James D Cook dinner, Manju B Reddy, Impact of ascorbic acid consumption on nonheme-iron absorption from a whole food plan, The American Journal of Scientific Vitamin, Quantity 73, Situation 1, January 2001, Pages 93–98, https://doi.org/10.1093/ajcn/73.1.93
ABSTRACT
INTRODUCTION
Vitamin C is the one dietary constituent aside from animal tissue that has been proven repeatedly to reinforce the absorption of nonheme iron in people (1–5). The stimulating affect of ascorbic acid has been proven when ascorbic acid is given with inorganic iron alone and is much more pronounced when it’s taken with meals (6, 7). The facilitating impact of vitamin C is dose associated. In a single research during which rising quantities of ascorbic acid starting from 25 to 1000 mg have been added to a liquid components meal containing 4.1 mg nonheme iron, iron absorption elevated progressively from 0.8% to 7.1% (3).
In distinction with the hanging impact of ascorbic acid on iron absorption, the advance in iron standing when the food plan is supplemented with vitamin C has been minimal. In a single research, the addition of 2000 mg vitamin C/d to the food plan for ≤2 y didn’t alter iron shops considerably as measured by serum ferritin concentrations (8). Repeat iron absorption research after 16 wk of supplementation confirmed that the shortage of impact on iron standing was not defined by adaptation of the gastrointestinal tract to a excessive consumption of vitamin C. In one other research, 100 mg ascorbic acid given 3 instances each day with meals to menstruating girls for 9 mo had no vital impact on iron standing (9). Equally, 25 wholesome girls aged 20–45 y with low iron shops as outlined by a serum ferritin focus <20 μg/L got 500 mg ascorbic acid 3 instances each day with meals for 10 wk. There was no vital alteration in biochemical indexes of iron standing in these girls, even in these consuming a food plan low in bioavailable iron (10). The reason for the disparity between the pronounced impact of ascorbic acid on iron absorption and its meager affect on iron standing after extended supplementation will not be obvious. One chance pertains to the tactic used to measure the absorption of nonheme dietary iron. The standard approach has been to manage single meals tagged extrinsically with radioactive iron to fasting topics. Nonetheless, this strategy exaggerates the impact of dietary composition on iron absorption. For instance, when iron absorption from a whole food plan was measured over a number of days by having topics eat a labeled bread roll with every meal of the day, the extremes in imply iron absorption between diets differing maximally in iron bioavailability ranged from solely 3.2% to eight.0% in contrast with a considerably wider vary of two.3–13.5% when iron absorption was measured with single meals (11). The outcomes of a number of different investigations utilizing this methodology of whole dietary labeling verify the diminished affect of varied dietary determinants of iron absorption when examined within the context of a whole food plan (12–15). The current investigation was undertaken to reexamine the significance of dietary ascorbic acid in iron steadiness by measuring nonheme-iron absorption from a whole food plan earlier than and after altering the food plan to maximally enhance or lower the consumption of dietary ascorbic acid.
SUBJECTS AND METHODS
Topics
We carried out 4 separate measurements of iron absorption in 10 girls and a pair of males. The themes’ ages averaged 25 y with a variety of 20–38 y. All topics have been interviewed extensively earlier than they have been enrolled within the research to ascertain their willingness and functionality to take care of detailed and correct dietary information whereas consuming the labeled diets. The individuals have been proven an educational video on strategies for assessing portion sizes and sustaining dietary information. All topics acknowledged that they have been in good well being, have been taking no iron drugs, and had no historical past of current infections or problems identified to affect iron absorption. Using mineral or vitamin dietary supplements was not allowed in the course of the investigation. Iron standing, on the premise of a serum ferritin focus of >12 μg/L, was regular in all however one topic and not one of the individuals have been anemic. Written, knowledgeable consent was obtained from all topics earlier than the investigation. The experimental protocol was accredited by the Human Topics Committee on the College of Kansas Medical Middle.
