Caffeinated
beverages such as coffee and tea have been shown to inhibit the absorption of
iron.
Caffeinated
foods and drinks have become staples in most modern diets.
Coffee
is one of the most popular coffees, with 80% of U.S. adults drinking it (1, 2).
Caffeine
is a natural stimulant. However, some people claim that it interferes with the
absorption of certain nutrients, such as iron.
Therefore,
some people are advised to avoid drinking coffee and caffeine.
Here is
everything you need to know about how coffee and caffeine affect iron
absorption.
Coffee and caffeine can
inhibit iron absorption
Multiple
studies have found that coffee and other caffeinated beverages reduce iron
absorption.
One
study found that drinking a cup of coffee while eating a hamburger reduced iron
absorption by 39%. Drinking tea, a known inhibitor of iron absorption reduces
iron absorption by up to 64% with meals (3).
Another
study found that drinking a cup of instant coffee during a bread meal reduced
iron absorption by 60 to 90% (4).
What is
more, the stronger the coffee or tea, the less iron is absorbed (3).
However,
caffeine does not appear to be the main substance interfering with iron
absorption.
In
fact, one study found that caffeine itself binds only to about 6% of the iron
in the diet. Given that this is a relatively small amount, other factors will
certainly affect the absorption of iron (5).
In
addition, regular coffee consumption may also have an impact on the level of
iron storage.
A large
study found that in older adults, drinking a cup of coffee a week was
associated with a 1% reduction in ferritin levels, a protein that indicates
iron storage levels. (6）。
However,
it is important to remember that the effects of coffee and caffeine on iron
absorption seem to depend on when you drink coffee. For example, drinking
coffee one hour before a meal had no effect on iron absorption (7).
Summary: Along
with meals, coffee and other caffeinated beverages are associated with a 39-90%
reduction in iron absorption. However, caffeine itself can only bind a small
amount of iron.
Other substances affect
the absorption of iron
Caffeine
is not the only substance known to interfere with iron absorption.
The
polyphenols in coffee and tea are considered major inhibitors of iron
absorption.
These
include Chlorogenic acid, which is mainly found in coffee, cocoa, and some
herbs. In addition, the tannins in black tea and coffee inhibit the absorption
of iron (4, 8).
These
compounds bind to iron during digestion, making it more difficult to absorb (9, 10).
Their
effect on iron absorption is dose-dependent, meaning that iron absorption
decreases as the number of polyphenols in food or drink increases. (9, 11）。
In one
study, drinking a beverage containing 20-50 mg of polyphenols per serving
reduced iron absorption in bread meals by 50-70%. At the same time, beverages
containing 100-400 mg of polyphenols per serving can reduce iron absorption by
60-90% (4).
Another
study found that ingesting 5 mg of tannin inhibited iron absorption by 20%,
while 25 mg of tannin decreased by 67% and 88% by 100 mg. (9）。
Summary:
polyphenols in coffee and tea inhibit iron absorption by up to 90%. The more
polyphenols you consume, the more likely they are to inhibit absorption.
Dietary type affects the
absorption of iron
The
absorption of iron is complex and is influenced by many dietary factors.
There
is evidence that the type of food you eat has a greater impact on iron
absorption than drinking coffee or caffeinated beverages.
Certain
types of foods can enhance the absorption of iron, while others inhibit it. The
type of iron you consume is also important.
Iron is
found in food in two forms – heme iron and non-heme iron.
Non-heme
iron, which is mainly found in plant foods and is relatively unstable, is
influenced by many dietary factors. Only 2-20% of non-heme iron is absorbed (10).
In
contrast, the absorption of heme iron, which is only present in animal tissues
(meat, poultry, and seafood), is much higher, at 15 to 35 percent. This is
because it is fully absorbed and is not affected by other dietary factors (12).
Therefore,
coffee and caffeinated beverages are more likely to inhibit the absorption of
non-heme iron in plant foods but have little effect on heme iron in animal
foods.
In
addition, the addition of animal protein, vitamin C, and copper to the diet can
enhance the absorption of non-heme iron and reduce the negative impact of
coffee and caffeinated beverages on iron absorption. (13）。
Therefore,
the food you choose and the type of iron you consume will determine the effect
of coffee and caffeinated beverages on iron absorption.
Summary: many
dietary factors affect the absorption of iron. Coffee and caffeinated products
inhibit the absorption of non-heme iron from plant foods. However, they have
little effect on the heme iron found in animal tissues.
Should you reduce your
intake of coffee and caffeine?
Several
studies have shown that for healthy people who are not at risk of iron
deficiency, coffee and caffeine are not associated with iron deficiency. (14, 15, 16）。
Many
people get enough iron from the food they eat. Regularly consuming adequate
amounts of vitamin C and heme iron from meat, poultry, and seafood can help
overcome iron suppression caused by drinking coffee and tea. (17, 18）。
However,
this may not be the case when the intake of polyphenols is very high (17).
For
those at risk of iron deficiency, drinking a lot of coffee and tea may not be
the best idea (19).
High-risk
groups include women of childbearing age, infants and young children, people on
poor or restrictive diets (such as vegetarians), and people with certain
medical conditions (such as inflammatory bowel disease).
However,
these groups may not necessarily want to quit coffee and caffeine altogether.
Instead,
people at risk are advised to follow these helpful tips (11, 14, 18):
- drink coffee or tea between meals
- wait at least an
hour after a meal before drinking coffee or tea
- increase heme
iron intake through meat, poultry, or seafood
- INCREASE YOUR
INTAKE OF VITAMIN C AT MEALTIMES
- eat
iron-fortified foods
- Eat calcium-rich
and high-fiber foods separately from iron-rich foods, such as whole
grains.
This
will help limit the effects of coffee and caffeinated beverages on iron
absorption.
Summary: healthy
people at low risk of iron deficiency do not need to limit coffee and caffeine.
However, those at risk of iron deficiency are advised to avoid coffee and
caffeine during meals and wait at least an hour after meals before consuming
them.
Conclusion
Caffeinated
beverages such as coffee and tea have been shown to inhibit the absorption of
iron.
However,
this is more likely due to their polyphenol content than the caffeine itself.
Caffeinated
foods and drinks are not associated with iron deficiency in healthy people, as
the absorption of iron is influenced by many other dietary factors.
However,
those at risk of deficiency benefit from avoiding coffee and tea during meals
and waiting an hour after a meal for coffee or tea.