Japanese Knotweed For Hair Loss: A Scientific Analysis

Article Summary

Japanese knotweed contains resveratrol and apigenin. In vitro studies suggest these compounds have antioxidant, anti-inflammatory, and anti-aging properties. Marketers claim these compounds support hair regrowth. So can Japanese knotweed regrow hair? In this article, we review the scientific literature on Japanese knotweed: its safety, efficacy for hair growth, and dosing considerations. Then we provide recommendations to hair loss sufferers interested in Japanese knotweed for hair growth.

Full Article

Japanese knotweed (Polygonum cuspidatum) is a plant native to Japan, China, and Korea.^[1]Royal Horticultural Society, (no date). Japanese Knotweed. Available at: https://www.rhs.org.uk/weeds/japanese-knotweed (Accessed: 11 May 2015) Japanese knotweed contains compounds such as resveratrol and apigenin – both of which might confer antioxidant, anti-inflammatory, and anti-aging properties.^[2]Galiniak, S., Aebisher, D., Bartuskik-Aebisher, D. (2019). Health benefits of resveratrol administration. Acta Biochimica Polonica. 66(1), 13-21. Available at: https://doi.org/10.18388/abp.2018_2749 Because of this, some marketers suggest that Japanese knotweed might support hair growth. But is there strong scientific data to support these claims?

In this article we’ll examine the science behind Japanese knotweed, and determine whether its usage is beneficial for treating hair loss.

Key Takeaways

• What is it?  Japanese knotweed is a perennial plant originating from East Asian countries, but it has spread to various parts of Europe and North America. Although there is some evidence suggesting that compounds isolated and extracted from the plant may have potential benefits for hair loss conditions, the studies have only been conducted on cells, isolated hair follicles, and animals, and are therefore limited in their scope.
• Evidence Quality: The evidence quality is 5/100 based on our metrics.
• Clinical Data: There is unfortunately no clinical data to suggest that Japanese knotweed or the compounds isolated from it such as resveratrol or apigenin can actually enhance hair growth or benefit those with hair loss disorders.
• Safety: Although there are no conclusive studies on the safety of Japanese knotweed, some research has found that resveratrol, a compound found in Japanese knotweed, can be safely used in concentrations of up to 5 g/day.
• Who Might Japanese Knotweed Benefit? While we do not recommend using Japanese knotweed alone due to the lack of data, resveratrol may be beneficial for those with telogen effluvium as it may induce the growing phase of the hair cycle. Another compound that can be isolated from Japanese knotweed called apigenin, may benefit those with androgenetic alopecia, however, in both cases more studies need to be completed.

Although Japanese knotweed is often recognized as an invasive species with harmful ecological effects, recent studies have revealed that this naturally occurring plant contains numerous bioactive compounds that can offer potential benefits to animals and humans alike.^[3]Cucu, A.A., Baci, G.M., Dezsi, S., Nap, M.E., Beteg, F.I., Bonta, V., Bobis, O., Caprio, E., Dezmirean, D.S. (2021). New approaches on Japanese knotweed (Fallopia japonica) bioactive compounds and … Continue reading So, considering its potential, is there any evidence that Japanese knotweed might benefit hair growth?

Is There Evidence for an Effect of Japanese Knotweed on Hair Follicles?

While there is no evidence for the usage of Japanese knotweed as a whole on hair follicle growth, it does contain a few compounds for which there is some evidence. So, let’s take a look at a couple of the ones that show evidence that they might enhance hair regrowth.

Resveratrol

Resveratrol (RSV) is a plant compound, known as a polyphenol. It is a naturally occurring compound found mainly in grape skin and seeds, but can also be found in other plants (like Japanese knotweed). RSV has a wide range of properties including as an antioxidant, anti-aging, anticancer, and anti-inflammatory.^[4]Galiniak, S., Aebisher, D., Bartuskik-Aebisher, D. (2019). Health benefits of resveratrol administration. Acta Biochimica Polonica. 66(1), 13-21. Available at: https://doi.org/10.18388/abp.2018_2749

In one study, 8-week-old male mice were treated with a topical application of 5% RSV over 18 days.^[5]Zhang, Y., Ni, C., Huang, Y., Tang, Y., Yang, K., Shi, X., Zhang, Y., Li, Z., Wang, J., Zhu, Y., Li, H., Ma, Y., Lin, J., Wang, J., Liu, Q., Wu, W. (2021). Hair growth-promoting effect of resveratrol … Continue reading

The backs of the mice were shaved and then randomly split into two groups (3 mice in each group). The treatment groups were:

• RSV group – topical application of 5% RSV dissolved in isopentyl diol once daily
• Control group – topical application of isopentyl diol alone once daily

Photos of the mice were taken on days 0, 7, 14, and 18 after shaving. The photos were analyzed using software called ImageJ to measure the amount of greyscale area (i.e. non-hair-filled areas) on the shaved backs of the mice. On day 18, new hairs on the shaved areas of the mice were plucked to measure hair length. 

From the photos provided, by day 14, the RSV-treated group did appear to show more hair regrowth than the control-treated mice (Figure 1). This is also evidenced in the grayscale ratio, where there was significantly less greyscale seen in the RSV-treated group at day 14 (which indicates more growth). By day 18 however, the amount of regrown hair appeared to be the same in both the control and RSV-treated groups. By day 18, RSV appeared to double hair length from around 5mm in the control to around 10 mm. 

