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Multivitamins:
Should you buy this insurance?
(This article was first printed in the September
2006 issue of the Harvard Health Letter.
For more information or to order, please go
to http://www.health.harvard.edu/health.)
The daily multivitamin pill is no substitute
for a good diet. But none of us is perfect when
it comes to healthful eating. We may know all
about the virtues of leafy green vegetables and
whole grains, but convenience and cravings lead
us astray. The multivitamin is partial protection
from our lapses.
It’s also an easy way to add surplus vitamins
and minerals to our diets. By definition, vitamins
are organic (carbon-based) compounds needed in
only small amounts. Minerals serve a similar
purpose, but are inorganic. Historically, nutrition
focused on vitamin deficiencies that cause disease.
But with fortification — the systemic addition
of nutrients, chiefly vitamins, to the food supply — and
no shortage of food, the focus changed to whether
vitamins and minerals in amounts larger than
we need might protect us against conditions like
heart disease and cancer.
Studies go against vitamins
Some people scarf down megadoses, an approach
most experts disagree with. The daily multivitamin
is the cautious wager that some extra vitamins
and minerals will pay off in better health even
if deficiencies aren’t a problem.
Lately, though, it’s been looking like
they might not, as high-profile studies have
come to negative conclusions.
It’s well established that a trio of B
vitamins — B6, B12, and folate — lowers
homocysteine, an amino acid that’s a risk
factor for heart attack, stroke, and dementia.
The logical supposition: Having an ample supply
of those Bs coursing through your veins (and
arteries) could improve your chances of avoiding
cardiovascular disease and cognitive decline.
But results from a large randomized controlled
trial published in the New England Journal
of Medicine (NEJM) in April 2006 showed
that while the B vitamins lowered homocysteine
levels, that didn’t result in fewer heart
attacks or other major cardiovascular events.
A second disappointing study was published in NEJM in
June 2006. Despite their homocysteine-lowering
prowess, B vitamins were no better than placebo
at protecting people from cognitive decline.
Vitamin E hasn’t been faring too well,
either. Johns Hopkins researchers dubbed 2005
the annus horribilis for the vitamin
because of all the disappointing studies, chief
among them their meta-analysis that found that
large daily doses (400 IU and up) increased mortality
risk.
NIH shrugs its shoulders
The National Institutes of Health (NIH) convened
a meeting on multivitamin and mineral supplements
in May 2006. The NIH holds these “consensus
conferences” several times a year on a
variety of subjects. Experts listen to presentations
by other experts for a couple of days, then issue
a “state of the science” statement.
In this case, the statement was extremely cautious.
Present evidence is “insufficient to recommend
either for or against the use of multivitamin/multimineral
supplements by the American public to prevent
chronic disease,” was the inconclusive
conclusion. The experts noted that the heaviest
users of vitamin and mineral supplements are
Americans who probably need them the least: People
who are well-educated, have higher incomes, exercise,
and already have healthy diets.
Yes to a multivitamin
Dr. Walter Willett, chair of the Harvard School
of Public Health’s nutrition department,
has suggested that taking a multivitamin daily
is a form of nutritional insurance. He still
says it’s a good policy, despite the spate
of negative study results.
Those results have come from randomized controlled
trials, which are usually regarded as the gold
standard. But there are problems with clinical
trials, too. They’re often fairly short,
so a nutrient’s long-term consequences
may be missed. For example, Dr. Willett says
that beta carotene didn’t look like it
was having any effect on cognition at the 12-year
mark in Harvard’s Physicians’ Health
Study, but at 18 years, benefits were detected.
There are also often questions about how applicable
the results of clinical trials are. Some of the
negative findings have come from studies that
enrolled people who had vascular disease or diabetes.
High-risk individuals tend to have more “events,” so
there’s more data for analysis, and the
results are more reliable statistically. But
how relevant are the findings to healthier folks?
With the B vitamin research, it’s the reverse:
The patients in those studies had homocysteine
levels that were normal or just slightly elevated,
so the results may not apply to people with higher
levels.
Multivitamins are already part of some official
recommendations. The federal government’s
2005 Dietary Guidelines suggest that people older
than 50 take them as a way to ensure adequate
vitamin B12 intake. And the Centers for Disease
Control and Prevention advises all women of child-bearing
age to take folic acid — and a multivitamin
is also a good way to do that — because
doing so lowers the risk of birth defects. That
leaves men age 50 and under as the only adult
group not covered.
