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ASK A QUESTION ABOUT GREEN TEA!
If you want to know more about the amazing health benefits of green tea,
you're not alone, as you'll see in this column!
Most of the answers to your questions can probably be found somewhere on
this website (a good place to start is
Green Tea FAQ), but if you still can't find
the answer, check out this page. You might find that someone else has already
asked your question.
If not, feel free to write to Nadine at
info@greentealibrary.com.
The answer to your question may appear in this column or you might
receive a personal reply.
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How much caffeine does a cup of green tea contain? I need to watch my intake.
An 8-oz. cup of green tea contains about 20 mg of caffeine, while white tea
contains even less – about 15 mg. Black tea has about twice as much caffeine as
green tea, weighing in at about 40mg, while drip coffee has a nerve-jangling
90-150mg. Although some people who are caffeine-sensitive may find that drinking
green tea (especially in large amounts) keeps them awake at night, most people
don't have this problem. That may be because
green tea also contains theanine, a natural
tranquilizer that counteracts the stimulating effects of caffeine.
(See more on Green Tea and Caffeine.)
******
Can you tell me about the fluoride content of tea? I have used all
types, the regular black/orange pekoe, green and white teas, and love
them all.
Tea plants accumulate fluoride in their leaves over
time, so the oldest leaves contain the most fluoride, while the youngest contain
the least. Therefore, white tea (which is made from youngest leaves and buds) is
your best bet if you’re super fluoride-conscious. Green tea that is made from
older leaves, oolong tea and black tea have slightly more fluoride.
The highest
amount of fluoride is found in brick tea, a lower quality tea manufactured from
the oldest tea leaves which is molded into the shape of a brick. Brick tea is
the one to watch out for, as symptoms of fluorosis (permanent discoloration of
the teeth) have been seen in Tibetan children and adults who drink large amounts
of this kind of tea.
(See more on Green Tea and
Fluoride.)
******
My wife drank 2 cups of green tea and felt nauseous, yet she's had this tea
before without getting these symptoms. Does green tea react with any
medications?
In some people, green tea can contribute to
heartburn, gastric irritation, nausea and reduction of appetite. If your wife
has had the same kind of green tea (and, I’m assuming, the same amount) in the
past without any symptoms, it seems likely that her nausea was caused by
something else. Green tea does interact with some medications due to its
caffeine content, but nausea is not typically a side effect of these
interactions.
******
If a pot of freshly-brewed tea is left to stand from morning till night, what
actually happens to the tea? Does it change chemically? If so, does it become
more alkaline?
When tea is left to stand at room temperature, the
health-promoting catechins begin to decrease. One study showed that the
catechins decreased appreciably after the brewed tea was store at 25 degrees
Celsius (77 degrees Fahrenheit) for 36 hours. However, when it was refrigerated,
(that is, stored at 4 degrees Celsius or 39 degrees Fahrenheit) for 36 hours,
there were no changes in catechin levels.
Green tea is alkaline, while black tea is on the low end
of acidic. If anything, the tea would become more acidic overnight, since the
catechins become oxidized and transformed into the theaflavins and thearubigens
that are characteristic of black tea. In other words, the longer green tea sits
out, the more it becomes like black tea. And that means it becomes less alkaline
and more acidic.
******
Does iced green tea have the same health benefits as freshly brewed green tea?
If you brew your green tea yourself and then ice it, it
should have the same health benefits as freshly brewed hot green tea. But don't
let the tea stand at room temperature for more than a few minutes before
refrigerating it, as its catechin content can start to diminish.
If your iced tea comes from bottled green tea, however,
chances are you are getting far fewer catechins than you would if you drank
freshly brewed green tea. The health-promoting catechins in green tea are
sensitive to heat and oxygen, so they're easily destroyed during the processing,
transporting and storing of bottled tea. Given that, it's not surprising that
researchers at Oregon State University found that the polyphenols and
antioxidant activity in some bottled tea products were 10 to 100 times lower
than those found in brewed tea!
(See study write-up)
******
I keep hearing about white tea. What is it, and does it have more health
benefits than green tea?
