- Email: [email protected]
Tea consumption does not affect iron absorption in rats unless tea and iron are consumed together
NutritionResearch. Vol. 17. No. 8, pp. 1303-1310.1997 Copyright Q 1997 Elsevier Science Inc. Printed in the USA. AII rights reserved 0271-5317/97 $17.00 + .OO
ELSEVIER
PI1 SO271-5317(97)OOIl4-0
TEA CONSUMPTION
DOES NOT AFFECT IRON ABSORPTION IN RATS UNLESS TEA AND IRON ARE CONSUMED TOGETHER
Paul K. South, M.S., William A. House, Ph.D. and Dennis D. Miller, Ph.D. Cornell University Institute of Food Science, Stocking Hall and U.S. Plant, Soil and Nutrition Laboratory, USDA-ARS Ithaca, NY 14853
??
ABSTRACT
Phenolic compounds may influence iron absorption by complexing iron in the intestinal lumen or by altering intestinal permeability. We assessed the effects of tea on iron absorption and intestinal permeability in rats in two experiments. In experiment 1, rats maintained on a commercial rat diet were fasted overnight with free access to water and then gavaged with 1 .O ml of 59Fe labeled FeCI, (0.1 mM or 1.O mM) and lactulose (0.5 M) in water or black tea. Iron absorption was estimated from 59Fe retention. Intestinal permeability was evaluated by lactulose excretion in the urine. Iron absorption was lower when given with tea at both iron concentrations but tea did not affect lactulose excretion. In experiment 2, rats maintained on a commercial rat diet were divided into two groups. One group was given black tea as the only source of water for 3 d. The other group was given water. Both groups were fasted overnight with free access to water and then gavaged with 1 .O ml of water or black tea containing 59Fe labeled FeCl, (0.1 r&I) and lactulose (0.5 M). Iron absorption was not affected by 3 d of tea consumption but was decreased when delivered in tea. Lactulose excretion was not affected by 3 d tea consumption or by delivery in tea. These data suggest that tea affects iron absorption by forming iron complexes in the lumen. 0 1997lzLwxiuscienceInc. Key Words: Iron Absorption,
Intestinal Permeability,
Tea, Rats, Lactulose
*Corresponding author: D.D. Miller, Cornell University, Stocking Hall, Ithaca, NY 14853 Phone: (607) 255-2895; FAX: (607) 254-4868; Email: [email protected]
1303
1304
P.K. SOUTH et al.
INTRODUCTION
Nonheme iron absorption may be affected by enhancing and inhibiting factors in the diet. Ascorbic acid and meat enhance iron absorption (1) while phytate inhibits iron absorption (2,3). Tea has also been shown to inhibit iron absorption (45). Presumably, phenolic compounds found in tea reduce iron bioavailability by forming insoluble complexes within the intestinal lumen (6). Intestinal permeability can be determined by quantifying urinary lactulose excretion after oral administration of this sugar (7). Lactulose, a disaccharide, is absorbed by passive diffusion. In healthy individuals, lactulose is absorbed at very low levels. Clinical studies have shown that the permeability of the small intestine to lactulose is significantly increased in patients with persistent diarrhea (8), coeliac disease (9) and Crohn’s Disease (10). Increased lactulose excretion has been attributed to increased permeability or leakiness as a result of a structurally damaged mucosa (7). High doses of tamric acid have been reported to cause gastroenteritis in rats (11) and rabbits (12). It is unclear how intestinal permeability is affected by tea and whether changes in intestinal permeability influence iron absorption. Our study was conducted to assess the effects of tea consumption on both iron absorption and intestinal permeability in the rat as a way to investigate the mechanism by which tea reduces iron absorption.
