Vitamin B7 (Biotin) — Structure, Food Sources, Health Benefits and Toxicity

by Victoria Mazmanyan | Last updated on June 03, 2024

Medically reviewed by Arpi Gasparyan

Introduction

Vitamin B7, or biotin, is a water-soluble B vitamin essential for the metabolism of carbohydrates, fats, and proteins and gene expression regulation. It also plays a role in maintaining healthy hair, skin, and nails.

This article will explore biotin, covering its physiological roles, nutritional benefits, deficiencies, toxicity, and more relevant information.

Table of contents

Absorption, Metabolism, and Functions

Food Sources of Vitamin B7

Recommended Intakes

Vitamin B7 & Human Health

Hair and Nail Health

Skin Health

Type 2 Diabetes

Vitamin B7 Deficiency: Risk Groups, Symptoms

Symptoms

Risk Groups

Vitamin B7 Toxicity

Vitamin B7 Supplements

Interactions With Medications

Summary

References

Absorption, Metabolism, and Functions

Vitamin B7, sometimes called vitamin H, is an essential nutrient. This means the body cannot produce it and must get it from external sources. Biotin is acquired from food or normal gut microbiota.

Before absorption, biotin bound to dietary proteins is converted into free biotin. The absorption of free biotin in both the small and large intestines relies on a sodium-dependent multivitamin transporter, which is also responsible for the absorption of pantothenic acid or vitamin B5 (1).

There are 8 different structural varieties of vitamin B7, but only one form is biologically active. Thus, the bioavailability of dietary biotin can vary significantly between different food sources, ranging from as low as 5% to nearly 100% (1). Overall, it tends to be less than 50%.

A deficiency in biotin causes a significant and specific increase in biotin uptake by human intestinal epithelial cells.

Biotin is present in all organisms, serving as a cofactor for enzymes known as biotin-dependent carboxylases. In human cells, biotin functions as a cofactor for five biotin-dependent carboxylases: propionyl-CoA carboxylase, pyruvate carboxylase, methylcrotonyl-CoA carboxylase, acetyl-CoA carboxylase 1, and acetyl-CoA carboxylase 2.

These carboxylase enzymes are crucial for catalyzing key reactions in gluconeogenesis or the formation of glucose, fatty acid synthesis, and amino acid breakdown (2). Vitamin B7 may also play a role in protein synthesis from RNA and DNA and liver enzyme regulation (2).

Food Sources of Vitamin B7

Biotin is found in the highest concentrations in organ meats such as liver and kidney, while it is present in lower amounts in meats, most vegetables, and fruits.

The biotin content is typically not listed in standard food nutrition data and has been determined for relatively few foods.

Below, you can find a list of 10 foods rich in vitamin B7 based on their average serving sizes, according to one research (3).

Food Name	Vitamin B7 Content	Serving Size
Beef liver (cooked)	31mcg	74g
Eggs (whole, cooked)	10mcg	47g
Salmon (pink, canned)	3.7mcg	63g
Mushrooms (canned)	2.6mcg	120g
Chicken nuggets (breaded, fried)	1mcg	75g
Avocado (raw)	0.4mcg	37g
Sweet potatoes (cooked)	1.16mcg	80g
Peanuts (salted, roasted)	4.9mcg	28g
Broccoli (raw)	1.1mcg	113g
Toast (grilled)	1mcg	84g

Recommended Intakes

There is no established recommended daily value for biotin; instead, guidelines provide an adequate intake (AI) value to indicate the amount considered sufficient for nutritional needs.

The adequate intake value of vitamin B7 for adults is 30 mcg/day. This value stays at 30mcg during pregnancy but increases to 35mcg during lactation (4).

The vitamin B7 requirement changes depending on age and physiological state. However, it is the same for men and women.

Up to 6 months	7 to 12 months	1 to 3 years	4 to 8 years	9 to 13 years	14 to 18 years	19 and above
5mcg	6mcg	8mcg	12mcg	20mcg	25mcg	30mcg

Consuming large amounts of raw egg white can influence biotin requirements, as it contains avidin, a substance that binds to biotin and decreases its absorption (4).

Smokers might need higher doses of vitamin B7 because smoking can accelerate biotin metabolism (5).

Vitamin B7 & Human Health

Biotin is commonly advertised as a treatment for hair, nail, and skin issues. This belief mainly stems from the fact that vitamin B7 deficiency leads to brittle nails, hair loss, and skin rashes.

An alternative recently popularized name for biotin, vitamin H, comes from the German words for hair and skin - Haar and Haut.

In this section, we will examine the scientific evidence supporting these claims to determine their validity.

Hair and Nail Health

The research regarding this topic is sparse and flawed. Only three small studies research the effects of biotin supplementation on nail health. These studies lack placebo groups and don’t consider the participants' initial biotin levels (6).

Regardless, these studies showed that vitamin B7 supplementation resulted in thicker, harder, and firmer nails for most participants (6, 7).

Research supporting the efficacy of biotin for hair health is also limited. A review of the use of biotin for hair loss looked at 18 reported cases where biotin was used for hair and nail issues. In every case, the patients had an underlying condition affecting hair or nail growth. All patients showed clinical improvement after taking biotin supplements. Most studies focused on children younger than the age of 5 (8).

While biotin supplementation may be beneficial in cases of biotin deficiency, whether acquired or inherited, as well as conditions like brittle nail syndrome or uncombable hair syndrome, these instances are rare. Moreover, there is insufficient evidence to justify biotin supplementation in healthy individuals (8).

Overall, there is limited evidence to suggest that biotin supplements benefit nail and hair health.