White tea is made up of the tender bud (the leaves that are not fully opened)
of the Camellia sinensis bush. Green tea, on the other hand, is made up of the
bud and the first one or two leaves. White tea gets its name from the fine,
white, hair-like fibers that cover the outside of the bud. As the youngest of
all tea leaves, white tea typically contains greater amounts of catechins than
green tea. Recent studies have shown that white tea is very efficient at
preventing DNA mutations (a first step in the cancer process) and fighting and
killing bacteria and viruses. It has also shown a significant anti-tumor effect
in rats inclined toward colon cancer.
******
How do they make green tea extract? Is it safe to use?
To make green tea extract, the catechins (most often EGCg) are isolated and
drawn out of the tea leaf using water or steam, then condensed before spray
drying. The resulting powder can be put into tablet or capsule form or made into
a liquid.
Green tea extract may contain many times more catechins than could be found in a
cup of green tea. Because it’s concentrated and measurable, it’s often used in
green tea studies, especially those with animals. (It’s hard to get a rat to
drink 10 cups of tea!) However taking too much green tea extract may be risky:
there have been some reports of liver damage after taking the extract in large
amounts.
******
Does adding
one sugar cube to a cup of green tea delete the benefits?
No, adding sugar does not delete the benefits of green tea, and apparently
adding milk doesn't do any harm either. What's most important is that your tea
is high quality, brewed properly and stored in an airtight container.
******
Has anyone ever eaten tea leaves? They are,
after all, a vegetable!
Yes, tea leaves were considered a food long before they were ever used to create
a beverage. In ancient times, the Siamese steamed tea leaves and ate them with
pig fat, dried fish, oil, garlic and salt. The Burmese pickled their tea leaves
and ate them as a salad. The Tibetans combined tea with goat’s milk butter,
barley meal and salt, forming a thick paste that they ate for breakfast.
I think we can all be glad that the world found
a much more pleasant and palatable way to utilize the tea leaf!
******
Does green tea contain estrogens?
No, there is no estrogen in green tea. In fact, there are numerous
studies showing that green tea helps lower the levels of estrogen circulating in
the blood, and may reduce a person’s risk of developing estrogen-dependent
cancers such as breast and uterine cancer.
******
Does caffeine have any health benefits?
Caffeine affects the central nervous system, activating blood circulation,
increasing mental alertness, counteracting sleepiness and helping you bounce
back from fatigue. It improves athletic endurance by stimulating the breakdown
and use of fat as an energy source, so the body doesn't deplete its glycogen
stores. A natural diuretic, caffeine increases urination, which can help
detoxify the body and lower the blood pressure. It's long been used as a remedy
for hangovers because it blocks absorption of alcohol and helps the body dispose
of it at a faster rate. (See
more on Green Tea and
Caffeine.)
******
Does green tea interfere with the absorption of iron?
When I tried to donate blood I was turned away because my iron was too low.
They gave me a list of iron-rich foods, but also indicated that tea hinders the
absorption of iron. I'm assuming they meant regular tea, not green tea.
Great question! It's black tea that interferes with the absorption of dietary
iron and should be avoided by people who are iron deficient. However, green tea
does appear to reduce absorption of the kind of iron found in plant foods (such
as blackstrap molasses, whole grains, iron-fortified cereals and legumes).
And, theoretically, green tea may reduce the absorption of iron supplements,
although the effect isn't clinically significant in most people. To lessen the
tea/iron interaction, you can try drinking your green tea between meals rather
than with them. And avoid black tea entirely.
******
I’ve been drinking green tea for about a week and have been surprised that it
seems to have a calming effect on me. Just wondering if it really does have
anti-stress properties or if it’s just my imagination.
The calming effect you've been experiencing after drinking green tea most likely
comes from its theanine content. Theanine is an amino acid found primarily in
green tea that has been shown to reduce mental and physical
stress and promote feelings of relaxation. One
human study found that after volunteers took 200 mg of theanine dissolved in
water there was a significant increase in alpha-brain wave activity, which is
that “relaxed yet alert” state you seek in yoga class. So your new-found
ability to relax is not just a figment of your imagination!
(See more on Green Tea and Theanine.) (See
more on Green Tea and Stress.)
