The B vitamin complex is a group of eight individual vitamins: thiamine, or B1; riboflavin, or B2; niacin, or B3; pantothenic acid, or B5; pyridoxine, or B6; biotin, or B-7; folic acid, or B9; and cobalamin, or B12. Because most people receive adequate amounts of B vitamins from their diet, taking a B vitamin supplement can lead to overdose if you do not have a deficiency. However, what happens to your body when you have a lot of vitamin B depends on the type of B vitamin you take.
B Vitamins Without Adverse Effects
According to the Institute of Medicine, some B vitamins do not have any measurable health risks in large doses. These include vitamins B1, B2, B5, B7, B9 and B12. The medical community still urges caution when taking these vitamins as supplements because further research is necessary to completely rule out any effects.
In large doses, niacin, or vitamin B3, can cause a fast, irregular heartbeat and skin redness and increased skin temperature that looks and feels similar to a sunburn. Taking too much niacin can also cause blurred vision and nausea. The Institute of Medicine recommends taking no more than 35 mg of vitamin B3 per day.
Vitamin B6 can disrupt the transmission of nerve signals from your brain to your muscles, especially those that control your arms and legs and your breathing. This leads to tingling sensations in the hands and feet, decreased muscle control and coordination, difficulty breathing and, in severe cases, paralysis of the affected muscles. According to the Institute of Medicine, the daily recommended dosage for vitamin B6 is 100 mg.
B-complex pills contain all eight of the B vitamins. Most B vitamin complex pills contain 100 percent to 400 percent of your daily required intake of B vitamins. For this reason, you may experience any of the symptoms of a niacin or vitamin B6 overdose, especially if you are getting enough of these vitamins from your diet.
B vitamins are water-soluble, meaning they are not stored in your body and any excess is eliminated in your urine. If you have too much vitamin B, drink large amounts of water to flush it out of your system and reverse the adverse effects.