Nutritional Bioavailability of Iron - American Chemical Society

5 Ascorbic Acid: An Enhancing Factor in Iron Absorption ELAINE R. MONSEN

Downloaded by MONASH UNIV on February 28, 2016 | http://pubs.acs.org Publication Date: November 1, 1982 | doi: 10.1021/bk-1982-0203.ch005

University of Washington, Division of Human Nutrition, Dietetics, and Foods and Department of Medicine, Seattle, WA 98195

Ascorbic acid concomitantly consumed enhances nonheme iron absorption 3-6 fold: a key factor in the model estimating bioavailable dietary iron. The 500 mgs iron store Reference Individual is assumed to absorb 23% of ingested heme iron (estimated at 40% of meat, fish or poultry iron) and 3-8% of ingested nonheme iron (plant iron plus remaining meat, fish, poultry iron). The quantity of enhancing factors consumed at a specific meal, i.e. mgs ascorbic acid plus gms cooked meat/fish/poultry, determines % absorption of nonheme iron: 1.

ΣEF < 75: % = 3 + 8.93 log

2.

ΣEF

-

+ ≥ 75:

n

%= 8

HANES 2 (1976 - 80) reports low intake of iron and ascorbic acid for large population segments, especially females below poverty line, e.g. at 10th percentile 4 mg iron and 7 mg ascorbic acid per day. Prevention of iron deficiency in populations not sustaining chronic blood loss is possible by judicious selection of diets which enhance the bioavailability of dietary iron. The recent decades have produced significant research on the availability of iron asitisaffected by various dietary components, those which enhance as well as those which inhibit iron absorption. This has allowed for the first time the quantification of dietary effects on a trace metal and the development of a model whereby the quantity of bioavailable iron in a diet may be estimated. This paper will discuss four related areas: the major 0097-6156/82/0203-0085$06.00/0 © 1982 American Chemical Society In Nutritional Bioavailability of Iron; Kies, Constance; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

86

NUTRT IO INAL BO IAVAL IABL IT IY OF R ION

s e c t i o n w i l l be focused on the r o l e o f a s c o r b i c a c i d i n nonheme i r o n absorption; the second s e c t i o n w i l l d i s c u s s b r i e f l y the model f o r e s t i m a t i n g the q u a n t i t y o f a v a i l a b l e i r o n ; the t h i r d s e c t i o n w i l l d e a l w i t h c u r r e n t estimates o f d i e t a r y i n t a k e o f i r o n and a s c o r b i c a c i d i n the United S t a t e s ; and the l a s t s e c t i o n w i l l d i s c u s s b r i e f l y the i n t e r r e l a t i o n s h i p s of a s c o r b i c a c i d and i r o n i n abnormal s t a t e s of metabolism.


