A biotin overdose is rare but is possible if someone takes high doses of the vitamin over a prolonged period of time. Possible signs of a biotin overdose include slower release of insulin, skin rash, lower vitamin C and vitamin B6 levels, and higher blood sugar levels. Biotin, which is vitamin B7, also called vitamin H, is water soluble, meaning the body excretes what it doesn’t use through urine.
The recommended daily intake of biotin for adults is 20-30 mcg per day. For children, the suggested level is 5-12 mcg daily. Physicians might advise pregnant women to take between 30-35 mcg daily, preferably through diet. Higher doses of the vitamin may be prescribed by a doctor for brittle nails or hair loss. Most of the biotin needed for health can come from food.
Biotin is an important element for genetic cell division and the metabolism of amino acids and carbohydrates. It converts glucose and fatty acids into energy, and prevents the kidneys and liver from storing excess fat. These properties lead some people to believe that biotin supplements can reduce high cholesterol and help those with diabetes. Researchers believe more study is needed before biotin is recommended for those conditions.
The potential for a biotin deficiency is greater than for a biotin overdose. Signs of too little vitamin B7 include loss of appetite, hair and nail problems, lethargy, or hallucinations, but deficiencies occur infrequently. Some medications and lifestyle habits may deplete biotin from the body.
Medication taken for seizures, as well as dialysis for kidney disease, might cause a deficiency of biotin. People who eat excessive amounts of egg whites may also become deficient in this nutrient. Smoking has been linked to depletion of biotin, and pregnant women might need additional supplements of the vitamin if their doctors recommend it.
In animal studies with pregnant rats, signs of a biotin overdose included a higher risk of miscarriage. The research found that the placentas of the animals also shrank with high doses of biotin, but a deficiency of biotin caused birth defects. There are no known side effects of biotin overdose in humans because human trials have not been done.
Supplements that may lead to a biotin overdose are generally not needed if a healthy diet is consumed. Egg yolks, dairy products, and legumes represent good sources of this nutrient. It is also found in meat and leafy, green vegetables.