Risks
Increased
prostate cancer risk from vitamin E supplements
Men
who took 400 international units (I.U.) of vitamin E daily had more prostate
cancers compared to men who took a placebo, according to an updated review of
data from the Selenium and Vitamin E Cancer Prevention Trial (SELECT). The
findings showed that, per 1,000 men, there were 76 prostate cancers in men who
took only vitamin E supplements, vs. 65 in men on placebo over a seven-year
period, or 11 more cases of prostate cancer per 1,000 men. This represents a 17
percent increase in prostate cancers relative to those who took a placebo. This
difference was statistically significant and therefore is not likely due to
chance. The results of this update appeared Oct. 12, 2011, in the Journal of the American Medical Association.
SWOG,
an international network of research institutions, carried out SELECT at more
than 400 clinical sites in the United States, Puerto Rico, and Canada. SELECT
was funded by the National Cancer Institute (NCI) and other institutes that
comprise the National Institutes of Health.
The
crystalline structure of Vitamin E“Based on these results and the results of
large cardiovascular studies using vitamin E, there is no reason for men in the
general population to take the dose of vitamin E used in SELECT as the
supplements have shown no benefit and some very real risks,” said Eric Klein,
M.D., a study co-chair for SELECT, and a physician at the Cleveland Clinic.
“For now, men who were part of SELECT should continue to see their primary care
physician or urologist and bring these results to their attention for further
consideration.”
The
SELECT study began in 2001 and included over 35,000 men. It was started because
earlier research had suggested that selenium or vitamin E might reduce the risk
of developing prostate cancer. However, based on an independent safety
monitoring review in autumn 2008, participants were told to stop taking their
study supplements because it had become clear that the trial would never
produce the 25 percent reduction in prostate cancer the study was designed to
show with the use of these supplements. In 2010, the study sites were closed
and over half of the participants consented to have their health monitored via
mail questionnaires. Now, because of this latest finding, researchers are
encouraging all participants to consider taking part in long-term study
follow-up so investigators can continue to track outcomes.
SELECT
was undertaken to substantiate earlier, separate findings from studies in which
prostate cancer risk was not the primary outcome. A 1998 study of male smokers
in Finland who took 50 I.U. of vitamin E daily to prevent lung cancer, showed
32 percent fewer prostate cancers in men who took the supplement. A 1996 study
of men and women with a history of skin cancer who took selenium for prevention
of disease recurrence showed that men who took the supplement had 52 percent
fewer prostate cancers than men who did not take the supplement.
Based
on these and other findings, men were recruited to participate in SELECT. They
were randomly assigned to take one of four sets of supplements or placebos,
with more than 8,000 men in each group. One group took both selenium and
vitamin E; one took selenium and a placebo that looked similar to vitamin E;
one took vitamin E and a placebo that looked similar to selenium; and the final
group received placebos of both supplements. Men who took selenium alone or
vitamin E and selenium together were also more likely to develop prostate
cancer than men who took a placebo, but those increases were small and possibly
due to chance.
“SELECT
has definitively shown a lack of benefit from vitamin E and selenium
supplements in the prevention of prostate cancer and has shown there is the
potential for harm,” said Lori Minasian, M.D., study co-author and acting
director of NCI’s Division of Cancer Prevention. “Nevertheless, this type of
research has been critically important to understanding the potential benefits
and risks from supplements.”
SELECT
researchers are now measuring the amount of vitamin E, selenium, and other
nutrients in the blood of participants when they joined the trial, to see if
the effect of the supplements depended upon this baseline level of
micronutrient. Other researchers are looking at single nucleotide
polymorphisms, which are DNA changes known as SNPs, to see if a change in one
or more genes could affect cancer risk or perhaps increase a man’s risk of
developing prostate cancer while taking vitamin E.
The
participant samples come from the study biorepository of blood and toe nail
clippings which, when coupled with the extensive clinical information on
participants, is a vital resource for further study. “SWOG is soliciting
proposals from researchers nationwide to use the SELECT biorepository to help
answer the biological question of why vitamin E increased risk instead of
decreasing it,” said Laurence Baker, D.O., study co-author and chairman of
SWOG. “There are many more questions raised by these study results than we have
answers for, and thus the need for further investigation.”
Except
for skin cancer, prostate cancer is the most common type of cancer in men in
the United States. The current lifetime risk of prostate cancer for American
men is 16 percent. In 2011, there will be an estimated 240,890 new cases of
prostate cancer and 33,720 deaths from this disease in the United States.
Vitamin E supplements hamper endurance training
Vitamin
C and E supplements may blunt the improvement of muscular endurance – by
disrupting cellular adaptions in exercised muscles – suggests a new study
published February 2014 in The Journal of
Physiology.
As
vitamin C and E supplements are widely used, understanding if they interfere
with cellular and physiological adaptations to exercise is of interest to
people exercising for health purposes as well as to athletes.
Dr
Gøran Paulsen, who led the study at the Norwegian School of Sport Sciences,
explains:
"Our
results show that vitamin C and E supplements blunted the endurance
training-induced increase of mitochondrial proteins, which are needed to
improve muscular endurance."
