An influential panel
of experts convened by the World Health Organization concluded on
Wednesday that regularly drinking coffee could protect against at least
two types of cancer, a decision that followed decades of research
pointing to the beverage’s many health benefits. The panel also said
there was a lack of evidence that it might cause other types of cancer.
The announcement
marked a rare reversal for the panel, which had previously described
coffee as “possibly carcinogenic” in 1991 and linked it to bladder
cancer. But since then a large body of research has portrayed coffee as a
surprising elixir, finding lower rates of heart disease, Type 2
diabetes, neurological disorders and several cancers in those who drink
it regularly.
In their report, the
scientists did identify one surprising risk for coffee and tea drinkers.
They said that drinking “very hot” beverages was “probably
carcinogenic,” because the practice was linked to esophageal cancer in
some studies.
Much of the evidence
for coffee’s health benefits stems from large epidemiological studies,
which cannot prove cause and effect. But the favorable findings on
coffee consumption have been so consistent across numerous studies in
recent years that many health authorities have endorsed it as part of a
healthy diet.
Last year, a panel of
scientists that shaped the federal government’s 2015 dietary guidelines
said there was “strong evidence” that three to five cups of coffee daily
was not harmful, and that “moderate” consumption might reduce chronic
disease. Another group, the World Cancer Research Fund International,
reported that coffee protects against multiple types of cancer. And
several systematic reviews of studies involving millions of people have
found that regular coffee drinkers live longer than others.
In its report, published Wednesday in Lancet Oncology,
the World Health Organization’s International Agency for Research on
Cancer said it had assembled a team of 23 international scientists who
reviewed more than 1,000 studies. The agency said the evidence showed
that drinking coffee was unlikely to cause several types of cancer,
including breast, prostate and pancreatic cancers, and that it was
associated with a lower risk of uterine and liver cancers. For 20 other
types of cancer there was “inadequate” evidence of a link to cancer,
said Dana Loomis, the deputy head of the agency’s program that
classifies carcinogens and the first author of the report.
Decades ago, the group
listed coffee as a “possible carcinogen” – along with lead and diesel
fuel – because of studies that suggested a weak link to bladder and
pancreatic cancer. But those early studies did not adequately account
for higher smoking rates among coffee drinkers and, since then, more
rigorous and better-quality studies have become available, Dr. Loomis
said. “There is less of a concern today than there was before,” he
added.
In its report, the
group cited evidence, for example, that coffee drinkers’ risk of liver
cancer decreases 15 percent “for each one cup per day increment.” Still,
the group did not give coffee a ringing endorsement. It placed coffee
in its Group 3 category for things with “inadequate” evidence of
carcinogenic potential, such as fluoride, low frequency electric fields,
and toluene, a solvent used to make nail polish.
Geoffrey Kabat, a
cancer epidemiologist at the Albert Einstein College of Medicine in New
York, said he felt that the agency did not go far enough in its report.
He said that coffee had been studied in populations across the globe and
that studies now show a clear lack of evidence of harm. He said the
agency tends to give greater weight to studies showing harm, even when
they are outnumbered by many more showing benefit.
“What the evidence
shows over all is that coffee drinking is associated with either reduced
risk of several cancers or certainly no clear increase in other
cancers,” he said. “There’s a strong signal that this is probably not
something that we need to be worrying about.”
Since 1971, the cancer
research agency has evaluated nearly 1,000 environmental and lifestyle
factors to determine the extent to which they can promote cancer. About
120 have been categorized as carcinogenic to humans, including asbestos,
cigarettes and plutonium. Other things it has classified as
carcinogenic include wood dust, salted fish and processed meats such as
bacon, ham and hot dogs.
But the agency’s
reports have at times been controversial. Critics have called the
agency’s ranking system arcane and confusing because it classifies
things according to the strength of the overall research, not their
actual level of danger. Dr. Kabat said the assessment system was useful
for cancer researchers but that it served no utility for the public.
“I really feel that it’s not contributing to the public good because it’s stoking these concerns,” he said.
Still, the news on
coffee is likely to be welcomed by many Americans – about 130 million of
whom drink coffee every day. Around the world, more than 1.6 billion
cups of coffee are consumed daily, making it one of the world’s most
popular drinks behind tea.
The agency said it was
not clear why coffee seems to protect against at least two types of
cancers. But it noted that drinking coffee produced “strong antioxidant
effects” in clinical trials, and that it promoted the death of cancer
cells in laboratory studies.
The report’s concerns
about “very hot” beverages included mention of mate, a type of tea
traditionally consumed in South America, the Middle East and some parts
of Europe, often at high temperatures. The agency said that regular
consumption of beverages hotter than 149 degrees Fahrenheit was
“probably carcinogenic” based on a small number of studies showing a
link between the practice and esophageal cancer.
One reason is that,
over time, scalding hot beverages may injure cells that line the throat,
setting the stage for rare cancers. But Dr. Loomis cautioned that the
increased risk was seen in people who regularly drink their tea or mate
at very high temperatures, typically at 158 degrees Fahrenheit or
greater.
That is very different
from the average tea or coffee drinker in the United States and Europe,
where coffee is generally consumed at temperatures below 140 degrees
Fahrenheit. It is also an issue that can be easily avoided.
“Those who are concerned should just wait a few minutes more before drinking their drink,” Dr. Loomis said.
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