May 21, 2026, 8:45 am | Read time: 4 minutes
For many people, coffee is indispensable, especially in the morning, but taking supplements is also part of the daily (morning) routine for many. However, combining certain supplements with coffee can be problematic. FITBOOK reveals which dietary supplements should not be taken with coffee.
Why Coffee Can Affect the Effectiveness of Dietary Supplements
Coffee contains not only caffeine but also polyphenols and tannins. These are natural plant compounds that have antioxidant effects and give coffee its slightly bitter taste. At the same time, they can also affect the absorption of certain nutrients in the body.
Additionally, caffeine has a mild diuretic effect, which can cause certain minerals and vitamins to be excreted more quickly. While this effect is usually minor with moderate coffee consumption, the timing of intake can play a larger role with high-dose supplements or existing deficiencies.
Caution is also advised with stimulating supplements. Combined with coffee, the stimulating effect can be intensified, potentially leading to nervousness, heart palpitations, or sleep problems.
Coffee Can Inhibit Iron Absorption
People should be particularly cautious with iron supplements. Research shows that coffee can impair iron absorption in the body. This is partly due to polyphenols and tannins, which can bind to iron in the digestive tract. Non-heme iron, or plant-based iron from supplements or vegetarian diets, seems to be particularly affected.
According to a study, high caffeine consumption can impair iron absorption in the body. This is likely due in part to the hormone hepcidin, which regulates iron absorption and utilization and is released more with increased caffeine consumption. Along with elevated inflammation levels, this can lead to poorer iron absorption.1
What It Can Mean for Magnesium and Calcium
Researchers are also discussing possible interactions between coffee and minerals like magnesium and calcium. Caffeine has a mild diuretic effect, which could lead to faster excretion of minerals. There are also indications that coffee can affect calcium absorption.
Researchers from Brazil have found that under the influence of caffeine, the body excretes more calcium and simultaneously relies on existing reserves. This could impair the long-term supply of essential minerals.2
The Impact of Coffee on Vitamins
Furthermore, potential interactions between vitamin D and coffee or caffeine are a focus of research. Some studies suggest that caffeine could affect certain vitamin D receptors in the body, potentially making it less efficient for the body to use vitamin D despite adequate intake.3
For water-soluble vitamins like B vitamins and vitamin C, similar effects to those with iron could occur. Caffeine’s mild diuretic effect can increase the excretion of certain water-soluble vitamins.
How Vitamin D and Magnesium Work Together
Ingredients and Effects of Black Tea
Caution with Caffeine-Containing Supplements
Vitamins and minerals can interact not only with coffee, but supplements with stimulating effects should not be underestimated. These include guarana, green tea extract, or so-called pre-workout boosters, which often contain large amounts of caffeine themselves. As a result, daily caffeine intake can add up faster than expected.
According to the European Food Safety Authority (EFSA), up to 400 milligrams of caffeine per day is considered safe for healthy adults, while a maximum of 200 milligrams is recommended for pregnant and breastfeeding women. Regularly exceeding these amounts can lead to sleep disturbances, nervousness, and heart rhythm disorders. During pregnancy, there can also be risks for the unborn child.4
Conclusion: Some Supplement-Coffee Combinations Are Best Avoided
Coffee is much more than just a pick-me-up. Its ingredients can influence various processes in the body, including the absorption and utilization of certain nutrients.
However, it is also clear that for most healthy people, moderate coffee consumption is not a cause for concern. Problems are more likely to arise when high caffeine levels meet high-dose supplements or existing deficiencies. Those who take supplements specifically for health reasons should pay attention not only to dosage but also to timing.