Brain tumor research is a relatively modern science that parallels the explosion of molecular biology and modern neuroimaging. While the science is new, Mayo Clinic has a long history of brain cancer treatment and research stretching back over 100 years.
But not all vitamins are water-soluble, and the ones that are lipid-soluble, meaning they like to hang around in your body's fat, don't get flushed out. Instead, if you take too much of a lipid-soluble vitamin over a few weeks to a month, they sit in the liver and can build up to toxic levels, causing problems ranging from weak bones to liver damage, according to Katherine Zeratsky, a registered dietician nutritionist at the Mayo Clinic.
This is called vitamin D toxicity. Vitamin D toxicity, where vitamin D can be harmful, usually happens if you take 40,000 IU per day for a couple of months or longer, or take a very large one-time dose. Vitamin D is fat-soluble, which means your body has a hard time getting rid of it if you take too much.