.26-0.74; P = 0.03). A dults and children with diarrhoea had greater losses of retinol in urine ov er a 24-h period than controls, but less than 1% of the ingested dose was e xcreted. Conclusions: These results suggest that persistent diarrhoea in this popula tion is associated with reduced bioavailability of retinol. Further work is required to determine the metabolic fate of therapeutic doses of retinol a nd to determine appropriate replacement strategies for HIV infected individ uals.