Fifteen
years ago, doctors believed that modern diets provided all
the vitamins anyone needed. Unless you were threatened by
scurvy, the argument ran, supplements were just a prescription
for expensive urine.
That hard line softened in the late 1980s and early ’90s,
when studies revealed that diets based on vitamin-rich plant
foods could lower the risk of cardiovascular disease and
some cancers. No one knew whether those benefits came from
the vitamins themselves or from other substances found in
food, so researchers began studying the long-term effects
of various supplements. Studies have yielded mixed results,
suggesting that different vitamins can have different effects
(good, bad or negligible) on different health risks. Here
are some of the most significant findings on the benefits,
risks and disappointments of vitamin pills. Each item is
followed by the recommended daily amount for adults.
Vitamin A and carotenoids (including beta carotene)
Beta carotene plus vitamin C, vitamin E and zinc can slow
the progression of age-related macular degeneration. Well-designed
studies have not shown a reduction in the risk of heart
disease, stroke or cancer. Large amounts—10,000 international
units (IU) or more — of supplemental vitamin A (but
not beta carotene) can harm bones and may make hip fractures
more likely. Very large amounts can cause brain damage,
liver damage and birth defects (if taken by pregnant women).
Men: 900 micrograms (mcg); Women: 700mcg.
Folic acid (often grouped with the B vitamins)
Helps
prevent birth defects in fetuses if taken during the first
few weeks of pregnancy. Lowers homocysteine levels and may
reduce heart disease and stroke risk. May also reduce the
risk of colon cancer. In women who consume alcohol, may
offset the increased risk of breast cancer. Can increase
the risk of neurological problems in people lacking adequate
vitamin B12.
400mcg to protect fetuses, 800mcg to 2,400mcg to lower homocysteine
levels. If you take a folate pill, be sure you also receive
at least 6mcg of B12.
Vitamin B6
Helps lower homocysteine levels and may reduce heart disease
and stroke risk. Regular intake of high doses can cause
nerve damage.
Men, 19-49: 1.3 milligrams (mg); 50 or older: 1.7mg. Women,
19-49: 1.3mg; 50 or older: 1.5mg.
Vitamin B12
Helps lower homocysteine levels and may reduce heart disease
and stroke risk.
Vitamin b12 deficiency is common
in people over 50. 6mcg to 9mcg.
Vitamin C
May
protect against cataracts. In one study a mix of vitamin
C, vitamin E, beta carotene and zinc slowed the progression
of age-related macular degeneration. Well-designed studies
have not found the hoped-for reductions in heart disease,
stroke or cancer, nor have they confirmed that vitamin C
can prevent or shorten colds. High doses may cause anemia
in certain people.
Men: 90mg; Women: 75mg. (smokers
should add 35mg.)
Vitamin D
Keeps bones healthy, boosts bone-mineral density and reduces
the risk of nonspinal factures. Many people need supplemental
vitamin D. High doses (more than 50,000IU) can cause dangerously
abnormal blood levels of several minerals.
Ages 19-50: 5mcg (200IU); 51-70:
10mcg (400IU); 70 and older: 15mcg (600IU).
Vitamin E
In one study a mix of vitamin E, vitamin C, beta carotene
and zinc slowed the progression of age-related macular degeneration.
May protect against prostate cancer and cognitive decline.
Well-designed studies have not found the hoped-for reductions
in heart disease, stroke or cancer. Can cause excessive
bleeding in surgical patients or people taking anticoagulants
such as warfarin.
At least 15IU.
Adapted
from “Vitamins,” published by Harvard Medical
School (health.harvard.edu/vitamins) 
