"Unless you are suffering from a severe deficiency, if you have a disease or disorder that is causing you to be nutrient-deficient, the most you are going to need is a high quality multivitamin supplement, to be taken as insurance, and not used as your main source of nutrients," says nutritionist Laurie Tansman. But many of us take much more than that, and it turns out that can be dangerous.
The fat-soluble vitamins A, D and E can be stored for long periods of time in the body, build up in the liver and become toxic. "Vitamin D is one of the most toxic supplements there is, and in extreme cases and in very large amounts can lead to liver and kidney failure," says nutritionist Jyni Holland.
Too much vitamin A can cause hair loss, nausea, vomiting and joint pain. Tansman says, "If you are pregnant, there is evidence to show that too much vitamin A may also cause birth defects."
Vitamin E can thin the blood so much that it can cause internal hemorrhaging, particularly if you are taking blood-thinning medication, which is commonly taken for high blood pressure. Vitamin K does the opposite?causes blood to clot?which can also cause problems when you?re taking blood-thinning drugs.
Water-soluble nutrients such as the B vitamins and vitamin C are fairly safe in high doses because they don't build up in tissues, so they rarely reach toxic levels. But high levels of B6 have been associated with neurological symptoms such as nerve tingling, while B3, also known as niacin, can cause problems if you have heart disease. "Even though B3 is often used as medication to treat high blood pressure, if you have a preexisting condition, particularly heart disease or hypertension, you should not be using mega doses of this or any vitamins unless directed to do so by your doctor," Holland says.
Even calcium, which women are urged to take to prevent osteoporosis, "has been linked to the formation of kidney stones, particularly if you have had this problem in the past," says Holland.
Tansman says, "Vitamin D helps the body absorb calcium, which is why it's often included in mineral supplements. But if you are mega-dosing on calcium, you may also be mega-dosing on vitamin D and setting yourself up for some toxic reactions without even realizing you are doing so."
Women are also told they need iron during the menstruating years, but Holland says, "What most people don't realize is iron is an oxidant. And when it's exposed to oxygen inside the body, it becomes a free radical, with much of the same destructive properties of other free radicals we try so hard to avoid." Free radicals have been linked to cancer.
Holland thinks that in people who are already at risk for cancer, due to environmental factors or their family history, too much iron might cause the disease process to start. Vitamin C enhances iron absorption, so you can get more iron that you bargained for that way.
This is another thing that doctors don't tell us.
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