When it comes to your hair, there isn’t just one single vitamin deficiency that can cause hair loss. Indeed, several different vitamins play an important role in hair growth, and when you are deficient in them, it can cause shedding and delayed growth. Healthy hair requires a well-balanced diet rich in essential nutrients that can bring oxygen-rich blood to your hair follicles and nutrients to fuel new growth. Here is a look at vitamin deficiencies that can cause hair loss.

B12 is essential for making red blood cells, which carry oxygen to your hair follicles. When your B12 levels are low, your whole body can suffer. Indeed, that is the case with most vitamin deficiencies. Yet, when it comes to B12, low levels of these nutrients can cause anemia, making it hard to support the healthy growth of any cells.

Hair thinning is a common sign of a vitamin B12 deficiency, but there are other symptoms to watch out for as well, including:

• Fatigue
• Muscle weakness
• Difficulty concentrating or formulating thoughts
• Loss of appetite
• Tingling or numb extremities
• Weight loss
• Nausea
• Irritability

Some of these symptoms are signs of severe anemia, whereas others can be more subtle cues, such as fatigue.

Diagnosing a vitamin B12 deficiency is relatively easy, as is treating it. If you suspect your hair loss is caused by this deficiency, ask your doctor to order a blood test to check your B12 levels. If they are low, your doctor may recommend getting B12 injections once a month, especially if you have a digestive disorder that inhibits your ability to absorb B12.

Like B12, iron deficiency can also lead to anemia, a common cause of hair loss. Pre-menopausal women are especially prone to iron deficiency. Iron is crucial for making hemoglobin, which helps carry oxygen on red blood cells throughout your bloodstream. Because oxygen does not come easily to your cells without sufficient iron, you may notice other symptoms such as brittle nails and fatigue.

Diagnosing iron deficiency is much the same as vitamin B12. Your doctor will need to take a blood test, usually a complete blood count (CBC). Your doctor will likely recommend you take supplemental iron and increase your iron intake in your diet if you are deficient. Iron-rich foods include:

• Spinach
• Shellfish like oysters and mussels
• Beef
• Sardines

Vitamin D is known as the sunshine vitamin. It gets its nickname because your skin can make vitamin D when exposed to UV rays. Vitamin D is essential for keeping your bones strong, maintaining healthy skin, supporting cellular growth, and driving new hair follicles to grow. People often find they struggle with hair loss when they are low in vitamin D. This nutrient stimulates both new and old follicles to grow. If you lack vitamin D, growth is suppressed. Thus, slow-growing hair can also be a sign of vitamin D deficiency. A vitamin D deficiency may also be linked to alopecia areata, an autoimmune condition that causes bald patches to form on your scalp and body.

Surprisingly, vitamin D deficiencies are quite common. However, the reasons behind this deficiency tend to make sense. As more people spend more time indoors, and with more people using UV protection when they are outside (such as hats, clothing, and sunscreen), it is hard to absorb vitamin D naturally. Therefore, it must come from your diet. And yet, despite the abundance of food in the American diet, our collective food choices are often nutrient-poor.

You can have your vitamin D levels checked to see if you are deficient. If you are low, your doctor may recommend taking a vitamin D supplement to make sure you meet your recommended daily allowance (RDA). Your RDA depends on your age, sex, and whether you are pregnant or breastfeeding.

Referred to as the “hair, skin, and nails vitamin,” biotin plays an essential role in enhancing hair growth. It supports your hair by stimulating keratin production and may increase the rate at which new follicles grow. People get most of their biotin from protein in their diet, and true biotin deficiencies are rare. That said, people often turn to biotin when they want to boost their hair growth.