There was a time when the only news about coffee and health
was how it was bad for the heart, likely to give us ulcers and aggravate our
nerves, but now it seems this popular beverage is receiving a more favorable
kind of press.
However, the researchers uncovering the good news are all saying the same thing: while there appear to be some health perks from drinking coffee, there are also a few cautions, and the evidence is not solid enough to actively encourage people to go out and drink coffee.
Another reason to reserve some caution, is that although the evidence is shifting toward a more favorable view of coffee's effect on health, it is not based on cause and effect but on links for which there could be other explanations: it could be that regular coffee drinkers have something else in common, that studies have yet to discover, to account for the effect on health.
One of the turning points in media reporting on coffee and health came with the publication in 2008 of a Harvard-led study, that examined data on over 130,000 participants from the Nurses' Health Study and the Health Professionals Follow Up Study who were followed for about 20 years.
This finding confirms the research picture that has been emerging in the last few years, says Rob van Dam, Assistant Professor in the Department of Nutrition, Harvard School of Public Health, one of the study researchers.
Mayo Clinic preventive medicine specialist Donald Hensrud suggests one explanation for the apparent reversal in thinking about coffee, is that:
For women, coffee drinking may mean a lower risk of stroke.
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However, the researchers uncovering the good news are all saying the same thing: while there appear to be some health perks from drinking coffee, there are also a few cautions, and the evidence is not solid enough to actively encourage people to go out and drink coffee.
Another reason to reserve some caution, is that although the evidence is shifting toward a more favorable view of coffee's effect on health, it is not based on cause and effect but on links for which there could be other explanations: it could be that regular coffee drinkers have something else in common, that studies have yet to discover, to account for the effect on health.
In this article we look at the shift in the research view on
coffee consumption, touching on some of the key studies, and finish off with
some facts and figures about coffee and caffeine.
One of the turning points in media reporting on coffee and health came with the publication in 2008 of a Harvard-led study, that examined data on over 130,000 participants from the Nurses' Health Study and the Health Professionals Follow Up Study who were followed for about 20 years.
The results showed regularly consuming up to 6 cups of
coffee per day (containing around 100 mg caffeine per 8 oz cup) was not linked
with increased deaths in either men or women, from any cause, or death from
cancer, or from cardiovascular disease.
This finding confirms the research picture that has been emerging in the last few years, says Rob van Dam, Assistant Professor in the Department of Nutrition, Harvard School of Public Health, one of the study researchers.
Coffee ingestion is, on average, about one third of that of
tap water in North America and Europe. (International Journal of Cancer)
"For the general population, the evidence suggests that coffee drinking
doesn't have any serious detrimental health effects," he adds.
Mayo Clinic preventive medicine specialist Donald Hensrud suggests one explanation for the apparent reversal in thinking about coffee, is that:
"Earlier studies didn't always take into account that
known high-risk behaviors, such as smoking and physical inactivity, tended to
be more common among heavy coffee drinkers at that time."
But perhaps what these more recent findings suggest, says
van Dam, is that outside of certain groups, like pregnant women and those who
have trouble controlling blood pressure, people should continue to enjoy their
coffee in moderation and focus instead on other lifestyle factors, such as
stopping smoking, getting more exercise, and eating more whole grains, as ways
to reduce risk of poor health.
Heart Disease and
Stroke
Some of the evidence that has emerged in recent years
suggests coffee consumption may lower the risk of heart disease and stroke.
A Kaiser Permanente study presented at an American Heart
Association conference in March 2010, found coffee drinkers were less likely to
be hospitalized for heart rhythm disturbances. The researchers examined data on
of 130,000 health plan members and found people who reported drinking between
one and three cups of coffee a day had a lower risk than non-drinkers,
regardless of other risk factors.
Reported more recently, in 2012, a US study found that
drinking coffee in moderation, may also protect slightly against heart failure.
For women, coffee drinking may mean a lower risk of stroke.
In March 2011, research led by the Karolinska Institute in
Stockholm, Sweden, that followed over 30,000 women for 10 years, found those
who drank more than one cup of coffee per day appeared to have a 22 to 25%
lower risk of stroke, compared to non-drinkers. The researchers also found that
"low or no coffee consumption was associated with an increased risk of
stroke in women".
The findings were the same, regardless of other factors such
as smoking, alcohol, body mass index, history of diabetes, and high blood
pressure.
