Coffee leaches magnesium: fact or myth?

Many of us start the day with an aromatic cup of coffee, and this drink has become an integral part of our culture and lifestyle. Opinions about the harmful or beneficial effects of coffee (and caffeine) on the body are divided, including among scientists. The latter sometimes argue that coffee prolongs life, helps in losing excess weight or prevents Alzheimer's disease, and sometimes they come to the conclusion that it "deceives" the brain, is addictive and leads to chronic fatigue and nervous arousal.

In this article, we will focus on one of the aspects of coffee's effect on the body, namely: its impact on our magnesium resources - a mineral that plays a key role in many physiological processes (read more about the role of magnesium in the body in a separate article ).

Coffee as a source of magnesium.

Coffee is a rich source of active ingredients. These are antioxidants, minerals, diterpenes, alkaloids, caffeine and others. Importantly, the content and proportion of these ingredients varies depending on the type of coffee, the country of its origin, the cultivation method and the method of preparing the drink itself based on the beans and even the degree of grinding.

Coffee beans do contain magnesium, but the infusion based on them "absorbs" less of this mineral. Polish scientists reviewed the research  ¹ on the magnesium content in various types of coffee infusions from 2000–2020 and here is their comparison:

• Coffee mixed with water (including Turkish coffee): magnesium content per cup (150 ml) ranges from 3.22 mg to 22.38 mg.

• Brewing by passing boiling water through ground coffee (espresso machine or filter coffee): a cup (150 ml) can provide from 3.22 to 16.05 mg of magnesium. A tiny espresso – approx. 7.5 mg of magnesium.

• Instant coffee : a cup can provide up to 9.75 mg of magnesium.

Taking into account that the daily requirement for magnesium in an adult is 310-320 mg for women and 400-420 mg for men  ² , 1 coffee can only cover a few percent!

The more coffee we drink, the more magnesium it should theoretically provide, but the problem is that we never know exactly how much magnesium is contained in our coffee. As scientists point out  ³ , the concentration of this mineral in the infusion is influenced by a large number of factors, as can be seen from the discrepancies in the numbers even for the same type of brewing, including:

• coffee type and its origin,
• type of grain processing,
• the intensity of their burning,
• degree of grinding,
• brewing temperature,
• brewing method,
• water, used for brewing, etc.

Relying on coffee as a significant source of magnesium in the diet is therefore risky. We cannot predict whether our little black dress will provide us with 3 mg of this mineral or 20 mg (which is only a few percent anyway).

However, even if we decide to drink 20 cups of coffee a day, ignoring all recommendations regarding healthy eating and thus supplementing magnesium, the chances of success are rather slim. The mineral content in the drink itself does not guarantee that we will absorb and use it, as described below.

Coffee and magnesium deficiency.

As we already know, coffee contains many substances, but not only those "good" for humans, such as antioxidants and minerals  ⁴ . Its composition also includes the so-called anti-nutritional substances that may block the absorption of micronutrients in humans. These compounds are part of the plants' defense strategy aimed at increasing their survival and reproduction.

Anti-nutrients.

The role of these substances from the plant's point of view is:

• protection against parasites and predators (including humans! Nobody wants to be eaten). Phytic acid (phytin) is an example of a substance that binds to minerals, creating difficult-to-absorb complexes. This can make these minerals more difficult to access for parasitic plants or predatory organisms that may want to use them as a food source.

• competition with other organisms. Substances such as tannins can affect the competitiveness of plants by limiting the availability of minerals to other organisms growing in their vicinity. This can help plants gain an advantage in the fight for resources.

• protection against microorganisms. Some anti-nutrients can also have antibacterial and antiparasitic properties, helping plants avoid infections and stay healthy.

Coffee contains tannins and phytin, which may impair the absorption of magnesium and other minerals, also in humans:

• tannins can combine with various minerals, such as iron, calcium and magnesium, forming sparingly soluble compounds  ⁵ . This may limit the absorption of these minerals in the digestive tract.

• phytic acid (phytin) binds magnesium, calcium, iron and zinc and may block their absorption  ^6.7 .

Thermal treatment can reduce the content of these substances by up to 30–50% in the case of phytic acid in dark roasted beans.  ⁸ . The most anti-nutritional substances can be found in green coffee (commonly considered "healthier"). Nevertheless, as in the case of magnesium, we cannot precisely determine how much of these compounds we will find in our specific cup.

The activity of these substances and the ability to block the absorption of minerals is also influenced by many factors, including the condition of our digestive system. Therefore, for now, scientists do not know exactly how much of the minerals from food we do not absorb due to anti-nutritional substances  ⁹ .

The presence of anti-nutritional substances in coffee may mean that we will not benefit from magnesium, which is also found in this aromatic drink. Moreover, if we consume coffee with a meal, we can also reduce the absorption of magnesium and other minerals from our colorful plate. If you struggle with mineral deficiencies and do not want to give up coffee, it is better to drink it between meals.

Diuretic effect of coffee.

Another reason that is often mentioned as an argument for the fact that coffee leaches magnesium is its diuretic effect (magnesium is excreted in urine). Caffeine has such properties, but scientists describe its effect on the frequency of urination as "mild"  ¹⁰ . Interestingly, women may be more likely to feel the urge to use the toilet after drinking coffee than men.

The popular advice "drink 3 glasses of water after 1 cup of coffee to replenish fluid in the body and avoid dehydration" has no scientific basis.  ¹¹ . The fluid contained in coffee balances its diuretic effect. And since we do not lose unnecessary amounts of urine after drinking coffee, it means that magnesium is not washed away with it. Therefore, this factor does not seem to have a significant impact on the stores of this mineral in our body.

Coffee and magnesium – everything you need to know in a nutshell.

So let's summarize the most important information from this text.

1. Coffee is a source of small amounts of magnesium. Its content varies depending on the type of beans, the method of growing them, the degree of grinding and the method of preparing the infusion. A cup of espresso can provide approximately 7.5 mg of magnesium, which is approximately 2% of the daily norm of this mineral.
2. Coffee also contains anti-nutritional substances (tannins, phytin). They may block the absorption of magnesium. The content of antinutritional substances in coffee also varies depending on the method of processing its beans, and their activity also depends on the health of the human digestive system.
3. Coffee does not lead to the excretion of unnecessary magnesium in the urine because it does not lead to dehydration.

What conclusion can we draw on this basis? It seems that when we drink coffee, we break even in terms of magnesium. This drink cannot be an important source of this valuable element in our diet. At the same time, with moderate consumption it does not lead to serious deficits.

If you want to ensure a sufficient amount of magnesium in your diet, it is worth, first of all, taking care of a varied and varied diet and supplementing any deficiencies, if any. You can check whether the problem of magnesium deficiency also applies to you at this link .

Bibliography:

1. Olechno, E.; Puścion–Jakubik, A.; Socha, K.; Zujko, ME Coffee Brews: Are They a Source of Macroelements in Human Nutrition? Foods 2021, 10, 1328. https://doi.org/10.3390/foods10061328
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3. Olechno, E., op. cit.
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