green tea and memory

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Green Tea and Memory

Colin Compas 9/20/06

Introduction

The lay public and health care professionals have long searched for a single

miracle cure for many or all of the medical problems that face humanity. So far no

single cure has been found nor is one likely to be discovered; however, one

supplement that seems to have health benefits in a wide range of areas is green tea

and green tea extract. Green tea is thought to have health benefits such as lowering

cholesterol, reducing the risk of heart disease, cancer prevention, weight loss,

increased immune system response, and improved memory (Daniells,

2006). Many of these claims have not been well substantiated and are based on

limited, if any, scientific evidence. One of these claims, however, has been studied

in some detail and that is the claim of improved memory. Interest in this benefit of

green tea has increased as the American population ages and the rate of age-related

dementia increases along with it. Alzheimer's disease and Parkinson's disease are

two common types of dementia that have been examined as part of the effort to

study the effect of green tea on memory loss. Because its effects may be relatively

subtle, it is difficult to quantitatively measure the possible benefits of green tea on

brain function in relatively healthy people. However, by studying people suffering

from neurodegenerative disorders the effects of green tea may be more readily

visible. A focus of considerable research has been to examine the possible effects

of green tea in helping to slow the effects of age related dementia (eg. Kim 2004,

Levites 2001).

Internet Claims

There are many claims on the internet for the “magical” properties of green

tea relating to memory loss. Many postings for green tea supplements list



improved memory as one of the benefits, however, they rarely give any of the

scientific evidence to support their claim. For example, a simple quote such as, "A

new generation of dietary supplements containing

pure EGCG may lead to the greatest benefit for

treating Alzheimer's disease,"

(http://news.bbc.co.uk/2/low/health/4261558.stm)

by a physician is often all that is given to

substantiate the claim. In another article the authors

state, "Green tea catechins may improve reference

and working-memory related learning ability" (Daniells, 2006). Green tea could

prove enticing for someone looking for some way to improve memory because

along with improved memory that could be able to, "treat headaches, body ache,

poor digestion, and improve well-being and life expectancy"

(http://www.bodybuildingforyou.com/health-supplements/green-tea-

extract.htm). Green tea also claims to offer all of these benefits without serious

side effects.

How Green Tea Works

The two main components of green tea that are thought to work on

improving memory are polyphenols and a particular type of polyphenol called

flavonoids. Polyphenols are substances found in plants that are often responsible

for their coloring. It is the antioxidative properties of polyphenols that are seen to

be an advantage in preventing memory

loss. Flavonoids, as seen in Figure 2, are a secondary

plant metabolite that is also seen to have antioxidative

properties. The most active polyphenol in green tea is

(-)-epigalochatechin-3-gallate (EGCG). EGCG

inhibits neuronal loss in two ways. It decreases the

production of Beta-amyloid (Aβ), which forms proteins that can develop into plaques in the brains of Alzheimer's patients (Okello,

http://news.bbc.co.uk/2/low/health/4261558.stm



http://www.bodybuildingforyou.com/health-supplements/green-tea-extract.htm









2004). It also decreases neuronal loss due to polyphenol (-)-epigallocatechin-3-

gallate (MPTP), which is a potent neurotoxin that specifically affects dopamine

production and receptors. The antioxidative properties of polyphenels are also

what is believed to cause many of the other health benefits of green tea because

nearly all of the conditions that green tea is able to help are caused by free radicals

in the body which come as a result of oxidative stress (Levites 2001).

The brain is particularly susceptible to free radical damage because of its

high metabolic rate. The high use of oxygen during the metabolic processes leads

to the generation of a large number of free radicals, which are molecules that have

unpaired electrons. When these molecules with unpaired electrons try to bond to

other molecules, it causes a bond in the second molecule to break in order to create

an electron pair. This series of events can cause a chain reaction that can

eventually lead to cell damage. The body's natural defense against free radicals

comes from antioxidants, which donate an electron to end the chain reaction. The

most common forms of antioxidants in the body are vitamins E and C. Green tea

has proven to be a source many additional antioxidants and this is why it is

beneficial in stopping cell degeneration. One of the reasons that green tea is so

beneficial in stopping this degeneration in neuronal cells is that EGCG has been

shown to be present in the brain, meaning that it is able to enact its antioxidative

affects on the free radicals causing damage in the brain.

Conditions Affecting Memory

The reason that neuronal loss is seen to be so prevalent in elderly people is

that free radicals tend to build up over time and therefore have a greater effect as

people age. This is the reason that at 65 years of age about 1.5% of the population

suffers from some type of dementia with the rate doubling every 4 years until 30%

of the population that is 80 years old suffer from dementia (Kuriyama, 2006). One

of the most common types of dementia is Alzheimer's disease which affects about4.5 million Americans. Alzheimer's disease is defined as a progressive brain



disorder that gradually destroys a person’s memory and ability to learn, reason,

make judgments, communicate and carry out daily activities (alz.org). The causes

of Alzheimer's are not well defined but are a combination of age, family history,

and genetics. One reason that green tea was originally looked at in the treatment of

Alzheimer's is because there is a much lower prevalence of the disease in Asia,

where green tea is the most popular drink. Green tea may inhibit the development

of Alzheimer's by increasing the amount of acetylcholine (ACh), an important

neurotransmitter, in synapses by inhibiting cholinesterases (AChE), which breaks

down ACh.

Parkinson's disease is another neurodegenerative disease for which green

tea is thought to have beneficial effects. Parkinson's disease occurs when neurons

in the substantia nigra of the brain die or become impaired (parkinson.org). The

cells of this area of the brain normally produce dopamine which is a

neurotransmitter that allows for the smooth coordinated function of the body's

muscles. Symptoms of Parkinson's disease appear when nearly 80% of these cells

are damaged. Symptoms of Parkinson's disease include tremors, slowness of

movement, and difficulty with balance. Green tea is able to help alleviate some of

the symptoms of Parkinson's by inhibiting MPTP which is the neurotoxin that

affects dopamine in the brain.

