Iron supplements are commonly taken to support energy levels, iron deficiency, and overall wellbeing. But what many people don’t realise is that when you take iron can be just as important as what you take it with.

With so many supplements now part of daily routines, it’s easy to take everything at once. However, certain supplements can interfere with how well iron is absorbed, meaning your body may not be getting the full benefit.

So, let’s take a look at seven supplements that are best not taken alongside iron, what happens when they’re taken together, and how a few small timing changes can make a big difference.

Why some supplements interfere with iron absorption

Iron is absorbed in the gut, and like many nutrients, it relies on specific pathways to enter the body. When certain supplements are taken at the same time, they can compete with iron or reduce how much of it your body is able to absorb.

Some minerals, such as calcium, magnesium, and zinc, use similar absorption pathways to iron. When they’re taken together, they can compete for space, meaning less iron may be absorbed.

Other supplements, like fibre or certain herbal compounds, can bind to iron or speed up digestion. This can reduce the amount of time iron has to be absorbed in the gut, lowering its effectiveness.

This doesn’t mean these supplements are bad or shouldn’t be taken. It simply means that timing matters. By spacing iron away from certain supplements, you can help your body absorb iron more efficiently and get the most benefit from your routine.

Common supplements not to take together with iron

If you take iron as part of your daily routine, it’s best to space it away from the following supplements to support better absorption as mentioned above. This doesn’t mean avoiding them altogether — just taking them at a different time of day.

1. Calcium supplements

How it interferes with iron absorption:

Calcium directly competes with iron in the gut. It can block iron from being absorbed by the intestinal cells, even when iron is taken in an easily absorbed form. This effect can happen whether calcium comes from a supplement or a fortified product.

2. Magnesium supplements

How it interferes with iron absorption:

Magnesium and iron are both minerals that rely on similar transport systems in the digestive tract. When taken at the same time, magnesium can compete with iron for absorption, particularly at higher doses.

Does the type of magnesium matter?

All magnesium forms can potentially interfere with iron absorption, but some are more likely to than others.

This is because:

All magnesium is a divalent mineral (like iron)
They share similar absorption pathways in the gut
Higher doses increase competition

Magnesium forms more likely to interfere

These forms are more commonly associated with absorption competition, especially when taken in higher doses:

Magnesium oxide
Magnesium citrate
Magnesium hydroxide

Why:

They release magnesium ions quickly in the gut
Often taken in larger doses (e.g. for constipation or muscle support)

3. Zinc supplements

How it interferes with iron absorption:

Zinc and iron share common transport mechanisms in the gut. When zinc is present in higher amounts, it can reduce iron uptake by competing for these shared pathways.

4. Fibre supplements

This includes:

psyllium husk
inulin
high-fibre blends

How it interferes with iron absorption:

Fibre supplements can bind to iron in the gut, forming complexes that are harder for the body to absorb. Fibre can also speed up digestion, reducing the amount of time iron stays in contact with absorption sites.

5. Multivitamins with minerals

How it interferes with iron absorption:

Multivitamins often contain several minerals — such as calcium, magnesium, zinc, and copper — all of which can compete with iron absorption when taken together.

6. Certain herbal or antioxidant supplements

How it interferes with iron absorption:

Some herbal supplements contain compounds called polyphenols. These compounds can bind to iron in the gut, forming complexes that are less easily absorbed by the body.

Examples include:

green tea extract
turmeric or curcumin supplements

7. Phosphorus or phosphate supplements

How it interferes with iron absorption:

Phosphorus can form insoluble compounds with iron in the digestive tract, making it harder for the body to absorb iron effectively.

Although phosphorus supplements are less common, separating them from iron helps reduce the chance of these compounds forming and interfering with absorption.

How to space iron and other supplements

Spacing your supplements doesn’t need to be complicated. A few simple timing adjustments can help your body absorb iron more effectively while still allowing you to take the other supplements you need.

General spacing rule

As a general guide, try to take iron at least 1–2 hours apart from supplements that may interfere with its absorption, such as calcium, magnesium, zinc, fibre, and multivitamins with minerals.

Choose a consistent time for iron

Many people find it helpful to take iron:

first thing in the morning, or
between meals, when fewer competing nutrients are present

The most important thing is consistency — taking iron at the same time each day can support better absorption.

Separate iron from mineral-heavy supplements

If you take several supplements, consider grouping them:

Iron on its own
Other minerals and multivitamins later in the day

For example, iron in the morning and magnesium or calcium in the evening can work well for many people.

Be mindful of fibre supplements

Fibre supplements can reduce iron absorption, so it’s best to take them at a different time of day, such as:

iron in the morning
fibre supplements with lunch or dinner

All in all, keep it simple

You don’t need a perfect schedule. Even small spacing adjustments can make a difference. If your routine feels manageable, you’re more likely to stick with it long term.

If you’re unsure how to space your supplements — or if you’re taking iron for a diagnosed deficiency — it’s always a good idea to speak with a healthcare professional for personalised advice.

What about vitamin C?

Vitamin C is often mentioned alongside iron because it can support iron absorption, particularly for non-heme iron (the form commonly found in supplements and plant-based foods).

Vitamin C helps by converting iron into a form that is easier for the body to absorb. This is why some people choose to take their iron supplement with a small amount of vitamin C or a vitamin C–rich food.

That said, more isn’t always better. Large doses of vitamin C aren’t necessary for most people and can sometimes cause digestive discomfort. In many cases, a modest amount — such as what’s found in a piece of fruit (like kiwi or orange) or a low-dose supplement of around 50–100 mg — is enough to support absorption.

Key takeaways

Iron supplements can be an effective way to support energy levels and address iron deficiency — but timing plays an important role in how well they work. Some supplements can compete with iron or reduce its absorption when taken at the same time, which may limit the benefit you receive.

If you’re ever unsure about how to take your supplements, or if iron has been recommended for a specific health reason, it’s always worth speaking with a healthcare professional for personalised guidance.

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December 18 2025, by Tatianna Gerard 7 Supplements You Shouldn’t Take at the Same Time as Iron