As children, we grow up with the notion that vitamins provide the key to thriving bodies. Without the proper vitamins, we wouldn’t grow up to be “big and strong,” and would instead be weak and useless versions of ourselves. Carrying this need for vitamins into adulthood, we can now buy vitamins in bulk, and consume them in pill form whenever we need to.  It seems that every other week, we are told another miracle that is carried out by vitamins. Vitamin C will stave off colds; vitamin E will help prevent Alzheimer’s, and Vitamin D will treat cancer.

Exactly how much of this is true is unknown, as there is a lot of conflicting evidence from clinical research that is available. Each vitamin does have a specific purpose in our bodies. Some may even positively affect us in ways that are unknown. But before you pop those pills, take a look to see which vitamins you get enough of from your diet, which you may need to supplement, and some of the harmful effects caused by vitamin overindulgence.

Vitamins can keep you healthy and functioning well, but can too many impair your health? Photo credit: USC Health Now

Vitamin/Nutrient name: Biotin

Function: Coenzyme (helper to enzyme function) in the synthesis of fat, glycogen and amino acids

Recommended Daily Value:  20-30 micrograms/day

Contained in foods: Biotin is in liver and in other meats and fruits

Considerations: There is limited data on the effects of increased Biotin, so caution is advised if consuming more than the recommended daily value.
Summary: Considering that the daily value is small, if you eat meat and fruit, you will have plenty in your diet.

Vitamin/Nutrient name: Choline
Function: Precursor for acetylcholine, phospholipids and betaine
Recommended Daily Value:  375-425 milligrams/day
Average daily intake: 2000-3500 milligrams/day
Contained in foods:  milk, liver, eggs, peanuts
Considerations: Intake over 3500 milligrams/day can cause fishy body odor, sweating, salivation, low blood pressure, liver toxicity. Persons with kidney or liver disease, depression and Parkinson’s disease may be at risk of negative effects from choline at upper levels of the average daily intake.
Summary: The average daily value of choline is well above the needed level, so supplementing this nutrient may cause more harm than good. Research is currently being done as to whether choline is actually a needed after fetal development or if the needed amount is synthesized in the body.

Vitamin/Nutrient name: Pantothenic Acid
Function: Coenzyme in fatty acid metabolism (breakdown)
Recommended Daily Value:  4-6 milligrams/day
Contained in foods:  Chicken, beef, potatoes, oats, cereals, tomatoes, yeast, eggs, broccoli, whole grains
Considerations: There are no documented adverse effects caused by increased intake of panthothenic acid.
Summary:  The daily recommended intake is fairly low, so a normal balanced diet is plenty for this nutrient.

Vitamin/Nutrient name: Vitamin A

Function: Vitamin A is required for normal vision function, gene expression, embryonic development and immune system function

Recommended Daily Value:  600-900 micrograms/day

Average Daily Intake: 1,700-3,000 micrograms/day
Contained in foods:  liver, dairy products, fish, dark colored fruits, leafy vegetables
Considerations:  Intake above the high amount of daily average can cause liver toxicity (preformed vitamin A, from supplements)
Summary:  Persons with high alcohol consumption, liver disease, or protein malnutrition are susceptible to the liver toxicity effects of vitamin A and should not take pre-formed vitamin A supplements.

Vitamin/Nutrient name:  Vitamin B2 (aka Riboflavin)
Function: Coenzyme in various reactions in the body
Recommended Daily Value:  0.9-1.1 milligrams/day
Contained in foods:  organ meats, milk, bread products and fortified cereals
Considerations: No documented adverse effects associated with the intake of riboflavin
Summary:  A bowl of cereal with milk and you’re good to go.

Vitamin/Nutrient name: Vitamin B1 (aka Thiamin)
Function: Coenzyme in the metabolism of carbohydrates and branched (complex) amino acids
Recommended Daily Value: 0.9-1.1 milligrams/day
Contained in foods:  Enriched and/or fortified whole grain products, bread and bread products, grains, cereals
Considerations: No associated negative effects from thiamin
Summary:  This vitamin is necessary for the breakdown of starches and proteins. However, it is also contained within those same foods, therefore if you consume them, you should also be able to metabolize them.

Vitamin/Nutrient name: Vitamin B6
Function: Coenzyme in the metabolism of amino acids, glycogen and sphingoid bases
Recommended Daily Value:  1.0 -1.5 milligrams/day
Average daily intake: 60-100 milligrams/day
Contained in foods:  fortified cereals, organ meats, soy-based meat substitutes
Considerations: Sensory neuropathy has been documented from a high intake of supplemental forms of vitamin B6
Summary:  The average amount of vitamin B6 from food is sufficient for the actions without negative effects.

Vitamin/Nutrient name:  Vitamin B12 (aka Cobalamin)
Function: Coenzyme in nucleic acid metabolism, prevents megaloblastic anemia
Recommended Daily Value:  1.8-2.4 micrograms/day
Contained in foods:  fortified cereals, meat, fish, poultry
Considerations:  No adverse data associated with the intake of Vitamin B12
Summary:  As the body ages, efficiency of vitamin B12 absorption is reduced, so it is recommended that older people eat foods fortified with B12 or take a supplement to get their recommended daily values.

Vitamin/Nutrient name: Vitamin C
Function:  Cofactor for reactions requiring reduced copper or iron, also acts as an antioxidant
Recommended Daily Value:  45-75 milligrams/day
Average Daily Intake: 1,200-2,000
Contained in foods:  citrus fruits, tomatoes, potatoes, various other fruits and vegetables
Considerations: Too much vitamin C can cause gastrointestinal irritation and disturbances, formation of kidney stones and excess iron absorption
Summary:  Smokers are advised to consume 35 mg/day more than the recommended daily values. Vitamin C is one of the vitamins with other clinical research documenting benefits, but care should be taken not to over-take supplements of vitamin C.

Vitamin/Nutrient name: Vitamin D
Function:  Helps with the absorption of Calcium and phosphorus concentrations
Recommended Daily Value:  5-15 micrograms/day
Average Daily Intake: 50 micrograms/day
Contained in foods:  Fish liver oils, fish, fortified milk and cereals
Considerations: The body is capable of making certain types of Vitamin D when skin is exposed to sunlight.
Summary:  Deficiencies of Vitamin D are associated with severe illness. Adequate intake coupled with minimal sun exposure is advised.

Vitamin/Nutrient name: Vitamin E
 Function:  Mostly ambiguous, appears to have properties including non-specific antioxidant
Recommended Daily Value:  11-15 milligrams/day
Average daily Intake: 600-1,000 milligrams/day
Contained in foods:  vegetable oils, cereals, grains, nuts, fruits, vegetables, meats
Considerations: Too much intake of vitamin E supplements has caused certain types of blood toxicities. Patients taking blood thinners should be monitored if taking vitamin E supplements. Vitamin E in foods has not caused any negative effects.
Summary: Care should be taken when taking supplements that are over the recommended daily intake.

Vitamin/Nutrient name: Vitamin K
Function:  Coenzyme during the synthesis of proteins involved in blood clotting and bone metabolism
Recommended Daily Value:  60-120 micrograms/day Contained in foods:  green vegetables, plant oils
Considerations: Patients taking blood thinners should be cautious of high vitamin K intake
Summary: Perhaps your parents were right about eating those vegetables.


NIH, Office of Dietary Supplements