In
the 11-week trial, 54 young, healthy men and women were randomly allocated to
receive either 1000mg vitamin C and 235mg vitamin E (consistent with amounts
found in shop supplements), or a placebo (a pill containing no active
ingredients). Neither the subjects nor the investigators knew which participant
received the vitamins or placebos.
The
participants completed an endurance training programme, consisting of three to
four sessions per week, of primarily running. Fitness tests, blood samples and
muscle biopsies were taken before and after the intervention.
Whilst
the supplements did not affect maximal oxygen uptake or the results of a 20
metre shuttle test, the results showed that markers for the production of new
muscle mitochondria – the power supply for cells – increased only in the group
without supplements.
The
National Health Service (NHS) says taking less than 540mg vitamin E and 1000mg
vitamin C supplements per day is unlikely to cause any harm.
Dr
Paulsen says:
"Our
results indicate that high dosages of vitamin C and E – as commonly found in
supplements – should be used with caution, especially if you are undertaking
endurance training."
A
significant trend has been identified, but the molecular processes requires
further research. Dr Paulsen says:
"Future
studies are needed to determine the underlying mechanisms of these results, but
we assume that the vitamins interfered with cellular signalling and blunted
expression of certain genes."
Previous
studies show that exercising increases muscle oxidant production, which
participates in the signalling processes leading to muscle adaption. It is
possible that high doses of vitamins C and E act as antioxidants and take away
some of this oxidative stress, hence blocking muscular endurance development.
Benefits/Risks
Vitamin E may decrease and increase mortality of male smokers
Six-year
vitamin E supplementation decreased mortality by 41% in elderly male smokers who
had high dietary vitamin C intake, but increased mortality by 19% in
middle-aged smokers who had high vitamin C intake, according to a study
published in the American Journal of
Epidemiology.
Large-scale
controlled trials have not found any overall effects of vitamin E
supplementation on the mortality of participants. Nevertheless, the effect of
vitamin E on respiratory infections has significantly diverged between
different population groups suggesting that the effects of vitamin E may not be
uniform over all the population.
Dr.
Harri Hemila, and Professor Jaakko Kaprio, of the University of Helsinki,
Finland, studied whether the effect of vitamin E supplementation on mortality
might diverge between different population groups. They analyzed the data of
the large randomized trial (Alpha-Tocopherol Beta-Carotene Cancer Prevention
Study) which was conducted in Finland between 1985-1993 and included male
smokers aged 50-69 years. There were 3571 deaths in 29,133 participants during
the 6-year supplementation of 50 mg/day of vitamin E.
Although
vitamin E had no overall effect on mortality, its effect was modified by age
and dietary vitamin C intake. Vitamin E had no effect on participants who had
low dietary vitamin C intake, less than 90 mg/day. However, in those who had
high vitamin C intake, over 90 mg/day, the effect of vitamin E diverged so that
it increased mortality in young participants (50-62 years), but decreased
mortality in old participants (66-69 years).
The
US nutritional recommendations, issued by the prestigious Institute of
Medicine, consider that vitamin E is safe in doses up to 1000 mg/day. This new
study gives further evidence indicating that in some population groups vitamin
E may be harmful in a substantially lower dose, 50 mg/day.
The
researchers concluded that "in people younger than 65 years, taking
vitamin E supplements should be strongly discouraged, until clear evidence
emerges that some population groups of younger or middle-aged people
benefit". They also concluded that the effect of vitamin E on elderly
people should be further investigated.
Benefits
Vitamin E may
increase the life expectancy of older men
Depending
on the level of smoking and dietary vitamin C intake, vitamin E supplementation
may extend the life-span of restricted groups of men, according to a study
published in the Age and Ageing.
Several
large randomized trials of humans found that vitamin E supplementation does not
reduce mortality. However, the average effect on mortality in a group of people
with a wide age range may mask an effect of vitamin E on the life-span.
Dr.
Harri Hemila, and Professor Jaakko Kaprio, of the University of Helsinki,
Finland, studied the age-dependency of vitamin E effect on mortality in the
large randomized trial (Alpha-Tocopherol Beta-Carotene Cancer Prevention Study)
which was conducted in Finland between 1985-1993. Their study was restricted to
follow-up period over 65 years and 10,837 participants contributed to the
analysis.
Among
all analyzed participants, vitamin E had no effect on mortality when
participants were 65 to 70 years old, but reduced mortality by 24% when
participants were 71 or older.
Among
2,284 men with dietary vitamin C intake above the median who smoked less than a
pack of cigarettes per day, vitamin E extended life-span by two years at the
upper limit of the follow-up age span. In the other participants, consisting of
80% of the cohort, vitamin E did not affect mortality, which shows that vitamin
E is no panacea for extending life expectancy.
The
researchers concluded that "if vitamin E influences the life-span, it is
possible that a benefit on the oldest participants might be camouflaged by the
large middle-aged majority of study participants". Therefore, they propose
that it might be useful to analyze the effect of vitamin E supplementation in
large controlled trials by the age of the participant at the follow-up and not
just by the time after randomization that has been customary.
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