Supplement interaction
These two supplements may interact. Here's what you need to know before taking them together.
Calcium is one of the strongest inhibitors of iron absorption. Taking 300mg+ of calcium with iron can reduce iron absorption by 50-60%. This is especially significant if you're taking iron for deficiency.
Never take Calcium and Iron at the same meal. Take Iron in the morning on an empty stomach (or with Vitamin C to boost absorption). Take Calcium at a completely different meal, ideally evening.
Quick facts
Calcium's inhibition of iron absorption is one of the most well-documented supplement interactions. Even 300mg of calcium — the amount in a single glass of milk — can reduce non-heme iron absorption by 50-60%.
This interaction affects both supplemental iron and dietary iron. If you're taking iron for anemia or deficiency, calcium co-administration can significantly undermine your treatment. The inhibition appears to occur at the intestinal mucosal transfer step, not at the initial uptake.
Take Iron first thing in the morning on an empty stomach if tolerable — this maximizes absorption. Pair it with Vitamin C (even just a glass of orange juice) to further enhance absorption. Avoid any calcium-containing foods or supplements within 2 hours of your iron dose.
Take Calcium at lunch or dinner, or before bed. If you take iron with breakfast, take calcium no earlier than lunch.
Can I take Calcium and Iron together?
You should not take them at the same time. Calcium dramatically reduces iron absorption. Take iron in the morning and calcium at a completely different meal, separated by at least 4 hours.
What happens if I take Calcium and Iron at the same time?
Calcium reduces iron absorption by 50-60%. This is a well-established interaction that can significantly impact iron levels, especially if you're treating a deficiency.
How far apart should I take Calcium and Iron?
At least 4-6 hours. The most effective approach: iron in the morning on an empty stomach with Vitamin C, calcium in the evening.
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