Women want hair that is beautiful, healthy, shiny, strong, full and manageable; however, most women face frequent frustration with their locks (or lack thereof). In fact, only one in ten women has a “great hair day” every day, and more than 40% are either “extremely” or “very” concerned about their hair health. They constantly search for new products and other ways to achieve optimal hair health—including making changes in their lifestyle or what they eat.
In the lifestyle category, there is much academic interest in the role that stress, exercise and sleep play in our skin, hair and health in general. The links between skin and overall health are well-documented, but connections to hair health are less clear. The academic literature tends to cover the detrimental role of lifestyle factors such as high UV exposure and smoking on hair rather than the impact of nutrition on hair. In the diet category, there is also no definitive answer as to whether what we eat has any impact on hair health.
For the present article, we delve a little deeper to determine truths and myths in this area—and to identify current gaps in the research.
The overall weight control and dietary supplement industry is worth many millions of dollars but even an internet search on “supplements for hair” alone retrieves more than 21 million hits. This confirms the strong level of interest from consumers for ways to improve hair health beyond topical care. There are even reports of how internet searches related to hair change seasonally. For example, more searches for “hair loss” occur in the late summer and early fall, when seasonal hair shedding is at its peak.1 Many search results are therefore for products claiming benefits such as increased growth, and stronger and thicker hair; although many articles also question the benefits of such products.
In a recent survey, Procter & Gamble asked 300 women if they believe diet impacts the quality of hair, e.g., shine, fullness and softness. The answer was yes from an overwhelming 87% of respondents.2 Women also were asked if they believed taking nutritional supplements such as vitamins could improve hair quality. Again, an 82% majority responded yes.
Supplement Substance and Hair Relevance
As we consider the scientific evidence for these consumer beliefs, we must consider what is predominantly in these supplements. A survey of the most popular brands shows they mostly contain micronutrients—chemical elements or substances required in trace amounts for the normal growth and development of living organisms. These are either vitamins such as C, A, E and B; biotin and niacin; and pantothenic acid plus minerals such as zinc and copper.
Such supplements are regulated in the United States by the Dietary Supplement Health and Education Act (DHEA) of 1994, which covers rules related to the definition, manufacturing, ingredients, safety and marketing claims for supplements. Most claims associated with these supplements are dietary and refer to the recommended daily allowance (RDA) for specified vitamins, minerals and macronutrients.
So, as we consider the evidence, what hair changes might we expect to be associated with nutritional differences? It is assumed most changes are associated with follicle function such as decreased growth rate; effluvium, i.e., rapid hair loss; changes in fiber quality, e.g., diameter, strength, curl, etc.; and a change in fiber color. There may also be changes in sebum production and scalp condition due to dietary changes; however, these are not covered in the present article.
In relation, it has been noted that hair quantity and quality will suffer in cases of severe malnutrition, where daily calorie intake is drastically reduced.3 This would be expected, as the follicle requires a high level of energy. In fact, a healthy individual grows 1.8 m of new hair across the whole head per hour. Therefore, if the body is starved of nutrition, this process will slow and eventually lead to sparse and brittle hair.
The same lack of macronutrients such as protein, carbohydrates and fat is also anecdotally related, to a lesser degree, in certain diet regimens where either total calorie intake is reduced for short periods of time, e.g., crash dieting, or certain food groups are reduced. Low-carbohydrate or low-fat/high-fiber diets are examples where long-term changes in hair have been observed, such as lower hair density and decreases in hair diameter. However, we should also consider that in the cases of these diets or malnutrition, not only are the macronutrients changed, but also the micronutrients. Therefore, it is difficult to make a direct academic correlation.
Severe vitamin deficiencies are also well-known to impact other organs such as the skin, in addition to hair. Scurvy, caused by a lack of vitamin C, can cause corkscrew hair—one of its many symptoms—as well as follicular hyperkeratosis and perifollicular hemorrhage. These skin conditions involve hair follicles containing excessive amounts of keratin.4 Pellagra, or rough skin, is another example, in this case caused by a deficiency in vitamin B3 or niacin. Its symptoms including photosensitive dermatitis with hyperpigmentation; sufferers may also exhibit diffuse hair loss.5 This has been seen in parts of Asia, Africa and India where maize and millet are the main food sources but it is rare in most developed countries where niacin is routinely added to food.
Levels of vitamin A are crucial in the hair follicle, as both deficiency and excess can cause follicular defects.
Vitamins: In vitro and Clinical Evidence
The role that diet plays in hair quality is thus relatively clear in cases of extreme deficiency; but whether vitamins and other micronutrients can impact more typical consumers is the real question at hand. The first set of data to consider is that from in vitro studies measuring the impact of vitamins on hair follicle function, and to elucidate their mechanisms of action. The second set of data is from clinics where patients generally are chosen based on their initial state of micronutrient deficiency to monitor changes in hair after administering supplementation.