The r o l e of a s c o r b i c a c i d i n nonheme i r o n a b s o r p t i o n Radioisotope techniques have allowed p r e c i s e measurement o f dietary i r o n absorption. I n i t i a l s t u d i e s u t i l i z e d t e s t meals o f i n d i v i d u a l food which had been i n t r i n s i c a l l y l a b e l e d with radio-a c t i v e i r o n p r i o r to h a r v e s t i n g (1,2), U t i l i z a t i o n o f these s i n g l e food meals allowed a rank order to be e s t a b l i s h e d among the t e s t e d foods. Subjects could serve as t h e i r own c o n t r o l s when an i d e n t i c a l r e f e r e n c e dose was given to each s u b j e c t . T h i s reference dose of f e r r o u s s u l f a t e : a s c o r b i c a c i d was absorbed at a higher r a t e i n i r o n d e f i c i e n t s u b j e c t s than i n i r o n r e p l e t e s u b j e c t s ; a r a t i o o f the a b s o r p t i o n o f the t e s t meal to the r e f e r e n c e dose allowed comparisons to be made between i n d i v i d u a l s u b j e c t s . As these e a r l y s t u d i e s were l i m i t e d to study o f s i n g l e food items an e f f o r t was made to extend the technique by developing designs u t i l i z i n g e x t r i n s i c a l l y tagged t e s t meals (3,4). U t i l i z a t i o n o f these techniques has given evidence that d i e t a r y i r o n forms two separate pools i n the gut, one a p o o l o f heme i r o n and the other a p o o l of nonheme i r o n . The predominate source o f i r o n i n human d i e t s i s i n the form o f nonheme i r o n ( 5 ) , A s c o r b i c a c i d as an enhancing f a c t o r i n nonheme i r o n absorpt i o n has been f r e q u e n t l y observed, C a l l e n d e r , e t a l . , f e d i n t r i n s i c a l l y l a b e l e d hen eggs i n a b r e a k f a s t meal composed o f bread, b u t t e r , jam, eggs, and t e a o r c o f f e e to 26 s u b j e c t s ; when an a d d i t i o n o f 100 mis o f orange j u i c e was added t o t h i s meal a b s o r p t i o n i n c r e a s e d to 280% o f the c o n t r o l meal (6), Cook, e t a l . , provided a meal o f i n t r i n s i c a l l y l a b e l e d maize to sub^ j e c t s and observed that when 500 mgs o f a s c o r b i c a c i d was added that a b s o r p t i o n o f both i n t r i n s i c and e x t r i n s i c a l l y l a b e l e d i r o n was 6 times higher (3), Sayers, e t a l , , u t i l i z e d both i n t r i n s i c a l l y and e x t r i n s i c a l l y l a b e l e d maize, wheat and soybean, p r o v i d i n g a d d i t i o n a l evidence o f the a p p l i c a b i l i t y o f the extrints i c a l l y l a b e l e d model (_7), To the s u b j e c t s whom they gave maize and 50 mgs o f a s c o r b i c a c i d , a b s o r p t i o n was i n c r e a s e d from 8,.8% to 14.9%; to those subjects given maize p l u s 100 mg o f a s c o r b i c a c i d a b s o r p t i o n was increased to 22,6%, The importance o f the p r o c e s s i n g procedure was i n d i c a t e d i n that the t e s t meals to which a s c o r b i c a c i d was added p r i o r to high temperature baking, no enhancement o f i r o n a b s o r p t i o n was observed, suggesting that the h i g h temperatures i n a c t i v a t e d the a s c o r b i c a c i d , Bjorn-Rasmussen gave meals o f maize p l u s 4.5 mgs o f i r o n ; to these meals were added 0-200 mgs o f a s c o r b i c a c i d (8). I n -

In Nutritional Bioavailability of Iron; Kies, Constance; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.


5.

MONSEN

Enhancement by Ascorbic Acid

87

