LA Times からです。
まるで常識のように思われている「風邪＝ビタミンCをとろう！」の公式ですが、残念ながら科学的根拠なしなんですよ。ご存じでしたか？でもビタミンCは（正確に言えばアスコービックアシッド、日本語だとアスコルビン酸）は強力アンタイオキシダント（抗酸化剤）で、いろいろな働きがあるのは科学的に証明されいます。
ちなみにこの、カゼに効く！と一生懸命研究しつづけたポーリング博士ですが、カゼ以外にも大量のビタミンC摂取はガンを予防する！という説をたてて毎日すっごい量（ほんとにびっくりする量）のビタミンCを摂取してらしたんですが、残念ながら1994年にお亡くなりになりました。ガンで。かなりアイロニックです。
ここから引用です。
Versatile vitamin
VITAMIN C
By Shari Roan
More than 30 years ago, Nobel Prize-winning chemist Linus Pauling launched the theory that high doses of vitamin C could prevent or lessen the severity of colds and other illnesses. Pauling was a convincing vitamin C advocate until his death in 1994, but today, researchers still don’t agree on whether the vitamin, found in many fruits and vegetables, helps curb colds. However, it is considered an important antioxidant, and the supplement form could help prevent a number of conditions.
— Shari Roan
Uses: To bolster immunity, particularly among people who are deficient in the vitamin (the elderly, smokers, diabetics and women who use oral contraceptives). Others use it to reduce cold and asthma symptoms, enhance exercise performance and protect against cancer and cataracts.
Dose: Most people get enough from food, but those with vitamin C deficiency usually need 200 milligrams to 500 milligrams a day.
Precautions: Doses exceeding 2,000 milligrams a day can cause diarrhea. Vitamin C supplements should not be used by people with iron-overload problems or kidney disorders.
Research: Vitamin C doesn’t appear to significantly reduce cold symptoms, except perhaps for people who are deficient in the nutrient. Some studies suggest that the vitamin can help prevent cancer, cataracts and gallbladder disease, but more rigorous studies are needed to establish a link. More recent research has suggested that vitamin C may promote collagen growth, a protein critical to healthy skin, and thus could aid in the healing of wounds.
Dietary supplement makers are not required by the U.S. government to demonstrate that their products are safe or effective. Ask your health-care provider for advice on selecting a brand.
VITAMIN C
By Shari Roan
More than 30 years ago, Nobel Prize-winning chemist Linus Pauling launched the theory that high doses of vitamin C could prevent or lessen the severity of colds and other illnesses. Pauling was a convincing vitamin C advocate until his death in 1994, but today, researchers still don’t agree on whether the vitamin, found in many fruits and vegetables, helps curb colds. However, it is considered an important antioxidant, and the supplement form could help prevent a number of conditions.
— Shari Roan
Uses: To bolster immunity, particularly among people who are deficient in the vitamin (the elderly, smokers, diabetics and women who use oral contraceptives). Others use it to reduce cold and asthma symptoms, enhance exercise performance and protect against cancer and cataracts.
Dose: Most people get enough from food, but those with vitamin C deficiency usually need 200 milligrams to 500 milligrams a day.
Precautions: Doses exceeding 2,000 milligrams a day can cause diarrhea. Vitamin C supplements should not be used by people with iron-overload problems or kidney disorders.
Research: Vitamin C doesn’t appear to significantly reduce cold symptoms, except perhaps for people who are deficient in the nutrient. Some studies suggest that the vitamin can help prevent cancer, cataracts and gallbladder disease, but more rigorous studies are needed to establish a link. More recent research has suggested that vitamin C may promote collagen growth, a protein critical to healthy skin, and thus could aid in the healing of wounds.
Dietary supplement makers are not required by the U.S. government to demonstrate that their products are safe or effective. Ask your health-care provider for advice on selecting a brand.