Skin Health

Once again, data on biotin supplementation for treating dermatologic conditions, particularly in patients with normal biotin levels, is limited. However, in children with atopic dermatitis and biotin deficiency, oral biotin improved symptoms of dry skin and itching (9).

Type 2 Diabetes

A systematic review and meta-analysis indicated that biotin supplementation may reduce total cholesterol and triglyceride levels. In patients with type 2 diabetes mellitus, higher doses of biotin were associated with reduced fasting blood glucose levels (10).

Limited evidence suggests it has no significant effect on insulin, low-density cholesterol (LDL), high-density cholesterol (HDL), and very low-density cholesterol (VLDL) levels.

Therefore, biotin supplementation could be a cost-effective and potentially beneficial option for type 2 diabetes patients (10).

Vitamin B7 Deficiency: Risk Groups, Symptoms

Biotin deficiency is rare, and severe deficiency in healthy individuals consuming a normal mixed diet has never been reported (6).

Symptoms

Biotin deficiency leads to various symptoms, primarily neurological and skin-related. Dermatological issues arise from impaired fatty acid metabolism and include hair loss (alopecia), periorificial dermatitis (a scaly, red rash around the eyes, nose, and mouth, also known as "biotin-deficient face"), conjunctivitis, and skin infections (11).

This rash resembles that seen in zinc deficiency.

Neurological symptoms include seizures, ataxia, numbness and tingling in the extremities, low blood pressure, intellectual disability, and developmental delays in children. Adults may experience depression, lethargy, and a history of hallucinations. Untreated, the condition can also cause optic atrophy, blindness, and hearing loss (11).

Gastrointestinal symptoms, such as nausea, vomiting, and anorexia, may also occur. Other presentations of biotin deficiency include metabolic issues, such as ketoacidosis, lactic acidosis, and organic aciduria.

Risk Groups

Biotinidase deficiency (a genetic defect): a rare autosomal recessive disorder that blocks the release of free biotin, causing biotin deficiency despite adequate intake. Left untreated, it can result in neurological and skin symptoms, with severe cases leading to coma or death. Screening newborns for this condition is standard practice in the US and many other countries (6).
Alcoholism: alcohol can inhibit the absorption of biotin and is often associated with poor dietary intake (12).
Pregnancy: approximately one-third of pregnant women have mild biotin deficiency, even though they consume sufficient amounts, though the exact cause is not fully understood (12).
Medications: certain medications, such as antiepileptics, antibiotics, and isotretinoin, can interfere with vitamin B7 absorption and metabolism (11).

Vitamin B7 Toxicity

The Food and Nutrition Board has not set upper limits on biotin intake values because there is no evidence of toxicity from high intakes in humans. Excess biotin accumulation in the body is uncommon, and because biotin is a water-soluble vitamin, any surplus is typically excreted in urine (5, 6).

Symptoms of biotin overdose may include insomnia, increased thirst, and urination, among others. As biotin plays a role in postprandial glucose control, excess intake could lead to symptoms resembling hyperglycemia (high blood glucose), such as increased thirst. Therefore, diabetic individuals should exercise caution when considering biotin supplementation (5).

According to an FDA warning issued recently, taking supplements with high levels of vitamin B7 can cause falsely low results on blood tests used to diagnose heart attacks. This can lead to missed diagnoses and potentially lethal consequences (13).

Levels of hormones, such as thyroid hormones, gonadotropins, and vitamin D, may also be affected (5).

Vitamin B7 Supplements

The 1986 National Health Interview Survey showed that around 17% of adults in the United States use biotin-containing supplements. Detailed information regarding biotin intake from supplements is not provided (4).

Biotin is found in dietary supplements that contain biotin alone and in supplements that combine various B-complex vitamins. Additionally, it is included in certain multivitamins or mineral products. The oral, free biotin absorption rate is 100%, even when individuals consume pharmacological doses of up to 20 mg a day (6).

Interactions With Medications

Anticonvulsants such as carbamazepine or phenobarbital may decrease biotin absorption in the intestines (5).

Long-term broad-spectrum antibiotic use can cause bacterial imbalances in the gut, leading to decreased biotin synthesis in the intestines (11).

Patients undergoing isotretinoin treatment for acne may also have low vitamin B7 levels (11).

Summary

Vitamin B7, also known as biotin or vitamin H, is a water-soluble B vitamin essential for the metabolism of carbohydrates, fats, and proteins while also playing a role in maintaining healthy hair, skin, and nails.

Biotin is acquired from food or normal gut microbiota. It is present in all organisms as a cofactor for a group of enzymes called carboxylases.

Biotin is found in the highest concentrations in organ meats such as liver and kidney, while it is present in lower amounts in meats, most vegetables, and fruits. However, biotin content is typically not listed in standard food nutrition data and has been determined for relatively few foods.

The adequate intake value for adults, both men and women, is 30 mcg/day. This value stays the same during pregnancy but increases to 35mcg daily during lactation.

Biotin is commonly advertised as a treatment for hair, nail, and skin issues, mainly because vitamin B7 deficiency leads to brittle nails, hair loss, and skin rashes. While the research on this topic is sparse and flawed, overall, there is limited evidence to suggest that biotin supplements benefit nail and hair health.

Biotin supplementation could be a potentially beneficial option for type 2 diabetes patients to lower fasting blood glucose.

Vitamin B7 deficiency or overdose cases are extremely uncommon.

References

Author name: Victoria Mazmanyan

Education: General Medicine at YSMU

Last updated: June 03, 2024

Medically reviewed by Arpi Gasparyan