Iron and your medicines: the same absorption trap as calcium
Iron — in food, and far more so in a supplement — binds the same drugs calcium does, and stops them being absorbed: levothyroxine, tetracyclines, fluoroquinolones. It also cuts both ways: those same medicines, and the coffee or tea people take them with, reduce how much iron you absorb from a meal. Every number below is one ordinary serving, from USDA FoodData Central.
The part people get wrong
Food iron is rarely the problem; an iron TABLET taken alongside your other pills is. Keep iron supplements a few hours away from levothyroxine and from tetracycline or fluoroquinolone antibiotics. And if you are taking iron for anaemia, the tea or coffee you swallow it with is working against you — vitamin C helps, tannins hurt.
Iron in common foods — per serving, not per 100 g
Values from USDA FoodData Central for the serving shown. These are foods people actually eat: ranking the whole USDA database by density would put dried thyme and defatted soy flour at the top, which is accurate and no use to anyone.
| Food | Serving | Iron (mg) |
|---|---|---|
| Beanswhite, mature seeds | 1 cup (262 g) | 7.8 |
| Lentilsmature seeds, cooked | 1 cup (198 g) | 6.6 |
| Spinachcooked, boiled | 1 cup (180 g) | 6.4 |
| Chickpeas (garbanzo beansbengal gram), mature seeds | 1 cup (164 g) | 4.7 |
| Tofuraw, firm | 0.5 cup (126 g) | 3.4 |
| Peasgreen, cooked | 1 cup (160 g) | 2.5 |
| Beefground, 85% lean meat / 15% fat | 3 oz (85 g) | 2.3 |
| Ricewhite, long-grain | 1 cup (158 g) | 1.9 |
| Eggwhole, cooked | 1 cup, chopped (136 g) | 1.6 |
| Potatoesbaked, flesh and skin | 1 potato small (1-3/4" to 2-1/2" dia) (138 g) | 1.5 |
| Chickenbroilers or fryers, breast | 0.5 breast, bone removed (145 g) | 1.1 |
| Broccolicooked, boiled | 1 stalk, small (5" long) (140 g) | 0.9 |
Frequently asked questions
- Which foods are highest in iron?
- Per serving, the highest on this list is beans — 7.8 mg in 1 cup (262 g), per USDA FoodData Central. These are common foods rather than the absolute maximum in the USDA database: ranking every food by iron density puts dried herbs and defatted soy flour at the top, which is true and useless to someone deciding what to have for dinner.
- Do I need to avoid iron if I take these medicines?
- Food iron is rarely the problem; an iron TABLET taken alongside your other pills is. Keep iron supplements a few hours away from levothyroxine and from tetracycline or fluoroquinolone antibiotics. And if you are taking iron for anaemia, the tea or coffee you swallow it with is working against you — vitamin C helps, tannins hurt.
- Where do these numbers come from?
- USDA FoodData Central (SR Legacy), for the household serving shown next to each food — not per 100 g. Per-100-g figures are what most "foods high in iron" lists use, and they are misleading: nobody eats 100 g of dried thyme.
Sources
- Iron — NIH Office of Dietary Supplements, Health Professional Fact Sheet ↗
- Levothyroxine Sodium tablet — FDA label, Drug Interactions (DailyMed) ↗
- USDA FoodData Central, SR Legacy ↗
Nutrient values are USDA reference data for the serving shown and vary with variety, growing conditions and cooking. This page is general information, not medical advice — never change your diet or your dose on the strength of a web page. Talk to whoever manages your treatment.