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Clay Ingestion (Geophagia) as a Source of Zinc for Rats^1,2,

Trace Element Research Laboratory, Veterans Administration Hospital; Departments of Biochemistry and of Epidemiology and Environmental Health, George Washington University School of Medicine, Washington, D. C. 20422

This study was designed to determine the effects of clay ingestion on zinc metabolism. Rats were fed 20% clay from Iran in a diet with different increments of zinc. The clay was leached with 3 N HCl to remove excess calcium. Forty-eight Sprague-Dawley weanling rats were assigned to three groups: 1) zinc deficient (1.4 ppm Zn), 2) borderline zinc deficient (10 ppm Zn), and 3) zinc supplemented (107 ppm Zn). Each group was divided into two subgroups. One subgroup (eight animals) was fed basal diet alone; the other subgroup received basal diet with 20% leached clay added. The clay contained 112 ± 16 ppm Zn. Animals fed the zinc-deficient diet failed to grow and died of zinc deficiency. In contrast, rats fed the deficient diet with 20% supplemented clay did not die and grew at a limited rate (21 ± 4.5 g in 25 days). The rate of growth of rats fed the borderline zinc-deficient diet with 20% leached clay was significantly greater than for rats fed the same diet without clay (84 ± 19 versus 102 ± 7.2 g in 25 days, P < 0.05). In contrast, there was no significant difference between the net gain of animals fed the zinc-supplemented diet with or without clay (163 ± 11 versus 171 ± 18 g for 25 days). A second experiment using 52 rats showed that zinc in clay was 13% as effective in promoting growth as zinc from ZnCO₃. Significant correlations existed between dietary zinc and plasma zinc (r = 0.76, P < 0.001) and between dietary and femur zinc (r = 0.86, P < 0.001). In summary, ingested clay can provide an essential trace element, indicating that geophagia is beneficial if there is a deficiency.

² Reported in part at the Fifty-fourth Annual Meeting of the Federation of American Societies for Experimental Biology, Atlantic City, New Jersey, 1970.

Manuscript received 4 March 1970.