Tea Preparation. One g of black tea (Black Tea Research Blend, T.J. Lipton, Englewood Cliffs, NJ) was added to 100 ml boiling water and allowed to stand at room temperature for 5 minutes. The brewed tea was then filtered (Whatman no. 1 qualitative, Whatman Limited, England). Animals and Care. The experimental protocol was approved by the Institutional Animal Care and Use Committee at Cornell University. Weanling, male Sprague-Dawley rats (Camm Research Institute, Wayne, NJ) were housed individually in metabolic cages placed in a room with a constant temperature (23” C) and with a 12 hour light/dark cycle. Rats had free access to a commercial rat ration (Prolab 1000, Agway, Syracuse, NY) unless otherwise noted. Blood samples were obtained from the tail and hemoglobin concentrations were determined by a cyanmethemoglobin method (Sigma kit 525-A, Sigma Chemical, St. Louis, MO). In experiment 1, rats were assigned to 4 groups so that each group had similar mean body weights and hemoglobin levels. Rats from experiment 1 were re-used in experiment 2 and were reassigned to groups so that each treatment group had similar weight and contained an equal number of rats from each treatment group in experiment 1. Experiment 1. Rats were weighed (range, 60 to 91 g), deprived of food for 12 h, then given 1 ml of a test solution by esophageal camnda. Test solutions were prepared immediately before the gavage and contained lactulose (0.5 M) and iron (0.1 mM or 1.O n&I) in either tea or water. Iron was labeled with
TEA CONSUMPTION
AND IRON
1305
59FeC1, (18.5 kBq/ml test solution, 1257 kBq/ug Fe, DupontNew England Nuclear, North Billercia, MA). A FeCl, solution (1 mg Fe/ml, Certified Atomic Absorption Standard, Sigma) was used as the non-labeled iron source. Rats were allowed water but were deprived of food for 8 hours after the gavage. Excrement collected daily for 1 week after gavage was assayed for 59Fe (Model 5530, Packard Instruments, Downers Grove, IL). Iron retention was determined by subtracting excreted 59Fe from the initial 59Fe dose. Absorption of Fe was calculated from iron retention data as described by Van Campen and House (13). Urine collected over the first 8 hours after administration of the test solutions was assayed for lactulose concentration (Lactose/D-Glucose Test Kit and Phospho-Glucoisomerase enzyme, Boehringer Mamrheim, Indianapolis, IN). NADPH was formed in the reaction and measured at absorbance 340mn. The amount of NADPH is stoichiometric with amount of lactulose present (14). Lactulose absorption was calculated as follows: Lactulose absorption (%) =
where :
C x A B
x
100
A is the urine produced during the 8 hours following gavage (L) B is the amount lactulose ingested by each rat (g) C is the lactulose concentration in the rat urine (g/L)
Experiment 2. Two of the 4 groups had drinking water replaced by tea for 3 days. The other 2 groups remained on water. Rats receiving tea for 3 days were returned to distilled water 12 hours before gavage while rats receiving water remained on water. Rats were weighed (range, 121 to 149 g) then given 1 ml of a test solution after being deprived of food for 12 h. Test solutions contained lactulose (0.5 M) and 59Fe labeled FeCl, (0.1 mM) in either tea or water. Radio-assay and intestinal permeability procedures were as described in experiment 1. Statistical Analysis. Data were analyzed by ANOVA. Whenever F was statistically significant (p
RESULTS
Weight gain was not affected by treatment in either experiment. Experiment 1. Lactulose absorption did not differ between treatment groups indicating that tea in place of water did not affect intestinal permeability (Table 1). At 0.1 mM Fe level, delivery in tea reduced iron absorption when compared to delivery in water. At 1 .O mM Fe level, iron absorption was also lower in tea but the difference was not significant. Percent Fe absorption was lower in the 1.O mM
1306
P.K. SOUTH et al.
Fe solution when compared to the 0.1 mM Fe solution in both tea and water though more total iron was absorbed from the larger dose. Experiment 2. Iron absorption was reduced when iron was administered in a tea solution when compared to water but there was no effect from prior tea consumption (Table 2). Administering lactulose in tea or water had no effect on lactulose absorption. ANOVA indicated replacement of drinking water by tea for 3 days prior to the gavage affected (p=O.O5) lactulose absorption but no differences between treatments were detected employing Tukey’s standardized range test.
