There is an optimal daily intake (ODI) for every vitamin and mineral. For each person, this will vary based on age, gender, chronic medical conditions and the ability to absorb nutrients. It is not likely you will get too many vitamins from food consumption alone, but it is possible to take in too many vitamins with supplementation. Certain vitamins are worse than others, causing more issues if taken in excess.
Liver and Kidneys
The kidneys are responsible for producing hormones and vitamins. They are critically important to maintaining fluid balance for magnesium, sodium, potassium, phosphorus, calcium, and bicarbonate. The liver detoxifies the body and must extract the needed and unwanted substances in all fluids and foods. It produces bile and stores and assimilates fat-soluble vitamins.
Active vitamin A in any form is stored in the liver; so intakes beyond recommended dosages could be toxic. Since the liver is the place of storage, too much might overwhelm this organ, causing it to overwork. The Hepatitis Foundation International warns of excess vitamin A intake as toxic to the liver. Taking in over 100,000 international units of vitamin A every day continuously for months could lead to toxicity symptoms such as nausea or vertigo.
There are two types of vitamin D; D-2 and D-3. Both become the form of D your body needs after the liver and kidneys process them. Too much vitamin D intake leads to an excess of calcium in the blood. If excess continues, calcium deposits could end up in the kidneys and other organs.
For individuals without liver issues, taking miacin, or B-3, is not an issue. But for those with liver problems or disease, too much B-3 can elevate tests of liver function. Have a physician monitor your vitamin doses to be safe.
Although it is a myth that excess vitamin C causes kidney stones, according to Dr. Shari Lieberman, PhD, author of "The Real Vitamin & Mineral Book," people with poor kidney function need to be careful with consuming too much vitamin C. Your kidneys may not be able to handle its excretion, and the oxalic acid in your urine may increase, which is a sign of worsening kidney functioning. Also, vitamin B-12 can be depleted, causing other health concerns, such as anemia. Dr. Lieberman recommends between 500 mg to 5,000 mg of vitamin C daily.
Take Vitamins Correctly
According to Dr. Lieberman, popping a bunch of vitamins at once is not ideal. Supplements are best taken with meals in most cases, and should be spread throughout the day. If you are taking 2,000 mg of vitamin C daily, take 1,000 mg twice a day with food, for example. Taking supplements correctly will improve their absorption and tolerance.