The B-complex vitamins include eight nutrients: thiamin, or vitamin B-1; riboflavin, or vitamin B-2; niacin, or vitamin B-3; pantothenic acid, or vitamin B-5; vitamin B-6; folate, or folic acid; biotin; and vitamin B-12. Unlike some vitamins that can be stored for future use, such as vitamins A and D, your body can't store B-complex vitamins, with the exception of vitamin B-12. This means that any excess B vitamin dissolves in your urine for elimination from your body. As a result, you need a daily supply of B vitamins. Each member of the B-complex family has its own set of functions in your body, but these vitamins also work together to maintain your health.
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Support for Your Metabolism
B-complex vitamins play a role in converting nutrients into energy, so they support your cellular metabolism. Riboflavin and niacin make up components of two coenzymes -- FAD and NAD, respectively -- that help your cells produce ATP, a major source of fuel for your tissues. Biotin activates coenzymes needed to metabolize fats, while folic acid helps your body process amino acids, the nutrients that make up protein. Thiamin also supports your metabolism. It helps your cells metabolize amino acids, and it also activates coenzymes that your cells need to perform the citric acid cycle, which is a series of chemical reactions that produce ATP.
Nervous System Function
Consuming B-complex vitamins also helps your brain function properly. Your brain uses vitamins B-5, B-6 and B-12 to make neurotransmitters, a class of chemicals your brain cells release to transmit information to neighboring cells. Niacin also supports nerve health, and low levels of this vitamin negatively affect your memory and cause depression. In addition to its other functions, vitamin B-12 helps maintain healthy myelin, an essential component of healthy nerve cells. Long-term vitamin B-12 deficiency causes nerve damage.
Red Blood Cell Function
The B-complex vitamins in your diet also help maintain healthy red blood cells, which your body needs for transporting oxygen. Each cell contains thousands of hemoglobin proteins, and each hemoglobin molecule has the ability to bind to the oxygen you inhale and release it into tissues throughout your body. Vitamin B-12 and vitamin B-6 both help your body synthesize heme, the compound responsible for hemoglobin's function. Thiamin and riboflavin also help activate enzymes found in red blood cells. Folic acid also plays a role in red blood cell development. Low levels of folic acid cause pernicious anemia, a condition characterized by abnormally large, immature and dysfunctional red blood cells.
The B-complex vitamins also affect other aspects of your health. For example, niacin and vitamin B-12 both control gene activity in your cells, which is a process important for cancer prevention. Some B-complex vitamins -- specifically vitamins B-12, B-6 and folic acid -- help lower the level of a toxic amino acid called homocysteine in your bloodstream. Vitamin B-5 aids in hormone synthesis, so it benefits your health by helping your body maintain a healthy hormone balance.