B vitamins are water-soluble vitamins that help the body convert food into energy. These vitamins also help form red blood cells and are essential to the nervous system. Eating a balanced diet helps prevent vitamin B deficiencies. If you take supplements because of a condition or illness, always follow your doctor's dosage instructions to prevent taking too much of a particular B vitamin.
Eat plenty of green vegetables beans and peas to get B vitamins. If you don't typically eat these foods, the vitamins can also be found in proteins like meat, fish, poultry, eggs and dairy products. Many cereals and breads are often fortified with B vitamins.
Vitamin B-1, or thiamine, helps the body convert food into fuel. Thiamine may also help strengthen the immune system in certain populations. Your doctor may prescribe a supplement in the case of a deficiency related to malnutrition because of alcoholism or another condition. According to the National Institutes of Health's Medline Plus, the typical dose for adults is 1 to 2 mg daily. Your doctor may prescribe a larger dose for a severe deficiency. Medline Plus indicates that thiamine is generally safe when taken correctly, and there is no information on an amount that is too much. Talk to your doctor about taking thiamine if you are pregnant or lactating, but a small amount -- 1.4 mg daily -- is generally considered safe.
Vitamin B-2, or riboflavin, produces energy, but it is also an illness-fighting antioxidant. In addition, riboflavin is important for growth and red blood cell production. Deficiencies are rare, but people with poor diets might need supplements. Symptoms of a riboflavin deficiency include fatigue, slow growth, digestive problems, a swollen and red tongue, sores around the mouth, a sore throat and eye fatigue and light sensitivity. According to the University of Maryland Medical Center, the recommended dose is 1.3 mg daily for adult males and 1.1 mg daily for adult females. Riboflavin is considered safe, and there is no information on an amount that is too much. Doses above 10 mg may cause eye damage from the sun, which can be prevented by wearing ultraviolet protective sunglasses. In addition, high does may cause itching, prickly, numb or burning sensations on the skin or yellow-orange urine.
Vitamin B-6 performs many functions in the body. It's needed for protein metabolism, red blood cell metabolism, efficient functioning of the nervous and immune systems and energy production from foods. A deficiency in this vitamin is rare in developed countries unless a person is malnourished for a long time. Symptoms of a vitamin B-6 deficiency include dermatitis, a sore tongue, depression, confusion and convulsions. A vitamin B-6 deficiency can also cause anemia. According to the Office of Dietary Supplements, National Institutes of Health, the recommended dose is 1.3 mg daily for both male and female adults. An upper tolerable intake level of vitamin B-6 has been established at 100 mg daily. A higher dose can result in nerve damage to the arms and legs.