This supports the possibility that Green et al 2 may have underestimated the exchangeable iron pool size of the men in their study. Mainly because of these differences in exchangeable body iron, the present iron excretion results for men 1. The range of iron excretion results in the present study would be further narrowed to 0. Overall, these comparisons generally validate the present data, which extend human iron excretion results to include women.
The menstrual iron losses accounted for most of the variation in excretion and for the skewed distribution of iron excretion in these women. The median iron losses used to derive the estimated average requirements EAR for men, menstruating women, and postmenopausal women are 1. However, the distribution of iron losses in the present study is generally wider in both directions than the distribution based on body weight that was used to determine the RDAs for iron.
The present data indicate only a weak relation between body weight and iron excretion and do not support the use of body weight data for estimating the population distribution of iron excretion. The present data are consistent with the early observations of McCance and Widdowson 21 , 22 that body iron excretion does not contribute to the regulation of iron homeostasis. Despite this substantial range in iron excretion, homeostatic control mechanisms were effective at maintaining body iron homeostasis for most subjects, with substantially impaired iron-status indexes in only one menstruating woman as delineated above.
These considerable differences in iron excretion and resulting requirements can generally be appropriately met by physiologic control of iron absorption, provided that dietary iron is accessible and reasonably bioavailable. In previous investigations, after 10 wk of equilibration to controlled diets containing 15 mg Fe per kcal, total heme plus nonheme iron absorption varied inversely with serum ferritin from 0.
These absorption results suggest that the women and most of the men in the present study would be able to absorb sufficient iron from a high-bioavailability diet to replace their excreted iron, but that some of the men in the present study may benefit from a somewhat lower iron bioavailability diet, so as not to absorb more iron than they excrete Table 1.
This is consistent with the finding that, after 10 wk, men significantly reduced their total iron absorption from the high-bioavailability diet from 0.
This reduction, together with the tendency in the present study for the men to nonsignificantly increase their body iron in 3 y may mean that dietary recommendations for men in Western countries may best focus on preventing body iron accumulation rather than iron deficiency. Together, these data suggest that the upper ends of the distributions of both iron excretion and iron absorption by menstruating women are greater than have been used in deriving current recommendations.
The median results are generally consistent with, although slightly greater than, previous results, and body iron excretion measurements had broad ranges, with a normal distribution in men and a skewed distribution in women. The latter was determined by a skewed distribution of menstrual iron losses. The distribution of body iron excretion was not strongly related to body weight. We are grateful for the valuable assistance of the staff at the Grand Forks Human Nutrition Research Center: Emily Nielsen for human subject coordination, Aldrin Lafferty for technical assistance with chemical and radioisotopic analyses, and Sandra Gallagher for supervising clinical chemistry analyzes.
We thank Glenn Lykken for consulting on health physics and deeply appreciate the unselfish service of the study participants. None of the authors had any conflict of interest with this research. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the US Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.
Cook JD. Adaptation in iron metabolism. Am J Clin Nutr ; 51 : — 8. Google Scholar. Body iron excretion in man. Children and Women of Childbearing Age. Iron deficiency anemia: recommended guidelines for the prevention, detection, and management among U. The quantitative assessment of body iron.
Blood ; : — Menstrual blood loss—a population study. Variation at different ages and attempts to define normality. Acta Obstet Gynecol Scand ; 45 : — Sources of variation in menstrual blood loss. J Obstet Gynaecol Br Commonw ; 78 : — 9. Control of iron absorption in iron deficiency anemia by regulation of mucosal iron transport kinetics. Blood ; 80 suppl 1 a abstr. Adaptation of iron absorption in men consuming diets with high or low iron bioavailability.
Am J Clin Nutr ; 71 : 94 — Adaptation in iron absorption: iron supplementation reduces nonheme-iron but not heme-iron absorption from food.
Am J Clin Nutr ; 72 : — 9. Initial uptake and absorption of nonheme iron and absorption of heme iron in humans are unaffected by the addition of calcium as cheese to a meal with high iron bioavailability. Am J Clin Nutr ; 76 : — Hunt JR. Am J Clin Nutr ; 78 : — Hunt JR , Zeng H. Am J Clin Nutr ; 80 : — Inhibitory effects of dietary calcium on the initial uptake and subsequent retention of heme and nonheme iron in humans: comparisons using an intestinal lavage method.
Am J Clin Nutr ; 82 : — An improved method for the simultaneous determination of iron and iron in blood liquid scintillation counting. Int J Appl Radiat Isot ; 17 : — 7. Iron metabolism in man.
Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. Red cell, plasma and blood volume in healthy men measured by radiochromium Cr51 cell tagging and hematocrit: influence of age, somatotype and habits of physical activity on variance after regression of volumes to height and weight combined.
J Clin Invest ; 38 : — Red cell, plasma, and blood volume in healthy women measured by radiochromium cell-labeling and hematocrit. J Clin Invest ; 41 : — Soluble transferrin receptor sTfR concentration quantified using two sTfR kits: analytical and clinical performance characteristics. Clin Chim Acta ; : 75 — Heinrich HC. Intestinal iron absorption in man. Methods of measurement, dose-relationship, diagnostic and therapeutic applications.
In: Hallberg L , Harwerth Vanotti , eds. Google Preview. While most of the iron in the universe is iron — a stable nucleus made up of 26 protons and 30 neutrons — iron 60 Fe has 34 neutrons and it is the four extra neutrons that make the isotope unstable to radioactive decay.
While there is no primordial 60 Fe still on the Earth from when the solar system formed, a small amount has been found in the deep-sea of the ocean floor. This material most likely originates from outer space — either from meteorites where 60 Fe is produced thanks to the meteorites being constantly bombarded by cosmic radiation or from stellar nucleosynthesis events such as supernovae that occurred only a few million years ago.
To use 60 Fe as an accurate chronometer though, its half-life must be known precisely. But the two best previous measurements — made in and in — found different answers that disagreed by nearly a factor of two. Indeed, the experiment found the half-life of 60 Fe to be 1. Anton Wallner from the Australian National University, along with colleagues in Austria and Switzerland, has now confirmed the latter measurement of 2.
Scientists normally measure half-lives by using different types of spectroscopy to measure the decay rate per second in a sample containing a known number of the nuclei. For 60 Fe, they detect the gamma rays that are emitted by its daughter nucleus 60 Co, which is no mean feat. Wallner tells physicsworld. Furthermore, the team must know to great precision the initial number of 60 Fe nuclei in the sample.
Ironically, this number is directly related to the half-life value itself, making the entire measurement very tricky. The team used accelerator mass spectrometry AMS — the same method used by the experiment, but different from the experiment — to determine the tiny concentration of 60 Fe isotopes in its sample. Wallner acknowledges that AMS does have a more complex measurement set-up than IC-PMS, allowing systematic errors to creep in, but the researchers can correct for these errors confidently.
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