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Harvard epidemiologist JoAnn Manson is working on
two trials aimed at measuring the effectiveness of
dietary supplements.
JoAnn Manson, Harvard Medical School’s Michael and
Lee Bell Professor of Women’s Health, professor of
epidemiology at the Harvard T.H. Chan School of
Public Health, and chief of the Division of
Preventive Medicine at Brigham and Women’s Hospital,
has made a career of studying population health.
Research studies on vitamins have often had
discrepant findings.
That’s partly because some studies are randomized
trials while others are observational.
Observational studies look at people who choose to
take supplements, and examine their risk of heart
disease, cancer, or other outcomes.
In contrast, in a randomized clinical trial, people
agree to be assigned at random to take vitamins
versus a placebo.
The different studies tend to provide different
results for dietary supplements, but often the media
does not make a distinction between the two.
Observational studies tend to show that people who
choose to take supplements are healthier, but that
may be because they are more health-conscious and
also have healthier diets and healthier lifestyles.
There can be selection for more health-conscious
people who are also compliant with taking
supplements long-term, as well as confounding by
other lifestyle practices, such as physical activity
and diet.
The randomized clinical trials avoid bias from
selection and confounding factors, and they tend to
show little, if any, benefit of these supplements in
healthy individuals.
And the randomized trials have also identified
risks.
Randomized trials of beta-carotene show increased
risk of lung cancer in smokers, randomized trials of
vitamin E show increased risk of heart failure,
bleeding-related strokes, prostate cancer, and even
all-cause mortality in some studies.
There’s also some concern about selenium in high
doses.
So it’s a very confusing literature because the
observational studies and randomized trials have
provided some discrepant results while the public is
bombarded with hype about supplements in the media
and advertising.
That said, the observational studies do have the
advantage of being able to assess long-term use —
over decades — while randomized trials tend to be
shorter, often less than five years, due to their
higher cost.
JoAnn Manson is now analyzing the data and finishing
up the vitamin D and omega-3 trial VITAL.
That’s a large-scale, randomized trial of vitamin D
with and without omega-3 fatty acids, or fish oil.
There are four treatment groups, more than 25,000
participants nationwide, and researchers are looking
at each of these interventions for prevention of
cancer and cardiovascular disease.
They are also looking at cognitive function,
diabetes, autoimmune diseases, and a number of other
disorders.
So they are testing these very commonly used dietary
supplements for their efficacy and safety over an
average of five years.
They are also doing a large-scale, randomized trial
of multivitamins and cocoa flavonol supplements, the
COSMOS trial.
There’s been only one previous large-scale,
randomized trial of multivitamins.
That was in men, the Physicians’ Health Study II,
and researchers are now testing it in both men and
women.
Researchers are looking at what they think are
promising supplements.
They are trying to identify dietary supplements that
are effective and have a favorable benefit/risk
profile.
People are generally encouraged to get vitamins and
minerals from a healthy, well-balanced diet.
Micronutrients are better absorbed through the diet
and a person will receive many other beneficial
components besides these micronutrients.
And through the diet, you get the optimal biological
ratio of vitamins and minerals as opposed to a
mega-dose of a particular supplement that can cause
harm and may interfere with the absorption or
bioavailability of other vitamins and minerals.
If someone is really concerned about their diet,
they’re not having fruits and vegetables for
whatever reason, they’re eating a lot of processed
foods — which actually can strip foods of vitamins
and minerals and healthful micronutrients — and they
don’t think they can improve or modify their diet,
then it’s reasonable to take a multivitamin or other
vitamin-mineral supplement as a form of insurance.
However, it’s still not a substitute for a healthy
diet.
It’s not going to be as good as having whole foods,
avoiding processed foods, getting benefits like
fiber, polyphenols, and phytochemicals from fruits
and vegetables and whole grains.
It’s really important to have a healthful diet
regardless.
Older adults often have a poorer diet. They may also
have a problem with absorption of some vitamins and
minerals.
The main ones to think about are B12, calcium, and
vitamin D.
B12 deficiency can be a problem, especially with
pernicious anemia.
With calcium and vitamin D, researchers encourage
food sources, but supplements may be necessary —
some people are lactose-intolerant or don’t eat
dairy products.
Avoid excess amounts of calcium supplements because
they’ve been linked to an increased risk of kidney
stones.
Vitamin D has also been implicated in heart health,
cognitive health, and reducing risk of cancer and
diabetes.
There’s no definitive evidence yet.
It’s very difficult for the public to separate fact
from fiction, and understand what is just hype and
marketing and promotion as opposed to actual
evidence and facts.
For more information
Vitamin and Mineral SupplementsWhat Clinicians Need
to Know
Link...
The Harvard Gazette
We’re in the dark on dietary supplements. She’s
working to change that.
Link...
The Harvard Medical School
Link...
The Harvard T.H. Chan School of Public Health
Link...
Brigham and Women's Hospital
Link...
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