While B vitamins are essential nutrients your body requires daily to function properly, taking in too many B vitamins can be detrimental - even dangerous in some cases. Consuming safe levels of B-complex vitamins is essential to avoid overdose.
Vitamin B Toxicity
Not all B vitamins pose a risk for toxicity (negative side effects from vitamin overdose). Some vitamins have tolerable upper intake levels (ULs) established by the Institute of Medicine's Food and Nutrition Board. ULs are maximum safe intakes that likely pose no negative health risks to the general (healthy) population. You don't have to worry about B vitamin toxicity from eating vitamin B-rich foods, as high-dose supplements are the only way to overdose on vitamins.
Mega doses of single B vitamins can result in an imbalance with the other B vitamins, so the University of Maryland Medical Center says taking B complex vitamin supplements (containing all B complex vitamins) is the way to go. However, very high doses can cause upset stomach (or other side effects) and interact with certain medications, so always check with your doctor before taking high-dose B vitamin supplements. Check the label on B complex vitamin supplements to make sure dosages for individual B vitamins are within safe limits. If you suffer symptoms of B vitamin toxicity, see a healthcare professional immediately.
Vitamin B1 (Thiamin)
Vitamin B1 doesn't have a UL, meaning it's unlikely you'll get too much of this vitamin from supplements. Thiamin is a water soluble vitamin, which means excess of this nutrient is excreted in the urine. MedlinePlus says there's no known poisoning that's occurred from taking thiamin supplements, and the University of Maryland Medical Center says consuming supplements in doses of 50 to 100 milligrams daily appears to be safe. Thiamin recommended dietary allowance (RDA) is 1.2 milligrams for men and 1.1 milligrams daily for women.
Vitamin B2 (Riboflavin)
As with thiamin, a UL for riboflavin doesn't exist, which means consuming high doses of vitamin B2 doesn't appear to pose a risk for toxicity. The Office of Dietary Supplements says adverse side effects haven't been reported from taking riboflavin supplements even in doses of 400 milligrams per day for three months. However, the University of Maryland Medical Center says itching, burning, or prickling sensations, numbness, orange or yellow urine, and light sensitivity may occur when taking high doses of B2 supplements. The RDA for vitamin B2 is 1.3 milligrams for men and 1.1 milligrams daily for women.
Vitamin B3 (Niacin)
Unlike vitamins B1 and B2, vitamin B3 (niacin) does have a tolerable upper intake level (UL), which is 35 milligrams daily for adult men and women. However, under medical supervision, you can take higher doses of supplemental niacin, which has been used to help lower cholesterol. The University of Maryland Medical Center says high doses of niacin can cause skin flushing, headache, dizziness, blurred vision, upset stomach, and an increased risk for liver damage and suggests periodic liver function tests for people taking over 100 milligrams of niacin daily. The niacin RDA is 16 milligrams for men and 14 milligrams for women.
Vitamin B5 (Pantothenic Acid)
There isn't an established UL for pantothenic acid, so the chance of toxicity from B5 supplements is rare. The adequate intake level for pantothenic acid is 5 milligrams daily for adults, which is the amount believed to meet the needs of most of the general population. MedlinePlus says large doses of B5 supplements may cause diarrhea or increase your risk for bleeding, but there aren't any known toxic symptoms. However, taking high doses of just one B vitamin can upset the balance of other B vitamins in your body and may interact with certain medications.
Vitamin B6 (Pyridoxine)
The UL for vitamin B6 is 100 milligrams daily for adults, so don't exceed this amount from supplements unless your doctor recommends it. The University of Maryland Medical Center says high doses (200 milligrams daily or higher) of B6 may cause nerve damage, neurological disorders, imbalance, and loss of feeling in the legs. Allergic skin reactions have also been reported from high doses of B6 supplements. Aim to consume at least the vitamin B6 RDA, which is 1.3 to 1.7 milligrams daily for adults (depending on gender and age).
Vitamin B7 (Biotin)
No tolerable upper intake level has been established for biotin, so the chance for toxicity is rare. MedlinePlus says there aren't known toxic symptoms that have occurred from biotin supplements. The University of Maryland Medical Center says there likely aren't medication interactions that occur with biotin supplements but always check with your doctor to be sure. The biotin adequate intake level is 30 micrograms daily for adult men and women.
Vitamin B12 (Cobalmin)
Vitamin B12 doesn't have a tolerable upper intake level, which means toxicity from vitamin B12 isn't too much of a concern. The Office of Dietary Supplements says no negative effects have been reported from high doses of vitamin B12 supplements in healthy individuals. However, it's still best to talk with your doctor before taking high doses of B12, especially if you're taking medications or have health conditions, such as Leber's disease (an eye disease), according to the University of Maryland Medical Center. The vitamin B12 RDA is 2.4 micrograms daily for adult men and women.
Vitamin B9 (Folic Acid)
The tolerable upper intake level for folic acid is 1,000 micrograms daily for adults. Avoid exceeding this amount from supplements unless your doctor okays it. MedlinePlus says doses higher than 1,000 micrograms daily can cause diarrhea, cramps, sleep disorders, rash, irritability, nausea, confusion, upset stomach, behavior changes, gas, excitability, seizures, skin reactions, and possibly increased heart attack and cancer risks. Furthermore, taking folic acid supplements can mask B12 deficiency symptoms, which can cause nervous system damage. The folate (folic acid) RDA is 400 micrograms daily for adults.
It's possible to get too much choline from supplements, as the UL is 3,500 milligrams (3.5 grams) per day for adults. The Office of Dietary Supplements says exceeding this amount can cause fishy body odor, excessive sweating, vomiting, low blood pressure, excessive salivation, liver toxicity, and higher heart disease risks. Choline adequate intake levels are 425 milligrams for women and 550 milligrams daily for men.
Should I Take B Vitamin Supplements?
In many cases, it's okay to take B vitamin supplements as long as you're not consuming mega doses of just one B vitamin (and not other B vitamins). However, avoid exceeding tolerable upper intake levels for B vitamins unless your doctor recommends it.