TABLE 1 Absorption of Lactulose and 59Fe for Each Treatment Group in Experiment Treatment 0.1 mM Fe in water 1 .O mM Fe in water 0.1 mM Fe in tea l.OmMFeintea
Lactulose Absorption (%) 4.7 2 0.51” 5.6 + 1 .OO” 8.2 + 1.75” 5.8 + 1.23”
,#, * 1 ?? ??
Iron Absorption (%) 76 + 3.8” 48 + 6.5b.C 55 + 3.1b 35 & 4.2”
*Values are means + SEM for each group (n=S) ‘All treatments contain 0.5 M lactulose **Means in each column not sharing a common letter are significantly (a=O.O5)
different
TABLE 2 Absorption of Lactulose and 59Fe for Each Treatment Group in Experiment 2.*-’ * ??
3 3 3 3
d d d d
Treatment water, Fe in water tea, Fe in water water, Fe in tea tea, Fe in tea
Lactulose Absorption (%) 5.1 + 0.46” 3.5 + 0.57” 4.5 + 0.68” 3.5 2 0.49”
Iron Absorption (%) 69 + 2.5” 59 + 5.4” 40&4b 41 It 4.4b
‘Values are means + SEM for each group (n=8) ‘All treatments contain 0.5 M lactulose and 0.1 mM Fe **Means in each column not sharing a common letter are significantly (a=0.05)
different
TEA CONSUMPTION
AND IRON
1307
Iron absorption from meals may be enhanced or inhibited by various food components. Phenolic compounds have been identified as potent inhibitors of iron absorption (3,4,15,16). Phenolic compounds are ubiquitous in plant foods and, therefore, significant amounts are consumed every day. Black tea, a widely consumed beverage, contains appreciable levels of phenolic compounds that have also been found to inhibit iron absorption in human studies (4,15,17). Presumably, phenolic compounds complex with iron within the intestinal lumen and thereby reduce iron bioavailability (6). Epidemiological studies investigating the effect of tea on iron status have been inconclusive. One study found tea and coffee consumption to be negatively correlated with anemia (18) while another found tea consumption to be positively correlated with anemia (19). To study changes in the intestinal mucosa, intestinal permeability has been investigated nonmetabolyzable, passively absorbed employing different permeability probes. Detection of compounds in the urine following oral administration has been used to determine changes in the permeability of the mucosa. Lactulose, a nonmetabolizable passively absorbed compound, has been used to assess intestinal mucosal abnormalities resulting from disease (8-10) and diet (20,21). Our results indicate that iron absorption in rats decreased when iron was administered in a tea solution. In contrast, the replacement of drinking water with tea for 3 days prior to the gavage did not affect iron absorption. A 3 day duration of tea consumption was chosen to represent the “chronic” treatment because it has been found that rats adapt to high tannin diets after 3 days (22). This data supports the hypothesis that the mechanism by which tea reduces iron absorption is by formation of a complex with iron rather than by damaging the mucosa (6). Therefore, consumption of tea with an iron-containing meal could significantly reduce iron absorption while previous tea consumption would not affect iron absorption. Iron concentration in water or tea also had a significant effect on iron absorption. Although percent absorption was lower in the 1.0 mM Fe solution than in the 0.1 mM Fe solution, more total iron was absorbed from the larger dose. These results are consistent with previous findings by Smith and Pamracciulli (23) who found a lo-fold increase in the test dose of iron resulted in only a 4-fold increase in the quantity of iron absorbed. Tea did not affect lactulose absorption when these components were administered together. The replacement of drinking water with tea for 3 days prior to lactulose ingestion, however, appeared to reduce lactulose absorption though not significantly (p=O.O5). Welsch et al. (24) and Motilva et al. (25) showed phenolic compounds reduce glucose transport in rats in intestinal brush border membrane vesicles and in vivo, respectively. Tarmic acid, a phenolic compound similar to those found in tea, has been shown to grossly denature both the glycocalyx and brush border (26). However, Mitjavila et al. (26) employed tamiic acid at levels much higher than those contained in tea. Both Welsch et al. (24) and Motilva et al. (25) suggest a slight modification of membrane proteins as the mechanism responsible for reduced glucose transport following ingestion of phenolic compounds.
