Differential effects of caffeine
Conducted at the Institute for Dermatology at Lübeck University, Germany.
Differential effects of caffeine on the length of the hair shaft, on the growth and reproduction of keratinocytes, and on growth factors that regulate the hair cycle in male and female human hair follicles in vitro*
The hormone testosterone is an important factor for the development of genetic hair loss, androgenetic alopecia (AGA). Testosterone is converted by an enzyme (5-alpha reductase) to dihydrotestosterone (DHT). DHT can initiate processes that shorten the growth phase of the hair due to lowering the energy level, thus resulting in hair loss. The hair follicles gradually become smaller and are finally destroyed so that over time, baldness develops.
Caffeine is one of the world's best known stimulants and is found in coffee, for example. Its stimulating effect arises mainly from the inhibition of an enzyme (phosphodiesterase), which leads to an increase in the messenger compound for energy cAMP. The energy level of cells is thus increased, promoting cell growth and reproduction.
Earlier studies have shown that caffeine neutralises testosterone's inhibitory effect on the growth and reproduction of keratinocytes and the growth of male hair follicles.
In this study, the effect of caffeine on the hair cycle and the hair matrix was analysed in more detail. In addition, the effect on the formation of two major factors that regulate hair growth (transforming growth factor TGF-β2 and insulin-like growth factor IGF-1) and on outer root sheath keratinocytes (ORSK) isolated from human hair follicles was analysed. It was also investigated whether there was a difference in the caffeine effect on male compared with female hair follicles in the presence of testosterone.
Method 1: Hair organ culture model (HOCM)
The effects of caffeine and testosterone on hair were illustrated using the hair organ culture model (HOCM). For this purpose, hair was harvested from the scalp and cultivated under laboratory conditions.
The effect of testosterone alone and in combination with various concentrations of caffeine was investigated in comparison with a pure culture medium (control).
The concentrations of caffeine (0.005%, 0.001%) that stimulated hair growth in follicles in the presence of testosterone in earlier studies was successful here as well on male follicles. Female hair follicles were more sensitive to caffeine than male follicles (Fig. 1). Lower levels of caffeine (0.0005%) in the presence of testosterone were therefore enough to stimulate female follicles.
The shape of the hair follicle and the phase of the hair cycle (growth or resting phase) as well as cell growth and reproduction (proliferation) and programmed cell death were visualized using dye reactions. Caffeine increases the proliferation of keratinocytes and acts as a testosterone antagonist.
Fig.1: The effect of testosterone and caffeine on hair follicle growth in female hair follicles (HOCM)
Fig.2: Neutralisation of the negative effect of testosterone on the anagen rate (growth rate) in male hair follicles by caffeine.
It was also demonstrated that the negative effect of testosterone on the hair cycle is neutralized by the addition of caffeine in male follicles (Fig. 2) and to some extent in female follicles as well.
The immediately formed major factors that regulate hair growth (TGF-β2 and IGF-1) could also be detected via a reaction with the respective antibody.
Method 2: ORSK model
The outer root sheath keratinocytes (ORSK) were cultivated with different concentrations of caffeine in comparison with growth-promoting substances (positive control: IGF-1 and minoxidil) and growth-inhibiting substances (negative control: tretinoin) and the resulting cell proliferation was analysed (Fig. 3).
All concentrations of caffeine investigated had a growth-enhancing effect in the ORSK after 24h in comparison with the control. The positive controls IGF-1 and minoxidil had a somewhat lower increase. The negative control (tretinoin) had no effect.
Fig.3: Positive effect of caffeine on cell growth in the ORSK model.
In male hair follicles, testosterone increased the expression of major factors for the transition of the follicle to the resting phase (such as TGF-β2). In the presence of caffeine, the formation of these factors was reduced to the level of the control. In female follicles, no increased formation of TGF-β2 due to testosterone was found.
Testosterone reduced the formation of IGF-1 in male follicles in comparison with the control, while co-cultivation with caffeine increased formation. In female hair follicles, the effect of testosterone on the formation of IGF-1 was not as pronounced. However, cultivation with caffeine led to the increased formation of IGF-1.
Using the same ORSK model, the neutralising and protective effect of caffeine was examined. The effect of substances that promote hair loss in vivo (e.g. TGF-β2, anandamide), as well as the effect of caffeine and known growth factors such as IGF-1 and KGF (keratinocyte growth factor) on ORSK were investigated.
ORSK treated with substances that promote hair loss such as TGF-β2 or anandamide showed signs of physiological and pathological cell death. When the same cells were additionally treated for 48h with growth-enhancing substances such as caffeine, IGF-1, or KGF, this effect was neutralised. A significant protective effect was found at a concentration of just 0.001% caffeine.
The gene expression of growth-regulating factors such as TGF-β2 and IGF-1 was verified in the outer (ORS) and inner (IRS) root sheaths after stimulation with different caffeine concentrations in comparison with positive controls (IGF-1, minoxidil) and negative controls (tretinoin).
This study demonstrated the growth-enhancing effect of caffeine on male and female hair follicles. Caffeine promotes the growth of hair follicles, prolongs the growth phase (anagen), and stimulates the growth and reproduction of keratinocytes of the hair matrix. Female hair follicles were shown to have greater sensitivity to caffeine.
The effect of caffeine on certain hair growth factors was proven: Caffeine increases the formation of the growth factor IGF-1 and inhibits the formation of the factor TGF-β2 that is responsible for the transition of the follicle to the resting phase.
Caffeine neutralizes the testosterone-induced formation of factors that promote hair loss such as TGF-β2 in male hair follicles. In female follicles, the formation of TGF-β2 is not induced by testosterone, but is reduced by caffeine. In both genders, the formation of the hair growth factor IGF-1 was increased by caffeine. These effects were observed in the HOCM and in the ORSM.
The results of these in vitro studies show the significance of caffeine at the molecular, cellular, and hair organ level for complex human hair growth. They prove the hair growth-enhancing and hair follicle-protective properties of caffeine for both genders.