Warning over three supplement combinations that could be dangerous
Daily mirror October 16, 2025 05:39 PM

An expert has warned people to avoid three supplement combinations as they could prove risky. Taking these vitamins and minerals together could be doing more harm than good.

Many people take supplements to top up a healthy balanced diet. But with lots of things we consume there are potential side effects or risks when it comes to taking supplements.

Speaking to Express.co.uk, registered nutritional therapist, Jen Walpole, warned of some of the dangers. She explained: "While supplements can be a great way to bridge nutrient gaps, it's important to be aware of potential interactions.

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"Here are three examples of supplements you shouldn't take together." The three combinations include:

  • Calcium and iron
  • Vitamin C and vitamin B12
  • Zinc and copper
Calcium and iron

Jen explained that calcium can "hinder" iron absorption by creating a barrier within your digestive system, preventing proper iron uptake.

She added: "This is particularly true for non-heme iron, the kind found in plant-based foods and supplements.

"Taking calcium and iron supplements together can significantly reduce your body's ability to absorb iron.

"This can be detrimental for those with iron deficiency or at risk, like vegetarians and menstruating women."

Her advice was backed by experts at Health.com who said: "You should not take calcium and iron supplements together, as calcium can decrease iron absorption." They recommended taking iron one hour before a meal, but taking calcium after eating.

Vitamin C and B12

Excessive doses of vitamin C (exceeding 1,000mg) may interfere with a stomach protein essential for B12 absorption, according to Jen.

She explained: "While the exact mechanism isn't fully understood, it could potentially decrease B12 uptake, especially for those with borderline B12 deficiency, like vegans.

"A B12 deficiency can lead to weakness, tiredness, or lightheadedness, heart palpitations and shortness of breath."

It can also lead to:

  • Digestive issues including constipation, diarrhoea, loss of appetite, or wind
  • Nerve problems like numbness or tingling, muscle weakness, and problems walking
  • Vision loss and even mental issues like depression, memory loss, or behavioural changes

The Mayo Clinic warned: "Taking vitamin B12 with vitamin C might lower the available amount of vitamin B12 in the body."

Zinc and copper

Zinc and copper are vital minerals, but they vie for absorption within the intestines. "When you consume high amounts of zinc, it takes up the 'absorption space', leaving less room for copper to be taken up," Jen continued.

"Long-term, excessive zinc intake (through supplements or certain medications) can lead to copper deficiency.

"This can manifest as impaired wound healing, fatigue, bone weakness, and changes in hair and skin pigmentation."

Medsafe added: "Zinc may inhibit the absorption of copper, leading to reduced copper levels and potentially copper deficiency. This deficiency is due to an interaction between zinc and copper, where zinc inhibits the intestinal absorption of copper."

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