Can you take supplements with coffee? What to know about timing

For many people, the day starts with a cup of coffee, with their supplement sitting right beside it. Whether the two go together depends on the nutrient. For most nutrients there’s little reason not to, but for iron the measurements are clear. This article covers what the studies measured and how to plan your morning without fuss.

Why can coffee slow down absorption?

Coffee contains more than caffeine. It also contains plant compounds from the polyphenol group, chiefly chlorogenic acid. In one study, every polyphenol-containing drink tested reduced the absorption of iron from a meal of bread, and how much it did so depended on its polyphenol content¹.

And it isn’t only coffee: black tea reduced absorption by 79 to 94%, peppermint tea by 84% and cocoa by 71%¹. Adding milk to the coffee or tea made little difference¹.

Iron with coffee: what do studies show?

A study from 2023 measured this directly with iron taken as a supplement. One cup of coffee taken with the iron reduced absorption by 54%. A breakfast with coffee and orange juice reduced it by 66%, even though the breakfast contained about 90 mg of vitamin C². So the vitamin C couldn’t make up for the effect of the coffee.

Timing matters. In an older study, coffee didn’t affect the absorption of iron from a meal when it was drunk one hour beforehand. Drunk one hour after the meal, however, it slowed absorption just as much as coffee taken with the meal. The stronger the coffee, the bigger the effect³.

That gives a simple rule of thumb: it’s better to drink your coffee one hour before your iron than soon after it. The study didn’t look at how long to wait after taking iron, so leave yourself plenty of time afterwards. Our article When should you take iron? covers everything else about iron, including liposomal forms.

Magnesium and calcium with coffee?

In a small study with 17 healthy participants, two doses of caffeine in the morning increased the amount of calcium and magnesium lost in urine for six hours⁴. Overnight, the body held on to some of it again. Over 24 hours, that left an extra loss of about 13 mg of calcium and 4 mg of magnesium⁴.

These are small amounts. A review also concludes that caffeine reduces calcium absorption in the gut only very slightly, and that as little as one to two tablespoons of milk makes up for it completely⁵.

So there’s little reason not to take magnesium or calcium with coffee. If you’d like to play it completely safe, take magnesium at another time of day, in the evening, for example.

Zinc and coffee: what do we know?

The data on zinc are limited. In an older study with young, healthy volunteers, dairy foods and wholemeal bread reduced zinc absorption, and coffee also seemed to slow it⁶. For coffee, though, this finding isn’t robust. If it’s practical, it’s still best to leave a little gap between your zinc and your coffee.

Our article Which minerals can you take together? explains which ones go well with each other.

Vitamin C, omega-3 and alpha-lipoic acid with coffee?

For vitamin C, omega-3 and alpha-lipoic acid, we found no study that looked at whether coffee changes their bioavailability. So there’s no sign of a problem, but no proof that there isn’t one either. The simplest approach is to follow the directions on the pack.

How much of a gap makes sense?

For iron, the studies above point the way. For the other nutrients, a few simple rules of thumb are enough:

• Iron: ideally have your coffee one hour before, and leave a generous gap after taking iron. The same goes for black tea.
• Zinc: keep it a little apart from your coffee, if that’s practical.
• Magnesium and calcium: coffee’s effect is small.
• Vitamin C, omega-3, alpha-lipoic acid: no known restrictions. Follow the directions on the pack.

Frequently asked questions about supplements and coffee