Note that many reported clinical studies include just a few subjects, so there is a certain lack of control and confirmation of reproducibility. However, with these caveats, a reasonable body of in vitro data supports the fact that certain micronutrients can play a role in the fundamental biochemistry of the follicle, and that deficiency can play a role in the final properties of hair including growth rate, fiber quality and color.
Vitamin A: Vitamin A has been relatively well-studied and shown to significantly impact the entire pilosebaceous unit (PSU); i.e., the entire structure consisting of the hair, hair follicle, arrector pili muscles and sebaceous gland. A review by H.B. Everts summarizes several studies demonstrating the localization of vitamin A in the follicle and its functions.6 Its levels were found to be crucial, as both the deficiency and toxicity of vitamin A can cause defects in the hair follicle. In fact, over-supplementation has been shown to cause hair loss as well as other negative health impacts.7
The effects of vitamin A also have been implicated in autoimmune diseases such as alopecia areata (AA)8 and cicatricial alopecia.9 While evidence from clinical studies is limited, in one study, all-trans retinoic acid showed a 58% success rate in stimulating hair growth for patients with androgenetic alopecia after one year’s use.10
Vitamin D: Vitamin D also has been linked to follicle function. Vitamin D3 (cholecalciferol), in particular, has been shown to promote differentiation and increased trichogenicity of cultured cells from the follicle’s dermal papilla.11 Several studies implicate a vitamin D3 pathway in the regulation of hair growth, and vitamin D3 also has been identified as capable of regulating epidermal keratinization by inducing terminal differentiation.12
However, once again, limited clinical testing has been completed. In one study, 80 patients with telogen effluvium (TE) or female pattern hair loss (FPHL), and 40 patients with no hair issues were tested for vitamin D2 (ergocalciferol) levels.13 Vitamin D2 levels were significantly lower for the TE/FPHL group but no supplement study was performed. This leaves the question open as to whether supplements in this group would be successful.
B vitamins: The B vitamins are all water soluble and mainly function as co-enzymes in vital biochemical processes; thus, they all likely play some role in the hair follicle. Biotin (B7) is one of the most popular nutritional supplements for hair and nails, likely due in part to its low cost, availability and evidence showing its positive effects for brittle fingernails and onychoschizia (brittle, splitting nails)—even in the absence of biotin deficiency.14
In the Procter & Gamble survey described previously, 36% of women thought this vitamin was the most important for hair health—the highest response of all the vitamins and minerals listed in the survey. Interestingly, however, its benefits for hair have not been substantiated. One study by R. Trüeb in more than 500 female patients afflicted by hair loss showed biotin deficiencies in 38% of the women; nearly 11% showed risk factors for biotin deficiency in their personal history.15 However, the study showed no impact on hair loss after treating women without biotin deficiency with additional biotin.
Minerals: In vitro and Clinical Evidence
Minerals are another important dietary micronutrient whose deficient levels can impact hair. In particular, these include iron, zinc, copper and selenium.
Iron: Iron is the most common deficiency, which has been linked to diffuse hair loss. It is most prevelant in women that are pre- or post-menopausal, or pregnant; in vegans or vegetarians—since iron found in plants has less bio-availability than iron in meat and fish; and in those affected by diseases that cause maladsorption, such as celiac disease.
The mechanism of action relating iron deficiency to hair loss has not been well-defined but in vitro studies have shown it to be a co-factor for ribonucleotase, the rate limiting enzyme for DNA synthesis.16 In other studies, multiple genes have been identified in the follicle that show some level of iron regulation.17 Clinical studies have given variable results but it should be noted that the reverse, i.e. iron overdose, can also cause hair loss.
A study in 1963 showed hair regrowth after iron treatment in 18 patients who were non-anemic but iron-deficient,18 as assessed by measuring serum ferritin levels; ferritin is an intercellular protein that stores iron and releases it in a controlled fashion. However, later studies are less convincing.
Zinc: Zinc is another essential mineral required by various enzymes. Its deficiency can lead to telogen effluvium, and thin and white brittle hair as well as nails and skin. This deficiency often occurs in pregnant women, vegetarians and those who have experienced gastric bypass surgery. As with iron, clinical data exists showing supplementation with zinc can help those who are deficient19, 20 but no apparent data exists supporting that additional levels, beyond the required dose, can have positive effects in hair. And once again, like iron, an overdose of zinc can be harmful to health.
