The B vitamins are essential to your health. You can usually get sufficient amounts of all of them from your diet. You can't overdose on vitamin B from food, but if you have certain medical conditions, or are taking supplements, multivitamins or herbal remedies, and eating fortified foods, you might exceed the upper level. It's helpful to know which B vitamins might cause toxicity or adverse effects and what symptoms to watch out for.
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About Vitamin B
The vitamin B benefits include assisting in energy production for the proper functioning of your heart, brain and blood cells. Eight vitamins make up the vitamin B complex group. They have some characteristics in common, but all have different functions and different recommended daily intakes. Some have established upper intake levels.
Since B vitamins are water-soluble, cases of toxicity are rare, but over-supplementation may result in an unsafe dose. Some multivitamins and vitamin B supplements contain substantially higher amounts than the daily value, RDA and even the established tolerable upper intake levels, according to the National Institutes of Health.
Read more: B-Complex Vitamin Benefits & Side Effects
Why Take Supplements?
There are several reasons why you may need to take a vitamin B supplement if you can't get enough through your diet. These include:
- Taking certain medications that interfere with vitamin absorption, including some anti-seizure medications, proton pump inhibitors and metformin. Oral contraceptives can also deplete several B vitamins according to University Health News.
- Eating a restricted diet, such as vegetarian, vegan or low-calorie
- Having a medical condition or disease that impairs digestion or absorption,
such as celiac or Crohn's disease
- Having a drug or alcohol dependency
- Having a reduction in stomach acid due to age
- Recovering from surgery such as for weight loss, gastric bypass or removal of part of the small intestine
- Being pregnant or lactating
- Having HIV or AIDS
- Having diabetes
Read more: The Best Form of B-Complex Vitamin
Thiamine — Vitamin B1
Thiamine, or vitamin B1, plays a key role in energy metabolism and the proper functioning of your muscles, nervous system, skin and brain. Food sources of thiamine include meats, whole grains, legumes and fortified foods. The recommended daily allowance is 1.2 milligrams for men and 1.1 milligrams for women.
Supplements usually contain 50 to 500 milligrams of vitamin B1 per tablet. There is no established upper limit because there is no known toxic effect from a thiamine overdose.
Riboflavin — Vitamin B2
Riboflavin, or vitamin B2, is important for healthy skin, hair, blood and your brain. Good dietary sources are milk, eggs, organ meats, green vegetables and fortified foods. The RDA for riboflavin is 1.3 milligrams for men and 1.1 milligrams for women.
Supplements often contain 25 to 100 milligrams, but your body can't absorb more than about 27 milligrams at a time. You'll know if you've taken more riboflavin than necessary because you'll experience bright yellow urine, which is just surplus vitamin B2.
Read more: Treatment for a Riboflavin Deficiency
Niacin — Vitamin B3
Niacin, or vitamin B3, helps your body metabolize carbs, fats and proteins for energy. Good food sources are animal proteins, fish, mushrooms, potatoes and legumes. The RDA for niacin is 16 milligrams for adult men and 14 milligrams for women.
Overdosing on niacin from over-the-counter or prescription medications may cause toxicity if you exceed the recommended upper limits — 30 milligrams for teens and 35 milligrams for adults. Supplements typically contain 20 to 500 milligrams per tablet.
The two main forms of supplemental niacin are nicotinic acid and nicotinamide. Niacin supplements with 30 milligrams or more of nicotinic acid can cause the skin on your face, arms and chest to turn red and burn, tingle or itch and can also induce headaches and dizziness.
With daily doses of 1,000 milligrams or more of nicotinic acid, serious symptoms may develop including:
- Easy bruising
- Increased bleeding from wounds
- Liver damage
Pantothenic Acid — Vitamin B5
Pantothenic acid, or vitamin B5, is necessary for producing blood cells, balancing glucose levels, managing cholesterol and helping your skin. Foods containing pantothenic acid include animal protein, eggs, milk, mushrooms, whole grains and nuts.
The recommended adequate intake for vitamin B5 is 5 milligrams. Dietary supplements typically range from about 10 milligrams in multivitamin products to up to 1,000 milligrams in individual supplements of vitamin B5. Pantothenic acid is considered safe, but very high doses, such as 10,000 milligrams a day, can cause:
- Upset stomach
- Increased risk of bleeding
Pyridoxine — Vitamin B6
Vitamin B6, or pyridoxine, is essential for protein metabolism, the health of your brain and production of hormones. Vitamin B6 is found in meat, fish, potatoes, grains and fruit (other than citrus). The recommended daily allowance for adults ages 19 to 50 years of age is 1.3 milligrams. For ages 51 and older, it's 1.7 milligrams for men and 1.5 milligrams for women. The upper limit for vitamin B6 long-term is 80 milligrams for teens and 100 milligrams for age 19 and older.