1308
P.K. SOUTH et al.
These results suggest that chronic tea consumption may reduce intestinal permeability but does not affect iron absorption as long as the tea is not consumed with an iron-containing meal. Therefore, our results support the hypothesis that tea reduces iron absorption by formation of a complex with iron. Furthermore, the mechanism by which phenolic compounds reduce iron absorption does not appear to involve changes in intestinal permeability.
1.
Hallberg L. Bioavailability
of dietary iron in man. Ann. Rev. Nutr. 198 1; 1: 123.
2.
Hallberg L, Rossander L, Skanberg AB. Phytate and the inhibitory absorption in man. Am. J. Clin. Nutr. 1987; 45:988-96.
3.
Gillooly M, Bothwell TH, Torrance JD, MacPhail AP, Derman DP, Bezwoda WR, Mills W, Charlton RW, Mayet F. The effect of organic acids, phytates and polyphenols on the absorption of iron from vegetables. Br. J. Nutr. 1983; 49:33 I-36.
4.
Disler PB, Lynch SR, Charlton RW, Torrance JD, Bothwell TH, Walker RB, Mayet F. The effect of tea on iron absorption. Gut 1975a; 16:193-200.
5.
Rossander L, Hallberg L, Bjom-Rasmussen J. Clin. Nutr. 1979; 32:2484-89.
6.
Disler PB, Lynch SR, Torrance JD, Sayers MH, Bothwell TH, Charlton RW. The mechanism of the inhibition of iron absorption by tea. S. Ah. J. Med. Sci. 1975b; 40:109-16.
7.
Menzies IS. Absorption 1974; 2: 1042-46.
8.
Sullivan PB, Lunn PG, Northrop-Clewes C, Crowe PT, March MN, Neale G. Persistent diarrhea and malnutrition: The impact of treatment on small bowel structure and permeability. J. Ped. Gast. Nutr. 1992; 14:208-15.
9.
Menzies IS, Laker MF, Pounder R, Bull J, Heyer S, Wheeler PG, Creamer B. Abnormal intestinal permeability to sugars in villous atrophy. Lancet 1979; 2: 1107-9.
10.
Pearson AD, Eastham J, Laker MF, Craft AW, Nelson R. Intestinal with Crohn’s disease and coeliac disease. Br. Med. J. 1982; 285:20-l.
11.
Boyd E.M, Bercezky K, Godi, I. The acute toxicity of tannic acid administered Can. Med. Assoc. J. 1962; 92:1292-97.
effect of bran on iron
E. Absorption of iron from breakfast meals. Amer.
of intact oligosaccharide
in health and disease. Biochem.
permeability
Sot. Trans.
in children
intragastically.
TEA CONSUMPTION AND IRON
1309
12.
Dollahite JW, Pigeon RF, Camp BJ. The toxicity of gallic acid, pyrogallol, Quercus havurdi in the rabbit. Am. J. Vet. Res. 1965; 23:1264-67.
13.
Van Campen DR, House WA. Effect of low protein diet on retention of an oral dose of 65Zn and on tissue concentrations of zinc, iron, and copper in rats. J. Nutr. 1974; 104:84-90.
14.
Andrews GR. Distinguishing pasteurized, UHT and sterilized milks by their lactulose content. J. Sot. Dairy Tech. 1984; 37:92-5.
15.
Hallberg L, Rossander L. Effect of different drinks on the absorption of nonheme composite meals. Human Nutrition: Applied Nutrition 1982; 36A:116-23.
16.
Brune M, Rossander L, Hallberg L. Iron absorption and phenolic compounds: different phenolic structures. J. Clin. Nutr. 1989; 43:547-58.
17.
Reddy MB, Cook JD. Assessment of dietary determinants humans and rats. Am. J. Clin. Nutr. 1991; 54:723-8.
18.
Mehta SW, Pritchard ME, Stegman C. Contribution NHANES II participants. Nutr. Res. 1992; 12:209-222.
19.
