Hair loss caused by lost weight may occur because your body is stressed, and it's conserving energy and protein for other functions. It may also be blamed on a dietary deficiency. While the key to reversing thinning hair because of lost weight is to have a healthy, nutritious and balanced diet, some vitamins can especially help with hair growth. If you start a balanced, healthy diet, Dr. Hammonds for Health.com states that hair loss should correct itself after six months.
Vitamin A is a double-edged sword for thinning hair. While it helps promote healthy skin and oil production in your follicles — the key to strong, healthy hair — too much can also cause hair loss. The recommended dietary allowance of vitamin A is 900 micrograms for men and 700 to 1,300 micrograms for women, who need more if they are lactating or pregnant. However, consuming more than 3,000 micrograms of vitamin A per day can lead to vitamin A toxicity, as excess amounts are stored in your liver and not flushed out. While you can get vitamin A toxicity from a diet high in vitamin A rich foods — such as carrots — toxicity most commonly occurs when you consume too many vitamin A supplements.
B vitamins are needed for healthy growth and development, and while deficiency is rare, it can cause hair loss if you don’t have enough in your daily diet. Because B vitamins are water-soluble, excess amounts are flushed away each day, so you need to meet your daily intake of B vitamins each day to ensure that you have sufficient amounts in your system. Leafy greens, as well as beans, peas, fish and eggs, are rich in B vitamins, and many cereals are fortified with B vitamins to ensure that you meet your daily requirements.
Vitamin C is also a water-soluble vitamin, so you need to consume some every day to meet your recommended dietary allowance of 75 to 125 milligrams per day. Women, including those who are pregnant or breastfeeding, as well as smokers, need more vitamin C. Vitamin C is needed to produce collagen, which is crucial for healthy hair and skin — including your scalp. A chronic lack of vitamin C, such as a result of poor nutrition on a crash diet, can lead to scurvy, a symptom of which is hair loss. Citrus fruits, kiwis and tomatoes are all rich in vitamin C, so ensuring that you have a diet rich in fruits and vegetables can help prevent this deficiency.
A 2010 issue of “Dermatology Online Journal” stated that vitamin D played an important role in hair cycling. Researchers conducting a large scale research review found that vitamin D promoted hair growth in animals and humans, and was associated with encouraging hair growth, primarily by encouraging protein production. Researchers stated that vitamin D does indeed help with hair growth, but more study is needed to fully understand its use in treating hair loss. While vitamin D is present in some foods, the majority of your vitamin D requirement -- 600 to 800 international units per day -- is provided by direct sun exposure. However, vitamin D is often added to milk and cereals.