An earlier US study, published in 2009, involving 80,000
women from the Nurses' Health Study, had also found a 20% lower risk of stroke
among coffee drinkers. None of the women had a history of stroke, coronary
heart disease, diabetes, or cancer at the start of the study, and the
researchers found the relative risk of stroke went down as coffee consumption
went up.
However, a recent
Harvard Health newsletter warns that while moderate coffee consumption (3 - 4
cups a day) may be linked to a lower risk for stroke, among infrequent
coffee consumers the risk of a stroke just after drinking coffee could be
higher.
One reason coffee consumption may lower longer term risk for
heart disease and stroke, is because it appears to reduce the chance of developing
type 2 diabetes, which is itself a risk factor for these diseases.
Type 2 Diabetes
Frank Hu, nutrition and epidemiology professor at the
Harvard School of Public Health, has been researching the effects of coffee on
health since before the 2008 Harvard study, on which he was also a co-author.
In 2005, he and his team published a paper in which they
reviewed nine studies covering more than 193,000 people in the US and Europe
that examined the link between coffee intake and type 2 diabetes. Their analysis
found participants who reported drinking more than 6 or 7 cups of coffee a day
were 35% less likely to have type 2 diabetes, compared with those who reported
drinking under 2 cups a day. For those drinking 4 to 6 cups a day, the risk was
reduced by 28%.
More recently, in 2009, an international study led by
researchers in Australia, reviewed 18 studies covering nearly 458,000 people
and found that for every extra daily cup of coffee consumed, there was a 7%
reduction in risk for developing type 2 diabetes. There were similar reductions
for tea and decaf coffee. However, the researchers warned that some of the
studies they reviewed were small and less reliable, so the link between heavy
coffee drinking and reduced risk of type 2 diabetes may be exaggerated. They
called for randomized trials to investigate their finding more robustly.
In a comment to WebMD in 2011, Hu describes the evidence on
coffee and type 2 diabetes, based on more than 15 published studies, as
"pretty solid", and now it appears decaf may have the same benefit.
In February 2012, researchers from Mount Sinai School of
Medicine who did a study on mice, wrote how they discovered decaffeinated
coffee may improve brain energy metabolism associated with type 2 diabetes.
This brain dysfunction is a known risk factor for dementia and other
neurodegenerative disorders like Alzheimer's disease. The researchers said the
new findings were evidence that some of the non-caffeine components in coffee
provide health benefits in mice.
Hu also speculates that caffeine is unlikely to be the
reason for the link between coffee consumption and reduced type 2 diabetes
risk, and the more likely explanation is "the whole package" of
nutrients. For instance coffee is rich in antioxidants, which are known to prevent
tissue damage caused by oxygen-free radicals.
Coffee also contains minerals such as magnesium and
chromium, both used by the body to regulate insulin which in turns controls
blood sugar. People with type 2 diabetes have lost the ability to use insulin
to regulate blood sugar properly.
Alzheimer's Disease
In 2009, researchers in Finland and Sweden reported a study
that followed over 1,400 people over 20 years, and found that those who drank 3
to 5 cups of coffee a day in their midlife years had a 65% lower chance of
developing dementia and Alzheimer's disease compared with those who reported
drinking no coffee at all or only occasionally.
In June 2012, researchers from the University of South
Florida (USF) and the University of Miami, published a paper describing how
they monitored the memory and thinking processes of 124 people, aged 65 to 88,
and found all those with higher blood levels of caffeine (mostly from drinking
coffee) avoided the onset of Alzheimer's disease in the 2-4 year follow up.
This was even true of those who had mild cognitive impairment (MCI), a
precursor of Alzheimer's.
Lead author Chuanhai Cao, a neuroscientist at the USF
College of Pharmacy and the USF Health Byrd Alzheimer's Institute, and
colleagues, have been publishing papers on the links between caffeine, coffee
and Alzheimer's disease since 2006.
For instance in 2009, Cao co-authored two significant
papers, with colleagues from USF and other research centers in the US and the
Saitama Medical University in Japan, that found giving aged mice with symptoms
of Alzheimer's the caffeine equivalent of five cups of coffee a day, reversed
two signs of the disease: memory impairment and the hallmark protein in the
animals' blood and brains.
Earlier studies at USF had already shown that giving
caffeine to elderly people who did not have dementia quickly affected their
blood levels of beta-amyloid (a protein that forms stickly clumps of plaque in
the brains of people with Alzheimer's), and found the same thing happened in
the Alzheimer's mice.