cremental i n c r e a s e s i n i r o n a b s o r p t i o n were observed as a s c o r b i c a c i d was i n c r e a s e d . I n another study, Cook and Monsen gave 63 male subjects 700 k i l o c a l o r i e meals composed o f s e m i s y n t h e t i c i n g r e d i e n t s o f dextrimaltose, corn o i l and ovalbumin; to these meals were added a s c o r b i c a c i d ranging from 0 to 1000 mgs (9)» With each i n c r e a s e i n a s c o r b i c a c i d an i n c r e a s e i n i r o n absorpt i o n occurred. The r a t e o f a b s o r p t i o n appeared to be l o g a r i t h m i c a l l y r e l a t e d to the a s c o r b i c a c i d content. I t was f u r t h e r shown i n t h i s experiment that a s c o r b i c a c i d must be present i n the stomach a t the same time that the nonheme i r o n i s present, Nonheme i r o n was absorbed a t a high r a t e from meals i n t o which the a s c o r b i c a c i d was i n c o r p o r a t e d . However i f the a s c o r b i c a c i d was given 4 o r 8 hours before the t e s t meal there was no enhancing e f f e c t observed. S e v e r a l i n v e s t i g a t o r s have looked a t the e f f e c t o f mixtures of foods on nonheme i r o n a b s o r p t i o n , L a y r i s s e t e s t e d meals that are reminiscent o f those w i t h i n v a r i o u s r e g i o n a l areas o f Venezuela: nonheme i r o n was absorbed a t a higher r a t e from meals that i n c l u d e d a s c o r b i c a c i d c o n t a i n i n g foods, the highest r a t e r e s u l t i n g from meals c o n t a i n i n g 66 mgs o f ascorbate cont r i b u t e d by 150 gms o f papaya (10). H a l l b e r g , e t a l . , t e s t e d 37 subjects with a d i e t c o n s i s t i n g o f a mixture o f r i c e , cabbage, c o l l a r d s , s t r i n g beans, c h i l i paste, f i s h sauce and coconut cream (11), When a f r u i t mixture c o n t a i n i n g banana, papaya and oranges was added t o t h i s v e g e t a l mixture, a b s o r p t i o n was reported to increase three f o l d . A s c o r b i c a c i d content was c a l c u l a t e d from food t a b l e s as being 35 mgs. Further a d d i t i o n of 80 gms o f l e a n beef to the v e g e t a l and f r u i t meal had an a d d i t i v e e f f e c t and enhanced the a b s o r p t i o n o f the b a s a l d i e t six-fold. Rossander, e t a l , , t e s t e d the impact o f adding 150 mis o f orange j u i c e t o a b r e a k f a s t c o n s i s t i n g o f bread, b u t t e r , marmalade, cheese and c o f f e e ; with the a d d i t i o n o f the orange j u i c e , a b s o r p t i o n increased from 3,7% t o 8% (12), When the b r e a k f a s t meal i n c l u d e d tea i n p l a c e o f c o f f e e , the enhancing e f f e c t o f the orange j u i c e was l e s s pronounced, A recent study compared v e g e t a r i a n meals (13), The f i r s t composed o f beans, r i c e , cornbread and apples contained 7 mg a s c o r b i c a c i d ; nonheme i r o n a b s o r p t i o n was 2.2%; the second meal, composed o f c a u l i f l o w e r , red kidney beans, white bread, cottage cheese and pineapple, contained 74 mg a s c o r b i c a c i d : from t h i s meal 16,9% of the nonheme i r o n was absorbed. Reviewing the s t u d i e s i n which nonheme i r o n a b s o r p t i o n has been assessed a t v a r i o u s l e v e l s o f a s c o r b i c a c i d i n t e s t meals composed o f e i t h e r s i n g l e food items o r food mixtures i t appears t h a t , w i t h i n any i n d i v i d u a l study, a d d i t i o n a l increments o f a s c o r b i c a c i d c o n s i s t e n t l y increased a b s o r p t i o n o f nonheme i r o n (Table 1), Considering the wide d i f f e r e n c e s i n experimental c o n d i t i o n s , the v a r i o u s s t u d i e s i n c o r p o r a t i n g 12.5 to 1000 mg a s c o r b i c a c i d i n d i c a t e c l e a r l y the enhancing e f f e c t that a s c o r b i c a c i d has on nonheme i r o n a b s o r p t i o n .