Copper: Copper is critical for the function of amine oxidases, which are required for the oxidation of thiol groups to dithiol cross-links. Perhaps the best known hair disease related to copper deficiency is Menkes Kinky Hair syndrome, a rare autosomal-recessive disorder that prevents the absorption of copper. This presents with hypo-pigmentation and pili-torti characterized by short and brittle hairs that appear flattened and twisted under the microscope.21
Selenium: Selenium is an important component of the antioxidant glutathione peroxidase, whose deficiency has been linked to hypopigmentation of the skin and hair, and also, in some cases, alopecia.22
Fatty Acids: In vitro and Clinical Evidence
The final micronutrients of note are the fatty acids linoleic (omega-6) and α-linoleic acid (omega-3). These are essential to human metabolism and are a structural component of cell membranes in the skin and hair. Either dietary deficiency or the impaired uptake of these fatty acids can lead to hair loss and depigmentation23 but again, there is limited data regarding supplementation. Some studies have shown a correlation between lipid levels such as cholesterol in hair and blood, indicating that diet could impact the hair cell membrane complex.24
The positive psychological impact of maintaining good health was extended to a sense of satisfaction with one's hair.
Mass Micronutrient Deficiencies?
Taken together, the evidence suggests supplementation with micronutrients could have a positive impact on hair quality for those deficient in daily recommended intake levels. The question then becomes: How many consumers are micronutrient-deficient? Data is difficult to access.
The National Health and Nutrition Examination Survey (NHANES) is a program of studies designed to assess the health and nutritional status of adults and children in the United States. Every two years, a study is completed that surveys diets and supplements over a 24-hr period, then translates this data into levels of micronutrients.
Several studies have been reported in the literature, including data obtained from 2001–2008 comparing the micronutrient intake of those who are overweight and obese with those of normal adult weight.25 More than 40% of the adult population showed an inadequate intake of vitamins A, C, D and E; calcium; and magnesium. In addition, compared with normal-weight adults, obese adults showed 5% to 12% (p < 0.05) lower micronutrient intake levels.
Approximately 50% of adults had vitamin A intake levels below the estimated average requirement (EAR), and more than 90% of adults were consuming less than the EAR for vitamins D and E. Similarly, 40% to 60% of the adult population was not consuming enough vitamin C, calcium and magnesium to meet the EAR. On the other hand, less than 20% of adults had intake levels of B vitamins, copper, iron, selenium and phosphorus below the EAR.
Comparable data from Europe showed more than 20% of adults were deficient in vitamin D, calcium, folic acid, selenium and vitamin C.26 A higher incidence of eating at fast food restaurants vs. eating at home27 also was connected to a higher incidence of micronutrient deficiency; as were at-risk groups including pregnant women and the elderly.
A final question relates to whether women believe diet and health are related to hair quality and a general sense of satisfaction with their hair. A recent study between P&G and Yale University was conducted in which 300 women from 10 countries (18-35 years) were surveyed about how satisfied they are with their own hair attributes such as look, shine, manageability and health in general.28 The participants also answered a series of questions relating to a healthy lifestyle including exercise, nutrition, vitamin intake, rejuvenation time, close relationships and a focus on the future. Questions specific to nutrition asked about a diet low in fat and cholesterol; food and drinks with sugar; and the consumption of 3-5 vegetable servings per day.
The results showed the more the women endorsed a healthy lifestyle, the more they indicated they were satisfied with their hair overall. There was also a positive correlation between being happier with their hair and eating well—i.e., 3-5 servings of fruits and vegetables each day, and taking vitamins along with other healthy lifestyle choices. Of all the lifestyle choices, exercise and a healthy diet had the highest correlation with hair satisfaction.
The data did not show the women to have a better diet or even better-quality hair; rather, it showed that the positive psychological impact of maintaining good health and a good diet was extended to a sense of satisfaction with their hair. However, it is important to consider these women may have already held the tendency to exercise and eat well, and in turn be less stressed and spend more time caring for their hair; i.e., getting regular haircuts, using good quality conditioning products, etc.
This review of the literature has shown that diet, in particular a balanced diet, can provide an adequate level of micronutrients including vitamins, minerals and fatty acids to optimize hair health. Supplements may help if consumers are deficient in given micronutrients due to dietary or absorption issues from certain diseases. However, so far there is limited academic data—i.e., no known studies using a significant population sample size—showing that taking additional supplements beyond the recommended daily dose can benefit hair health. In conclusion, more data is required in this area before clear conclusions can be made.