"We are not saying that moderate coffee consumption
will completely protect people from Alzheimer's disease. However, we firmly
believe that moderate coffee consumption can appreciably reduce your risk of
Alzheimer's or delay its onset," Cao told the press at the publication of
the June 2012 paper.
While they believe caffeine to be the key, Cao and
colleagues don't think it acts alone, but in conjunction with another, yet to
be identified component in coffee, that boosts blood levels of a critical
growth factor that seems to fight off the Alzheimer's disease process.
Parkinson's Disease
For Parkinson's Disease, another neurodegenerative disorder,
it appears there is also a link between higher coffee consumption and decreased
risk. And like Alzheimer's, this also seems to be due to caffeine, but it is less
clear how it works. However, one study of caffeine and risk of developing the
two diseases that was published in Journal of Alzheimer's Disease in 2010, by
Xuesong Chen and colleagues from the University of North Dakota in the US,
suggest it might be something to do with a protective effect that caffeine has
in preserving the blood-brain-barrier.
In another Journal of Alzheimer's Disease study also
published in 2010, João Costa of the University of Lisbon, Portugal, and
colleagues present an analysis of 26 studies that suggests an inverse
association between coffee drinking and the chance of developing Parkinson's
disease. For every increase of 300 mg per day in caffeine intake, they found a
drop of 24% in the relative risk of developing Parkinson's. Among those who
regularly drank two to three cups of coffee a day, there was a 25% lower chance
of developing the disease compared to non-coffee drinkers. However, among women
coffee drinkers only, this fell to 14%. The researchers said their findings could
"hardly by explained by bias or uncontrolled confounding".
Cancer
Studies have also suggested coffee consumption is linked to
a lower risk for some cancers, including endometrial, aggressive prostate,
estrogen-negative breast cancer, liver cancer, and a common form of skin
cancer, but not others (eg esophageal).
In 2011, researchers working with data from the Nurses'
Health Study published findings that showed coffee drinkers who consumed more
than four cups a day had a 25% lower risk of developing endometrial cancer.
Senior researcher Edward Giovannucci, professor of nutrition
and epidemiology at the Harvard School of Public Health, said coffee is
starting to emerge as a protective agent in cancers that are linked to obesity,
estrogen and insulin.
He and his colleagues suggest antioxidant and
anti-inflammatory substances in coffee may be responsible for anti-cancer
activity. Giovannucci said lab tests show coffee has more antioxidants than
most fruits and vegetables.
Giovannucci was also co-author of another 2011 study that
found men who regularly drink coffee appear to have a lower risk of developing
an aggressive, lethal form of prostate cancer. They also found the lower risk
was the same for caffeinated as for decaffeinated coffee.
A link with coffee consumption and lower risk of
estrogen-negative breast cancer was made in a Swedish study that also appeared
in 2011.
When they first looked at their data, the researchers from
Karolinska Institute found women who drank coffee had a lower incidence of
breast cancer than women who rarely drank coffee, but when they took into
account other risk factors, including lifestyle and age, they found the lower
risk was only measurable for estrogen-negative breast cancer.
The case for linking reduced risk of liver cancer to coffee
drinking has been building steadily for a while.
In 2007, a study led by the Mario Negri Institute for
Pharmacological Research in Milan, Italy, that did a pooled analysis of ten
studies that included over 2,200 people with hepatocellular carcinoma (HCC),
reported that among coffee drinkers overall, there was a 41 per cent reduction
in risk of HCC compared to those who never drank coffee. HCC is the most common
liver cancer and accounts for about 90% of them.
But the researchers concluded that while they found this
link, they could not say if it was coffee that was reducing the risk of liver
cancer, or if it was that people with liver cancer tended to drink less coffee
for other reasons.
Then in 2008, there followed the publication of a new large,
prospective population-based study involving over 60,000 Finns followed for a
median of 19 years, that confirmed higher coffee consumption was linked to
lower risk of developing liver cancer.
Researchers led by Gang Hu at the University of Helsinki
noted a significant inverse relationship between coffee drinking and the risk
of primary liver cancer. The more coffee people drank, the lower their risk.
But the authors said the biological mechanism behind this link was not known,
and in an accompanying editorial, Carlo La Vecchia of Milan said that while the
study solidly confirmed the link between coffee drinking and lower risk of
liver cancer, it "remains difficult" to translate it into potential
ways to prevent of liver cancer by increasing coffee consumption.