If you take a multivitamin, be sure to buy a
major brand-name or store-brand product. When
Consumers Union tested cut-rate products, it
found that almost half didn’t contain the
listed amount of at least one nutrient.
Below we give some pointers about many of the
vitamins and minerals you’ll find in a
multivitamin. We’ve separated vitamins
and minerals because of space constraints. In
reality, they are all in one pill.
Vitamin |
Daily
Value set by FDA |
Advice |
Vitamin A* |
5,000 IU |
Look for a
brand that gets a large percentage of its
vitamin A from beta carotene. Large amounts
of retinol, which in multivitamins comes
in the form of vitamin A palmitate or acetate,
have been linked to an increased risk of
hip fractures. Too much beta carotene can
also be a problem: Controlled trials have
shown that high doses increase lung cancer
incidence and mortality among smokers and
male asbestos workers, but the amounts
tested in those studies were much larger
than those in multivitamins. |
Thiamine (B1) |
1.5 mg |
You’re
probably getting enough from your diet
because of fortification and our abundant
food supply, so the multivitamin isn’t
protecting against deficiency. Extra thiamine
doesn’t seem to have any health benefits. |
Riboflavin
(B2) |
1.7 mg |
The same story
as thiamine: A normal diet provides enough,
and large amounts don’t bring anything
extra to the table. |
Niacin (B3) |
20 mg |
Rare instances
of deficiency are associated with alcoholism
or uncommon metabolic diseases. Niacin,
which is sometimes called nicotinic acid,
is used as a cholesterol medicine, but
in doses much larger (1,000–2,000
mg a day) than the 20 mg in the typical
multivitamin. |
B6 (Pyridoxine) |
2 mg |
The 2 mg in
the typical multivitamin, on top of what
you get in your diet, may pay health dividends.
A Harvard study found that fairly large
amounts (8.6 mg daily) may protect against
colon cancer. When taken with B12 and folate,
B6 lowers homocysteine, a risk factor for
heart disease, although whether those reductions
translate into a lower risk for heart problems
is still up in the air. |
B12 (Cobalamin) |
6 mcg |
If you’re
older than 50, B12 may be one of the main
reasons to take a multivitamin. With age,
a large percentage of people don’t
produce the stomach acid needed to separate
the vitamin from animal protein so it can
be absorbed, whereas the crystalline form
in vitamin pills and fortified cereals
is readily taken up. Well before you reach
outright deficiency, low levels of B12
may produce subtle cognitive and neurological
deficits. Another reason to get lots of
B12: Low amounts, in combination with high
folate intake, may hasten cognitive decline. |
Folate (Folic
acid) |
400 mcg |
Low levels
are rare now that all grain products are
fortified with folate, so the 400 mcg in
most multivitamins isn’t as critical
as it might have been pre-fortification.
Still, folate supplements for women of
childbearing age have been a big success
story, making neural-tube defects in babies
far less common. |
Pantothenic
acid |
10 mg |
Diet supplies
enough, and there’s no evidence that
extra amounts have any benefits. |
Biotin |
300 mcg |
It’s
in the same category as pantothenic acid. |
Vitamin C |
60 mg |
Does the C
stand for confusion? There’s a lot
surrounding this vitamin. It’s a
powerful antioxidant, but studies have
flip-flopped on whether it prevents cancer
or heart disease. Some even suggest that
it can promote oxidative damage. Overall,
the vitamin seems to do more good for our
health when it’s in food rather than
packed into a pill. As for the common cold,
large amounts (1,000 mg) may shorten a
cold, but evidence for prevention is shaky
at best. |
Vitamin D |
400 IU |
We probably
should be taking more than the Daily Value — up
to 800–1,000 IU. It’s good
for bones because it aids absorption of
calcium, but it may also help protect against
cancer, diabetes, and multiple sclerosis.
More multivitamins with 1,000 IU will be
available soon. Look for them. |
Vitamin E** |
30 IU |
It ranks with
vitamin C in the confusion department.
Randomized trials have been inconsistent.
A meta-analysis hinted at possible harm.
