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 Regular/diet
soft drinks and caffeine linked to metabolic
syndrome?
 Coffee's
impact on sugar metabolism is currently
unclear.
Coffee
has been linked to a reduced risk of
diabetes and an increased risk in the general
population (see below) but it is not yet
known whether this is due to the caffeine
content or other compounds in coffee.
Furthermore,
caffeine may behave differently in people
with diabetes. The
Canadian Diabetes Association says the
following about coffee "Drinking caffeine
in large amounts as coffee over a short
period of time has been shown to raise blood
sugar. Caffeine does this by enhancing the
effect of two hormones (adrenaline and glucagon).
These two hormones release stored sugar
from the liver resulting in high blood sugar".
This can be advantageous in very active
people like athletes who need a surge of
glucose (atheletes have been known to take
caffeine supplements for extra "energy")
but may be undesirable in the inactive person.
Emerging
studies are shedding more light on caffeine
metabolism.
In
the July 23, 2007 online issue of the
journal Circulation, Dhingra
et al linked the consumption of more
than one soft drink per day to the risk
of developing metabolic syndrome or high
levels of blood insulin (a precursor to
developing diabetes). The association was
found to be true for diet soft drinks (i.e.
zero calorie) as well as those packed with
sugar. The investigators suggest that the
culprit might not be the soft drinks themselves,
but instead the eating habits that soft
drink consumption reflect. This study has
fueled speculation by suggesting that some
unknown ingredient (like caffeine) in diet
sodas might be contributing to metabolic
syndrome in susceptible individuals. The
sweet taste in the mouth (from sugar or
artificial sweeteners) may trigger the pancreas
to release insulin which could result in
hyperinsulinaemia (leading to metabolic
syndrome) if intake is chronic.
In
2006 Rush et al from the Auckland University
of Technology in New Zealand published a
study in Asia
Pacific
Journal of Clinical Nutrition showing
that an energy drink containing sugar and
added caffeine caused the body to convert
sugar into fat more rapidly than lemonade.
The energy drink tested by Rush's team contained
28g sucrose and 81mg caffeine per 250ml
can, which is similar to the amount of sugar
in soft drinks and caffeine in a brewed
cup of coffee. The author believes these
results could have huge implications when
you think about how much sugar and caffeine
people consume these days, and the high
rates of inactivity. For the study, the
New Zealand team recruited 10 healthy women
aged 18 to 22 from a range of ethnicities.
The subjects fasted overnight and were randomly
given either 250ml of an energy drink or
lemonade on the first day and the alternative
on the second day of testing. The sugar
in both drinks was absorbed rapidly into
the bloodstream - within a minute and when
caffeine is also present the sugar
is more quickly converted to fat.
Sugar is a simple carbohydrate and evidence
from this study shows that, coupled with
a large amount of caffeine, the body
rapidly turns it into stored fat.
Professor Rush highlights that simple carbohydrates
and caffeine were not such a large part
of our diet in the past. Inactive people
have trouble burning off excess energy and
this leads to weight gain.
The findings are supported by a recent UK
study, which found that caffeine increased
cyclists' absorption of carbohydrates from
a sports drink. But for those consumers
not doing much exercise, these carbohydrates
will be turned into fat.
The study also raises questions about the
effects of consuming high-sugar foods
and highly caffeinated drinks together in
a short period of time. Caffeine
lasts in the body for four to six hours,
so people who have caffeinated drinks, including
sugar-free energy drinks or coffee, and
then eat sugary food within this time frame,
may experience similar effects. This study
is limited by its small sample size and
the fact that the subjects were all young
women. But the results are important as
this area has not been explored before.
This area needs further research, as well
as the long term effects of combined caffeine
and sugar on sedentary people's health.
 Coffee
Many
epidemiological and intervention studies
have examined the actions of caffeine on
human health. The findings are equivocal.
We cannot say for certain that caffeine
is linked to any health conditions. There
is evidence on the one hand of a link with
impaired insulin action, hypertension and
feelings of stress and on the other hand
there is evidence that coffee drinking may
decrease the risk of developing type 2 diabetes.
With the proliferation of caffeine containing
soft drinks and food products, all of which
are easily accessed by children, more research
is needed to explore the effects of caffeine
on human health.
Diabetes
Decreased
risk?
A
study on 84,000 women and 42,000 men, published
in the Annals
of Internal Medicine January 2004, reported
that people who drink the most caffeinated
coffee have less risk of developing type
2 diabetes. Coffee drinking ranged from
0-6 cups a day. The diabetes risk was reduced
by about 50% in men and 30% in women drinking
the most coffee. However, coffee drinking
was correlated with alcohol intake and alcohol
drinking has been previously associated
with less diabetes. Other studies have also
reported that coffee consumption is linked
to less diabetes - this study is different
in that caffeinated coffee had the greatest
effect. Decaffeinated coffee had a small
effect and tea had no effect. This study
suggests that there is something in coffee
which may help lower blood sugar levels
or that there is something about the lifestyle
of coffee drinkers. So does this study suggest
we should drink more coffee?
