The symptoms of a vitamin overdose vary depending on which vitamin has been ingested in excess. Typically, only the fat-soluble vitamins can cause overdoses. These vitamins, including vitamin A, vitamin D, and vitamin K, can accumulate in fat cells and reach toxic concentrations. In contrast, if high quantities of the water-soluble vitamins are taken in excess, they are simply excreted in the urine. The two exceptions to this rule are the fat-soluble vitamin E, which does not have any toxicities, and the water-soluble vitamin B6, which can cause overdose symptoms.
The term "vitamin A" refers to a class of molecules called the retinoids, including the substances retinol, retinal, retinoic acid, and beta-carotene. Humans need to obtain vitamin A from the diet to ensure proper growth, vision, reproduction, and skin health. One of the most obvious symptoms of a vitamin overdose with vitamin A is skin dryness and itchiness. Other problems caused by excess intake, such as an increase in the pressure within the brain, can cause symptoms including blurred vision and headaches.
Vitamin D plays an important role in regulating the body’s calcium levels and in maintaining strong bones. Unfortunately, some experts consider vitamin D to be the most toxic of all the vitamins. High levels of this substance can cause increased levels of calcium in the blood, which causes symptoms such as abdominal pain, kidney stones, constipation, depressed mood, and calcification of the arteries.
In contrast to the serious side effects caused by vitamin D, the symptoms of a vitamin overdose with vitamin K are typically minor and only cause problems in select patients. This vitamin is critical for forming proteins that help the blood to clot. Infants are typically given a vitamin K injection after birth in order to prevent excessive bleeding or bruising. Giving excess vitamin K to infants can cause them harm, however, as high levels of the substance can destroy the membranes of the red blood cells. This causes symptoms such as jaundice, shortness of breath, and fatigue.
Tocopherol, another name for the fat-soluble vitamin E, is important because it serves as an antioxidant. It is unique out of the fat-soluble vitamins in that no toxicities have been associated with it. Even taking high doses of the vitamin does not result in any overdose symptoms.
Another exception to the rule that fat-soluble vitamins can be toxic is vitamin B6, also known as pyridoxine, pyridoxal, or pyridoxamine. This molecule is important in helping the body metabolize food. Symptoms of a vitamin overdose with B6 can include numbness or tingling of the extremities.