Longer studies in different sorts of people
(healthy versus those with pre-existing
disease) might come out differently. Regardless,
the 30 IU dose in many multivitamins is
probably too little to have much of an
effect either way. |
Vitamin K |
80 mcg |
Epidemiologic
studies have found that it might be a bone
protector. People taking the blood thinner
warfarin need to watch their intake. The
more vitamin K in your diet, the more warfarin
you’ll need. |
*Based
on a conversion of 1 Retinol Activity Equivalent
= 3 IU
**Based on a conversion of 1 Alpha-Tocopherol
Equivalent =1.5 IU |
Mineral |
Daily
Value set by FDA |
Advice |
Calcium |
1,000 mg |
Multivitamins
make a minor contribution to calcium intake.
Most brands contain 10% or less of the
recommended daily intake of 1,200 mg. The
mineral is too bulky to fit much more than
that into a single pill already crammed
full with other minerals and with vitamins.
Although calcium is important for bone
health, adequate doses of vitamin D probably
do more for it than the recommended daily
intake of calcium. |
Potassium |
3,500 mg |
Multivitamins
make an even smaller contribution when
it comes to our potassium intake. For example,
Centrum Silver has 80 mg, or just 2% of
the 3,500 mg Daily Value. Too bad there
isn’t more, because it’s difficult
to get the recommended amount from a normal
diet alone, and it’s an important
nutrient that helps offset the blood pressure–raising
effects of sodium. |
Iron |
18 mg |
Premenopausal
women are supposed to get 18 mg daily,
and women who are pregnant should aim for
27 mg. But the rest of us only need 8 mg
of iron, which is relatively easy to get
with a normal diet, so a multivitamin with
a small amount of iron is okay. In fact,
large amounts might do some harm. They’ve
been associated, albeit tentatively, with
increased risk for heart disease and possibly
some neurological disorders. One of the
more common genetic diseases, hemachromatosis,
can cause even modest amounts of iron supplements
to damage vital organs. |
Phosphorus |
1,000 mg |
It’s
amply supplied by normal eating and readily
absorbed, so it probably doesn’t
need to be in your multivitamin. Most brands
throw in a small amount (about 50 mg, or
5% of the recommended intake). |
Iodine |
150 mcg |
Many brands
contain 100% of the recommended amount.
Because people are avoiding table salt,
iodine intake is down, so an iodine boost
from a multivitamin might help prevent
goiter, an enlargement of the thyroid gland.
But too much iodine can be a problem too,
causing other types of thyroid disorders. |
Magnesium |
400 mg |
Look for a
multivitamin that contains at least 100
mg. Most of us don’t get enough magnesium
from our diets, so a multivitamin helps
make up the shortfall (eating more fruit
and vegetables and whole grains helps too).
Don’t fret too much. Moderately low
magnesium levels have been linked to cardiovascular
disease, but the evidence so far is weak. |
Zinc |
15 mg |
The 15 mg in
many multivitamins is an important nutritional
safety net for many people. Vegetarians
may run low on zinc because it’s
poorly absorbed from plant foods. Heavy
drinkers may too, because alcohol interferes
with absorption of zinc. People with gastrointestinal
disorders like Crohn’s disease are
prone to zinc deficiency. Even if you’re
not in those groups, extra zinc may have
some benefits, ranging from wound healing
to preserving sense of taste and smell.
The vitamin and mineral combination that
slows the progression of macular degeneration
includes 80 mg zinc. The amounts in multivitamins
don’t pose problems, but don’t
overdo it with zinc supplements. Too much
of the mineral can lower “good” HDL
cholesterol, cause gastritis, and create
copper deficiency. |
Copper |
2 mg |
This is not
a nutrient to worry about unless you’re
plying yourself with zinc. Outright deficiencies
occur only in special circumstances, and
there’s not much evidence of health
problems if your intake is low. |
Selenium |
70 mcg |
Most people
get enough from their diet. The jury is
out on whether selenium might protect men
against prostate cancer. Some multivitamins
for men aren’t waiting for the verdict
and contain 200 mcg. That’s three
times the recommended amount, but well
below 400 mcg, the daily amount that’s
considered unsafe. |
Chromium |
120 mcg |
Low intake
may increase your risk of developing diabetes
or having a heart attack. Extra chromium
may help people who already have diabetes
by enhancing the effects of insulin, which
helps control blood sugar. But the research
is mixed, so there’s a lot of debate
among experts about chromium. Some brands
of multivitamin contain 150 mcg. There’s
no evidence that high amounts of chromium
in pill form cause bad health effects. |
(This article was first printed in the September
2006 issue of the Harvard Health Letter.
For more information or to order, please go
to http://www.health.harvard.edu/health.)
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