Humans are prone to iron deficiency - it's the most common nutrient deficiency on the planet. But too much iron is dangerous, too.
New Cornell research shows that individuals of East Asian ancestry have greater risk of elevated iron stores than people of Northern European ancestry, putting them at higher risk of chronic conditions such as heart disease, Type 2 diabetes, liver disease and cancer.
That's why proper iron intake to both prevent deficiency and avoid toxicity is not a one-size-fits-all approach across populations, according to three new papers published in January in the American Journal of Clinical Nutrition. All three are co-authored by Kimberly O'Brien, professor of Human Nutrition in the Division of Nutritional Sciences, in the College of Human Ecology, and reflect the doctoral research of Alexa Barad, Ph.D. '24, who is now a postdoctoral scholar at Stanford
The authors suggest that continued discovery of genetic influences on nutritional requirements might lead to more specific recommendations for population subgroups.
"There's a lot of focus on preventing anemia. But at the other extreme of this, if you don't limit how much iron you're absorbing, it starts to collect in the liver, heart and pancreas," O'Brien said. "Humans have evolved this interesting way of regulating iron. Our bodies have to tightly control how much iron we absorb from our diet, because once it's in you, you can't excrete it, so we don't want to let too much in."
We get iron from the food we eat in two forms, O'Brien said - heme (from animal products) and non-heme (primarily from plant-based foods). Heme is much more easily absorbed and thought to contribute the most to iron stores in the body. The researchers specifically looked at non-heme iron to see how some populations stockpile it.
Iron stores that exceed physiological needs can result in increased risk of chronic conditions.
"This is a precision nutrition issue," O'Brien said. "We need to move away from saying there is one dietary guideline for everyone. In this case, if you are East Asian you may have an increased risk of over-accumulating iron."
Most studies working to identify genes that influence nutrient requirements have been undertaken in subjects of European ancestry. Underrepresented groups were seldom the subject of scrutiny, which may have skewed the recommendations for nutrient intakes for some individuals and groups.
Comparing East Asians to Northern Europeans, the researchers found no significant differences in diet that would explain a marked difference, with the problem more significant in men than women (women who menstruate eliminate blood, which can mitigate the toxicity). O'Brien calls it "a silent problem." In healthy young men there are no symptoms; consequences start to manifest after age 50.
"In our study population, Northern Europeans drank slightly more alcohol, East Asians ate slightly more protein," O'Brien said, "but nothing that would explain what we were seeing."
The majority of iron is incorporated in red blood cells. In this research study, all participants ingested a stable iron isotope. Two weeks later, a blood sample was collected to see how much of the isotope was absorbed and incorporated into the subjects' red blood cells. The blood samples were also used to isolate DNA to see if they can identify genes linked to iron absorption and if these relationships differ between the East Asian and Northern European participants.
"We hypothesize that the reason why East Asians have this enhanced ability to store iron is that they evolved on a plant-based, low-iron diet," O'Brien said. "But now we have (fast food) on every corner. Since a study first found Asian individuals to have elevated body iron stores 20 years ago, no one has explored how and why this is occurring."
The papers, "Characterization of Iron Status Biomarkers and hematological indices among young adults of East Asian or Northern European ancestry from FeGenes: A cross-sectional study," "A Cross-sectional Comparison of Iron Regulatory Hormones and Their Associations With Iron Status Biomarkers Among Healthy Adults of East Asian or Northern European Ancestry From the FeGenes Study," and "Differences in Nonheme Iron Absorption Between Healthy Adults of East Asian or Northern European Ancestry from FeGenes: A Cross-sectional Stable Iron Isotope Study," were all supported by grants from the National Institutes of Health / National Institute of Diabetes and Digestive and Kidney Health.
