If you’ve ever taken a supplement designed to support healthy hair or nails, it’s likely that high doses of biotin were a main ingredient. 

Biotin (vitamin B7) is an essential B vitamin that helps to break down the protein, fat, and carbohydrates in the foods we eat—but it’s most well known for its purported role in supporting hair and nail growth. 

While there isn’t much solid evidence for the use of supplemental biotin in those without a deficiency, many people anecdotally report improvements in hair and nail health when taking them. 

However, biotin supplements can vary widely in dosage. So, how much is too much, and conversely, how much do you need to take to see results? Let’s find out.

Biotin Dosage: How Much Biotin to Take

The Food and Nutrition Board has set either an RDA (Recommended Dietary Allowance) or AI (Adequate Intake) for vitamins and minerals.

The RDA is the average daily nutrient intake level needed to meet the requirements of 97-98% of healthy adults.

The AI is an intake level that is assumed to be nutritionally adequate for most people, but the available evidence is insufficient to develop an RDA. 

The Food and Nutrition Board has not found sufficient data to set an RDA for biotin, which is why you’ll only see AIs for this nutrient.

While the AI for adults is 30 micrograms (mcg) per day, many supplements contain much more.

Unlike the fat-soluble vitamins (A, D, E, and K), biotin is a water-soluble vitamin, meaning it will be excreted once your body is replete with it.

Biotin Side Effects and Upper Level

There is no UL (Tolerable Upper Intake Level) for biotin, as toxicity or adverse effects from taking this vitamin have never been reported.

The UL is the maximum intake level of a nutrient that has been determined unlikely to pose a risk of adverse effects in humans. However, the key word is “unlikely”—upper intake levels cannot take into consideration every population and health condition.

Although toxicity is not reported from biotin, some people experience mild side effects like nausea and digestive issues, especially at high doses.

Plus, biotin megadoses are known to cause breakouts in acne-prone people—often doing the opposite of what a biotin-loaded skin health supplement claims. This may happen because biotin increases keratin production, and hyperkeratinization is critical to acne development.

Lastly, consuming more than the recommended daily amount—just 30mcg for adults—can cause false results in some laboratory tests, including hormone, thyroid, pregnancy, and vitamin D tests.

Do You Need to Take Biotin Supplements?

The average dietary biotin intake from food in Western populations is about 35–70 mcg per day, which is above the AI levels for biotin consumption.

As you can find biotin in many foods, including meat, fish, eggs, nuts, seeds, sweet potatoes, and beans, most people consume adequate amounts of biotin in their typical diet. 

Therefore, biotin deficiency is rare in the United States—although it can cause thinning hair, skin infections, hair loss, brittle nails, skin rashes, fatigue, and nervous system disorders if it does occur.

If you don’t consume enough dietary biotin (or another B vitamin), taking a B complex supplement that contains biotin may benefit cellular function, energy levels, mood, and nerve health.

Like many other B complex vitamins, biotin is involved with gene regulation, cell signaling, and promoting the metabolism of fatty acids, glucose, and amino acids. 

However, some people are more likely to become biotin deficient, including pregnant or lactating women and those with genetic mutations causing changes in biotin metabolism.

People who consume large quantities of raw egg whites can also experience biotin deficiency, as the whites contain a protein called avidin that binds tightly to the vitamin and prevents biotin absorption (cooking the egg white denatures avidin, so people who eat lots of cooked eggs don’t have to worry).

In cases of biotin deficiency, daily biotin supplementation is certainly recommended.

Biotin and Nail Strength

Most people do not need biotin supplementation unless biotin intake is low. Biotin supplementation may help promote nail strength or growth. However, this is supported by only a few case reports and small older studies. 

For example, a small study from 1993 found that 63% (22 of 35) of participants showed clinical improvement in brittle nails when taking biotin for six months, although the dosage given is unknown.

Biotin and Hair Growth

Some evidence suggests that biotin stimulates keratin protein production and can increase the rate of follicle growth, which would be supportive for hair strength and growth.

In a 2017 review of 18 studies on biotin and hair or nails, people with biotin deficiency, brittle nails, or uncombable hair syndrome (yep, that’s a thing) saw benefits from taking biotin, while the healthy population did not. 

Larger and more recent studies on biotin and nail strength have yet to be performed. It’s possible that taking biotin supplements may only benefit hair or nail growth if the person has a biotin deficiency.

Biotin and Pregnancy

Biotin is also essential during pregnancy, as it’s necessary for embryonic growth.

Over one-third of pregnant women can develop marginal biotin deficiency during pregnancy due to changes in biotin metabolism, so doses of 30mcg are recommended during this time. 

Excess biotin (over 35 mcg/day) is not recommended during pregnancy or lactation, as it can be dangerous to the baby.

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