Research design
4 separate iron absorption checks have been carried out in every topic by utilizing twin radioactive iron labels sequentially. One of many preliminary pair of absorption checks included a normal hamburger meal that was utilized in prior research in our laboratory (11). Iron absorption from this meal was used as a reference to facilitate comparisons with printed research of iron absorption. Expression of iron absorption from the entire food plan as a share of the iron absorption from the usual meal in every topic minimized the impact of variations in iron standing on iron absorption.
For the three remaining iron absorption checks, the entire food plan was tagged by having the topics eat radioactive bread rolls with every of the three fundamental meals of the day for five d. Snacks between meals weren’t allowed. The themes have been instructed to take care of detailed each day information of all meals gadgets consumed in the course of the 5-d labeling interval. Throughout the preliminary interval of dietary tagging, termed the self-selected (SS) food plan, the individuals have been allowed to eat their common diets with out restrictions on composition. For the remaining 2 dietary durations, the topics have been required to change their typical diets to maximally enhance (HC food plan) or lower (LC food plan) their dietary consumption of vitamin C. This was achieved by offering a listing of vitamin C–wealthy meals to both embody or exclude when the topics consumed the HC and LC diets, respectively. The quantity of ascorbic acid in every meals was offered as factors, with 1 level corresponding to fifteen mg ascorbic acid. Topics have been requested to eat 12–13 factors in the course of the HC dietary interval and ≤2 factors in the course of the LC dietary interval. One-half of the topics have been assigned randomly to the HC food plan because the preliminary absorption check and the rest to the LC food plan.
The dietary information have been analyzed for dietary content material by utilizing the NUTRITIONIST IV program (N-squared Computing; First Information Financial institution Division, Hearst Company, San Bruno, CA). Tea consumption was estimated based mostly on black tea equivalents as follows: 2 cups (480 mL) of iced tea and 1.5 cups (360 mL) of natural tea or espresso have been coded as 1 cup (240 mL) of black tea (16). Animal tissue content material was estimated by figuring out the consumption of beef, pork, fish, poultry, and seafood with every meal. Heme iron was calculated on the belief that 40% of the iron in animal tissue is heme iron (17). Nonheme iron was calculated because the distinction between whole and heme-iron consumption.
Iron absorption checks
Two days earlier than the preliminary absorption check, 30 mL blood was drawn from every topic for measurement of background 59Fe and 55Fe in blood, serum ferritin focus (18), and packed cell quantity. Extra blood was obtained for these measurements at first of the fifth week and a remaining pattern 2 wk after the final absorption check.
For the preliminary absorption check, iron absorption was measured from the SS food plan by utilizing wheat rolls labeled with 55FeCl3. The themes reported to the laboratory every weekday morning, at which period their dietary information for yesterday have been reviewed intimately. The themes have been then given bread rolls labeled with 55Fe to be consumed with every meal of the day. The 15 wheat rolls used for every dietary labeling interval have been tagged extrinsically by mixing 0.1 mg Fe as FeCl3 with both 59FeCl3 or 55FeCl3 (Du Pont, Wilmington, DE) with the dough earlier than baking (19). Every roll weighed 12–13 g and contained 1/15 of the overall quantity of administered radioactivity for every check. The latter was 37 kBq for 59Fe and 74 kBq for 55Fe.
The next week, absorption was measured from the usual meal that was consumed 2 successive mornings to reduce day-to-day variations in iron absorption. These meals have been eaten between 0700 and 1000 by topics who had fasted for ≥10 h. The usual meal contained 113 g floor beef, 53 g bun, 68 g French fries, and 148 g milk shake. The full iron content material was 4.8 mg Fe. Every meal was tagged extrinsically by pipetting 1 mL 0.01 mol HCl/L containing 0.1 mg Fe and 18.5 kBq 59FeCl3 onto the hamburger bun. Two weeks later, 30 mL blood was drawn from every topic to measure 59Fe and 55Fe in blood.
