Dr. Roach: Very high doses of vitamin A are dangerously toxic
DEAR DR. ROACH: My son, on the advice of his doctor, has been taking high daily doses of vitamin A (100,000 IU) and vitamin D (50,000 IU). Since this has been explained to him as a cancer preventive and a possible cure, I have been doing the same for several weeks.
However, I noticed recently in one of my health books that 25,000 IU of vitamin A is the highest recommended daily dosage. Could you please let me know about the most recent research on these vitamins? – A.
ANSWER: I could not disagree more strongly with your regimen; these doses of vitamins are likely to be dangerously toxic, and I recommend stopping them immediately.
Most vitamins, if taken even in very high doses, are water-soluble and the excess is simply excreted by the kidneys. However, vitamins A and D are fat-soluble, and have the potential to build up in the body. The maximum recommended daily dose of Vitamin A in adults is 10,000 units, and you and your son are taking 10 times this amount. The vitamin is stored in the liver, where it can cause cirrhosis if taken for long enough. Other symptoms of vitamin A excess include nausea, headache, dry skin, hair loss and irritability. Vitamin A, when taken by pregnant women, can cause serious abnormalities in the developing fetus.
Although diets high in vitamin A reduce cancer risk, there is no evidence that vitamin A supplementation reduces cancer risk. Beta carotene, a closely related substance, actually increases risk of lung cancer in smokers.
The highest recommended dose of vitamin D for daily use is 4,000 units. There are some people who need higher doses, but these should not be taken without careful follow-up. Based on what you tell me about your son’s recommendations on vitamin A, I have little confidence in his medical care. Too much vitamin D drives calcium levels to high, even potentially dangerously high, levels. This causes confusion, weakness and vomiting. Unlike vitamin A, where blood levels are not reliable to diagnose toxicity, a blood level of vitamin D can guide treatment. I have seen one case where vitamin D toxicity from overingestion required steroid treatment.
DEAR DR. ROACH: What is your professional experience with the vegetarian life style? Do vegetarians live healthier lives? Do they live longer? – N.M.G.
ANSWER: I often am asked to comment on the health impact of a vegetarian diet, but there is a surprising lack of high-quality research, probably because of two issues. The first is that there is no single vegetarian diet. Fruits, vegetables, legumes, nuts and whole grains all are very healthy choices that make up many vegetarians’ diets. However, I have known people who subsist on sugar cereals, highly processed snack foods, vodka and cigarettes – which, though vegetarian, is as unhealthy a diet as could be imagined.