88


Table 1 The E f f e c t o f A s c o r b i c A c i d on Absorption of Nonheme Iron i n Humans Ascorbic Iron Absorption Ratio Test Meal + Ascorbic Acid Acid - Ascorbic Acid mg. 1.3 Maize 12.5 1.7 700 K c a l SS* 25 3.0 Maize 25 2.7 V e g e t a l meal + f r u i t s 35 1.7 Maize 50 2.5 700 K c a l SS 50 2.6 Maize 50 2,8 Bread, egg, + orange j u i c e 50 5.0 Maize + 150 g papaya 66 1.2 Bread, cheese, t e a + orange j u i c e 70 2,2 Bread, cheese, c o f f e e + orange j u i c e 70 7,7 600-700 K c a l v e g e t a r i a n 74 2,6 Maize 100 4.1 700 K c a l SS 100 4,6 Maize 100 6.1 Maize 200 4,7 700 K c a l SS 250 6.0 Maize 500 6.2 700 K c a l SS 500 9.6 700 K c a l SS 1000 *Semi-synthetic meal composed o f d e x t r i m a l t o s e , corn o i l and ovalbumin.


Ref. 8 9 8 11 7 9 8 6 10 12 12 13 7 9 8 8 9 3 9 9

89 Enhancement by Ascorbic Acid S e v e r a l d i e t a r y f a c t o r s have been i d e n t i f i e d which i n h i b i t nonheme i r o n a b s o r p t i o n . Tea and tannates appear p a r t i c u l a r l y i n h i b i t i n g (14). Rossander, e t a l . , reported only a s l i g h t i n crease i n a b s o r p t i o n when orange j u i c e was added to a t e a c o n t a i n i n g b r e a k f a s t meal (12). Other food a d d i t i v e s such as EDTA may have an i n h i b i t i n g e f f e c t on nonheme i r o n a b s o r p t i o n i f the EDTA i s i n h i g h molar concentrations r e l a t i v e to nonheme i r o n (JL5). A s c o r b i c a c i d has a l s o been shown to i n t e r a c t with t h e r a p e u t i c i r o n . Derman, e t a l . , have reported that a s c o r b i c a c i d i n c r e a s e s a b s o r p t i o n of v a r i o u s i r o n f o r t i f i c a t i o n compounds i n i n f a n t formulas i n c e r e a l s ; t h i s t h r e e - f o l d i n c r e a s e i n i r o n a b s o r p t i o n induced by a s c o r b i c a c i d was observed i n multiparous women (16). El-Hawary, e t a l . , s t u d i e d 97 i n f a n t s and young c h i l d r e n and observed that a s c o r b i c a c i d increased a b s o r p t i o n from a f o u r mg i r o n supplement as f e r r o u s s u l f a t e (17). McPhail, e t a l . , have a l s o reported i n c r e a s e s i n a b s o r p t i o n of i r o n from e i t h e r f e r r o u s s u l f a t e or iron:EDTA with i n c o r p o r a t i o n of three to s i x molar concentrations of a s c o r b i c a c i d (18), When these mixtures of a s c o r b i c a c i d and i r o n f o r t i f i c a t i o n compounds were added to foods such as maize p o r r i d g e before the foods were cooked a b s o r p t i o n was not enhanced.


5.

MONSEN

E s t i m a t i n g b i o a v a i l a b l e i r o n i n the d i e t Extensive research on the a b s o r p t i o n of i r o n from v a r i o u s types of meals has allowed g u i d e l i n e s to be developed by which the amount of d i e t a r y i r o n a v a i l a b l e f o r a b s o r p t i o n may be estimated. I r o n i s the f i r s t t r a c e mineral to be thus t r e a t e d and thus serves as a model f o r other n u t r i e n t s (19), The model f o r e s t i m a t i n g b i o a v a i l a b l e i r o n i s based on the concept that i r o n forms a) a p o o l of heme i r o n which i s r e a d i l y a v a i l a b l e to humans and i s u n e f f e c t e d by other d i e t a r y components and b) a p o o l of nonheme i r o n which i s of low b i o a v a i l a b i l i t y unless enhancing f a c t o r s are present concommitantly (20). Recognition i s made of the importance of the extent of an i n d i v i d u a l ' s i r o n s t o r e s as i t w i l l i n f l u e n c e the amount of nonheme i r o n and heme i r o n that would be absorbed. The conservat i v e model suggests u t i l i z a t i o n of an i n d i v i d u a l with 500 mgs of i r o n s t o r e s as the r e f e r e n c e i n d i v i d u a l f o r whom b i o a v a i l a b l e i r o n may be c a l c u l a t e d . As the purpose of such a model i s to compare one d i e t with another, i t i s immaterial what l e v e l of i r o n s t o r e s an i n d i v i d u a l has i n that the comparison between d i e t s w i l l not be a f f e c t e d . The c a l c u l a t e d values w i l l , of course, be lower f o r the amount of t o t a l a v a i l a b l e i r o n with an i n d i v i d u a l with moderate i r o n s t o r e s of 500 mgs than they would be f o r an i n d i v i d u a l w i t h zero i r o n s t o r e s . The enhancing f a c t o r s considered f o r the a b s o r p t i o n of nonheme i r o n are a s c o r b i c a c i d and meat, f i s h and p o u l t r y . The


90



e a r l i e r model c l a s s i f i e d meals as low, moderate o r h i g h a v a i l ability; t h i s produced a r t i f i c i a l s t a i r step increments. Thus, the model has been f u r t h e r r e f i n e d t o show that the enhancing f a c t o r s a r e a d d i t i v e i n t h e i r e f f e c t and smoothly i n c r e a s e d i e t a r y nonheme i r o n a b s o r p t i o n i n a l o g a r i t h m i c f a s h i o n (21). Thus the amount o f nonheme i r o n a v a i l a b l e f o r a b s o r p t i o n from each meal o r snack can be estimated from the summation o f enhancing f a c t o r s (milligrams o f a s c o r b i c a c i d p l u s grams o f cooked m e a t / f i s h / p o u l t r y ) . Absorption o f nonheme i r o n f o r the r e f e r e n c e i n d i v i d u a l with 500 mg i r o n s t o r e s i s assumed to change from 3% f o r a meal w i t h no enhancing f a c t o r s to 8% from a meal o f 75 enhancing f a c t o r s . The formulas f o r c a l c u l a t i n g the r a t e o f a b s o r p t i o n o f nonheme i r o n f o r the r e f e r e n c e i n d i vidual are: For EF

Nutritional Bioavailability of Iron - American Chemical Society

Recommend Documents