Gabe Mirkin, M.D.

Many people take large doses of antioxidant vitamin pills, even 
though there is little evidence that large doses of antioxidant 
pills prevent disease, and there is some evidence that they may 
cause disease.

Does it bother you that taking large doses of beta carotene, which 
is vitamin A, increases risk for heart attacks in men and increase 
risk for lung cancer in smokers? Does it bother you that large doses 
of vitamin C do not prevent colon cancer, and do not prolong life 
in people with cancer? Other studies show that large doses of vitamin
 E do not prevent lung cancer, heart disease or stroke, or that 
large doses of selenium do not prevent cancer.

Last year, Barry Haliwell of the National University of Singapore 
wrote an article in the British medical journal, Lancet, explaining 
why large doses of antioxidant vitamins sometimes prevent cancer and 
sometimes cause it. Every chemical reaction in the body releases 
chemicals called free radicals that damage tissue, which releases 
certain metals into the cell fluid. Antioxidants convert these free 
metals, which are harmless, to powerful oxidants that cause further 
cell damage. So sometimes antioxidants protect cells and other times, 
they damage them. For example, paraquat is a powerful cancer-causing 
chemical. If you give vitamin C to animals before giving them 
paraquat, the vitamin C prevents cells damage and helps protect them 
from cancer, but if you give these same animals vitamin C after they 
take paraquat, the vitamin C spreads the cancer. The paraquat causes 
cells to release large amounts of minerals and the vitamin C then 
causes these minerals to damage cells and spread the cancer. For 
this reason and others, the American Cancer Society advises patients 
not to take large doses of vitamins A, E, C and selenium. 

Another reason not to take large doses of antioxidant vitamins is 
that free radicals kill cancer cells. Rapidly multiplying cancer 
cells take up antioxidants and use them to protect the cancer cells 
from being destroyed by oxidants. So antioxidant vitamins can 
protect preexisting cancer cells from being damaged by oxidants, to 
spread the cancer. If you think we know all about antioxidants, you 
do not understand the tremendous controversy going on right now. 
You should get all the vitamins that you need from the food that you 
eat. If you want to take recommended dietary allowances of vitamins, 
go ahead, there is little evidence that you will harm yourself. 
However when you take large doses of any vitamin, you don't have the 
foggiest idea whether you are harming yourself and I do not 
recommend large doses of vitamins to anyone. 

Checked 1/7/04