Hair loss, or alopecia, of the scalp
Alopecia, which means hair loss, can occur anywhere on the body, but most often is thought of as affecting the scalp (1).
Hair loss can affect men or women, and it can occur as a gradual thinning on the head, as patchy bald spots, or a sudden loosening of the hair with handfuls of hair being lost as it is brushed or washed (1).
We all lose hair each day, but for most this hair is replaced with new hair growth, so it is not as noticeable.
Why does hair loss happen?
Alopecia can result from auto-immune conditions (alopecia areata), like thyroid issues that disrupt hormones, which can be caused by environmental factors (2).
Certain medications like those used for acne, birth control, cancer treatment, depression, gout, and high blood pressure, can also cause hair loss (1).
Nutrients like protein, B complex, zinc, iron, omega 3, vitamin C, and selenium in proper amounts are all necessary for healthy hair growth. And, nutrient deficiencies, like vitamin D, or nutrient excesses, like vitamin A, have been linked to hair loss (3).
Vitamin D Deficiency and Hair Loss
There are about 100,000 hair follicles on the scalp, and about 90% of these are in the active phase of the hair growth cycle which requires essential nutrients like vitamins and minerals for healthy hair (3).
Vitamin D regulates the growth and differentiation of the cells responsible for keratin production, which is the main structural protein of the hair (3).
So, when vitamin D levels are deficient, new hair growth can be affected.
Autoimmune-related hair loss (alopecia areata) causes inflammation around the hair follicles that are actively growing, and vitamin D plays a role as an anti-inflammatory nutrient able to reduce inflammation (4) (6).
Vitamin D Sources
The recommended daily amount for vitamin D is 1500-2000 IU for adults (5).
While we can get vitamin D from certain foods like fatty fish, egg yolk, and mushrooms, it can be difficult to get the level we need each day through our diet alone.
Most of our vitamin D comes from the sun as the body makes this nutrient when the skin is exposed to sunlight (5).
Diseases affect Vitamin D levels
Vitamin D is metabolized in the liver and then converted in the kidneys to its active form, 1,25-dihydroxyvitamin D, which is regulated by the parathyroid, calcium, and phosphorus levels in the body (5).
Disease states of these organs and low levels of necessary nutrients that regulate the production of vitamin D can lead to low levels of this vital nutrient.
A simple and relatively inexpensive blood test can help determine if you have a vitamin D deficiency. The most common test is the 25-hydroxy vitamin D test because it is easier to detect in the body.
Vitamin A Excess and Hair Loss
Vitamin A is a group of compounds (retinol, retinal, retinoic acid, provitamin A carotenoids) that can activate hair follicle stem cells which lead to new hair cells and hair growth (7).
Studies show that too much supplemental vitamin A (hypervitaminosis) can lead to hair loss as well as skin, vision, and bone changes (7).
One animal study showed that dose-dependent dietary vitamin A was able to activate hair follicle stem cells which may have made the hair follicles more susceptible to an autoimmune reaction leading to the destruction of the follicles (2) (8).
Vitamin A Sources
There are two sources of vitamin A in the diet, preformed vitamin A and provitamin A carotenoids.
Preformed vitamin A (retinol, retinyl esters) is found in animal products such as eggs, fish, organ meat, and dairy products and is more bioavailable, meaning the body can absorb most (75-100 %) of what is consumed (9).
Provitamin A carotenoids come from plants and the body converts these into vitamin A in the intestines. Colorful plant foods like carrots, sweet potatoes, dark leafy greens, plums, and grapes are sources of provitamin A carotenoids (10). The body absorbs less vitamin A from plant sources, but cooking can increase the bioavailability of some, like beta-carotene (9).
Ingestion of very high levels of preformed vitamin A can be toxic to the body. The tolerable upper intake level of preformed vitamin A (animal) is 10,000 IU for adults over 19 years of age (11). There is no upper intake level set for provitamin A carotenoids (plants).
Hair loss, according to research, is not well understood, and many things like genetics and our environment can play a role in this condition.
When nutritional or environmental issues are the cause of hair loss, we have options to correct the problem. For example, if nutrient deficiencies or excesses are preventing proper hair growth or the destruction of follicles, such as in the two examples above, we can use diet and lifestyle modifications to restore nutritional balance and move toward correcting the issue.
If you suspect that nutritional or environmental factors may be playing a role in your hair loss, talk with a nutrition specialist and your health care provider to find the underlying cause of this condition.