Any ingredient in a multi-vitamin supplement can be toxic in large amounts, but the most serious risk comes from iron or calcium. High or toxic doses of calcium, vitamin D, and vitamin A. Symptoms of vitamin A toxicity include dry and itchy skin, headache, nausea, and loss of appetite. Signs of serious overconsumption over a short period include dizziness, blurred vision, and stunted growth.
Vitamin A toxicity can also cause serious birth defects and increase the risk of bone loss and hip fractures. In two randomized trials, an antioxidant cocktail that included vitamin E (unspecified form) mitigated the beneficial increase in HDL2 levels associated with treatment with niacin and simvastatin. People taking anticoagulant (blood-thinning) medications may have a vitamin K deficiency, but they should not change their vitamin K intake without consulting a doctor. Taking vitamin E supplements is not recommended due to the lack of evidence to support any additional health benefits.
In addition, people with chronic diarrhea may have trouble absorbing sufficient amounts of vitamin K through the intestine and should consult their doctor to determine if supplements are needed. If you take a multivitamin, check the label to make sure that most of the vitamin A supplied is in the form of beta-carotene, which seems to be safe. They dissolve easily in water during cooking and some of these vitamins can be destroyed when heated. Some plant-based foods contain the antioxidant beta-carotene, which the body converts to vitamin A.
Vitamin C is generally safe, but in high doses (more than 2000 mg) it can cause diarrhea and nausea. In addition, some health problems, such as inflammatory bowel disease (IBD), chronic pancreatitis, and cystic fibrosis, can decrease fat absorption and, in turn, decrease the absorption of vitamins A, D, E, and K. To help ensure that people receive sufficient amounts of vitamin K, an adequate intake (IA) has been established for each age group (table). The efficacy of vitamin A supplements to treat measles in countries such as the United States, where vitamin A intake is generally adequate, is uncertain.
It is a fat-soluble vitamin that acts as an antioxidant and free radical scavenger in lipophilic environments. It's especially important that infants and young children don't consume excessive amounts of vitamin D on a regular basis because of their small body size. Vitamin K2 is synthesized by the body's gut bacteria and can be found in dairy products, fermented foods, and animal products. While it's difficult to overdose on these vitamins naturally with a well-balanced diet, vitamin supplements can have negative consequences.
