Is cast iron cookware good for you, and does it add iron to food?

Where the iron comes from. Iron dissolves from the pan into food, and acid speeds it up. In Malawian kitchens, food cooked in an iron pot carried more iron than the same food cooked in glass: about 3 micrograms more per gram of nsima (a maize porridge), 36 more in relish vegetables and 147 more in beans. The more acidic the food, the more iron it picked up, and added oil cut the pick-up in stir-fried vegetables¹. Seasoning matters here. It is oil baked onto the surface until it hardens, and in a Korean lab test, oiling cast iron cut release of arsenic, cadmium, chromium and nickel into acidic liquid by 66, 83, 71 and 15 percent⁶.

How much you absorb. Iron in the pot is not the same as iron in your blood. In an Ethiopian laboratory comparison, foods cooked in iron pots had more total and more available iron, except legumes, where available iron did not differ by pot type³. Your own iron status then decides what is absorbed, and it matters more than what is on the plate. Because the body has no way to excrete iron, absorption is its only control⁷.

Who it may help. A 2019 systematic review of 11 studies in low- and middle-income countries found significant gains in hemoglobin or iron markers in 4 of 8 pot studies, and daily use of the pots ranged from about 27 to 71 percent². Results were positive more often in children (4 of 8 studies) than in women of reproductive age (2 of 7)². These trials enrolled anemic or at-risk children and women, so they say little about people with normal iron. See Iron basics and anemia.

Who should skip it. Hemochromatosis, a genetic condition in which the body absorbs too much iron, is one of the most common genetic disorders in people of northern European descent, and its main treatment is regular blood removal⁵. In parts of sub-Saharan Africa, large volumes of home-brewed beer made in iron pots or drums have caused dietary iron overload and liver scarring⁸. That is an extreme exposure, not a skillet dinner, but it shows that iron from metal vessels can build up.

Other pans. We found no human study of seasoning oils, so the choice of oil is cooking practice, not evidence. Enameled iron cookware, which is iron covered in glass, released almost no iron and very little of 14 other elements in a lab test in Japan, so it is a non-reactive option for long tomato simmers⁹. See Safer Cookware Alternatives.

Randomized trials of iron pots. Adish and colleagues assigned 407 Ethiopian children, one per household, to iron or aluminum pots for 12 months. Hemoglobin rose 1.7 g/dL with iron pots and 0.4 g/dL with aluminum, a difference of 1.3 g/dL (95% CI 1.1 to 1.6), and the iron-pot group gained about 0.6 cm more in length (95% CI 0.1 to 1.0)³. In rural Malawi, 164 people ate from aluminum pots and 158 from iron pots for 6 weeks in an area with heavy malaria. Among adults who used the pot consistently, hemoglobin rose 3.6 g/L in the iron group and fell 3.2 g/L in the aluminum group (difference 6.8 g/L, 95% CI 0.86 to 12.74). Children had less iron deficiency but no significant hemoglobin change, possibly because of malaria¹⁰.

Trials that found nothing. In Benin, 161 households (339 people) were randomly given cast-iron pots, blue-steel pots or iron supplements for 6 months. Hemoglobin did not differ between groups, ferritin was higher with supplements, and the authors concluded there was no evidence that iron pots work against iron-deficiency anemia⁴. In Cambodia, 340 anemic women were randomized to a fish-shaped iron ingot for the cooking pot, 18 mg a day of iron, or no treatment. After 12 months hemoglobin was 115 g/L in all three groups. Only 9 percent had a low ferritin at the start, and the authors note that inherited hemoglobin disorders are common there, so most of the anemia may not have been iron deficiency¹¹.

Putting them together. In the 2019 review, hemoglobin or iron markers improved significantly in 4 of 8 pot studies (hemoglobin change ranging from a 0.4 g/dL fall to a 1.20 g/dL rise) and 1 of 3 ingot studies (0.32 to 1.18 g/dL). The authors called iron cookware promising with reasonable use, especially in children, and asked for more work on both efficacy and safety². The weaknesses are plain: participants cannot be blinded to which pot they get, and malaria and diet differ from high-income settings.

Metal release. The Korean study that showed the oiling effect also measured arsenic, cadmium, chromium, nickel and lead release from stainless steel, aluminum, copper-alloy and cast iron utensils. Release depended strongly on acidity and generally fell with repeated use. Chromium and nickel from stainless steel were significantly higher in the first test than in the third. The authors' margin-of-exposure calculation judged it improbable that current exposure from metal kitchen utensils poses a health risk in Korea. That is a lab estimate using food-simulating liquids, not a measurement in people⁶.

Too much iron. The American College of Gastroenterology guideline describes hereditary hemochromatosis as one of the most common genetic disorders in people of northern European descent, with phlebotomy as the mainstay of treatment⁵. Dietary iron overload from iron-brewed beer in sub-Saharan Africa has been linked to liver fibrosis, cirrhosis and, in case-control studies, a higher risk of liver cancer⁸. We found no study of everyday cast-iron cooking in people with hemochromatosis, so the caution rests on how iron is regulated, not on direct evidence⁷.

What is missing. No trial has tested cast iron in people with normal iron stores, compared seasoning methods or oils, or followed iron stores in adults who cook in cast iron every day. Iron deficiency itself is a leading contributor to the global burden of disease and should be investigated, not just topped up¹².

Bottom line (moderate confidence). Food cooked in iron does pick up measurable iron, especially when acidic. Trials in deficient populations show a gain in some settings and none in others, so cast iron is a modest extra and not a treatment. For most people with normal iron it is probably harmless, and with iron overload it is best avoided.

Swaps, ranked by evidence

1. Iron pot instead of aluminum or nonstick, if you are iron deficient (best evidence, still mixed). Two randomized trials and a systematic review support a gain in hemoglobin, especially in children^3,10,2. Two other trials found none^4,11.
2. Keep cast iron seasoned (lab evidence). Oiling cut metal release into acidic liquids, and added oil lowered iron pick-up in vegetables^6,1.
3. Enameled iron or glass for iron overload, or for acidic simmering (lab evidence). Enameled cookware released almost no iron, and glass was the low-iron comparison in the Malawian tests^9,1.
4. Choice of seasoning oil (no evidence). Pick what you like to cook with.