******
I’ve read that green tea may be able to help clear
up acne, but only if the tea is decaffeinated. Is this true?
I’m not aware of any studies that have found a relationship between drinking
green tea and acne. But green tea does have antibacterial and anti-inflammatory
properties, both of which should be of help with acne control.
As for whether or not you should drink decaffeinated
green tea, many dermatologists advise limiting or excluding caffeine from the
diet because it increases the release of stress hormones, which can make acne
worse. Yet green tea is actually quite low in caffeine (only 25mg per 8 oz. cup,
compared to 65 mg in black tea, and 185 mg in coffee). So you may want to try it
and see how your skin reacts. If your complexion starts to look better, keep
drinking! If not, try green tea that’s been decaffeinated using the carbon
dioxide or “effervescent” method. (It should say so on the label.) You want tea
that’s been decaffeinated in this way as the standard method (involving ethyl
acetate) destroys most of the catechins, which means that most of the health
benefits are negated, as well. (See
more on Green Tea and Caffeine.)
******
I read on the internet some time ago that the Japanese
government conducted a survey of elderly people and found that those who drank 2
cups of green tea a day had much, much higher cognitive function than those who
drank no green tea. Any truth to this?
The only somewhat similar study that I’m aware of is one published
in the American Journal of Clinical Nutrition in 2006, involving 1,003 Japanese
people age 70 or older. The researchers evaluated the volunteers’ cognitive
function and measured the frequency of their green tea consumption. They
concluded that drinking higher amounts of green tea was associated with a lower
incidence of cognitive impairment.
Specifically, drinking 4-6 cups of green tea per week or
1 cup per day lowered the incidence of cognitive impairment by 38%. And drinking
2 or more cups of green tea per day lowered the incidence of cognitive
impairment by 54%. It certainly sounds like an easy (and tasty) way to cut your
risk of cognitive impairment in half! (See
more on Green Tea and Brain Health.)
******
My husband
is a diabetic and on medication. Is green tea is okay for him to drink?
In general, green tea appears to be helpful for diabetics. One
human study found that green tea reduces the risk of developing Type II
diabetes, while animal studies have shown that it lowers blood sugar, enhances
glucose tolerance and protects against damage to insulin-producing cells. It may
even be able to improve the release of insulin from the beta cells of the
pancreas!
(See more on Green Tea and Diabetes.)
But for those taking medication for their diabetes,
drinking green tea (especially a lot of it) may not be a good
idea. That's because the caffeine in green tea can make blood sugar control more
difficult in some people. This shouldn't be a problem if the green tea is
decaffeinated. However, be sure to buy green tea that's been decaffeinated
through the effervescent or carbon dioxide process, which preserves the
catechins. And, as always, consult your physician before drinking green tea,
especially when taking any medications.
(See more on Green Tea's Possible
Interactions with Medications.)
******
I used to buy my tea in the form of unwrapped paper tea
bags that came in a small cardboard box. Should I buy those little airtight
foil envelopes instead, in order to keep the tea fresher?
I do not recommend green tea that comes in little paper tea bags
(especially those packaged in a non-airtight container) as they are exposed to
too much oxygen, which destroys the health-promoting catechins. Studies have
shown that tea that’s packaged this way provides very few catechins, especially
once the box has been opened. Airtight foil envelopes are a much better idea and
should stay fresh until you’re ready to brew yourself a cup.
******
I’ve heard that there is aluminum in green tea. Is this
dangerous?
Like potatoes, spinach and foods processed with aluminum
additives, tea plants contain greater amounts of aluminum than most other foods.
However, most experts believe that our exposure to the levels of
aluminum naturally present in our food, water and aluminum pots and pans is
generally not harmful. Medications like antacids or buffered aspirin, however,
are a much larger (and more worrisome) source of aluminum. While the daily
intake of aluminum from food is estimated to be about 5-20 mg., it can be as
high as 5 grams if you take aluminum-containing medications like these on a
daily basis!
But if you’re still concerned about the
aluminum content of your tea, be aware that it’s significantly higher in brick
tea, a lower quality tea manufactured from the oldest tea leaves, which
is molded into the shape of a brick. To limit your aluminum intake, avoid brick
tea and consider making your tea with non-fluoridated water. Although
aluminum by itself is not readily absorbed by the body, when it's combined with
fluoride, it forms a compound that is easily absorbed. Since tea is
already a natural source of fluoride (especially brick tea), brewing it with
fluoridated water may increase aluminum’s absorbability.