Merhav H, Amitai Y, Palti H, Godfrey S. Tea drinking and mycrocytic J. Clin. Nutr. 1985; 41:1210-1213.
20.
Thomson ABR, Keelan M. Rechallenge following an early life exposure to a high cholesterol diet enhances diet associated alterations in intestinal permeability. J. of Pediatr. Gastrenterol. Nutr. 1990; 9(1):98-104.
21.
Jalonen T. Identical intestinal permeability changes in children with different manifestations of cow’s milk allergy. J. Allergy Clin. Immtmol. 1991; 88(5): 737-42.
22.
Mehanso H, Hagerman A, Clements S, Butler L, Rogler J, Carlson D. Modulation of prolinerich protein biosynthesis in rat parotid glands by sorghums with high tannin levels. Proc. Natl. Acad. Sci. USA 1983; 80:3948-3952.
23.
Smith MD, Pannacciulli IM. Absorption of inorganic iron from graded doses: Its significance in relation to iron absorption tests and the mucosal block theory. Br. J. Haematol. 1958 4:428-32.
24.
Welsch CA, Lachance PA, Wasserman BP. Dietary phenolic compounds: Inhibition of Na’dependent D-glucose uptake in rat intestinal brush border membrane vesicles. J. Nutr. 1989; 119:1698-1704.
25.
Motilva MJ, Martinez J.A, Ilundian A, Larralde J. Effects of extracts from bean (Phuseolus vulgar-is) and field bean (Viciufabu) varieties on intestinal D-glucose transport in rat in vivo. J. Sci. Food Agric. 1983; 34:239-46.
on non-heme
tannic acid and
iron from
Importance
of
iron absorption
in
of coffee and tea to anemia
among
anemia in infants. Am.
clinical
P.K. SOUTH
1310
26.
et al.
Mitjavila S, LaCombe C, Carrera G, Derache R. Tannic acid and oxidized tannic acid on the functional state of rat intestinal epithelium. J. Nutr. 1977; 107:2113-21.
Accepted
for
publication
June
10,
1997.
ELSEVIER
PI1 SO271-5317(97)OOIl4-0
TEA CONSUMPTION
DOES NOT AFFECT IRON ABSORPTION IN RATS UNLESS TEA AND IRON ARE CONSUMED TOGETHER
Paul K. South, M.S., William A. House, Ph.D. and Dennis D. Miller, Ph.D. Cornell University Institute of Food Science, Stocking Hall and U.S. Plant, Soil and Nutrition Laboratory, USDA-ARS Ithaca, NY 14853
??
ABSTRACT
Phenolic compounds may influence iron absorption by complexing iron in the intestinal lumen or by altering intestinal permeability. We assessed the effects of tea on iron absorption and intestinal permeability in rats in two experiments. In experiment 1, rats maintained on a commercial rat diet were fasted overnight with free access to water and then gavaged with 1 .O ml of 59Fe labeled FeCI, (0.1 mM or 1.O mM) and lactulose (0.5 M) in water or black tea. Iron absorption was estimated from 59Fe retention. Intestinal permeability was evaluated by lactulose excretion in the urine. Iron absorption was lower when given with tea at both iron concentrations but tea did not affect lactulose excretion. In experiment 2, rats maintained on a commercial rat diet were divided into two groups. One group was given black tea as the only source of water for 3 d. The other group was given water. Both groups were fasted overnight with free access to water and then gavaged with 1 .O ml of water or black tea containing 59Fe labeled FeCl, (0.1 r&I) and lactulose (0.5 M). Iron absorption was not affected by 3 d of tea consumption but was decreased when delivered in tea. Lactulose excretion was not affected by 3 d tea consumption or by delivery in tea. These data suggest that tea affects iron absorption by forming iron complexes in the lumen. 0 1997lzLwxiuscienceInc. Key Words: Iron Absorption,
Intestinal Permeability,
Tea, Rats, Lactulose
*Corresponding author: D.D. Miller, Cornell University, Stocking Hall, Ithaca, NY 14853 Phone: (607) 255-2895; FAX: (607) 254-4868; Email: [email protected]
1303
1304
P.K. SOUTH et al.
