Answer:

Although B vitamins are water soluble and don't stay long in your body, large doses of certain B vitamins can cause serious toxicity, as summarized below. The same is true of vitamin C, the other water soluble vitamin.

Unfortunately, there is no requirement for supplement labels to warn of these toxicities. As we have shown in our B Vitamin Supplements Review, many vitamins and energy drinks exceed the established Upper Tolerable Intake Levels (which vary by age) for B vitamins. If you have an established deficiency, high doses may be necessary; otherwise, remember that "more" does not necessarily mean "better."

Toxicities from B Vitamins
B-3 (Niacin) Skin flushing/pain; liver toxicity; elevated blood sugar
B-6 Nerve damage, skin lesions
B-9 (Folate/Folic Acid) Kidney damage; masking of B-12 deficiency
B-12 Acne/rosacea a side effect in some people


More information about the beneficial and toxic effects of these vitamins, including associated dosage, is found in the B Vitamin Supplements Review.

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6 Comments

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Janice8014
October 18, 2015

there is something odd about B6- I know of several people who have had blood tests that showed elevated levels of B6- tested because of peripheral neuropathy symptoms- and were not taking any or lower dose B supplements. have others heard of this?

Stan13877
March 29, 2017

Natural food sources?

Marysue6882
July 23, 2015

What about the use of B 50 along with Biotin and D 3 for nails & hair?

ConsumerLab.com
July 31, 2015

Hi Marysue - Please see the information about biotin in the B Vitamins Review: https://www.consumerlab.com/reviews/_/bvitamins/#biotin. Also see the Encyclopedia article about Brittle Nails: https://www.consumerlab.com/tnp.asp?chunkiid=21425

sharon5845
July 8, 2015

I took 5000 B12 two times a day and developed hives on both arms. I was taking it for phantom pain. Hives disappeared when I stopped taking such a large dose.

Beth (Elizabeth J)5839
July 5, 2015

I order a B complex that is called B natural complex. It is made up of all the B vitamins in the suggested daily dose.

The only one I have been able to find is by Nutrilite - sold by Amway.

Martha5838
July 5, 2015

I had a similar neurological reaction to too much B-6 and folic acid. You will slowly recoup your nerve function if you stop taking B vitamins and concentrate on just eating healthily. Check with your doctor to see if you have a genetic condition such as hemochromatosis. If you do - you can definitely take too much vitamin C. In this condition the liver hangs on to too much iron and seems to be more vulnerable to other toxicities. Some of us also have genes that require folate instead of folic acid - I am always searching for vitamins and foods that don't have folic acid added. I avoid most baked goods and bread for that reason. You are smart to be asking these questions

Diane20325
July 6, 2020

According to a new peer reviewed study, niacinamide (not niacin) 500 mg twice a day has been shown to be safe and effective in lowering non melanoma skin cancer rates by 23%. This is a very encouraging study for those of us with substantial sun exposure and ongoing skin cancers as a result. My dermatologist just recommended that I start this after yet another Moh's surgery. I came looking for a brand of niacinamide to buy. This should be noted in consumerlab for those investigating niacinamide/nicotinamide.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4570055/#:~:text=The%20pill%E2%80%94the%20vitamin%20B,common%20precancer%20of%20the%20skin.

ConsumerLab.com
July 7, 2020

Actually, the study you reference is from 2015 and we wrote about it then. We noted some important caveats to the findings. Details are in our B Vitamin Supplements Review, at https://www.consumerlab.com/reviews/Review_Best_B_Vitamins_and_Complexes_Energy_B6_B12_Biotin_Niacin_Folic_Acid/bvitamins/#skincancer

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