Throughout the fifth week of the research, the HC or LC food plan was tagged for five d in line with the identical protocol used for the SS food plan. The alternate food plan was tagged the next week. Bread rolls labeled with 55Fe have been used for the primary dietary interval (LC or HC) and bread rolls labeled with 59Fe for the second. As with the SS food plan, dietary information have been reviewed each day with every topic. Two weeks after the ultimate dietary labeling interval, 30 mL blood was drawn to measure the rise in 55Fe and 59Fe in blood.
Radioactivity was measured in duplicate 10-mL blood samples by a modification of the tactic of Eakins and Brown (20). Proportion absorption was calculated based mostly on the overall blood quantity estimated from the peak and weight of every topic (21, 22). The pink cell incorporation of absorbed radioactivity was assumed to be 80% in all topics (23).
Statistical evaluation
The imply each day intakes of vitamins with the SS, LC, and HC diets have been in contrast by utilizing evaluation of variance (ANOVA) adopted by Duncan’s new multiple-range check. Iron absorption percentages have been remodeled to logarithms for statistical comparisons and the outcomes recovered as antilogarithms (24). Two-way ANOVA was used to check the impact of the order during which the HC and LC diets have been consumed. Pupil’s t checks have been used to check the absorption ratios between any 2 dietary durations by figuring out whether or not the imply log absorption ratio differed considerably from zero. The research design had an 80% probability of detecting a 50% shift within the ratio with a significance stage of 0.05. Pearson’s correlation coefficients between nutrient consumption and log absorption information have been calculated. A number of regression evaluation with stepwise choice was used to check the mixed affect of dietary elements on absorption. When the outcomes of all 3 dietary durations have been pooled, the variation inside topics was eliminated by forcing the topics to be a part of the regression mannequin together with the dietary variables. The impact was to eradicate the correlation between observations on the identical topic. All statistical analyses have been carried out by utilizing the SAS program (SAS Institute, Inc, Cary, NC).
RESULTS
The each day nutrient intakes in the course of the 3 labeling durations are listed in Desk 1. Power, carbohydrate, protein, and fats intakes didn’t differ considerably among the many 3 dietary durations. The imply each day consumption of heme iron was not considerably totally different among the many dietary durations however nonheme and whole iron intakes differed as decided by one-way ANOVA. This mirrored totally different intakes with the SS and HC food plan of 11.4 and 16.6 mg for nonheme iron and of 12.1 and 17.6 mg for whole iron. These variations have been associated partially to the next imply power consumption with the HC food plan as a result of the distinction in whole iron consumption was now not vital when iron consumption was expressed as a share of power consumption.
By design, there was a extremely vital distinction within the imply each day consumption of ascorbic acid among the many 3 dietary durations. The imply consumption of 90 mg/d for the SS food plan was practically similar to the median worth of 87 mg/d reported for girls aged 20–29 y within the third Nationwide Well being and Vitamin Examination Survey (25). The imply vitamin C consumption elevated to 247 mg/d with the HC food plan and fell to 51 mg/d with the LC food plan, leading to a 5-fold distinction in ascorbic acid consumption between these 2 dietary durations.
Variations within the imply absorption of dietary nonheme iron among the many 3 dietary durations have been modest (Desk 2). For the SS food plan, share absorption averaged 4.57% with a variety of 1.18–24.27%. When vitamin C consumption was elevated in the course of the HC food plan, imply absorption elevated to 7.69%, though the imply absorption ratio for the HC to SS food plan of 1.67 (±1 SE: 1.25, 2.24) was not vital. In contrast with the HC food plan, there was a modest discount in iron absorption with the LC food plan to a imply of 5.69%, which was greater than that noticed with the SS food plan. The variations in imply absorption for the three dietary durations have been small in relation to the attribute broad variation in absorption between topics (Determine 1).
