B-complex is a vitamin supplement made of a blend of B-vitamins. There are eight B vitamins in all -- thiamine, riboflavin, niacin, pantothenic acid, B-6, biotin, B-12 and folate or folic acid. All B vitamins are water-soluble, and your urinary tract prevents them from accumulating to toxic levels in your body by moving the excess vitamin into the urine and out of the body. It is very difficult to reach vitamin toxicity of most of the B vitamins save for three: B-6, folate and niacin.
Intake Levels: RDA and UL
RDA -- recommended dietary allowance -- is the amount of vitamin recommended for optimum function. The RDA includes your total intake level -- any vitamins you get from your diet as well as supplementation. The UL, or tolerable upper intake level, is the highest amount vitamin that you can ingest, per day, without a significant risk of toxicity. As with the RDA, the UL includes both food and supplement sources of the vitamin. Both the RDA and UL of any vitamin varies by age group. To avoid the risk of toxicity, choose a B-complex supplement that has less than 100 percent of the RDA of any one vitamin, and take the supplement as directed by your doctor.
Vitamin B-6 is assists the metabolism of protein, carbohydrate and fat, and helps red blood cell production. It occurs naturally in animal products, such as meat and eggs, and in plants, such as bananas, avocados and whole-grain products as well as beans and nuts. The RDA of B-6 is 1.3 milligrams for adults aged 19 to 50, 1.5 milligrams for women over age 50 and 1.7 milligrams for men over age 50. The UL is 100 milligrams. B-6 toxicity can cause nerve damage, resulting in burning, pain and numbness and sensitivity to sunlight.
Folate is responsible for neurotransmitter production and prevents neural tube defects in developing fetuses. It occurs naturally in leafy green vegetables, organ meats and beans as well as dark red and orange fruits and vegetables, such as beets and cantaloupe. You can also find processed foods fortified with folate. The RDA of folate is 400 micrograms for adults and the UL is 1,000 micrograms for adults. Folate toxicity does not have any outward symptoms but may mask other B-vitamin deficiencies, according to the Office of Dietary Supplements. Because some deficiencies, such as vitamin B-12, have the potential to cause permanent nerve damage, it's important to be able to diagnose them early -- a task that's difficult when you're consuming too much folate.
Niacin plays a role in converting carbohydrates to energy, breaking down fatty acids and red blood cell production. Food sources of niacin include animal products, such as meat, fish and poultry, whole grains and fortified processed foods. The RDA for niacin is 16 milligrams for men and 14 milligrams for women. The UL for niacin is 35 milligrams for adults over 19. Niacin toxicity causes skin flushing, nausea and vomiting and liver damage.