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Alexandra Barry/Demand Media

Thinning hair makes men and women alike seek treatment, as it can affect self-esteem and confidence. Shampoos and hair-care products cannot treat thinning hair, but can only manage what is left, says the Bauman Medical Group. Genetics, medications, medical conditions, illness, stress, surgery and nutritional deficiencies are often to blame for thinning hair. Eating well and taking vitamins and minerals can make hair stronger and boost hair growth, and certain supplements are better than others.

Vitamin A

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Alexandra Barry/Demand Media

Vitamin A is important for cell growth, but too much can damage hair. All excess is stored in the liver and vitamin A toxicity causes hair thinning according to "The Real Vitamin & Mineral Book." So beware of oversupplementation. If an adult takes 100,000 international units daily for a period of several months, toxicity is possible. About 5,000 to 50,000 international units daily is all you need.

Vitamins B and C

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Alexandra Barry/Demand Media

Male hair loss can start as early as your 20s and might be due to a lack of folic acid (B9). Taking B vitamins individually is not recommended, says Dr. Shari Lieberman, unless you are advised to do so by a medical professional. Instead both men and women can benefit from supplementing with B-complex vitamins (50-300 mg for both men and women).

Getting enough vitamin C as you age is challenging. Take at least 500 mg per day of vitamin C, though you can exceed this without toxicity.

Biotin & Zinc

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Alexandra Barry/Demand Media

Deficiencies in biotin and zinc can cause, or accelerate, hair thinning. Biotin does not cure baldness but resolves the underlying skin conditions due to deficiencies says Dr. Shari Lieberman. Get 300 micrograms of biotin daily in your supplements. There is no need to take it as an individual supplement, according to "The Real Vitamin & Mineral Book." A good daily vitamin should contain enough biotin, says to Dr. Alan J. Bauman of Bauman Medical group.

Zinc is present in your hair, but is difficult to store so it must be replenished often. You need 15 milligrams of zinc daily. Dr. Shari Lieberman suggests zinc gluconate and zinc citrate (chelated zinc) as the best forms. People tolerate these and they are relatively inexpensive.

Iron

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Alexandra Barry/Demand Media

Women can have thinning hair after child birth or as the result of an iron deficiency. Iron deficiency is more common in menstruating and pregnant women and vegetarians. If you know that anemia is a problem, iron supplementation (18-30 mg for women) is necessary for thick hair. Iron glycinate, fumarate or gluconate are suggested to avoid constipation and stomach upset.