The order during which absorption from the HC and LC food plan was measured didn’t have an effect on imply absorption considerably as decided by two-way ANOVA. Imply absorption from the HC averaged 6.1% when measured in the course of the fifth week with 55Fe and 9.68% when measured in the course of the sixth week with 59Fe. Corresponding imply absorption values of 5.81% and 5.58% have been obtained with the LC food plan. The imply absorption ratios for the three dietary durations relative to the imply of 8.00% for the usual meal have been 0.57 (±1 SE: 0.45, 0.72) for the SS food plan, 0.96 (±1 SE: 0.78, 1.18) for the HC food plan, and 0.71 (±1 SE: 0.57, 0.89) for the LC food plan.
It was of curiosity to evaluate the relation between iron absorption from a whole food plan and the food plan’s nutrient composition. When the imply ascorbic acid intakes for the three dietary durations have been in contrast with iron absorption in every topic, no relation was obvious (Determine 2). To attenuate the impact on absorption of variations in iron standing, iron absorption in subsequent analyses was adjusted to a serum ferritin focus of 30 μg/L as described beforehand (11, 26). With this adjustment, iron absorption was decreased if the serum ferritin focus was <30 μg/L and increased if >30 μg/L. When iron absorption from the SS food plan was evaluated, not one of the correlation coefficients between iron absorption and the nutrient intakes listed in Desk 1 have been statistically vital. When all 3 dietary durations have been included, solely phosphorus was considerably correlated with iron absorption (r = −0.45, P < 0.001). The relation between the nutrient composition of the food plan and iron absorption was additional examined by utilizing a number of regression. With use of log absorption values adjusted to a serum ferritin focus of 30 μg/L because the dependent variable, the relation with the consumption of vitamins that have been reported to affect the absorption of nonheme iron (phosphorus, ascorbic acid, fiber, calcium, tea, animal tissue, and heme and nonheme iron) was examined. Analysis of the SS food plan alone didn't establish any vital dietary determinants of iron absorption. We then examined the relation between dietary elements and iron absorption in all 3 dietary durations. The outcomes indicated that the overall variation in absorption was 85%, of which 54% was as a result of topic variability and 31% was as a result of dietary elements (Desk 3). The strongest affiliation was with phosphorus (19%), adopted by ascorbic acid (8%) and animal tissue (4%).
DISCUSSION – “vitamin c enhances the absorption of”
The current investigation was undertaken to find out whether or not the impact of vitamin C on iron absorption has been exaggerated by measuring absorption from single meals fairly than from a whole food plan. As in different iron absorption measurements from a whole food plan, the impact on iron absorption of identified dietary determinants reminiscent of vitamin C was a lot lower than reported with single-meal measurements. We discovered a 5-fold distinction in imply dietary vitamin C consumption between the LC and HC diets: 51 in contrast with 247 mg/d. In a earlier iron absorption research during which a meatless meal was fed to fasting topics, a 100% enhance in iron absorption was noticed when the vitamin C content material was elevated from 50 to 250 mg (3). This enhance was far better than the modest 35% greater absorption from the HC food plan than from the LC food plan within the current research. Even at these extremes in dietary vitamin C, the variations in imply iron absorption from a whole food plan have been small relative to the variations in absorption between topics (Determine 1).
A number of regression evaluation confirmed that phosphorus had a major inhibitory affect, an impact that was stronger than the enhancing impact of both ascorbic acid or animal tissue. The character of the inhibitory impact of dietary phosphorus on iron absorption is unclear. One chance is that this inhibitory impact displays the content material of dietary phytate, which accounts for the potent inhibitory impact of wheat bran (27, 28) and soy protein (29–32) on iron absorption. Research with varied isolates of soy protein confirmed that even comparatively small quantities of residual phytate can strongly inhibit iron absorption (33). In a current investigation, nonheme-iron absorption from 25 advanced meals correlated extremely with phytic acid content material (26). Nonetheless, word that phosphate per se additionally has a strongly inhibitory impact on iron absorption (34, 35). The unfavorable impact of phosphorus might replicate dietary sources aside from phytate, reminiscent of meat and dairy merchandise, or might even be a spurious results of testing a number of dietary variables.
