Caffeinated foods and beverages have become staples in most modern-day diets.
Coffee is among the most popular, with 80% of US adults drinking it (, ).
Caffeine is a natural stimulant. However, some claim it interferes with the absorption of certain nutrients, such as iron.
As a result, some people have been advised to avoid coffee and caffeine.
Here’s everything you need to know about how coffee and caffeine affect iron absorption.
Several studies have found that coffee and other caffeinated drinks can reduce iron absorption.
One study found that drinking a cup of coffee with a hamburger meal reduced iron absorption by 39%. Drinking tea, a known inhibitor of iron absorption, with the same meal reduced iron absorption by a whopping 64% ().
Another study found that drinking a cup of instant coffee with a bread meal reduced iron absorption by 60–90% ().
What’s more, the stronger the coffee or tea, the less iron absorbed ().
However, caffeine alone does not seem to be the main substance interfering with iron absorption.
In fact, one study found that caffeine itself only binds to about 6% of the iron from a meal. Given that this is a relatively small amount, other factors must affect iron absorption ().
Furthermore, regular coffee consumption may also have an effect on iron storage levels.
A large study found that among elderly people, each weekly cup of coffee was associated with a 1% lower level of ferritin, a protein that indicates iron storage levels ().
However, it’s important to remember that the effects of coffee and caffeine on iron absorption seem to depend on when you drink your coffee. For example, drinking coffee one hour before a meal had no effect on iron absorption ().
Summary: Drinking coffee and other caffeinated beverages with a meal is associated with a 39–90% reduction in iron absorption. However, caffeine itself only binds a small amount of iron.
Caffeine is not the only substance known to interfere with iron absorption.
The polyphenols found in coffee and tea are thought to be major inhibitors of iron absorption.
These include chlorogenic acid, which is found mainly in coffee, cocoa and some herbs. Also, tannins found in black tea and coffee inhibit iron absorption (, ).
These compounds bind with iron during digestion, making it more difficult to absorb (, ).
Their effect on iron absorption is dose-dependent, meaning that iron absorption decreases as the polyphenol content of the food or beverage increases (, ).
In one study, drinking beverages containing 20–50 mg of polyphenols per serving reduced iron absorption from a bread meal by 50–70%. Meanwhile, beverages containing 100–400 mg of polyphenols per serving reduced iron absorption by 60–90% ().
Another study found that consuming 5 mg of tannins inhibited iron absorption by 20%, while 25 mg of tannins reduced it by 67% and 100 mg by 88% ().
Summary: The polyphenols in coffee and tea inhibit iron absorption by up to 90%. The more polyphenols you consume, the more they may inhibit absorption.
Iron absorption is complex and affected by many dietary factors.
Evidence suggests that the type of food you eat has a greater influence on iron absorption than the effect of drinking coffee or caffeinated drinks.
Certain types of foods enhance iron absorption, while others inhibit it. The type of iron you consume is also important.
Iron is present in food in two forms — heme and non-heme iron.
Non-heme iron, which is found mainly in plant-based foods, is relatively unstable and affected by many dietary factors. Only 2–20% of non-heme iron is absorbed ().
In contrast, heme iron, which is found only in animal tissues (meat, poultry and seafood) has a much higher absorption rate of 15–35%. This is because it is absorbed intact and not influenced by other dietary factors ().
Thus, coffee and caffeinated drinks are more likely to inhibit the absorption of non-heme iron from plant-based foods but have very little effect on heme iron from animal foods.
In addition, including animal protein, vitamin C and copper in meals can enhance non-heme iron absorption and reduce the negative effects of coffee and caffeinated drinks on iron absorption ().
As a result, your food choices and the type of iron you consume will determine the effect of coffee and caffeinated drinks on iron absorption.
Summary: Many dietary factors influence iron absorption. Coffee and caffeinated products can inhibit absorption of non-heme iron found in plant-based foods. However, they have little effect on heme iron found in animal tissues.
Several studies show that coffee and caffeine are not associated with iron deficiency in healthy people with no risk of iron deficiency (, , ).
Many people get enough iron from the food they eat. Regularly getting an adequate amount of vitamin C and heme iron from meat, poultry and seafood can help overcome iron inhibition from drinking coffee and tea (, ).
However, this may not be the case when polyphenols are consumed at very high levels ().
For those at risk of iron deficiency, high consumption of coffee and tea may not be the best idea ().
Groups at risk include women of childbearing age, infants and young children, people with a poor or restrictive diet, such as vegetarians, and people with certain medical conditions like inflammatory bowel disease.
Yet, it may not be necessary for these groups to completely cut out coffee and caffeine.
Instead, people at risk are advised to follow these helpful tips (, , ):
- Drink coffee or tea between meals
- Wait at least one hour after eating before drinking coffee or tea
- Increase heme iron intake through meat, poultry or seafood
- Increase vitamin C intake at mealtimes
- Eat iron-fortified foods
- Eat foods high in calcium and high-fiber foods like whole grains separately from iron-rich foods.
This will help limit the effects that coffee and caffeinated drinks have on iron absorption.
Summary: Healthy people at a low risk of iron deficiency should not need to limit coffee and caffeine. However, those at risk of iron deficiency are advised to avoid coffee and caffeine at mealtimes and wait at least one hour after a meal before consumption.
Caffeinated drinks like coffee and tea have been shown to inhibit iron absorption.
However, this is more likely due to their polyphenol contents, not caffeine itself.
Caffeinated foods and drinks are not associated with iron deficiency in healthy people, as iron absorption is affected by many other dietary factors.
However, those at risk of deficiency would benefit from avoiding coffee and tea at mealtimes and waiting an hour after a meal to drink coffee or tea.