Millions of people—especially elderly women—take calcium supplements daily to protect their bones. But few realise that this well-intentioned habit can quietly trigger another serious problem: iron deficiency anaemia.

It is a hidden paradox. Calcium is essential for bone strength, while iron keeps our blood healthy and oxygen flowing. Yet, when taken together, calcium and iron compete for absorption in the same part of the small intestine. And in this silent contest, calcium often wins—reducing iron absorption from your meal by more than half.

How it happens: Calcium carbonate can unintentionally interfere with the body’s natural processing of another vital nutrient—iron. Both calcium and dietary iron (especially non-heme iron from plant foods) are absorbed in the same section of the small intestine. When taken together, calcium wins the battle, cutting iron absorption from around 10.2% to just 4.8% in a single meal.

A real-life scenario: Imagine you have just enjoyed a fresh salad bowl rich in green leafy vegetables or a beetroot smoothie to boost your iron. Immediately after, you take your daily calcium supplement. Inside your body, a silent tug-of-war begins—one that leaves your iron intake defeated. Over time, this can lead to chronic anaemia, fatigue, and weakness.

What can we do? The solution starts with awareness.

• Do not take calcium supplements with iron-rich meals.

• Keep a 2–3 hour gap between calcium and iron intake.

• Follow your doctor’s or nutritionist’s timing instructions closely.

This small change can make a big difference to your nutrient status—and ultimately, your health.

The writer is a nutritionist and humanitarian aid worker. Email: [email protected]