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Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 12, 2016 | http://pubs.acs.org Publication Date: January 20, 1983 | doi: 10.1021/bk-1983-0210.ch018
Competitive Mineral—Mineral Interaction in the Intestine ImplicationsforZinc Absorption in Humans 1
NOEL W. SOLOMONS
Massachusetts Institute of Technology, Department of Nutrition and Food Science, Cambridge,MA02178 Competition with other minerals may reduce the biological a v a i l a b i l i t y of dietary zinc. Studies in experimental animals describe biological mineral-mineral interactions between and among metals of similar chemical configurations. Chemically-similar nutrients could theoretically reduce zinc absorption by interfering with: 1) its uptake into the cell; 2) its transfer across the cell; and/or 3) its transport into the c i r c u l a t i o n . Competitive i n t e r actions between zinc and copper, iron, cadmium and tin have been demonstrated i n animals. In human subjects, high zinc levels can reduce copper absorption; the converse has not been demonstrated. Fe/Zn ratios of 2:1 or greater reduce the absorption of dietary zinc.In the formation of vitamin-mineral supplements and infant foods, adverse n u t r i t i o n a l consequences from an Fe:Zn imbalance could result. Sn/Zn ratios of about 4:1 reduced the apparent absorption of zinc in human subjects. Storage of food i n tin-plated cans might compromise zinc a v a i l a b i l i t y . Calcium and and magnesium have no competitive effect on zinc absorption i n humans based on available evidence. This symposium t e s t i f i e s to the concern among n u t r i t i o n a l scientists and food technologists that the biological a v a i l a b i l i t y of dietary zinc may be a major determinant of zinc nutriture i n humans.Those assessing dietary adequacy with respect to a nutrient such as zinc, must be concerned with two features: the density (metallo-caloric ratio) and b i o a v a i l a b i l i t y . The Food and Nutrition Board of the National Academy of Sciences has established levels of recommended daily intake for healthy individuals of various age-groups, sexes and reproductive states: for infants 0-6 mo, 3 mg; for infants 7-12 mo, 5 mg; for children 1-10 yrs, 10 mg; for adults, 15 mg; for pregnant women, 20 mg; for lactating women, 25 mg (1). More refined estimates Current address:InstituteofNutritionofCentralAmericaandPanama, Division of Human Nutrition and Biology,GuatemalaCity,Guatemala,Central America 0097-6SeCittyo|Jbriff7$06.00/0 ©1998AmericalChemicalSociety 1
In Nutritional Bioavailability of Zinc; Inglett, George E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
NUTRITIONAL BIOAVAILABILITY OF ZINC
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f o r young c h i l d r e n , i n c l u d i n g premature i n f a n t s , have been devel oped by Hambidge and Casey 02). The l i m i t e d survey data on cus tomary z i n c intakes i n the United States (3^) suggest that most i n d i v i d u a l s consume from 45 t o 70% of the RDA f o r z i n c . This low intake r e s u l t s from the r e l a t i v e l y low t o t a l energy consumption of the sedentary U.S. population and the r e l a t i v e l y low d e n s i t y of z i n c i n the mixed U.S. d i e t . To achieve the RDA f o r z i n c w i t h a 3000 k c a l d a i l y i n t a k e , d i e t a r y z i n c density would have t o be 5-7.5 mg/1000 k c a l . The average mixed d i e t has a z i n c d e n s i t y i n the 3-4 mg/1000 k c a l range (4^)· The amount of z i n c that must be absorbed d a i l y , i . e . , the parenteral requirement f o r maintenance of normal z i n c balance, i s considerably l e s s than the RDA l e v e l s . Based on the estimate of an Expert Committee of the American Medical A s s o c i a t i o n f o r the p a r e n t e r a l dosage of z i n c i n s t a b l e a d u l t s ( 5 ) , absorbing anywhere from 17 t o 27% of the RDA l e v e l s would provide the z i n c needed f o r n u t r i t i o n a l maintenance. Thus, the e f f i c i e n c y o f a b s o r p t i o n of d i e t a r y z i n c can be an even greater determinant of adequacy than the d i e t a r y z i n c density or d a i l y t o t a l z i n c i n t a k e , per se. With a focus on b i o l o g i c a l a v a i l a b i l i t y of z i n c i n human n u t r i t i o n , the present paper reviews conceptual and experimental information from many l a b o r a t o r i e s , i n c l u d i n g our own, and draws conclusions about the p o s s i b l e impact of mineral-mineral i n t e r a c t i o n s as f a c t o r s a f f e c t i n g z i n c b i o a v a i l a b i l i t y from human d i e t s . The calcium:zinc i n t e r a c t i o n has been addressed by Dr. Spencer i n the preceding chapter and w i l l not be discussed here. B i o l o g i c a l I n t e r a c t i o n s of Chemically S i m i l a r Minerals I n t e r e s t i n m i n e r a l - m i n e r a l i n t e r a c t i o n s emerged i n the 1960s. Most e a r l y experiments i n laboratory animals involved either r a d i o i s o t o p i c t r a c e r s or manipulation of the d i e t a r y r a t i o s be tween and among m i n e r a l s . In the l a t t e r feeding experiments, the exacerbation of m a n i f e s t a t i o n s of d e f i c i e n c y of one mineral (M^) by excess amounts of a second ( M ) , o r the a m e l i o r a t i o n of the c l i n i c a l signs of M t o x i c i t y by i n c r e a s i n g the d i e t a r y l e v e l s of 2
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Table I . I n t e r a c t i o n of z i n c and copper on hemoglobin concentration, m o r t a l i t y , and body weight of c h i c k s
Z i n c , ppm 0 50 100 200 300
10 | 0 Hb, g/100 ml 6.5 8.5 5.9 8.0 6.0 8.8 4.8 8.0 4.1 6.6
Copper, ppm 10 o % Mortality 8.7 0 18.2 4.5 7.7 52.0 20.0 70.8 88.0 4.2
10 o wt, δ 262 272 320 205 182 294 139 291 127 310
a f t e r H i l l and Matrone, 1970 (