(See more on
Green Tea and Fluoride.)
Finally, remember that moderation is the key. Most likely,
drinking a couple of cups of green tea every day won’t increase your aluminum
intake too drastically. However, if you consistently drink 10 daily cups of
brick tea, it could be another story!
******
Is green tea okay for children to drink?
Yes, children can drink green tea – they have been doing so in
Asian countries for decades! And with its cavity-fighting abilities and
protective effects on the teeth, green tea is certainly a better alternative
than those sugary drinks kids typically guzzle throughout the day. One study
involving Japanese children found that those who drank a cup of green tea
immediately after lunch had significantly fewer cavities than those who did not
drink the tea. Just be sure you let it cool for a few minutes before serving it.
******
I was wondering if there are any negative effects from
drinking a gallon of green tea a day?
High doses of green tea (equivalent to 5 or more liters or 1.3
gallons per day) can contribute to nausea, vomiting, abdominal bloating,
insomnia, fatigue, agitation, restlessness, the thinning of the blood and
increased blood pressure.
And while a cup of green tea has only a moderate amount
of caffeine (about 20 mg per 6 oz. cup), drinking a gallon of it packs a punch
of about 425 mg. of caffeine -- about twice as much caffeine as most doctors
recommend as a daily intake. This amount of caffeine increases the risk of
caffeine side effects like jitteriness, restlessness and insomnia and also
increases the urinary excretion of calcium, which can promote osteoporosis.
Large amounts of green tea also appear to reduce the
body’s absorption of iron from non-meat sources, increasing the risk of anemia.
So although drinking several cups of green tea per day can be great for your
health, drinking a gallon a day doesn’t look like a good idea. Even half that
amount sounds like a bit much.
******
Is it okay to drink green tea if you have high blood
pressure?
Many doctors advise their patients with high blood pressure to
limit their caffeine intake to about 100 mg per day since caffeine is a
stimulant that could push blood pressure up. Luckily, green tea is actually
quite low in caffeine (only 25mg per 8 oz. cup, compared to 65 mg in black tea,
and 185 mg in coffee). So theoretically you may be able to drink as many as 4
cups a day and still be within the "safe" range, as long as you stay away from
all other sources of caffeine. And you can always drink decaffeinated green tea,
if you prefer.
If you do opt for decaffeinated tea, get one that has
been processed using the carbon dioxide or “effervescent” method. The “other”
(standard) method of decaffeinating green tea involves the use of the chemical
ethyl acetate, which destroys most of green tea's catechins, effectively
negating most of the health benefits of the tea.
(See more
on Green Tea and Cardiovascular Disease.)
******
Is there a difference between green tea that is brewed
from a tea bag and that brewed from the actual leaf itself?
The catechin content of the tea, whether it’s loose-leaf or in tea
bag form, depends greatly on the way the tea has been packaged and whether or
not the packaging has been opened. That’s because exposure to air destroys
catechins. To preserve the catechins, tea in loose-leaf form should be
vacuum-packed in a tin or a foil packet to seal out oxygen. If it's in tea bag
form, each bag should be enclosed in its own individual, airtight foil packet
for the same reason. Then, once opened, loose-leaf tea should always be stored
in an airtight container.
******
I have been told that green tea is linked to kidney
stones and possibly constipation. Is there any truth to this? I happen to drink
a lot of it.
Some people have trouble with stomach irritation or even diarrhea if they drink
too much green tea, but I have never heard of any complaints about constipation.
As for promoting kidney
stones, green tea actually appears to do just the opposite. A study published in
the Journal of
Urology in 2005
found that green tea inhibited the formation of the most common kind of kidney
stones (those made of calcium oxalate) in laboratory animals. The researchers
believe that it interferes with the calcification process through its
antioxidant effects.
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Nadine Taylor, M.S., R.D. presents
GreenTeaLibrary.com,
the most comprehensive collection of scientific information
describing the health benefits of green tea.
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