B complex and vitamin B12
Also called: B vitamins, cyanocobalamin, methylcobalamin, folic acid, P5P.
A group of vitamins sold for energy, where the real issues are B12 in deficiency and B6 at high doses.
What it is
B vitamins serve as coenzymes in energy metabolism, DNA synthesis and nervous system function. A complex usually brings together B1, B2, B3, B5, B6, B8, folate and B12. People buy it mostly for energy and concentration.
What the label does not say
- The 1,000 mcg of B12 on the label is not 1,000 mcg absorbed: the NIH indicates about 2% absorption at 500 mcg and 1.3% at 1,000 mcg, versus about 50% at doses below 1 to 2 mcg, the capacity limit of intrinsic factor. The high dose makes up for a very low percentage with quantity.
- B6 has an upper limit of 100 mg per day, but the NIH reports several cases of sensory neuropathy at doses below 500 mg per day, and severe, progressive neuropathy with ataxia at 1 to 6 g per day for 12 to 40 months. Symptoms generally stop on discontinuation if it happens as soon as they appear. A complex dosed in tens of milligrams of B6 deserves a careful read.
- Bright yellow urine comes from riboflavin (B2). The Linus Pauling Institute describes this flavinuria as an effect of no consequence. It is not a sign that the product is working, only that the excess is leaving.
- The upper limit of 1,000 mcg for folate applies only to the synthetic forms in supplements and fortified foods, not to food folate. A high dose can correct the megaloblastic anemia of a B12 deficiency without correcting the neurological damage.
The forms on the shelf
- B12: cyanocobalamin is the most common form in supplements. The NIH writes that no data indicate that absorption rates vary by form, between cyanocobalamin, methylcobalamin, adenosylcobalamin and hydroxocobalamin.
- Folate: synthetic folic acid is about 85% bioavailable when taken with food, versus about 50% for food folate. 5-MTHF (methylfolate) also exists; the NIH notes that the data on the MTHFR 677C>T polymorphism are divided and that the CDC recommends standard folic acid at 400 mcg for people who could become pregnant.
- B6: pyridoxine hydrochloride or pyridoxal 5'-phosphate (P5P).
Published reference values
- B12: 2.4 mcg per day for adults, 2.6 mcg during pregnancy, 2.8 mcg during breastfeeding. No upper limit has been set.
- Folate: 400 mcg of dietary folate equivalents per day for adults, 600 mcg during pregnancy; upper limit of 1,000 mcg per day of synthetic forms. The Government of Canada recommends a multivitamin containing 400 mcg (0.4 mg) of folic acid for anyone who could become pregnant, ideally 3 months before conception, and not exceeding 1 mg per day without medical advice.
- B6: 1.3 mg per day from 19 to 50; 1.7 mg for men and 1.5 mg for women from 51 onward. Upper limit of 100 mg per day.
- B2: 1.3 mg for men, 1.1 mg for women. No upper limit; the body absorbs little beyond about 27 mg per dose.
When
Usually taken in the morning with a meal. On long-term metformin or antacids, what counts is monitoring your B12 status, not the time you take it.
Keep apart from
- Metformin: the NIH indicates that it could reduce B12 absorption and significantly lower serum concentrations. This calls for monitoring, not spacing doses by the hour.
- Proton pump inhibitors and H2 antagonists: interfere with absorption of B12 from food by slowing the release of stomach acid.
- Antiepileptics (valproic acid, carbamazepine, phenytoin): increase B6 catabolism, and pyridoxine can reduce their serum concentrations.
To mention to a professional
- Vegan or vegetarian diet, atrophic gastritis (2% of the general population, 8 to 9% after 65 according to the NIH), long-term use of metformin or antacids, pregnancy and breastfeeding: check with a health care professional.
From the plate first
B12 is found naturally only in foods of animal origin: beef liver (70.7 mcg per 3 ounces), clams, oysters, salmon, tuna, beef, milk, yogurt. Fortified nutritional yeast and fortified cereals are the non-animal sources.
Sources
- NIH Office of Dietary Supplements, Vitamin B12 (Health Professional)
- NIH Office of Dietary Supplements, Vitamin B6 (Health Professional)
- NIH Office of Dietary Supplements, Folate (Health Professional)
- NIH Office of Dietary Supplements, Riboflavin (Health Professional)
- Linus Pauling Institute, Micronutrient Information Center, Riboflavin
- Government of Canada, Folic acid and neural tube defects
Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.