Hair loss is a common condition known as alopecia in the medical field.

It has many known causes, including (1, 2):

  • genetics
  • hormonal dysregulation
  • hypothyroidism
  • tension on the hair
  • trauma
  • infection
  • chemotherapy

Hair loss can also be caused by diet-related factors, such as nutrient deficiencies and supplement use (3).

This article explains how diet can affect hair loss.

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Hair is made up of two main structures — the hair shaft, which is what you see, and the hair follicle, which is hidden underneath the skin. Hair grows from the hair follicle (4).

Hair typically grows at a rate of 0.35 mm per day. The scalp sheds about 100 hairs per day, which can increase with hair care practices like washing and brushing (5).

Hair follicles are highly active and sensitive. In fact, hair follicle cells are among the most rapidly dividing cells in your body, so it’s no surprise that nutrient deficiencies can negatively affect hair growth (3).

Iron

Iron deficiency is the most common nutrient deficiency in the world and can cause hair loss (3).

This condition is related to a type of hair loss known as telogen effluvium (TE), a type of hair loss characterized by a disruption in the normal hair growth cycle. This leads to excessive hair shedding and hair loss (5).

Researchers are still studying how iron deficiency causes hair loss, but it appears to disrupt hair growth by diverting iron stores in the hair follicle to other areas of the body (6).

Some studies have shown that people with hair loss tend to have lower iron levels in their blood and hair compared with people who don’t have hair loss (7, 8).

Vitamin D

Vitamin D plays an important role in hair growth and the health of your hair follicles (6).

Research has shown that vitamin D levels are lower in people with hair loss conditions, including female pattern hair loss and an autoimmune skin disease called alopecia areata (9, 10, 11, 12).

Research has shown that taking vitamin D supplements promoted hair regrowth in some people with hair loss related to vitamin D deficiency (13).

A 2020 study that included 109 people found that those with hair loss had significantly lower blood levels of vitamin D than people without hair loss. In fact, nearly 80% of the people with hair loss had low vitamin D levels (14).

Iron deficiency was common among those with hair loss as well (14).

These findings led the researchers to recommend that all people with diffuse hair loss be tested for low vitamin D and iron levels (14).

Zinc

Zinc is a mineral that plays important roles in immune function, protein synthesis, cellular division, and more.

It’s necessary for hair follicle function and helps protect against hair follicle shrinkage and slowed growth. It also helps promote hair follicle recovery (15).

Zinc deficiency can cause hair loss, and studies show that people with certain hair loss conditions tend to have lower zinc levels than people without hair loss. Those conditions include (6, 15):

  • alopecia areata
  • male pattern hair loss
  • female pattern hair loss
  • telogen effluvium (TE)

Other nutrients that may affect hair loss

In addition to the vitamins and minerals listed above, research has found that deficiencies in the following nutrients are associated with hair loss (6, 16, 17, 18):

  • copper
  • biotin
  • vitamin B12
  • folate
  • riboflavin

Keep in mind that a number of factors may cause hair loss, including one or more nutrient deficiencies (18).

If you think that you may be experiencing hair loss due to a nutrient deficiency, talk with a healthcare professional. They may suggest you get a blood test to assess your micronutrient levels and rule out deficiencies.

Summary

A deficiency in one or more micronutrients may lead to hair loss. If you’re experiencing hair loss, you may want to be tested for deficiencies in iron, vitamin D, zinc, B vitamins, and copper.

The cells that make up the hair bulb, which is the part of the hair follicle that produces hair, have a high turnover rate, meaning new cells grow and replace old cells at a rapid rate (4).

For this reason, the hair is very sensitive to deficiencies in protein and calories, both of which your follicles need in constant supply to grow and function properly (6).

Calorie restriction affects the energy supply to the hair follicle, which can lead to hair loss.

Studies have shown that very low calorie diets can result in hair loss in some people (19, 20, 21).

Protein restriction can happen in some very low calorie diets and lead to hair thinning and hair loss.

Your hair needs amino acids, the building blocks of protein, to grow properly, so a diet without enough protein may lead to hair growth abnormalities, such as hair loss and thin, brittle hair (22, 23, 24).

A very low calorie intake and protein restriction can negatively affect health in many other ways, too.