More recently, a large US study of over 110,000 people found
that the more caffeine there was in their diets, the lower their risk of
developing basal cell carcinoma, the most common type of skin cancer.
Pregnancy
Pregnant women are
advised not to drink too much coffee. In 2010, the American College of
Obstetricians and Gynecologists (ACOG) put out a statement that said drinking
less than 200 mg of coffee a day (which they equate to 12 oz of coffee),
doesn't seem to increase risk of miscarriage, or premature delivery, but above
this level it is not clear what the risks might be.
William H Barth, Jr, chair of ACOG's Committee on Obstetric
Practice, told the press:
"After a review of the scientific evidence to date,
daily moderate caffeine consumption doesn't appear to have any major impact in
causing miscarriage or preterm birth."
"Given the evidence, we should reassure our pregnant
patients and let them know that it's OK to have a cup of coffee," he
added.
The ACOG statement pointed out that caffeinated tea and soft
drinks also contain caffeine, although less than coffee, and so do chocolate
candy bars.
Global Consumption of
Coffee
Coffee is one of the most widely consumed beverages in the
world, and the most commonly consumed psychoactive drug. Some its behavioral
effects, such as arousal, are not dissimilar to those of other stimulants like
cocaine and amphetamines.
From 1950 to 1990, world production of coffee doubled, and
despite the economic downturn, consumption is still rising. Overall, the world
consumes about 7.4 million metric tons a year, or 1.3 kg per person per year,
ranging from nearly zero in countries like China and India, to upwards of 7 kg
per person per year in Switzerland, Iceland and Scandinavia, with the Finns
being the biggest coffee consumers (12 kg per person per year).
The United States consumes 1.3 metric tons per year, at a
rate of 4.2 kg per person. The latest figures for 2012 suggest 65% of American
adults drink coffee, placing the beverage "neck and neck with soft
drinks", says the National Coffee Association.
How Much Caffeine in
a Cup of Coffee?
It can be confusing when you read about coffee consumption
in cups because of the difference in cup sizes from country to country. For
instance, in the US, coffee is typically served in an 8 oz (240 ml) cup, which
is twice the amount in a typical European serving.
Working out how much caffeine you are consuming each day can
be a confusing experience. It can be even more confusing if you want to know
how much caffeine is in a cup, because that varies depending on the beans, how
they are roasted, and how the coffee is prepared.
For example, a restaurant-style serving of Espresso in a 1
oz (30ml) cup can contain from 40 to 75 mg of caffeine. Even a decaffeinated
Espresso can contain up to 15 mg of caffeine.
On the other hand, an 8 oz (240 ml) cup of generic instant
coffee can contain any amount from 27 to 173 mg of caffeine, while a Starbucks
Pike Place 16 oz (480 ml) cup of brewed coffee contains 330 mg of caffeine.
Tea has about half as
much caffeine as coffee.
How Much Is a Moderate Intake of Caffeine?
A moderate intake of caffeine is probably around 300 mg per
day. This is roughly 3 to 4 cups of ground roasted coffee or 5 cups of ins
For pregnant women, this level would be considered
excessive, and they are advised to keep their consumption below 200 mg a day.
Coffee is not the only source of caffeine in the diet. 300
mg is also the amount of caffeine in 5 or 6 servings of tea and some colas, and
the average chocolate candy bar has about 35 mg.
Some painkillers also contain caffeine, because it can make
them 40% more effective in treating headaches. The range here also varies; for
instance, from 16 mg per capsule (Dristran) to 200 mg (Vivarin), among popular
over-the-counter painkillers in the US.
In the American diet, coffee accounts for about 75% of the
adult intake of caffeine.
Caffeine is probably the most investigated substance in
coffee, but there are many others, which is probably why coffee seems to have
good sides and bad sides, and the overall effect may depend on how much they
cancel each other out.
After being absorbed in the stomach and small intestine,
caffeine travels to the rest of the body and the brain. The amount in the
bloodstream peaks about 30 to 45 minutes after ingestion, petering out some 10
hours later, as it is metabolized in the liver.
As yet no study has said that coffee does more good than
harm and therefore drinking it should be recommended. But perhaps that is just
a matter of time, and the meantime, those who thought they should give it up
for the good of their health, unless their doctor advises them differently, can
continue to enjoy it, and focus on other ways to improve health