Vitamin C accounted for under 8% of the variation in iron absorption as in contrast with 19% for phosphorus (Desk 3). This comparatively small affect is stunning in view of the wide selection of vitamin C intakes examined; the common vitamin intakes in the course of the LC and HC dietary durations have been much like the imply dietary intakes of 45 and 203 mg/d reported for the tenth and ninetieth percentiles, respectively, in middle-aged girls (36). The fairly restricted impact of vitamin C agrees with the observations by Hunt et al (10), who measured iron absorption from a whole food plan by utilizing the fecal steadiness methodology. These investigators have been unable to detect a major enhance in absorption when 1500 mg vitamin C/d was added to both a food plan low in bioavailable iron or to a typical Western food plan in girls with low iron shops. Taken collectively, the outcomes of the research by Hunt et al and the current findings point out that the affect of ascorbic acid on iron absorption from a whole food plan is lower than generally assumed.
Another strategy to evaluating the affect of ascorbic acid consumption on iron steadiness is to look at the relation in a inhabitants between the consumption of dietary elements identified to affect iron absorption and iron standing. In a current epidemiologic investigation together with 634 aged people aged 67–93 y, iron shops as measured by serum ferritin have been in contrast with dietary consumption in the course of the earlier yr as assessed by a food-frequency questionnaire (37). People with a pathologic elevation in serum ferritin have been excluded and a number of regression evaluation was used to regulate for intercourse, age, physique mass index, whole power consumption, smoking, and the usage of drugs identified to have an effect on blood loss. A big optimistic affiliation was noticed between iron shops and dietary consumption of vitamin C (P = 0.04), heme iron (P = 0.0001), supplemental iron (P = 0.0001), and alcohol; espresso had a unfavorable affiliation. It’s of curiosity {that a} vital affiliation was noticed solely with dietary vitamin C, which averaged 153 ± 79 mg/d, however not with supplemental vitamin C, which offered an extra 98 mg/d. Though the energy of the relation between iron standing and the dietary consumption of vitamin C was modest, most epidemiologic research have failed to point out an affiliation between ascorbic acid consumption and iron standing.
The impact of phosphorus, ascorbic acid, and animal tissue on iron absorption noticed within the current research agrees remarkably properly with a not too long ago printed mannequin for predicting meals iron absorption in people from the biochemical composition of the meal (26). On this research, animal tissue, phytic acid, and ascorbic acid have been considerably associated to iron absorption, suggesting that phytic acid accounts for the impact of dietary phosphorus noticed within the current report. Moreover, within the earlier research, the affect of each animal tissue and phytic acid (P = 0.0001) was better than that of ascorbic acid (P = 0.0441), whereas animal tissue gave the impression to be much less essential than ascorbic acid within the current investigation. Nonetheless, the identification of comparable dietary elements within the 2 experiences underscores their significance as dietary determinants of nonheme-iron absorption in people.
The explanations for the diminished affect of dietary elements when iron absorption is measured from a whole food plan fairly than from particular person meals are unknown. One chance is that residual gastric contents from meals eaten all through the day dampen the affect of dietary elements in contrast with that in fasting topics. One other is that the vary of meals consumed over a 5-d interval is way better than with an remoted meal and consequently the biochemical composition of the overall food plan is extra diversified. The unfavorable affect of phosphorus consumption on dietary absorption proven on this research helps the concept the facilitating impact of ascorbic acid on iron absorption from a whole food plan is not less than partly offset by dietary inhibitors. For no matter purpose, the affect of dietary ascorbic acid on iron absorption is considerably lower than indicated by absorption research with single meals. There’s a want for added info on the exact position of dietary vitamin C in iron vitamin.
REFERENCES
FOOTNOTES