- E Hsiang, Y Semenov, C Aguh and S Kwatra, Seasonality of hair loss: A time series analysis of Google Trends data 2004-2016, Br J Dermatol 178(4) 978–979 (Apr 2018)
- P&G internal survey placed via internet of 300 women in United States, ages 18–38; 311 respondents
- AM Finner, Nutrition and hair deficiencies and supplements, Dermatol Clin 31 167–172 (2013)
- S Ragunatha, AC Inamadar, A Palit, VV Sampagvi and NS Deshmukh, Diffuse nonscarring alopecia of scalp: An indicator of early infantile scurvy? Ped Dermatol 25, 644–646 (2018)
- JL Spivak and DL Jackson, Pellagra: An analysis of 18 patients and a review of the literature, John Hopkins Med J 140(6) 295–309 (1977)
- HB Everts, Endogenous retinoids in the hair follicle and sebaceous gland, Biochim BioPhys Acta 1821, 222–229 (2012)
- DH Ruston, Nutritional factors and hair loss, Clin Exp Dermatol 27(5) 396–404 (2002)
- FJ Duncan et al, Endogenous retinoids in the pathogenesis of alopecia areata, J Invest Derm 133 (2) 334–343 (2013)
- HB Everts et al, Retinoid metabolism is altered in human cicatricial alopecia, J Invest Derm 133 (2) 325–333 (2013)
- BS Bazzano, N Terezakis and W Galen, Topical tretinoin for hair growth promotion, J Am Acad Dermatol 15(4 pt 2) 880–3, 890–3 (1986)
- N Aoi et al, 1a,25-Dihydroxyvitamin D3 modulates the hair-inductive capacity of dermal papilla cells: Therapeutic potential for hair regeneration, Stem Cells Transl Med 1(8), 615–626 (2012)
- L Hu, DD Bikle and Y Oda, Reciprocal role of vitamin D receptor on b-catenin regulated keratinocyte proliferation and differentiation, J Steroid Biochem Mol Biol 144 Pt A 237–41 (Oct 2014)
- H Rasheed et al, Serum ferritin and vitamin D in female hair loss: Do they play a role? Skin Pharmacol Physiol 26, 101–107 (2013)
- VE Colombo, F Gerber, M Bronhofer and GI Floersheim, Treatment of brittle fingernails and onychoschizia with biotin: Scanning electron microscopy, J Am Acad Dermatol 23 (6 pt 1) 1127–1132 (1990)
- RM Trüeb, Serum biotin levels in women complaining of hair loss, Int J Trichol 8 73–7 (2016)
- DH Rushton, Decreased serum ferritin is associated with alopecia in women, J Invest Dermatol 121(5) 985–988 (2003)
- M Ohyama, A Terumuma, CL Tock, Characterization and isolation of stem cell-enriched human hair follicle bulge cells, J Clin Invest 116(1) 249–260 (2006)
- S Hard, Non-anemic iron deficiency as an etiologic factor in diffuse loss of hair of the scalp in women, Acta Derm Venerol 43 562–569 (1963)
- MS Kil, CW Kim, SS Kim and CW Park, The therapeutic effect and the changed serum zinc level after zinc supplementation in alopecia areata patients who had a low serum zinc level, Ann Dermatol 21(2) 142–146 (2009)
- T Karashima, D Tsuruta and T Hamada, Oral zinc therapy for zinc deficiency-related telogen effluvium, Dermatol Ther 25(2) 210–213 (2012)
- MJ Aguilar, DL Chadwick and K Okuyama, Kinky hair disease. I. Clinical and pathological features J Neuropathol Exp Nurol 25(4) 507–522 (1966)
- NE Vinton, KA Kahistrom and CT Strobel, Macrocytosis and pseudoalbinism: Manifestations of selenium deficiency, J Pediatr 111 711–717 (1987)
- P Skolnik, WH Eaflstein and VA Ziboh, Human essential fatty acid deficiency: Treatment by topical application of linoleic acid, Arch Dermatol 113(7) 939–71 (1977)
- T Mogos, C Panuš, I Tânase, C Mogos and I Mincu, The hair levels of unsaturated fatty acids (oleic, linoleic and linolenic) indicators of the lipid metabolic balance, Rom J Intern Med 32(2) 159–63 (Apr-Jun 1994)
- S Agarwal, C Reider, JR Brooks and VL Fulgoni III, Comparison of prevalence of inadequate nutrient intake based on body weight status of adults in the United States: An analysis of NHANES 2001–2008, J Am Coll Nutr 34(2) 126–134 (2015)
- BR Viñas et al, Projected prevalence of inadequate nutrient intakes in Europe, Ann Nutr Metab 59 84–95 (2011)
- R An, Fast-food and full-service restaurant consumption and daily energy and nutrient intakes in U.S. adults, Eur J Clin Nutr 70, 97–103 (2016)
- Internal P&G study in collaboration with Prof. Marianne LaFrance, Yale University