An overdose of biotin is rare, but it is possible if someone takes high doses of the vitamin over an extended period of time. Possible signs of a biotin overdose include slower insulin release, skin rash, lower levels of vitamin C and vitamin B6, and higher blood sugar levels. Biotin, which is vitamin B7, also called vitamin H, is water-soluble, which means 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. Doctors may advise pregnant women to take 30 to 35 mcg daily, preferably through diet. Your doctor may prescribe higher doses of the vitamin 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 lower high cholesterol and help people with diabetes. The researchers believe that more study is needed before biotin is recommended for these 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 can deplete biotin from the body.
Medications taken for seizures, as well as dialysis for kidney disease, can cause a biotin deficiency. Those who eat excessive amounts of egg whites can also become deficient in this nutrient. Smoking has been linked to biotin depletion, and pregnant women may need additional supplementation of the vitamin if recommended by their doctors.
In animal studies with pregnant rats, signs of a biotin overdose included an increased risk of miscarriage. The research found that the animals' placentas also shrank with high doses of biotin, but a biotin deficiency caused birth defects. There are no known side effects of biotin overdose in humans because no human trials have been done.
Supplements that can lead to biotin overdose are generally not necessary if a healthy diet is consumed. Egg yolks, dairy products, and legumes are good sources of this nutrient. It is also found in meat and green leafy vegetables.