The B vitamins -- B-1, B-2, B-3, B-5, B-6 and B-12 -- work together to help improve digestion, lung and nervous system function, and also provide other benefits vital to your good health. This harmony exists when you obtain the B vitamins from foods in your diet. If you take B complex supplements, you may get too much of a good thing and experience unwanted side effects. If you take excessive amounts of vitamin B complex, you could put your health at serious risk.
Dietary Sources
Most people get all the B vitamins they need from their diets. If you regularly consume foods such as nuts, meat, chicken, turkey, eggs, milk, beans and leafy green vegetables, you likely don't need to take vitamin B complex supplements. Persons who abuse alcohol may not absorb enough B vitamins from food. Age and medical conditions might make you deficient in some, but not all, of the B vitamins. Persons older than 50, stomach surgery patients and people with Crohn's disease, for instance, may benefit from taking vitamin B-12 supplements. Vegans may not get enough vitamin B-12 in their diets because plant foods do not provide reliable sources of the vitamin.
Vitamins B-1 and B-2
Vitamins B-1 and B-2 -- thiamine and riboflavin -- will likely not harm you if you take them in recommended amounts. If you check the label of a vitamin B complex supplement, it will tell you the amount of each vitamin it contains and compare it to the recommended daily allowance -- RDA -- for that vitamin. Serious side effects of taking excessive amounts of vitamin B-1 seem unlikely, but whether thiamine interacts with other medications remains unknown. If you drink coffee or tea, eat betel nuts or consume raw fish, you may offset the benefits of vitamin B-1. If you take vitamin B-2 in excessive amounts, your urine may change color -- more orange than yellow -- and you may experience diarrhea. If you take probenecid or phenobarbital, among other medications, vitamin B-2 may speed metabolism of these drugs.
Vitamins B-3 and B-5
If your dose of vitamin B complex includes an excessive amount of vitamin B-3 -- more than 100 mg a day -- you could face serious side effects. Vitamin B-3 is also called "niacin," and it can cause skin rashes, stomach ulcers, irregular heartbeat, gout and liver damage. It can also increase your level of homocysteine, an enzyme associated with heart disease. If you have type 2 diabetes, vitamin B-3 in excessive doses could dramatically elevate your blood glucose levels. It can also worsen kidney disease. You should not take vitamin B-5 -- pantothenic acid -- in supplement form if you have hemophilia as it could make it harder for you to control bleeding incidents.
Vitamins B-6 and B-12
Vitamin B-6 -- pyridoxine -- may cause tingling, vomiting, headache and loss of appetite. If you take excessive amounts of B-6 in a B-complex supplement for an extended period of time, you could face nerve and brain damage. If you take vitamin B-12 alone or in a B-complex supplement, you may not experience unwanted side effects. Some antibiotics, ulcer medications and diabetes drugs may interfere with your body's ability to use vitamin B-12. Talk to your doctor about the benefits and risks of taking vitamin B-12 complex supplements and adhere to dose guidelines.
References
- University of Maryland Medical Center: Vitamin B-3 (Niacin); June 18, 2009
- Medline Plus: Niacin and Niacinamide (Vitamin B-3)
- Medline Plus: Thiamine (Vitamin B-1;) May 9, 2011
- Medline Plus: Riboflavin (Vitamin B-2); Nov. 19, 2010
- Medline Plus: Pantothenic Acid (Vitamin B5); Nov. 19, 2010
- Office of Dietary Supplements, National Institutes of Health: Vitamin B-6
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