Just as some foods can improve iron absorption, others can hinder it.

Foods Containing Phytate

Phytate, or phytic acid, is found in foods like whole grains, cereals, soy, nuts and legumes ( 3 ).

Even a small amount of phytate can significantly decrease iron absorption ( 1 , 3 ).

In one study, as little as 2 mg of phytate in foods inhibited iron absorption by 18% when added to wheat rolls. And when 250 mg of phytate was eaten, up to 82% was not absorbed ( 4 ).

Nonetheless, the negative effect of phytate can be counteracted by consuming foods that enhance non-heme iron absorption, such as vitamin C or meat.

Calcium-Rich Foods

Calcium is an essential mineral for bone health.

However, some evidence shows that it hinders iron absorption, regardless of whether the source is a dairy product or calcium supplement ( 16 ).

Studies have shown that 165 mg of calcium from milk, cheese or a supplement reduced iron absorption by around 50–60% ( 4 , 17 ).

This is worrisome, as increased calcium intake is commonly recommended for children and women, the same populations that are at risk of iron deficiency.

However, most studies were short-term and conducted in single meals. A thorough review of long-term studies found that calcium and milk products did not have any adverse effects on absorption ( 16 ).

To maximize absorption, calcium-rich foods should not be eaten with meals that provide most of your dietary iron.

In the case of supplements, calcium and iron supplements should be taken at different times of the day, if possible.

Foods Containing Polyphenols

Polyphenols are found in various amounts in plant foods and beverages, including vegetables, fruits, some cereals and legumes, tea, coffee and wine.

Coffee and tea, both of which are widely consumed around meals, have a high content of polyphenols, and they have been shown to inhibit the absorption of non-heme iron ( 13 ).

In one review, drinking a cup of black tea with a meal reduced iron absorption by 60–70%, regardless whether the tea was weak, normal or strong.

However, when participants drank tea between meals, the reduction in absorption was only about 20% ( 4 ).

To counteract the negative effect of polyphenols, be sure to leave a couple of hours between your iron-rich meal and your afternoon tea or coffee.