Many people experience thinning hair because they have nutrient deficiencies.  Vitamin B plays a large role in the health of your hair, and getting enough of it is essential to keeping thick hair and reducing how much you shed. Good sources of vitamin B include fruits, vegetables, nuts, and brown rice, among others. Diets deficient in iron lead to poor hair growth. Good sources of iron include beef, pork, lamb, poultry, fish, green leafy vegetables and iron-enriched grain products. Take prenatal vitamin supplements. Prenatal vitamins contain the right mix of vitamins for healthy hair, and as a bonus, healthy nails and skin. It's difficult to avoid exposure to everyday environmental toxins, but there are a few preventative methods you can try:  Wrap your hair in a scarf or hat when you walk or bike through heavy traffic. Pollution caused by cars can dull and flatten your hair, making it appear limp and unhealthy. Wear a swim cap in chlorinated pools. Have you ever had a stylist ask you if you're a swimmer? Chlorine stays in hair and makes it visibly dry and damaged. Protect your hair in the pool, or be sure to wash it with a good shampoo before the chlorine dries. Stressful situations often lead to hair loss. If you have a source of stress you can remove from your life, consider doing so.  Some sources of stress are unavoidable, but they usually go away after awhile. If your hair is falling out due to a stressful situation, it will probably grow back with the situation is resolved. Thinning hair itself can be a source of stress. Calm your mind by doing everything you can to help your hair be healthy, like using natural products, making healthy lifestyle choices, and getting all your vitamins.

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Write a summary of the previous text in Vietnamese:
Chọn khẩu phần ăn điều độ, khỏe mạnh, giàu Vitamin B và sắt. Bảo vệ mái tóc khỏi thành phần hóa học và chất gây ô nhiễm. Cân bằng áp lực trong cuộc sống.