If you've ever been warned that drinking coffee with or immediately after a meal might not be the best idea, you should know that there might be a grain of truth to that.
There are more than 1.000 chemical compounds in coffee, and a few, such as caffeine, polyphenols, and tannins, can interfere with the way you absorb nutrients from your food.
The good news is that for most people, these effects are minimal - not significant enough to cause any drawbacks.
Nutrients are substances in our food and drink that perform certain vital jobs in our bodies.
We need different nutrients to stay healthy.
"Not all absorption is 'blocked' completely - there may just be some reduction," says Alex Ruani, a doctoral researcher at University College London's School of Nutritional Science Education and chief scientific educator at the Academy of Health Sciences.
The impact depends on the strength of the coffee in question; the amount of nutrients consumed and individual risk factors such as age, metabolism, health status and genetics, explains Ruani.
The nutrients we are talking about include calcium, iron, and B vitamins.
There's no need to worry if your "nutrient levels are already adequate, but for those on the verge of deficiency or with pre-existing low levels, excessive coffee intake could contribute to further depletion," says Emily Ho, director of the Linus Pauling Institute and professor in the College of Health Sciences at Oregon State University.
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Who needs to be careful with cappuccino?
Since the 1980s, studies have linked coffee to lower iron absorption.
"When you drink coffee with a meal, the polyphenols in it can bind to certain minerals in your digestive system," says Ho.
She explains that this binding process can make it harder for your body to absorb iron because the minerals have to pass through the cells of your intestines to enter your bloodstream.
"If they stay attached to the polyphenols, they simply pass through the body and end up in the feces."
This is especially important for iron, especially the type found in plant-based foods, called 'non-heme iron'.
Non-heme iron from foods such as fruits and vegetables is more difficult for the body to absorb.
The polyphenols in coffee, especially chlorogenic acid, can bind to this type of iron, preventing it from being absorbed into the bloodstream properly.
As a result, iron gets stuck in these compounds as they move through the digestive system.
They are eventually excreted through feces instead of being used by the body.
All of this means that people with iron deficiency anemia should be careful about drinking coffee too close to iron-rich meals.
"It may be best to enjoy your coffee at least an hour before or a few hours after eating iron-rich foods so they don't interfere in your stomach," says Alex Ruani.
Women who are menstruating or pregnant often fall into this category of people who need to monitor their iron levels.
They usually need more iron and are more likely to develop iron deficiency anemia, so they need to be careful about when and how much coffee they consume.
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Calcium
Calcium is crucial for bone health, yet nine per cent of people aged between 16 and 49 in the UK consume less than the Lowest Reference Nutrient Intake (LRNI) for calcium through food.
This deficit puts them at risk of having weaker bones later in life.
The kidneys remove waste and excess water from the blood (such as urine) and help maintain the balance of chemicals in the body (such as sodium, potassium, and calcium).
They also make hormones.
Studies suggest that caffeine can make it harder for your body to retain calcium by interfering with how it is processed in your kidneys and absorbed in your intestines.
Once again, these effects are minimal and are more significant for people who already consume foods with less calcium or are more susceptible to bone health problems.
"A popular study published in the journal Osteoporosis International suggests that caffeine may contribute to bone loss by interfering with bone metabolism," says Ruani.
"But more studies are needed to determine the true impact of caffeine on osteoporosis risk."
Calcium can be stored in the body, so you don't need to take the recommended daily amount, but over a period of several months, adults between the ages of 19 and 64 should get an average of about 700 milligrams of calcium per day.
It is also important to keep in mind that caffeine has a diuretic effect, meaning it increases the frequency of your need to urinate.
"This can lead to the loss of water-soluble vitamins (such as some B vitamins) and minerals (such as iron and calcium), as bowel movements play an important role in regulating their levels in the body," adds Ho.
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Vitamin B
"Due to coffee's effects on kidney function and nutrient metabolism, drinking large amounts of coffee (such as four cups a day or more) can lead to increased urination and the loss of water-soluble vitamins, including B vitamins," explains Ruani.
B vitamins are water soluble, so they are not stored in the body.
Instead, any excess is excreted through urine.
probiotics
Probiotics are live bacteria and yeasts that are promoted as having health benefits.
They may be useful in restoring the natural balance of bacteria in your gut in some cases, according to the NHS website, but there is little evidence to support the many health claims made about them.
However, if you want to try probiotic supplements or probiotic-rich foods like yogurt or kimchi, it's best to avoid taking them with hot beverages like coffee.
"The live bacteria in probiotics are extremely sensitive to heat, and exposing them to high temperatures, such as the heat in coffee, can reduce their survival rate in the gastrointestinal tract, making them less effective," says Ruani.
Sometimes prescribed by doctors to relieve diarrhea caused by taking antibiotics, to get the maximum effect, wait 30-60 minutes before taking a probiotic if you've already had a cup of coffee.
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And tea instead of coffee?
If you're considering switching to tea, it's important to know that some of the same concerns apply to tea.
"Furthermore, the polyphenols in tea can have a similar effect on the bioavailability of nutrients, so it's important to pay attention to the timing of your tea if you want to preserve nutrient absorption," warns Ho.
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