INTRODUCTION
Nonheme iron absorption may be affected by enhancing and inhibiting factors in the diet. Ascorbic acid and meat enhance iron absorption (1) while phytate inhibits iron absorption (2,3). Tea has also been shown to inhibit iron absorption (45). Presumably, phenolic compounds found in tea reduce iron bioavailability by forming insoluble complexes within the intestinal lumen (6). Intestinal permeability can be determined by quantifying urinary lactulose excretion after oral administration of this sugar (7). Lactulose, a disaccharide, is absorbed by passive diffusion. In healthy individuals, lactulose is absorbed at very low levels. Clinical studies have shown that the permeability of the small intestine to lactulose is significantly increased in patients with persistent diarrhea (8), coeliac disease (9) and Crohn’s Disease (10). Increased lactulose excretion has been attributed to increased permeability or leakiness as a result of a structurally damaged mucosa (7). High doses of tamric acid have been reported to cause gastroenteritis in rats (11) and rabbits (12). It is unclear how intestinal permeability is affected by tea and whether changes in intestinal permeability influence iron absorption. Our study was conducted to assess the effects of tea consumption on both iron absorption and intestinal permeability in the rat as a way to investigate the mechanism by which tea reduces iron absorption.
Tea Preparation. One g of black tea (Black Tea Research Blend, T.J. Lipton, Englewood Cliffs, NJ) was added to 100 ml boiling water and allowed to stand at room temperature for 5 minutes. The brewed tea was then filtered (Whatman no. 1 qualitative, Whatman Limited, England). Animals and Care. The experimental protocol was approved by the Institutional Animal Care and Use Committee at Cornell University. Weanling, male Sprague-Dawley rats (Camm Research Institute, Wayne, NJ) were housed individually in metabolic cages placed in a room with a constant temperature (23” C) and with a 12 hour light/dark cycle. Rats had free access to a commercial rat ration (Prolab 1000, Agway, Syracuse, NY) unless otherwise noted. Blood samples were obtained from the tail and hemoglobin concentrations were determined by a cyanmethemoglobin method (Sigma kit 525-A, Sigma Chemical, St. Louis, MO). In experiment 1, rats were assigned to 4 groups so that each group had similar mean body weights and hemoglobin levels. Rats from experiment 1 were re-used in experiment 2 and were reassigned to groups so that each treatment group had similar weight and contained an equal number of rats from each treatment group in experiment 1. Experiment 1. Rats were weighed (range, 60 to 91 g), deprived of food for 12 h, then given 1 ml of a test solution by esophageal camnda. Test solutions were prepared immediately before the gavage and contained lactulose (0.5 M) and iron (0.1 mM or 1.O n&I) in either tea or water. Iron was labeled with
TEA CONSUMPTION
AND IRON
1305
59FeC1, (18.5 kBq/ml test solution, 1257 kBq/ug Fe, DupontNew England Nuclear, North Billercia, MA). A FeCl, solution (1 mg Fe/ml, Certified Atomic Absorption Standard, Sigma) was used as the non-labeled iron source. Rats were allowed water but were deprived of food for 8 hours after the gavage. Excrement collected daily for 1 week after gavage was assayed for 59Fe (Model 5530, Packard Instruments, Downers Grove, IL). Iron retention was determined by subtracting excreted 59Fe from the initial 59Fe dose. Absorption of Fe was calculated from iron retention data as described by Van Campen and House (13). Urine collected over the first 8 hours after administration of the test solutions was assayed for lactulose concentration (Lactose/D-Glucose Test Kit and Phospho-Glucoisomerase enzyme, Boehringer Mamrheim, Indianapolis, IN). NADPH was formed in the reaction and measured at absorbance 340mn. The amount of NADPH is stoichiometric with amount of lactulose present (14). Lactulose absorption was calculated as follows: Lactulose absorption (%) =
where :
C x A B
x
100
A is the urine produced during the 8 hours following gavage (L) B is the amount lactulose ingested by each rat (g) C is the lactulose concentration in the rat urine (g/L)
Experiment 2. Two of the 4 groups had drinking water replaced by tea for 3 days. The other 2 groups remained on water. Rats receiving tea for 3 days were returned to distilled water 12 hours before gavage while rats receiving water remained on water. Rats were weighed (range, 121 to 149 g) then given 1 ml of a test solution after being deprived of food for 12 h. Test solutions contained lactulose (0.5 M) and 59Fe labeled FeCl, (0.1 mM) in either tea or water. Radio-assay and intestinal permeability procedures were as described in experiment 1. Statistical Analysis. Data were analyzed by ANOVA. Whenever F was statistically significant (p
RESULTS
Weight gain was not affected by treatment in either experiment. Experiment 1. Lactulose absorption did not differ between treatment groups indicating that tea in place of water did not affect intestinal permeability (Table 1). At 0.1 mM Fe level, delivery in tea reduced iron absorption when compared to delivery in water. At 1 .O mM Fe level, iron absorption was also lower in tea but the difference was not significant. Percent Fe absorption was lower in the 1.O mM
1306
P.K. SOUTH et al.
