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List of vitamins, what are they
good for, where you can find them.
If you eat a healthy diet, do you
need to take vitamins? Not long ago, the answer from most
experts would have been a resounding "no". Today, though,
there's good evidence that taking a daily multivitamin makes
sense for most adults.
What's changed? Not only have
scientists determined why we need pyridoxine (vitamin B6), but
they are also accumulating evidence that this vitamin and others
do much more than ward off the so-called diseases of deficiency,
things like scurvy and rickets. Intake of several vitamins above
the minimum daily requirement may prevent heart disease, cancer,
osteoporosis, and other chromic diseases.
This summary will focus on
vitamins with newly recognized or suspected roles in health and
disease. It will present some of the evidence about vitamins'
possible new roles, point out how to get more of these in your
diet, and assess the value of taking a daily multivitamin.
Vitamin A:
Vitamin A does
much more than help you see in the dark. It stimulates the
production and activity of white blood cells, takes part in
remodeling bone, helps maintain the health of endothelial cells
(those lining the body's interior surfaces), and regulates cell
growth and division.
The 3 Bs:
Vitamin B6, Vitamin B12, and Folic Acid:
One of the advances that changed
the way we look at vitamins was the discovery that too little
folic acid, one of the eight B vitamins, is linked to birth
defects such as spina bifida and anencephaly. Fifty years ago,
no one knew what caused these birth defects, which occur when
the early development of tissues that eventually become the
spinal cord, the tissues that surround it, or the brain goes
awry. Twenty five years ago, British researchers found that
mothers of children with spina bifida had low vitamin levels.
Folic acid, vitamin B6, and vitamin B12 play key roles in
recycling homocysteine into methionine, one of the 20 or so
building blocks from which the body builds new proteins. Without
enough folic acid, vitamin B6, and vitamin B12, this recycling
process becomes inefficient and homocysteine levels increase.
Several observational studies show that high levels of
homocysteine are associated with increased risks of heart
disease and stroke. Increasing intake of folic acid, vitamin B6,
and vitamin B12 decreases homocysteine levels. And some
observational studies show lower risks of cardiovascular disease
among people with higher intakes of folic acid, those who use
multivitamin supplements, or those with higher levels of serum
folate (the form of folic acid found in the body).
Vitamin C:
Vitamin C has
been in the public eye for a long time. Even before its
discovery in 1932, nutrition experts recognized that something
in citrus fruits could prevent scurvy, a disease that killed as
many as 2 million sailors between 1500 and 1800. More recently,
Nobel laureate Linus Pauling promoted daily megadoses of vitamin
C as a way to prevent colds and protect the body from other
chronic diseases. There's no question that vitamin C plays
a role in controlling infections. It's also a powerful
antioxidant that can neutralize harmful free radicals, and it
helps make collagen, a tissue needed for healthy bones, teeth,
gums, and blood vessels.
Vitamin D:
If you live north of the line connecting San Francisco to
Philadelphia, odds are you don't get enough vitamin D. The same
holds true if you don't, or can't, get outside for at least a
15-minute daily walk in the sun. African-Americans and others
with dark skin tend to have much lower levels of vitamin D, due
to less formation of the vitamin from the action of sunlight on
skin. A study of people admitted to a Boston hospital, for
example, showed that 57% were deficient in vitamin D. Vitamin D
helps ensure that the body absorbs and retains calcium and
phosphorus, both critical for building bone. Laboratory studies
also show that vitamin D keeps cancer cells from growing and
dividing.
Vitamin E:
For a time, vitamin E supplements looked like an easy way to
prevent heart disease. Promising observational studies,
including the Nurses' Health Study and Health Professionals
Follow-up Study, suggested 20% to 40% reductions in coronary
heart disease risk among individuals who took vitamin E
supplements (usually containing 400 IU or more) for least two
years.
Vitamin K:
Vitamin K helps make six of the 13 proteins needed for blood
clotting. Its role in maintaining the clotting cascade is so
important that people who take anticoagulants such as warfarin (Coumadin)
must be careful to keep their vitamin K intake stable.
Antioxidants:
Our cells must constantly contend with nasty substances called
free radicals. They can damage DNA, the inside or artery walls,
proteins in the eye--just about any substance or tissue
imaginable. Some free radicals are made inside the body,
inevitable byproducts of turning food into energy. Others come
from the air we breathe and the food we eat. We aren't
defenseless against free radicals. We extract free-radical
fighters, called antioxidants, from food. Fruits, vegetables,
and other plant-based foods deliver dozens, if not hundreds, of
antioxidants. The most common are vitamin C, vitamin E,
beta-carotene and related carotenoids. Food also supplies
minerals such as selenium and manganese, which are needed by
enzymes that destroy free radicals. Antioxidants are proven as
agents that could prevent heart disease, cancer, cataracts,
memory loss, and a host of other conditions.
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