Vitamin B7 (Biotin)

As mentioned above, biotin deficiency is rare. Adequate intake for adults is 30µg and 35µg for lactating women. It is less for those under 18. Blood tests that show reduced propionyl-CoA carboxylase (PCC) and reduced urinary excretion of biotin are indicators of a deficiency. The following populations are at elevated risk: 

• Those with liver diseases, since most biotin is stored in the liver.
• Those who have an alcohol addiction. Chronic exposure to alcohol has been linked to lower biotin levels. 
• Up to a third of pregnant women have a slight decrease in biotin because of the increased demand on their bodies.
• Those who have had their stomach surgically removed, those who are on intravenous feeding (food tubes) long term. 
• Those who have been taking anticonvulsant medications long term.
• Those who consume high quantities of raw eggs. Caesar salad dressing and eggnog are common examples. 
• Chronic smokers: Smoking increases the risk of biotin deficiency.

Biotinidase deficiency is a rare autosomal recessive disorder (a type of genetic disorder) that prevents the body from releasing excess biotin. Without treatment, the disorder can cause serious symptoms and even death. Oral biotin is given for life to those with the disorder and the outcome is generally positive. These are the signs and symptoms of a biotin deficiency: 

• Thinning hair, or alopecia
• Scaly skin on the face, including eyes, nose, mouth
• Brittle nails
• Impaired coordination 
• Depression
• Fatigue
• Numbness in extremities 

More severe symptoms—mostly seen with untreated congenital disorders—include: 

• Impaired immune system function and lower immunity 
• Seizures
• Optical atrophy

There are many natural sources of biotin, including: 

• Cooked eggs
• Salmon
• Pork
• Sweet potato
• Almonds
• Spinach
• Broccoli
• Sunflower seeds

Good bacteria in the gut also produce biotin but this itself is not sufficient for bodily requirements. If testing reveals that you are deficient in this vitamin, you may be advised to take a supplement. 

According to the US National Institutes of Health (NIH), there is only limited and insufficient evidence to suggest that biotin supplements improve the condition of brittle nails. There is also scant evidence to support a link to alopecia (hair loss) and rashes. A meta-analysis conducted in 2017 showed that biotin therapy did help slightly with hair and nail growth, but largely in cases with rare inherited diseases or in people with underlying pathologies. The authors concluded that for healthy people with normal biotin levels, supplementation did not help. 

(Read more: Home remedies for glowing skin)

As for the brittle nail studies, there were no placebo groups and the baseline levels of biotin were not measured. The studies were also small in size and more evidence is needed before any claims can be made.

For skin and hair growth, the vast majority of studies have been done in children, and again the evidence is thin. In terms of hair health, it was found that children with uncombable hair syndrome (a rare disorder involving the hair shaft) benefited from biotin treatment. These findings seem to underline the fact that supplementation won’t benefit those who don't have underlying conditions.

(Read more: Natural remedies for hair loss)

There is also some very limited evidence that biotin supplementation can improve the symptoms of MS (multiple sclerosis) and type 2 diabetes. MS is characterized by the progressive degeneration of myelin sheaths in the central nervous system (brain and spinal cord). Biotin plays a role in the intermediary metabolism required for myelin formation, so use was hypothesized as a potential therapy. The results of a randomized controlled trial were mildly encouraging; 13 out of 103 patients receiving daily biotin for 48 weeks achieved a sustained improvement of MS-related symptoms. Out of 51 placebo patients, no one showed any improvement.

As for diabetes, it has been shown that biotin can improve glucose utilization and there is evidence to suggest that biotin levels may be low in patients with type 2 diabetes. Studies so far have been limited and contradictory—one investigation showed that fasting blood glucose levels were lower after biotin therapy whereas another showed that biotin had no effect whatsoever on blood glucose levels. 

Biotin supplementation is the preferred treatment for congenital defects that lead to lower levels of biotin in the body. Those who are not treated can suffer serious symptoms or even death. 

All in all, the evidence for biotin therapy is solid only for clinically low levels of the vitamin. It has generated interest because of its relation to hair loss, skin rashes and brittle nails, but further research is needed to solidify these claims. 

Fortunately, even high doses of biotin do not seem to have adverse health effects. However, biotin supplements can influence blood tests and produce skewed results. This can have harmful effects if treatment is based on these flawed diagnostic results. 

It has been found that long-term use of anticonvulsant medication (used for the management of epilepsy) reduces biotin levels in the patient's body. These drugs catabolize (break down) biotin which leads to lower rates of absorption in the gut. It has been suggested in the literature that long term treatment with antibiotics can also lower biotin levels but this has not been confirmed with any studies.

Vitamin B5 may compete with biotin in cellular uptake as they both rely on human sodium-dependent multivitamin transporter (hSMVT) for absorption. However, this has not been confirmed in human studies and there is only limited evidence in rats.