One has to really go overboard to develope an actual vitamin toxicity. The FDA has admitted that it automatically puts a 10-fold redundancy into it's RDA's and toxic exposure guidelines.
In the case of vitamin A, the RDA is 10,000 iu's per day but if one looks at the Merck Manual on vitamin toxicities, you'll find that virtually no reports of vit A toxicity occur unless you dose well over 100,000 iu's per day for weeks and months at a time. Most cases of A toxicity come from either freaks who eat bottles of vitamins per day OR people who eat polar bear fat or seal livers. So yeah, not real likely.
Many of the other RDA's are antiquated being based on 60 year old research of dubious qulaity. RDA's for most B-vitamins and iodine desperately need to be updated IMO.
As for this latest study, it's eerily reminiscent of the "Vitamin E Causes Death" study put out by Johns Hopkins that came out last year and was heavily criticized for poor methodology.
From Dr Ray Sahelian's site;
3. Danger: Relying on nutritional information through headlines may be hazardous to your health
A new study published in The Journal of the American Medical Association claims that taking antioxidant supplements such as beta carotene and vitamin E can shorten lifespan. This study is worthless and I will explain why.
Researchers first included 68 studies involving 232,606 people and found no significant effect on mortality -- neither good nor bad -- linked to taking certain antioxidants. When they eliminated the "lower-quality" studies and looked only at the most trustworthy ones, they actually found a higher risk of death for people taking vitamins: 4 percent for those taking vitamin E, 7 percent for beta carotene and 16 percent for vitamin A.
My comments: Who determined which studies were "lower quality?" It is possible that another group of researchers may have had a different opinion on what constitutes lower or higher quality. I can already sense a bias. Donald Berry, chairman of the department of biostatistics at the University of Texas M.D. Anderson Cancer Center, said of this study "There are so many choices you can make when you're doing these analyses."
Final findings were based on an analysis of 47 studies involving 180,938 people who were randomly assigned to get real vitamins or dummy pills. Some involved very high doses far exceeding the recommended daily amount of the vitamins; others involved normal or low doses.
My comments: The pooled studies were too diverse to make any sense. The trials ranged from a three-month study of 109 elderly nursing home residents to a 12-year study of 22,071 male doctors. And the vitamin dosages varied significantly from study to study. What if I analyzed various studies on the benefit or harm of drinking wine and pooled studies that included the health effect of one glass of wine a day and other studies where people drank a bottle of wine a day. It's possible that those who drink one glass of wine may live longer while those who drink a bottle of wine a day may die sooner due to liver damage. But when the results of the one drink and the full bottle studies are pooled, the statistical analyses could indicate that drinking wine shortens lifespan. Meir Stampfer, professor of nutrition and epidemiology at the Harvard School of Public Health, agrees with my viewpoint. Dr. Stamfer said the studies were too diverse to pool together because they looked at various combinations and doses of antioxidants tested in different groups of people. "This study does not advance our understanding, and could easily lead to misinterpretation of the data," said Stampfer.
The study's senior author, Dr. Christian Gluud of Copenhagen University Hospital, said, "The main message is that prevention by beta carotene, vitamin A and vitamin E cannot be recommended. These three antioxidant supplements may increase mortality."
My comments: Dr. Christian Gluud should take a sabbatical from interpreting research results from nutritional supplement studies and go back to school to take a course in nutrition 101. I can, without hesitation, say that this doctor is ignorant. Firstly, Dr. Gluud, does not seem to recognize that different dosages of supplements can have different effects. There is also no mention that most people who took vitamin E in the past, and also currently, take a synthetic version of one form of vitamin E, dl-alpha tocopherol, whereas there are several forms of natural vitamin E. It is possible that high doses of synthetic vitamin E may not be helpful, whereas low doses of a natural vitamin E complex including alpha, delta, and gamma tocopherol could be beneficial. This is also true of beta carotene. There are many forms of carotenoids, and taking a high dose of a single carotenoid, such as beta carotene by itself, is not the answer.
Bottom line: There is no proof at this time that taking vitamins will help you live longer, nor is there good evidence that they will shorten lifespan. In order for us to know how vitamins influence longevity, several well controlled studies have to be done on individual vitamins in varying dosages for at least a 20 to 30 year period while keeping dietary intake similar in all the study participants. This is not practical and not likely to be done soon. For the time being if you do plan to take antioxidant supplements, take products that have a wide range of nutrients in low amounts as opposed to just 2 or 3 in high dosages. I am not convinced that taking megadoses of a single form of synthetic vitamin E or single carotenoid is a good option. One good daily formula with lots of different nutrients and antioxidants in small amounts is MultiVit Rx which can be taken at one, two, three, or four capsules a day depending on your preference."