Vitamins are essential nutrients that your body needs in small amounts to function properly. While most vitamins are safe to consume, taking too much of certain vitamins can be harmful.
Fat Soluble Vitamins
The fat soluble vitamins – A, D, E and K – are stored in your body fat and liver when you ingest too much. This can lead to toxicity if taken in excess over a long period of time.
Vitamin A
Vitamin A is important for eye health, immune function and cell growth. The recommended daily intake for adults is 700-900 mcg RAE (retinol activity equivalents).
Consuming too much preformed vitamin A (retinol) over time can lead to vitamin A toxicity. Symptoms include:
- Headaches
- Dizziness
- Nausea
- Skin redness
- Blurry vision
- Bone pain
- Liver damage
The tolerable upper intake level (UL) for adults is 3000 mcg RAE per day. Consuming above this level over months or years can lead to toxicity.
Food sources high in preformed vitamin A include:
- Beef liver
- Cheese
- Butter
- Fortified milk
- Fish oils
Beta carotene from plant foods like carrots and sweet potatoes does not lead to toxicity, as the body only converts as much as it needs into active vitamin A.
Vitamin D
Vitamin D helps regulate calcium absorption and promotes bone health. The recommended intake is 600-800 IU per day.
Taking too much vitamin D over time can lead to a toxic buildup of calcium in the blood, causing:
- Nausea
- Vomiting
- Poor appetite
- Constipation
- Weakness
- Kidney stones
The UL for adults is 4000 IU. Blood levels should not consistently exceed 150-200 ng/mL.
Too much vitamin D can come from supplements, fortified foods like cereal, as well as foods like:
- Salmon
- Tuna
- Mackerel
- Milk
- Beef liver
- Egg yolks
Vitamin E
Vitamin E functions as an antioxidant that protects your cells. The recommended intake is 15 mg per day.
High doses of vitamin E greater than 1000 mg per day have been linked to adverse effects like:
- Nausea
- Diarrhea
- Fatigue
- Blurred vision
- Bleeding problems
- Stroke
Food sources high in vitamin E include:
- Wheat germ oil
- Sunflower seeds
- Almonds
- Spinach
- Broccoli
The UL for adults is 1000 mg per day from supplements only, not food.
Vitamin K
Vitamin K is essential for proper blood clotting. The recommended intake is 90-120 mcg per day.
Consuming very high amounts of vitamin K from supplements can interfere with blood thinning medications. Otherwise, toxicity from food sources has not been established.
Food sources high in vitamin K include:
- Kale
- Spinach
- Broccoli
- Brussels sprouts
- Cabbage
The UL for adults is not definitively established but likely above 1000 mcg per day.
Water Soluble Vitamins
The water soluble vitamins – C and B vitamins – are generally not stored in your body. Excess amounts are flushed out in urine, which makes toxicity rare.
Vitamin C
Vitamin C is an antioxidant that supports immune function. The recommended intake is 75-90 mg per day.
Large doses of vitamin C greater than 2000 mg per day may lead to side effects like:
- Diarrhea
- Nausea
- Abdominal cramps
- Headache
- Insomnia
Food sources of vitamin C include:
- Citrus fruits
- Peppers
- Strawberries
- Broccoli
- Potatoes
The UL for adults is 2000 mg per day from all sources.
B Vitamins
The B vitamins help convert food into energy and play various roles in nervous system health. Here is a breakdown of each:
Thiamin (B1)
Supports energy metabolism. Recommended intake is 1.1-1.2 mg per day. The UL is unknown but likely above 50 mg per day.
Riboflavin (B2)
Important for cell function. Recommended intake is 1.1-1.3 mg per day. The UL is unknown but cases of toxicity are extremely rare.
Niacin (B3)
Helps enzymes function. Recommended intake is 14-16 mg per day. Upper safe limit is 35 mg per day, with transient flushing the main side effect above this level.
Pantothenic Acid (B5)
Involved in energy metabolism. Recommended intake is 5 mg per day. Very high doses greater than 2000 mg per day may cause diarrhea, but toxicity is unlikely.
Pyridoxine (B6)
Supports amino acid metabolism. Recommended intake is 1.3-1.7 mg per day. Doses over 100 mg per day can cause nerve problems but this is reversible when intake is reduced.
Biotin (B7)
Helps enzymes function. Recommended intake is 30 mcg per day. No signs of toxicity have been seen, even with large doses of 10,000 mcg per day.
Folate (B9)
Critical for cell growth and DNA production. Recommended intake is 400 mcg as folic acid or dietary folate equivalents (DFE) per day. Excessive doses above 1000 mcg per day can mask B12 deficiency symptoms.
Cobalamin (B12)
Needed for red blood cell formation. Recommended intake is 2.4 mcg per day. There have been no reports of toxicity from large doses of B12 supplements or shots.
Vitamin | Recommended Intake | Tolerable Upper Intake Level (UL) |
---|---|---|
Vitamin A | 700-900 mcg RAE | 3000 mcg RAE |
Vitamin D | 600-800 IU | 4000 IU |
Vitamin E | 15 mg | 1000 mg (supplements only) |
Vitamin K | 90-120 mcg | 1000 mcg (estimated) |
Vitamin C | 75-90 mg | 2000 mg |
Thiamin (B1) | 1.1-1.2 mg | 50 mg (estimated) |
Riboflavin (B2) | 1.1-1.3 mg | No UL established |
Niacin (B3) | 14-16 mg | 35 mg |
Pantothenic Acid (B5) | 5 mg | 2000 mg (estimated) |
Pyridoxine (B6) | 1.3-1.7 mg | 100 mg |
Biotin (B7) | 30 mcg | 10,000 mcg (estimated) |
Folate (B9) | 400 mcg DFE | 1000 mcg |
Cobalamin (B12) | 2.4 mcg | No UL established |
Who’s at Risk of Vitamin Toxicity?
Those at highest risk of vitamin toxicity include:
- People taking high-dose vitamin supplements above the UL
- Individuals with certain medical conditions affecting vitamin metabolism or excretion
- Infants given inappropriate doses of vitamin D
Toxicity from food sources alone is very rare, as levels are generally not high enough to reach unsafe amounts when eaten in variety.
Precautions
Here are some precautions to take regarding vitamin intake:
- Avoid very high-dose supplements above the UL
- Don’t exceed the UL regularly from fortified foods plus supplements
- Only take a multivitamin or supplements your doctor recommends
- Tell your doctor about all supplements you take
- Have blood levels monitored if you take high-dose supplements
- Give vitamin D supplements with caution to infants
Symptoms of vitamin toxicity may develop slowly over months or years. Seek medical advice if you experience any concerning symptoms.
In general, get vitamins and minerals from a balanced diet when possible, and use supplements cautiously under the supervision of a health professional.
Conclusion
Excess amounts of the fat soluble vitamins A, D, E and K can accumulate in the body and lead to toxicity when taken long-term above the tolerable upper intake level (UL).
Toxicity from water soluble vitamin C and B vitamins is less likely due to rapid excretion from the body.
Those at highest risk include people taking high-dose supplements long-term. Toxicity from food alone is very rare.
Symptoms may take months or years to develop. Have blood vitamin levels monitored if taking high doses of supplements.
In summary, be cautious with vitamin supplements, don’t regularly exceed the UL, and get blood work done if concerned.