Not necessarily, because there have also
been studies showing that coffee drinking
can increase the risk of diabetes.
Increased
risk?
In
2002, two studies reported that caffeine
affects insulin action (Kiejzers et al.,
Diabetes Care 2002; Thong et al Diabetes
2002). The findings are not completely new,
but the degree to which the action of insulin
was reduced was surprising. Impaired insulin
action is the key step in the development
of adult-onset diabetes. Impaired insulin
means the pancreas is forced to secrete
more insulin to have the same effect till
at some point the pancreas starts to fail,
leading to the death of insulin producing
cells. In these studies the equivalent of
five to six espresso coffees were given
either as tablets or injections and the
effectiveness of insulin fell by 15 to 50%.
This is similar to the effect obesity has
on insulin action (lowers insulin action
by 40%). It is well known that exercise
increases the effectiveness of insulin,
but after the ingestion of caffeine, insulin
action was impaired, even though the subjects
had exercised for one hour (Thong et al.,
2002). It is speculated that caffeine activates
receptors (adenosine) in adipose tissue,
increasing both the concentration of fatty
acids in the blood (which in turn may impair
insulin action) and blood pressure. Caffeine
also increases the levels of the stress
hormone adrenaline which may also impair
the action of insulin.
So should we avoid coffee, especially if
we have a family history of diabetes? These
studies (and no other studies) have proven
that caffeine causes the development of
diabetes. However, with the proliferation
of caffeine containing soft drinks, more
research is needed to explore the effects
of caffeine on insulin action.
Hypertension
& Stress
In
another study (Lane et al., Psychosomatic
Medicine 2002) 500mg of caffeine in the
form of two tablets (equivalent to 4-6 cups
of coffee) was given on a certain day of
the week. Caffeine was found to cause a
slight but signifcant increase in blood
pressure and subjects reported feeling more
stressed on the day they took caffeine;
they also had greater levels of stress hormones.
People with conditions that are aggravated
by stress or who have high blood pressure
need to be conscious of the amount of coffee
they drink; alternatively they could switch
to decaffeinated coffee.
Heart
disease
Drinking
6 cups of unfiltered plunger coffee a day
may increase the risk of heart disease (Grubben
et al. AJCN 2000; 71: 480-4) because blood
homocysteine and cholesterol levels increased
by 10% and triglycerides by 36%. Sesquiterpenes
in coffee is removed by filtering and is
known to increase blood cholesterol levels.
Caffeine may also lower blood levels of
vitamin B6 which may explain the effect
on homocysteine. However, coffee contains
potentially cardio-protective flavonoids
which have been shown to be antioxidants.
Filtered coffee in moderation (2-3 cups
per day) is probably OK.
Sport
Coffee
has been shown to release fat from fat cells
and hence have a possible benefit in a weight
control diet. Marathon runners will drink
a cup of coffee before a race to prevent
hitting the wall. The theory behind this
is that glycogen, or sugars, are the primary
source of energy in the muscles, whereas
fat is used as a ‘back-up’ fuel. Once glycogen
supplies are exhausted (after 2 hours of
vigorous activity) fat comes more into play,
but this is not as easily accessible. Caffeine
before a race may release fat into the blood
stream quicker and help ‘save’ glycogen
so this does not run out suddenly, leaving
a feeling of ‘hitting a wall’ (Vinson &
Dabbagh; Nut Research 1998; 18 (6): 1067-75).
Caffeine
content of tea and coffee
Green tea has about half the caffeine
(20mg) as black tea (40mg). A typical eight-ounce
cup of tea prepared from one tea bag brewed
for three to five minutes contains 40 milligrams
of caffeine, compared with 100 milligrams
in a cup of brewed coffee. The caffeine
content of tea can range from 20 to 90 milligrams
a cup, depending on the blend of tea leaves,
method of preparation and length of brewing
time, whereas a cup of coffee may contain
from 60 to 180 milligrams of caffeine. Decaffeinated
tea, like decaffeinated coffee, has about
4 milligrams of caffeine per cup. Instant
teas and prepared iced teas, which can be
purchased with or without caffeine, may
be too highly processed to contain phytochemicals.
In
conclusion, coffee in moderation (1 cup
per day) is probably not an issue for most
adults.
If
you would like to find out about 'caffeine'
- its dietary sources and whether it is
harmful of beneficial - read this good on-line
summary by
Choice Magazine May 2000
Last
Updated: August 2007
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