B-complex vitamins are water-soluble, so your body takes what it needs from them and sends the excess to your liver, which purges it through your urine. It may seem safe to take excessive amounts of these vitamins, but doing so can still cause problems, including damage to your liver, pancreas or nervous system.
The Institute of Medicine recommends that adults up to age 50 get 1.3 milligrams of vitamin B-6 per day. Women over 50 need 1.5 milligrams and men over 50 need 1.7 milligrams. It also recommends that all adults get 400 micrograms of vitamin B-9, or folate, and 2.4 micrograms of vitamin B-12 each day. The IOM has set tolerable upper intake limits, ULs, for vitamins B-6 and B-9 at 100 milligrams and 1,000 micrograms per day, respectively, and warns that exceeding that intake could cause problems. Due to a lack of data, it has not set a UL for vitamin B-12.
Excessive Vitamin B-6
High concentrations of pyridoxine, the form of vitamin B-6 that nutritional supplement manufacturers use in their products, may lead to sensory neuropathy, a neurological condition that causes numbness and impaired walking. To avoid consuming excessive pyridoxine, you can safely get your recommended amount of vitamin B-6 by eating fish, chicken, turkey, beans, spinach, bananas, papaya, strawberries or cantaloupe.
Excessive Vitamin B-9
It is safe to get large amounts of vitamin B-9, also called folic acid or folate, from food, but excessive B-9 from synthetic supplements can be harmful, according to LPI, especially if you are deficient in vitamin B-12. People with vitamin B-12 deficiencies who take large doses of vitamin B-9, usually 5,000 micrograms or more per day, can develop irreversible neurological damage. A deficiency in B-12 is difficult to detect because the symptoms are similar to those of a vitamin B-9 deficiency.
Excessive Vitamin B-12
Vitamin B-12 is safe to take in large doses. Doing so may benefit those on certain medications that inhibit your body's absorption of this nutrient. If you are taking medications for Zollinger-Ellison syndrome, gastroesophageal reflux disease, or peptic ulcers, you may be at an increased risk of B-12 deficiency because proton pump inhibitors and H2-receptor antagonists prevent your body from absorbing it, according to NIH researchers who published a study in "American Journal of Medicine" in 1997. Some cholesterol medications, antibiotics and gout treatments can inhibit vitamin B-12 absorption, as well.
- Linus Pauling Institute: Vitamin B6
- Linus Pauling Institute: Folic Acid
- Institute of Medicine: Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline
- American Journal of Medicine: Effect of Long-Term Gastric Acid Suppressive Therapy on Serum Vitamin B12 Levels in Patients with Zollinger-Ellison Syndrome
Maia Appleby is a NASM-certified personal trainer with more than 15 years of experience in the fitness industry. Her articles have been published in a wide variety of print magazines and online publications, including the Gale Encyclopedia of Nursing and Allied Health, New Moon Network and Bodybuilding.com.