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Dietary Iron Bioavailability Less Than Previously Thought

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Several of us CR practitioners, particularly those who eat little or not meat and therefore get most/all of their iron from plant sources, tend to have low iron levels, sometimes bordering on (or progress to) outright anemia. This new study [1], might help understand why. 


For the purposes of dietary recommendations, the USDA uses estimates of nutrient absorption, but according to this study, the estimated rate of iron absorption (based on a single human study) is too high, at 18%. The found that total iron absorption from heme and non-heme sources in the US diet to be somewhat lower - at 15% rather than 18%.


But what really caught my eye was how much lower non-heme iron absorption was - 3.5% in non-hispanic whites. That's 5x lower than the absorption rate the USDA uses in its estimates to set the RDI. 


I know there is some cushion built into the RDI numbers (which is 8mg/day of iron for adult men), but if one gets all their iron from non-heme, plant souces, it would seem like we might need to consume 5x that 8mg per day to reach the RDI. Even with my rather large calorie intake  :)xyz , I'm getting only around 30mg/day of non-heme iron from my vegan diet. So it is perhaps not surprising that I need to supplement with additional iron to avoid anemia.


Am I interpreting this study, and its implications, correctly?





[1] J Nutr. 2015 Nov;145(11):2617-21. doi: 10.3945/jn.115.210484. Epub 2015 Sep 16.

Total Iron Bioavailability from the US Diet Is Lower Than the Current Estimate.

Armah SM(1), Carriquiry AL(2), Reddy MB(3).

Author information:
(1)Department of Food Science and Human Nutrition and. (2)Department of
Statistics, Iowa State University, Ames, IA. (3)Department of Food Science and
Human Nutrition and mbreddy@iastate.edu.

BACKGROUND: Total (heme and nonheme) iron bioavailability from the US diet has
been estimated to be 18% based on a single human absorption study. New data,
however, suggest that it may be time to revisit this estimate.
OBJECTIVE: We estimated total iron bioavailability from the US diet with the use
of our recently reported algorithm that estimates nonheme iron absorption and a
conservative value for heme iron absorption.
METHODS: We used dietary intake and biomarker information from the NHANES
2001-2002, MyPyramid Equivalents Database, and Food and Nutrient Database for
Dietary Studies. The survey package in R software was used to estimate means and
CIs, taking into account the strata, primary sampling units, and appropriate
survey weight. We implemented 2 different approaches to estimate total iron
absorption. In the first approach, we included all survey participants but
adjusted the geometric mean of nonheme iron absorption to 15 μg ferritin/L serum
to mimic values of individuals with no iron stores; in the second approach,
absorption was estimated for only nonanemic subjects with no iron stores. A total
sample size of 6631 was used based on availability of dietary and iron status
biomarker data and C-reactive protein concentration ≤6 mg/L.
RESULTS: The geometric mean (95% CI) of unadjusted nonheme iron absorption for
all subjects was 3.7% (3.6%, 3.8%), higher in female subjects [5.6% (5.4%, 5.7%)]
than male subjects [2.6% (2.5%, 2.7%)] (P < 0.0001). Nonheme iron absorption was
lower in non-Hispanic whites [3.5% (3.4%, 3.6%)] than Mexican Americans [4.5%
(4.2%, 4.8%)] and non-Hispanic blacks [4.4% (4.1%, 4.7%)]. Estimated total iron
absorption was 15.5% or 15.1%, depending on which approach was used to carry out
the calculations.
CONCLUSION: This study provides useful data for evaluating the current value of
iron bioavailability from the US diet.

© 2015 American Society for Nutrition.

PMID: 26377760

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Do not forget that is non-heme iron absorption in the US diet. You do not eat the US diet. Vit C enhances absorption a lot.


Also iron deficiency anemia is no more common among vegetarians than among the general population: http://ajcn.nutrition.org/content/70/3/586s/T3.expansion.htmlfrom (http://ajcn.nutrition.org/content/70/3/586s.long)

and http://www.ncbi.nlm.nih.gov/pubmed/12460231although our iron stores are lower.

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