Fe solution when compared to the 0.1 mM Fe solution in both tea and water though more total iron was absorbed from the larger dose. Experiment 2. Iron absorption was reduced when iron was administered in a tea solution when compared to water but there was no effect from prior tea consumption (Table 2). Administering lactulose in tea or water had no effect on lactulose absorption. ANOVA indicated replacement of drinking water by tea for 3 days prior to the gavage affected (p=O.O5) lactulose absorption but no differences between treatments were detected employing Tukey’s standardized range test.
TABLE 1 Absorption of Lactulose and 59Fe for Each Treatment Group in Experiment Treatment 0.1 mM Fe in water 1 .O mM Fe in water 0.1 mM Fe in tea l.OmMFeintea
Lactulose Absorption (%) 4.7 2 0.51” 5.6 + 1 .OO” 8.2 + 1.75” 5.8 + 1.23”
,#, * 1 ?? ??
Iron Absorption (%) 76 + 3.8” 48 + 6.5b.C 55 + 3.1b 35 & 4.2”
*Values are means + SEM for each group (n=S) ‘All treatments contain 0.5 M lactulose **Means in each column not sharing a common letter are significantly (a=O.O5)
different
TABLE 2 Absorption of Lactulose and 59Fe for Each Treatment Group in Experiment 2.*-’ * ??
3 3 3 3
d d d d
Treatment water, Fe in water tea, Fe in water water, Fe in tea tea, Fe in tea
Lactulose Absorption (%) 5.1 + 0.46” 3.5 + 0.57” 4.5 + 0.68” 3.5 2 0.49”
Iron Absorption (%) 69 + 2.5” 59 + 5.4” 40&4b 41 It 4.4b
‘Values are means + SEM for each group (n=8) ‘All treatments contain 0.5 M lactulose and 0.1 mM Fe **Means in each column not sharing a common letter are significantly (a=0.05)
different
TEA CONSUMPTION
AND IRON
1307
Iron absorption from meals may be enhanced or inhibited by various food components. Phenolic compounds have been identified as potent inhibitors of iron absorption (3,4,15,16). Phenolic compounds are ubiquitous in plant foods and, therefore, significant amounts are consumed every day. Black tea, a widely consumed beverage, contains appreciable levels of phenolic compounds that have also been found to inhibit iron absorption in human studies (4,15,17). Presumably, phenolic compounds complex with iron within the intestinal lumen and thereby reduce iron bioavailability (6). Epidemiological studies investigating the effect of tea on iron status have been inconclusive. One study found tea and coffee consumption to be negatively correlated with anemia (18) while another found tea consumption to be positively correlated with anemia (19). To study changes in the intestinal mucosa, intestinal permeability has been investigated nonmetabolyzable, passively absorbed employing different permeability probes. Detection of compounds in the urine following oral administration has been used to determine changes in the permeability of the mucosa. Lactulose, a nonmetabolizable passively absorbed compound, has been used to assess intestinal mucosal abnormalities resulting from disease (8-10) and diet (20,21). Our results indicate that iron absorption in rats decreased when iron was administered in a tea solution. In contrast, the replacement of drinking water with tea for 3 days prior to the gavage did not affect iron absorption. A 3 day duration of tea consumption was chosen to represent the “chronic” treatment because it has been found that rats adapt to high tannin diets after 3 days (22). This data supports the hypothesis that the mechanism by which tea reduces iron absorption is by formation of a complex with iron rather than by damaging the mucosa (6). Therefore, consumption of tea with an iron-containing meal could significantly reduce iron absorption while previous tea consumption would not affect iron absorption. Iron concentration in water or tea also had a significant effect on iron absorption. Although percent absorption was lower in the 1.0 mM Fe solution than in the 0.1 mM Fe solution, more total iron was absorbed from the larger dose. These results are consistent with previous findings by Smith and Pamracciulli (23) who found a lo-fold increase in the test dose of iron resulted in only a 4-fold increase in the quantity of iron absorbed. Tea did not affect lactulose absorption when these components were administered together. The replacement of drinking water with tea for 3 days prior to lactulose ingestion, however, appeared to reduce lactulose absorption though not significantly (p=O.O5). Welsch et al. (24) and Motilva et al. (25) showed phenolic compounds reduce glucose transport in rats in intestinal brush border membrane vesicles and in vivo, respectively. Tarmic acid, a phenolic compound similar to those found in tea, has been shown to grossly denature both the glycocalyx and brush border (26). However, Mitjavila et al. (26) employed tamiic acid at levels much higher than those contained in tea. Both Welsch et al. (24) and Motilva et al. (25) suggest a slight modification of membrane proteins as the mechanism responsible for reduced glucose transport following ingestion of phenolic compounds.
1308
P.K. SOUTH et al.
These results suggest that chronic tea consumption may reduce intestinal permeability but does not affect iron absorption as long as the tea is not consumed with an iron-containing meal. Therefore, our results support the hypothesis that tea reduces iron absorption by formation of a complex with iron. Furthermore, the mechanism by which phenolic compounds reduce iron absorption does not appear to involve changes in intestinal permeability.
1.
Hallberg L. Bioavailability
of dietary iron in man. Ann. Rev. Nutr. 198 1; 1: 123.
2.
Hallberg L, Rossander L, Skanberg AB. Phytate and the inhibitory absorption in man. Am. J. Clin. Nutr. 1987; 45:988-96.
3.
Gillooly M, Bothwell TH, Torrance JD, MacPhail AP, Derman DP, Bezwoda WR, Mills W, Charlton RW, Mayet F. The effect of organic acids, phytates and polyphenols on the absorption of iron from vegetables. Br. J. Nutr. 1983; 49:33 I-36.
4.
Disler PB, Lynch SR, Charlton RW, Torrance JD, Bothwell TH, Walker RB, Mayet F. The effect of tea on iron absorption. Gut 1975a; 16:193-200.
5.
Rossander L, Hallberg L, Bjom-Rasmussen J. Clin. Nutr. 1979; 32:2484-89.
6.
Disler PB, Lynch SR, Torrance JD, Sayers MH, Bothwell TH, Charlton RW. The mechanism of the inhibition of iron absorption by tea. S. Ah. J. Med. Sci. 1975b; 40:109-16.
7.
Menzies IS. Absorption 1974; 2: 1042-46.
8.
Sullivan PB, Lunn PG, Northrop-Clewes C, Crowe PT, March MN, Neale G. Persistent diarrhea and malnutrition: The impact of treatment on small bowel structure and permeability. J. Ped. Gast. Nutr. 1992; 14:208-15.
9.
Menzies IS, Laker MF, Pounder R, Bull J, Heyer S, Wheeler PG, Creamer B. Abnormal intestinal permeability to sugars in villous atrophy. Lancet 1979; 2: 1107-9.
10.
Pearson AD, Eastham J, Laker MF, Craft AW, Nelson R. Intestinal with Crohn’s disease and coeliac disease. Br. Med. J. 1982; 285:20-l.
11.
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Accepted
for
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June
10,
1997.