Some people may need to supplement with iron, a mineral your body needs for basic functioning. But taking certain supplements at the same time as iron can reduce absorption or cause uncomfortable side effects. Here are six supplements you should avoid mixing with iron.
Calcium and iron both get absorbed in the same part of the gut, explained Meena Malhotra, MD, a double board-certified physician in internal medicine and obesity medicine. When taken together, calcium “wins,” meaning your body will absorb less iron.
That doesn’t mean you can’t use both if needed, but it’s best to space out when you take them by at least two hours, advised Cherokee Layson-Wolf, PharmD, BCACP, FAPhA, a pharmacist and professor of practice, sciences, and health outcomes research at the University of Maryland.
Magnesium—especially magnesium oxide—uses the same gut cells as iron to move into the bloodstream, said Supti Talwalkar, PharmD, MS, a clinical ambulatory pharmacist at Baptist Health South Florida. This can reduce iron absorption and may also lead to side effects such as nausea, cramping, diarrhea, and constipation.
To avoid these problems, Layson-Wolf recommended taking magnesium in the evening and an iron supplement one hour before meals or two hours after, when absorption is most effective.
Zinc and iron are chemically similar and, like calcium and magnesium, compete for the same transport cells, Talwalkar said. But in this case, taking an iron supplement can significantly reduce zinc absorption instead of iron.
That said, if someone takes a higher dose of both at once, neither is absorbed well, added Malhotra. “To fix this, alternate them. Do iron in the morning and zinc later in the day,” she suggested.
High-fiber supplements like psyllium husk can support digestion, but they may bind minerals and move them through the gut before they are absorbed. “In the case of iron, it makes the supplement a lot less effective,” Malhotra said.
For optimal absorption, Talwalkar suggested taking iron at least one to two hours before or after a fiber supplement. Ideally, Malhotra added, it’s best to take them at opposite ends of the day.
Some herbal supplements, like green tea extract, can bind to iron and reduce absorption, Talwalkar said. “For instance, turmeric (curcumin) binds iron into a complex, reducing its absorption by 20% to 90%,” she said.
To avoid the absorption problem, Layson-Wolf recommended spacing out iron and herbal supplements by one to two hours.
Because calcium and magnesium can reduce iron absorption, it’s best not to take a multivitamin or prenatal vitamin that contains iron at the same time as a standalone iron supplement. Talk to your healthcare provider to determine whether you need an iron supplement if you’re also taking an iron-containing multivitamin or prenatal vitamin.
Some research suggests that vitamin C can boost iron absorption. Combining the two may be especially helpful for people taking antacids or medications that reduce stomach acidity, like proton pump inhibitors, Layson-Wolf noted.
However, she cautioned that consuming too much vitamin C—more than 2 grams daily—can increase the risk of iron overload in people with hemochromatosis, a condition that causes excessive iron buildup in organs. It can also raise the risk of side effects like nausea, diarrhea, bloating, cramps, and heartburn.
If your iron supplement isn’t working properly, your levels may remain low. That could show up on a blood test, or you might start noticing symptoms of anemia, such as:
- Diarrhea
- Stool discoloration
- Black, tarry, or bloody stools
- Abdominal cramps
- Staining of the mouth, teeth, or dental fillings
- Persistent iron-deficiency anemia
- Continued fatigue or low energy
Keep in mind that it can take a few weeks to months after starting an iron supplement to see improvement, Layson-Wolf said. If you’re still experiencing low energy or side effects after two months, it’s a good idea to contact your healthcare provider.