Scientific Literature

The first scientific studies of green tea as a prevention of age related

memory loss came as a result of the knowledge that the memory loss was the result

of free radical buildup in the brain (Levites 2001). It was known that antioxidants

could prevent damage by free radicals and green tea was known to be a good

source of antioxidants. It is difficult to study normal memory loss due to aging

because it is a very slow process and difficult to quantify. It is even more difficult

to study this process in mice because the life span of a mouse is short enough thatthere is little free radical buildup in the brain leading to memory loss. For this



reason it proved easier to study the affects of neuronal degradation by looking at a

mice model for Parkinson's disease. Also, this would open the possibility for

treatments found in animal research to be applied to treating this debilitating

disease in humans. In Levites et al. (2001) they showed the effectiveness of

MGCG on slowing the neurodegenerative process of MPTP. They looked at

different groups of mice who were given MPTP, EGCG and a combination of

MPTP and EGCG and examined subsequent neuronal loss as a result of the

neurotoxin. They found that EGCG was effective in inhibiting the neuronal

loss. They believe that this is the result of the catechol-containing compounds,

found in green tea, which are known to inhibit free radicals. By inhibiting the free

radicals they found that they could inhibit neuronal loss in the mouse model for

Parkinson's disease.

In a follow up study by Levites et al. (2002) the first potential side effects

of green tea were seen. Green tea only exhibits antioxidative properties at

relatively low concentrations and at high concentrations can actually prove to be

pro-oxidative (Levites, 2002). This finding was concurrent with other studies of

antioxidants that showed the same properties. This means that there is a correct

dosage that should be taken in order to experience the beneficial effects of green

tea as an antioxidant. It was later shown that an average of two cups of tea per day

provide the correct amount of polyphenols and flavonoids necessary to prevent

neural degeneration (Mandel, 2004).

Following studies on the effects of

green tea on Parkinson's disease, Kim et al.

(2004) looked at the role that green tea

could play in inhibiting the progression of

Alzheimer's disease. It was already known

that ACh and AChE played a role in the

development of Alzheimer's and drugs hadalready been developed to increase ACh or

Figure 3. Inhibition of AChE by green tea,

black tea, and coffee based on concentration of

each. (Okello, 2004)



decrease AChE in order to slow the progression of Alzheimer's but many of these

drugs proved ineffective and had many side effects. Following procedures similar

to those used in studies of green tea in mice with Parkinson's, Kim et al. looked at

the effects of green tea in a mouse model for Alzheimer's. They found that green

tea inhibited AChE and improved overall cognitive ability in the mouse

model. These findings were furthered by Okello et al. as shown in Figure 3

(Okello, 2004). This graph shows the relationship between concentration and

inhibition of AChE for green tea, black tea, and coffee. The graph shows that the

greatest inhibition results from the green tea. They also showed similar findings to

Levites et al. showing that there is a limit in the concentration that is effective in

inhibiting AChE. The findings of Okello et al. went further in showing that EGCG

also inhibits the production of Aβ, which may be responsible for plaque deposits in

the brains of Alzheimer's patients. This could prove very beneficial because

synthetic inhibitors of Aβ have proven ineffective due to their high molecular

weights.

It has been shown that green tea is effective in slowing neural loss due to

free radicals and oxidative stress, but Mandel et al. (2004) have gone further in

looking at the specific pathways that the antioxidants in green tea are taking in

order to prevent the degeneration. They have found that the radical scavenger

properties of green tea may not be the sole explanation of the neuroprotective

behavior of green tea (Mandel, 2004). They have found that the benefits may also

come from the pharmacological effects of catechins and there derivatives. Mandel

et al. found that the neuroprotective effect of EGCG is actually due to the down

regulation of certain genes rather than the up regulation of the antigens of those

genes. Concurrent with other studies they found that this effect was reversed at

high concentrations of EGCG. They found that the flavonoids activate a signal

pathway that has a neuroprotective affect rather than acting directly on preserving

neural cells themselves.



The drawback in many of these studies is that they have been performed

either in vitro or in a mouse model. These models often prove applicable to human

patients but it cannot be proven until studies in people are performed. The problem

with human studies of this type is challenge in controlling other variables that may

be involved and the time scale necessary for the observance of symptoms due to

cognitive loss. To address some of the limitations of prior research, Kuriyama et

al. (2006) attempted to look at a large subset of Japanese population in order to

determine the effects of green tea in people. Three different groups were selected

based on the amount of green tea they drank. The groups were those who drank

less than three cups a week, those who drank four to six cups a week, and those

who drank two or more cups per day. It was found that with each increase in green

tea consumption there was a corresponding decrease in prevalence of cognitive

impairment (Kuriyama, 2006). While this is a limited demographic that could

have many other confounding variables, it is encouraging that many of the finding

in vitro and in mice may be applicable to human populations.

Conclusion

In summary, many claims have been made on the internet about the health

benefits of green tea, including its prevention of memory loss. These claims are

often made without reference to adequate scientific research. However, there is

now research that may support the claim that green tea helps prevent cognitive loss

due to aging and age related dementia. Many of the studies that have recently been

conducted rely on evidence from in vitro and in mouse models, so further human

studies are needed. With that said, the findings of the positive effects of the

antioxidative properties of green tea are encouraging and may likely prove to be an

effective and side effect free method for treating and perhaps preventing age

related memory loss.

green tea and memory

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