As with other B vitamins, high intakes from food sources have not been reported to cause symptoms of toxicity. Supplements typically range from a dosage of 5 to 500 milligrams per tablet. The National Institutes of Health warns that a daily intake of 1 to 6 grams of vitamin B6 for 12 to 40 months can result in symptoms of:
- Progressive nerve damage causing lack of muscle control or coordination
- Painful, disfiguring skin lesions with numbness, tingling or burning
- Sensitivity to light
- Gastrointestinal conditions, such as nausea and heartburn
- Reduced ability to sense pain or extreme temperatures
The severity of symptoms is dose dependent and often disappears when the supplement is discontinued.
Folate — Vitamin B9
Folic acid, sometimes called vitamin B9, is vital for cell creation and helps prevent birth defects when taken before and during pregnancy. You can get folate from consuming beef liver, spinach, asparagus and fortified grains. The RDA for folic acid is 400 micrograms for age 14 years and older. Folic acid is the synthetic form of folate available in supplements. Common doses in supplements range from 400 to 800 micrograms for adults.
A safe upper limit has not been established for folate, but an intake of more than 5,000 micrograms a day could mask a deficiency in vitamin B12 and pernicious anemia. Neurological consequences may be irreversible. In addition, McGill reports that a supplemental dose of 1,000 micrograms showed an increased incidence of prostate cancers and a slight increase in cancerous polyps.
Cyanocobalamin — Vitamin B12
Vitamin B12, or cyanocobalamin, is essential for nerve tissue health, brain function and the formation of red blood cells. Foods that supply vitamin B12 are primarily limited to animal products like meat and dairy, so vegetarians and vegans often take vitamin B12 supplements.
The recommended daily allowance for vitamin B12 is 2.4 micrograms for ages 14 and older. Megadoses of up to 2,000 micrograms are considered safe in treating B12 deficiency. Because of its low potential for toxicity, there is no established upper limit for vitamin B12.
The most common form of B12 supplement is cyanocobalamin, which is chemically synthesized. There are several forms of administration, including injectable, pill form, atopic creams, nasal sprays and "under the tongue" tablets or lozenges. However, only about 10 micrograms of a 500-microgram oral supplement is actually absorbed by your body.
According to B12-Vitamin.com, in very rare individual cases, intramuscular injections of high doses of B12 have led to mild immune responses, but the reactions may have been attributed to preservatives contained in the B12 supplement. The symptoms included:
- Skin irritations such as a particular form of acne
- Hot flushes
Some precautions and safety concerns for taking vitamin B12 supplements include:
- Avoid taking vitamin B12, folate and vitamin B6 after receiving a coronary stent since the combination may increase the risk of blood vessel narrowing.
- If you have an allergy or sensitivity to cobalt or cobalamin, do not use vitamin B12.
- Don't take vitamin B12 if you have Leber's disease, which is a hereditary eye disease. B12 can seriously harm the optic nerve and lead to blindness.
- Taking high doses of B12 to treat a deficiency can unmask the symptoms of polycythemia vera, which is a condition of high numbers of red blood cells.
Read more: The Side Effects of Too Much Vitamin B12
- National Institutes of Health: Multivitamin/Mineral Supplements
- University Health News: Side Effects of Birth Control Pills Include Nutrient Depletion
- National Institutes of Health: Niacin
- Mayo Clinic: Vitamin Deficiency Anemia
- National Institutes of Health: Thiamin
- National Institutes of Health: Folate
- Medscape: Vitamin Toxicity
- National Institutes of Health: Riboflavin
- Mayo Clinic: Niacin Overdose: What Are the Symptoms?
- Case Reports in Pediatrics: Acute Liver Failure Secondary to Niacin Toxicity
- National Institutes of Health: Pantothenic Acid
- National Institutes of Health: Vitamin B6
- Mayo Clinic: Vitamin B6
- McGill Office for Science and Society: Can You Overdose on Folic Acid?
- National Institutes of Health: Vitamin B12
- Healthline: Is Taking High Doses of B12 Helpful or Harmful?
- RxList: Vitamin B12
- B12-Vitamin.com: Vitamin B12 Overdose