Deficiency of some B vitamins can cause several problems, most notably anemia, fatigue, poor appetite, abdominal pain, depression and numbness, tingling in the arms and legs, muscle cramps, respiratory infections, hair loss, eczema, poor growth in children, and birth defects.
Some doctors believe that vitamin B deficiency weakens the immune system and increases susceptibility to cancer, but there is no scientific evidence to support this claim, according to the American Cancer Society.
The vitamin B group includes B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folic acid, a synthetic supplement or folic acid) in some foods. And B12 (cobalamin).
This group of vitamins is essential for growth and development, especially in the fetus, as evidence indicates that taking folic acid during pregnancy reduces the risk of birth defects, but controlled studies indicate that human-made folic acid supplementation increases the risk of colon and rectal cancer and breast cancer. Some practitioners believe that a diet rich in vegetables and enriched grain products can help protect against cancer.