Iron has always struck me as the nutritional equivalent of Stanley Tucci: It's frequently popping up in unexpected places, and experts say that's a good thing. One of those mysterious minerals that can be found in lentils or a steak, iron is critical to health, but to understand exactly why it's so important and whether some sources of iron are better than others, I asked nutritional specialists.
"Iron is a mineral, and what's unique about iron and makes it so beneficial to humans is that it can actually change its [chemical] state pretty easily," says Andrew Jones, an assistant professor of nutritional sciences at the University of Michigan School of Public Health. "That allows it to have a number of different roles in the body."
Iron's most conspicuous role is as a part of hemoglobin, the protein in red blood cells that transports oxygen throughout the body. Though iron is essential to anyone trying to stay alive, the amount one needs changes over the years. Children need varying levels of iron depending on age. Men ages 19 and older should get 8 mg of iron per day, while women ages 19-50 should get 18 mg daily and then 8 mg in the years after.
"It's more common for women to be low in iron," says Vandana Sheth, a spokesperson for the Academy of Nutrition and Dietetics and a nutritionist practicing in the Los Angeles area. "Our body stores iron, but some of our storage capacity goes away every month during our menstrual cycle." A pregnant woman needs even more iron — 27 mg per day — because she must share hers with a fetus. People who aren't getting enough iron may have pale skin, feel easily tired, and develop headaches.
Not all iron is the same. There are two types: heme iron and non-heme iron. Heme iron is found in meats, especially in red meat and in organ meat like liver, which stores excess iron in humans and other animals. Non-heme iron, on the other hand, is found in beans, lentils, spinach, kale and apricots, to name a few sources. The body does not absorb non-heme iron as well as heme iron, so vegetarians may need to consume as much as double the daily amount of iron as someone who eats meat.
Fortunately, according to Andrews and Sheth, most people who eat a balanced diet get enough iron without actively thinking about it. This is thanks in part to iron's Tucci-ness; it shows up in a lot of things. In addition to foods in which iron occurs naturally, grain products, like cereals and pasta, are often iron-fortified. People can also influence the amount of iron they actually absorb based on what foods they pair with iron.
For instance, "Vitamin C can help to increase the absorption of non-heme iron. So if you're eating a meal and you have some orange juice or other citrus fruits with it, that can increase the absorption," says Jones. "Animal[-based] foods themselves... independent of containing heme iron ... can help enhance absorption of non-heme iron. And we don't actually understand why this is." In other words, eating a steak not only has a lot of heme iron; it also helps to better absorb the non-heme iron in a side of beans.
Some foods, by contrast, decrease the ability to absorb iron. Because they contain compounds called polyphenols, tea and red wine can reduce iron uptake if enjoyed in the same meal as, say, an iron-rich hamburger. Polyphenols are also found in leafy greens like spinach, so although spinach is rich in iron, a spinach muncher may only have limited iron uptake. (Sorry, Popeye.) Sheth recommends pairing a salad of leafy greens with a citrus vinaigrette, to increase the iron absorbed, and Jones says cooking spinach can also help absorption.
Making sure young children get enough iron may require a little thought, according to Jones, because they eat less in general, so the foods they eat need to be especially nutrient-dense. For this reason, Jones has made the decision to feed his young children meat to ensure they get enough iron, even though he is a vegetarian himself. "I do see some young kids who don't have enough variety in their diet" and have low iron, says Sheth. "It's actually really easy to get iron from plant-based foods. ... A simple way is to make sure their cereal is fortified with iron." Sheth also recommends pairing a peanut butter and jelly sandwich on iron-laden whole wheat bread with a glass of orange juice to increase absorption.
Sheth adds that for children, it's important to remember that calcium can inhibit iron uptake. She advises against giving children a glass of milk to wash down an iron supplement.
Despite iron's importance, people shouldn't be double-fisting iron supplements, according to Jones and Sheth. Although supplements can be important for people at risk of deficiency, there is such a thing as too much iron.
"You want to have the right balance," says Jones, "and that's why through evolution, we've developed really elegant ways of regulating our amount of absorption." People who have a lot of iron in their bodies tend to absorb less iron, thanks to action by regulatory proteins, while people who have low iron tend to absorb iron more efficiently.
But humans have evolved consuming iron from food, not from pills. The body may be less well evolved to regulate absorption of a "big lump of iron coming through in a supplement," says Jones.
Sheth also advises against too much supplementary iron. "If you get more than you need, you can have GI issues," says Sheth. "Abdominal pain, constipation, nausea — some of those things."
Presumably, the same cannot be said of having too much Stanley Tucci.
Natalie Jacewicz is a science writer based in New York City. You can find more of her work here. Gnawing Questions is a semi-regular column answering the food mysteries puzzling us and our readers. Got a question you want us to explore? Let us know via our contact form.