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Does Vitamin C Prevent Cataracts? -- bottle of vitamin C


Modest but not high doses of vitamin C from supplements may help prevent cataracts if taken for a long enough period. Get the details in the Full Answer >>

For extensive information about vitamin C supplements, see the Vitamin C Product Review.

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March 5, 2018

Your website has been significantly improved with your recent new medical input.
However regarding vit C, it is actively concentrated mainly in the eye and brain, when blood levels drop. Most mammals produce the human equivalent of more than 5-10 grams a day over a 24 hour period, except primates, guinea pigs, and a bird species.
Plants can produce Vit C at 70 gm per day in direct sunlight. Knockout genetic studies of these plants failed to produce any results until the second gene was found. Both knockouts were lethal to the plant!! No gluconeogenesis. I think all of this bias comes from the historical medical dislike of Linus Pauling's work on vit C, which he took as a powder, averaging 20 gm per day. He died at the age of 92, even after all the work needed to get 2 Nobel prizes.

The medical profession even now is just beginning to raise maximal dose recommendations. Just to play it safe, I still take only 2 gm per day 4 hour controlled release, now for more than 20 years. My eyesight and hearing is unusually good.
No cataract surgery yet.

JT Flick, PhD astrophysics, (Princeton 1975)
March 5, 2018

Hi James - Please see the information in our CL Answer "Is is possible to take too much vitamin C" -- just to play it safe.

March 5, 2018

I agree that one can take too much vit C. The question is how much. The old IOM recs, or the newer one? In my humble opinion,the old AREDS studies also reccommended too little. Another non human example would be the 5 gms a day gorillas need at the Zoo. I think that was the St Louis Zoo. In human equivalents that would be much too much, IMHO.

Also, as far as I can recall, toxicologic cases of VitC ODs were in a few (1?) patient that already had too much oxalic acid due to a metabolic variation.

Are you aware of any documented large clinical studies where deaths or severe toxic effects occured in normal individuals taking too much slow release Vit C ? And how much?
March 5, 2018

Not deaths, but there are reports of negative effects with higher doses of vitamin C ranging from reduced benefit from athletic training to increased risk of cataracts. Not clear if the supplementation was with regular-release or slow release. Please see the information at

March 11, 2019

Not now, but at certain points in my life I have taken high dose Vit C (2-3gms/day). However, when I read about increased risk of cataracts associated with high dose Vit C supplementation that was reported by CL, I checked it out w/my optometrist. She acted like "Oh yeah, doesn't everyone know that?" According to her, excess Vit C deposits in the lenses of the eyes clouding the lense, thereby compromising your vision. I'd rather not have cataract surgery if possible, so I limit Vit C supplementation to about 250mg per day (think CL's studies recommended less than 500mg/day). There are enough factors that cause cataracts that cannot be controlled; I'd rather not pay for supplements that increase the risk of cataracts!
March 11, 2019

Hi Peggy - Thank you for sharing this. Just to clarify, while high dose vitamin C is associated with increased risk of cataracts, the mechanism is unclear, i.e., it's probably not that vitamin C itself is being deposited.

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