Drinking coffee with certain supplements is not necessarily harmful, but it may reduce the body's absorption of them. This means you may not get their full benefits.

The good news is that you don't have to give up your morning coffee; rather, taking supplements at the right time helps your body absorb them better.

Caffeine acts as a diuretic, which may cause loss of water-soluble vitamins (such as B vitamins). These are the most notable supplements you should avoid taking with caffeine, according to Health:

1. Iron

Coffee contains plant compounds called polyphenols. These compounds are known for their antioxidant properties, but they also bind to iron, limiting the amount of iron the body absorbs.

Some research suggests that drinking coffee with an iron-rich meal may reduce iron absorption by about 35 percent.

A 2023 study, which specifically focused on the absorption of iron supplements taken with coffee, either with or without breakfast, found that coffee reduces iron absorption by 54-66 percent. This means that taking iron with coffee will not boost iron levels in the body as desired.

2. Calcium

To get the most benefit from calcium supplements, it is important to avoid taking them with coffee so the body can absorb them better. Caffeine in coffee may hinder the body's ability to absorb calcium from food or supplements. Coffee may also interact with vitamin D, a nutrient that helps the body absorb calcium.

Coffee is a diuretic, meaning it increases urine output. The body produces urine by filtering blood. Some research suggests that coffee's diuretic effect filters calcium from the body, which is then excreted or eliminated through urine.

3. Vitamin D

In general, research indicates that people who want to increase their vitamin D levels and get the maximum benefit may want to avoid taking vitamin D supplements with coffee.

For example, some research suggests that caffeine may reduce the effectiveness of vitamin D. This occurs by interfering with vitamin D receptors in the body.

Other studies have found that people who consume higher amounts of caffeine, such as those who drink a lot of coffee, have lower blood levels of vitamin D. However, these studies do not prove that coffee or caffeine is the cause of the deficiency; they only suggest an association.

4. B Vitamins

Taking B vitamins with coffee may prevent optimal absorption of these nutrients, or it may prompt the body to eliminate them. This means you may not get the same intended benefits. Some research has shown that drinking coffee may reduce blood levels of B vitamins.

Research from 2018 indicates that caffeine may also interfere with folic acid, reducing its levels in the blood. B vitamins are water-soluble, meaning they may be eliminated through urine. Coffee can increase this effect by increasing urination.

5. Magnesium

Coffee may affect the levels of water-soluble magnesium supplements in ways similar to its effect on lowering calcium and B vitamin levels: by increasing urine volume, magnesium is filtered from the body with increased urination.

In other words, taking magnesium with coffee means the body eliminates it more quickly, and you may not get the full benefit.

6. Zinc

Combining coffee and zinc may not be ideal, because drinking coffee may hinder zinc absorption — that is, the amount of zinc that enters the bloodstream and effectively affects the body. This may also be due to coffee's effect on vitamin D absorption, as vitamin D helps absorb zinc.

When should you drink coffee?

To get the most out of supplements and avoid interactions that reduce their effectiveness, the timing of coffee consumption is crucial. Research indicates that you can drink coffee one to two hours before taking supplements or vitamin-rich foods.

Read also