That’s why it’s essential to fuel your body with enough calories and include protein-rich foods in your diet to ensure your body is getting the nutrients it needs (25).

Summary

Not eating enough calories and protein, such as in very low calorie diets, may lead to hair loss.

When people lose a significant amount of weight, they may experience hair loss.

However, people tend to experience this in extreme situations, such as after bariatric surgery, or after following an extreme diet that didn’t provide adequate calories or nutrients (26).

You might think that nutrient deficiency may cause hair loss after bariatric surgery, and this is true. However, interestingly, in some people the causes may actually be the stress of the surgery and the rapid weight loss that follows it.

Research suggests that acute hair loss that occurs within 3 months after bariatric surgery is associated with the surgery itself (26).

Yet, hair loss that occurs 6 months after surgery and beyond may be caused by nutrient deficiencies that develop as a result of surgery-related malabsorption (26).

That’s why it’s important for people who have undergone bariatric surgery to take micronutrient supplements. These help prevent hair loss related to the surgery, as well as other serious complications (27, 28).

Research has shown that the rapid weight loss often experienced among people following very low calorie, restrictive diets may also lead to hair loss (29, 30, 31, 32).

Summary

If you lose weight very fast, including from crash dieting or after bariatric surgery, you may also experience hair loss.

Consuming some nutrients in supplement form may help your hair stay healthy and grow at an optimal rate. However, taking other kinds of supplements can have the opposite effect. In fact, some supplements are associated with hair loss.

If you don’t have a nutrient deficiency, taking high doses of certain nutritional supplements can harm your hair. These supplements include (3):

  • selenium
  • vitamin E
  • vitamin A

For example, overconsuming vitamin A by taking vitamin A supplements can overwhelm your liver, where excess vitamin A is normally stored.

When there’s too much vitamin A for the liver to handle, the extra vitamin A goes into circulation, leading to high levels in the blood.

Because maintaining optimal blood levels of vitamin A is essential for hair follicle function, excessive amounts of this nutrient in the body can cause hair loss. Having too much vitamin A in your system is also called hypervitaminosis A (33).

Excessive nutrient intake from food may lead to hair loss as well.

One case report found that a woman who consumed 10–15 paradise nuts, which are very high in selenium, per day for 20 days developed severe health issues and lost all the hair on her head.

Healthcare professionals found that her blood levels of selenium were nearly five times higher than the normal range. Doctors reasoned that this was the cause of her hair loss (34).

What’s concerning is that many supplements that claim to boost hair growth contain high amounts of nutrients that may lead to hair loss if you consume too much of them.

Other dietary supplements, including herbal supplements, may likewise lead to hair loss, especially at high dosages. That’s why it’s essential to speak with a trusted healthcare professional before you start taking supplements (35, 36).

Summary

If you don’t have a vitamin deficiency, taking high dosages of certain nutrients, such as vitamin A, vitamin E, and selenium, may trigger hair loss.

Other factors may also be associated with an increased risk of hair loss, according to research. These include:

A 2013 study including 92 male identical twins found that smoking, consuming more than four alcoholic drinks per week, increased caffeine consumption, and increased stress duration were linked to hair loss.

Interestingly, the study found that complete abstinence from alcohol and increased exercise duration were also associated with hair loss (37).

Smoking has likewise been linked to the autoimmune condition alopecia areata, which causes hair loss (38).

Research has also shown that poor sleep quality is a risk factor for alopecia areata (39).

A 2020 study that included 1,825 women found that alcohol consumption and poor sleep were associated with more severe female pattern hair loss (40).

On the other hand, avoiding alcohol and getting sufficient sleep were associated with less severe female pattern hair loss (40).

If you want to limit the other factors that may cause hair loss, consider avoiding smoking, limiting your alcohol intake, getting optimal sleep, and managing your stress levels.

In combination with a nutritious diet, these actions may help keep your hair healthy and reduce your risk of hair loss.

Summary

Smoking, drinking, stress, and lack of sleep may increase your risk of hair loss.

Many factors can affect hair loss, including medical conditions, hormonal dysregulation, and infection.

Other factors that can lead to hair loss include micronutrient deficiencies, not consuming enough calories or protein, and taking high doses of certain dietary supplements.

If you’re experiencing significant hair loss, it’s important to visit a healthcare professional to find the cause or causes of your hair loss so that you can get the treatment you need.