May 21, 2026, 8:45 am | Read time: 4 minutes
For many people, coffee is an essential part of their morning routine, but taking supplements is also a daily habit for many. However, combining certain supplements with coffee can be problematic. FITBOOK reveals which dietary supplements should not be taken with coffee and consulted nutrition experts and diabetologist Dr. Matthias Riedl for insights.
Why Coffee Can Affect the Efficacy 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. However, they can also affect the absorption of certain nutrients in the body.
Additionally, caffeine has a mild diuretic effect, which can lead to faster excretion of certain minerals and vitamins. While this effect is usually minor with moderate coffee consumption, the timing of intake can be more significant with high-dose supplements or existing deficiencies.
Caution is also advised with stimulating supplements. When 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. Polyphenols and tannins, which can bind to iron in the digestive tract, are partly responsible. 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. Combined with elevated inflammation levels, this can lead to poorer iron absorption.1
When asked if there are specific times of day when supplements should not be taken with coffee, Dr. Riedl says: “Iron supplements should ideally be taken separately from coffee, about one to two hours before or after. This also applies to magnesium or calcium supplements.” Those who don’t want to give up their morning coffee might consider taking iron supplements in the evening before bed.
What It Can Mean for Magnesium and Calcium
Researchers also discuss possible interactions between coffee and minerals like magnesium and calcium. Caffeine’s mild diuretic effect could lead to faster excretion of minerals. There are also indications that coffee can affect calcium absorption.
Brazilian researchers have found that under the influence of caffeine, the body excretes more calcium and simultaneously taps into existing reserves. This could potentially impair the long-term supply of essential minerals.2
The Impact of Coffee on Vitamins
Possible interactions between vitamin D and coffee or caffeine are also 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 seen 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
Copper: Functions, Requirements, and Sources of the Trace Element
Caution with Caffeine-Containing Supplements
Not only vitamins and minerals can interact 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. This can lead to a quicker accumulation of daily caffeine intake 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
Also interesting: Those taking these medications should avoid drinking coffee
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. Dr. Riedl adds: “It becomes problematic with existing deficiencies, high coffee consumption, or when supplements are used therapeutically.”
He also mentions that people with iron deficiency, pregnant women, older adults, or those with chronic intestinal diseases are often more sensitive to such interactions or supplement-coffee combinations.