You should not take more vitamins than you need. If you take high doses of some B vitamins, you face serious side effects, including increased risk of heart disease, stroke, stomach ulcers and liver damage. Ask your doctor if you need to take either a multivitamin, a vitamin B complex supplement or both. Although high doses of vitamin B can treat specific medical conditions, most people get all the vitamin B they need from their diets.
Recommended Doses
To find out if you can safely combine multivitamins and vitamin B complex supplements, add the totals of the doses of vitamin B in both supplements. Here are the recommended daily allowances for the B vitamins most commonly used in B complex formulas: vitamin B-1, 1.1 mg to 1.5 mg; vitamin B-2, 1.1 mg to 1.6 mg; vitamin B-3, 14 mg to 17 mg; vitamin B-5, 5 mg to 7 mg; vitamin B-6, 1.3 mg to 2.0 mg; vitamin B-12, 2.4 mg to 2.8 mg. In general, men need more vitamin B than women, but pregnant and breastfeeding women as well as older adults also might need higher amounts.
Some Benefits of Higher Doses
Medical reasons exist for taking some B vitamins in doses higher than the RDA. Taking a multivitamin plus vitamin B complex that increases your intake of vitamin B beyond the RDA might prove prudent, but ask your doctor first. Reasons to take extra vitamin B-1 include thiamine deficiency, prevention of cataracts and to alleviate symptoms of alcohol withdrawal. Extra vitamin B-2 might treat riboflavin deficiency and prevent migraine headaches and cataracts. Doctors might prescribe niacin, or vitamin B-3, in amounts up to 4 g a day to treat high cholesterol or prevent heart disease in people with high cholesterol. Other reasons to take extra niacin include to prevent cataracts and Alzheimer's disease and delay the progression of type 1 diabetes. You can take up to 10 mg of vitamin B-5 daily as a supplement. Vitamin B-6 in doses higher than the RDA can treat B-6 deficiency, premenstrual syndrome and kidney disease and prevent a vision problem called macular degeneration. Older adults, people with pernicious anemia, people who've undergone gastric bypass surgery and people with Crohn's disease might need extra doses of vitamin B-12.
Insufficient Evidence
Popular reasons for taking vitamin B complex supplements with or without multivitamins include efforts to increase athletic performance, improve mood, pass drug screening tests and improve orgasm. The long list of other possible uses for vitamin B complex includes treating AIDS, attention-deficit hyperactivity disorder, alcoholism and acne. Evidence for such uses ranges from insufficient to nonexistent. Don't take vitamin B based on anecdotes from friends or rumors on the Internet. Taking too much vitamin B can prove toxic.
Risks
Don't take vitamin B complex supplements and multivitamins without consulting a medical professional and don't exceed dose recommendations unless a doctor specifically recommends that you do so. Long-term use of some B vitamins can cause vision loss and nerve damage and worsen kidney and liver disease. Short-term use of some B vitamins in high doses also can put your health in jeopardy. In 2005, for instance, more than 3,000 people in the United States who took niacin in high doses contacted poison control centers with symptoms of serious overdose.
References
- University of Maryland Medical Center; Vitamin B3 (Niacin); June 18, 2009
- Medline Plus: Niacin and Niacinamide (Vitamin B3)
- Centers for Disease Control and Prevention; Use of Niacin in Attempts to Defeat Urine Drug Testing -- Five States, January to September 2006; C Mendoza, M.D.; April 20, 2007
- Medline Plus; Thiamine (Vitamin B1); May 9, 2011
- Medline Plus; Riboflavin (Vitamin B2); Nov. 19, 2010
- Medline Plus; Pantothenic Acid (Vitamin B5); Nov. 19, 2010
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