NEW YORK (Reuters) - A decades-old medical mystery - why
antioxidants such as vitamin E and beta carotene seemed to
accelerate the growth of early lung tumors in high-risk
populations such as smokers, rather than protect them from
cancer, as theory suggests - may have been solved, according to
research published on Wednesday.
In essence, "antioxidants allow cancer cells to escape
cells' own defense system" against tumors, biologist Per Lindahl
of Sweden's University of Gothenburg and a co-author of the
study told reporters. That lets existing tumors, even those too
small to be detected, proliferate uncontrollably.
The findings imply that "taking extra antioxidants might be
harmful and could speed up the growth of (any) tumors," said
biologist and co-author Martin Bergo of Gothenburg, adding, "If
I had a patient with lung cancer, I would not recommend they
take an antioxidant."
The study, published in Science Translational Medicine, did
not examine whether antioxidants can also initiate lung cancer,
rather than accelerate the growth of existing tumors. Nor did it
examine whole foods naturally high in antioxidants. But it adds
to a growing pile of research challenging the health benefits of
taking vitamin supplements except in cases of malnutrition.
Last month, a review of dozens of studies found "no clear
evidence of a beneficial effect of supplements" on heart
disease, cancer or mortality. An accompanying editorial in the
Annals of Internal Medicine warned that "beta carotene, vitamin
E, and possibly high doses of vitamin A supplements are
harmful," while other antioxidants "are ineffective."
The new antioxidant study "seems quite sound," said Eliseo
Guallar, professor of epidemiology at Johns Hopkins Bloomberg
School of Public Health and a co-author of the editorial. "It's
unfortunate that the public has the idea that vitamin
supplements are good and antioxidants are better."
One concern about the new study is that the mice received
doses of vitamin E at least four times, and as much as 50 times,
Americans' recommended daily intake, noted Duffy MacKay of the
Council for Responsible Nutrition, the supplement industry trade
Government data show that 90 percent of Americans have diets
that contain less than the recommended intake of vitamin E, he
said, calling the Swedish study "very interesting and
hypothesis-generating," but not one that should change behavior.
Of all the gaps between biological theory and medical
reality, few are as stark as that involving antioxidants.
In cells growing in the lab, antioxidants scavenge and
disable free radicals, reactive chemicals produced during normal
metabolism that can harm DNA and other components of cells. By
the 1980s that had led to the idea that by protecting DNA from
damage, antioxidants might prevent cancer and other disease and
launched a bull market in antioxidants that continues unabated,
with packages of cereal, granola bars, juice and more all
touting their antioxidants and health magazines and television
shows urging consumers to load up on them.
For the new study, the Gothenburg scientists gave vitamin E
and a generic drug called N-acetylcysteine, both antioxidants,
to mice with early lung cancer. The vitamin E doses were
comparable to those in supplements; the doses of acetylcysteine,
which is prescribed for chronic obstructive pulmonary disease
(COPD) to reduce mucus, were relatively low.
The antioxidants caused a 2.8-fold increase in lung tumors,
made the tumors more invasive and aggressive, and caused the
mice to die twice as quickly - all compared to mice not given
When the antioxidants were added to human lung tumor cells
in lab dishes, they also accelerated cancer growth.
That result jibed with the many studies finding that
"antioxidants do not protect against cancer in healthy people
and may increase it" or promote it in those who already have
cancer, said Bergo.
The significant advance in the study was pinpointing how
this can be. What seems to happen is that antioxidants indeed
decrease DNA damage, as expected. But the damage becomes so
insignificant as to be undetectable by the cell. The cell
therefore does not deploy its cancer-defense system, which is
based on a protein called p53.
Ordinarily, if the p53 system detects significant DNA
damage, such as from ultraviolet light, it kills the cell before
it can become malignant. By allowing cancer cells to stay below
the radar of p53, antioxidants allow tumors to thrive, the study
The scientists stressed that the results do not pertain to
foods such as fruits and vegetables that are naturally high in
As for people with COPD who are taking acetylcysteine, "we
think that should be carefully evaluated," Bergo said.
Although the study investigated only lung cancer and two
antioxidants, previous research suggests that other cancers can
also be accelerated by antioxidants, Bergo said, and that other
antioxidants have this effect.
The National Cancer Institute already advises cancer
patients that antioxidant supplements "should be used with
The discovery of how antioxidants thwart cells' innate
cancer-fighting machinery might explain why a groundbreaking
1994 study found an 18 percent higher incidence of lung cancer
among 29,133 male smokers who received beta carotene than those
who did not. The result was so unexpected and unwelcome that the
editorial in the journal where it was published tried to dismiss
it as "an extreme play of chance."
"It's disappointing but not surprising that people's beliefs
are not modified by scientific evidence," said Dr. Paul Marantz,
an epidemiologist at Albert Einstein College of Medicine in New
York. "People so want to believe there is a magic bullet out
SOURCE: http://bit.ly/1d8gb1s Science Translational
Medicine, online January 29, 2014.