These results indicate that RSV may induce the entrance of hair follicles into the growing stage (anagen), therefore increasing the speed at which hairs regrow and subsequent hair length.

The percentage of hair follicles in each stage of the hair cycle was also measured. RSV treatment decreased the number of hair follicles in early anagen, slightly increased the number of hairs in mid-anagen, and increased the number of hairs in late anagen – which also confirms the early induction into anagen (Figure 2).

The effect of RSV treatment was also measured in isolated human dermal papilla cells and human hair follicles. Human hair follicles were treated with either a control or 6 µM RSV for 6 days and were measured on days 0, 2, 4, and 6. RSV treatment enhanced hair follicle growth significantly over the 6 days of treatment with a final mean length of 1.44 mm compared to the control length of 0.73 mm (Figure 3). Furthermore, when looking at the bulb, by day 6, the control follicles had clearly moved out of anagen and were in the transition stage (catagen) whereas the RSV-treated follicles appeared to be in late anagen still. Some of the classic features of the catagen stage (that we can see in Figure 3) are: 

• A rounded condensed dermal papilla
• Matrix volume loss
• Visible epithelial strand.^[8]Oh, J.W., Kloepper, J., Langan, E.A., Kim, Y., Yeo, J., Kim, M.J., His, T.C., Rose, C., Yoon, G.S., Lee, S.Y., Seykora, J., Kim, J.C., Sung, Y.K., Kim, M., Paus, R., Plikus, M.V. (2016). A guide to … Continue reading

Of course, the researchers have only shown representative images from one hair follicle so it’s entirely possible that the researchers could have chosen the worst-looking control follicle and the best-looking RSV-treated follicle.

To summarize, it appears that RSV can induce and elongate the anagen phase of hair follicle growth, allowing for more hair follicle growth. However, unfortunately, there have not been any further studies in animals or humans to determine the regrowth effect of resveratrol.

Apigenin

Apigenin is a bioflavonoid compound that is found in a wide variety of plants and herbs. Very abundant in chamomile tea, apigenin has antioxidant, anti-inflammatory, and anti-tumor properties.^[10]Abid, R., Ghazanfar, S., Farid, A., Sulaman, S.M., Idrees, M., Amen, R.A., Muzammal, M., Shazad, M.K., Mohamed, M.O., Khaled, A.A., Safir, W., Ghori, I., Elasbali, A.M., Alharbi, B. (2022). … Continue reading These properties have made it an attractive ingredient for use in several hair loss treatments. But is there any evidence to support its use?

One in vitro (in cells) study was conducted in which HaCaT cells (a keratinocyte cell line) and isolated rat hair follicles were treated with a range of apigenin concentrations.^[11]Huh, S., Lee, J., Jung, E., Kim, S.C., Kang, J.I., Lee, J., Kim, Y.W., Sung, Y.K., Kang, H.K., Park, D. (2009). A cell-based system for screening hair growth-promoting agents. Archives of … Continue reading In HaCaT cells, the researchers measured the concentration of transforming growth factor – β1 (TGF- β1). TGF- β1 inhibits the rate of hair follicle growth and promotes the transition of the hair follicle cycle from the growing stage (anagen) to the transition stage (catagen).^[12]Mori, O., Hachisuka, H., Sasai, Y. (1996). Effects of transforming growth factor beta 1 in the hair cycle. Journal of Dermatology. 23(2). 89-94. Available at: … Continue reading In androgenetic alopecia, progression is closely related to TGF-β1 secretion by dermal papilla cells so it is an important therapeutic target.

The researchers found that sixteen hours of apigenin treatment led to a dose-dependent decrease in TGF-β1 levels in HaCaT cells (Figure 4). This indicates a potential for affecting the hair follicle cycle by inhibiting the onset of catagen, however, it’s important to note that while HaCaT cells are a decent model for keratinocytes within the hair follicle, they are not actually cells that are found within the hair follicle. Moreover as previously mentioned it is dermal papilla cells that secrete TGF-β1 in androgenetic alopecia, so it would have been more appropriate for the researchers to use dermal papilla cells in this experiment.

The researchers next looked at the effects of apigenin treatment on the growth of rat hair follicles and compared these effects to minoxidil treatment. Hair follicles were isolated from rats and then treated with either 1, 5, or 10 µM of apigenin or 1 µM Minoxidil for 21 days. Photos were taken of the hair follicles on day 0 and day 21 and measured using a special microscope camera (Figure 5). The 5 and 10 µM treated hair follicles showed an increased level of growth compared to the control, however, these effects were still slightly lower than the effect of minoxidil. Moreover, looking at the images it is hard to tell what stage of the hair follicle cycle they are in by day 21. Typically, hair follicles are cultured for around 7 – 10 days as it is reported that hair follicle growth stops after this time in culture.^[14]Philpott, M.P. (2013). Hair follicle culture – a historical perspective. Hair Transplant Forum International. Available at: https://www.ishrs-htforum.org/content/htfi/23/4/130.full.pdf (Accessed: … Continue reading It would be interesting to see if there was any growth past day 10 for any of the hair follicles, with images taken at more time-points.

So, to summarize it looks like apigenin has the potential to inhibit the secretion of TGF-β1 and therefore potentially lengthen the growing stage of the hair follicle cycle. In the 5 and 10 µM treatments of apigenin, an improvement in hair follicle growth was seen over the control, however, this did not reach the same level of growth enhancement as minoxidil. The researchers could conduct further studies to determine the stage of the hair cycle over 21 days of treatment which would tell us whether apigenin actually does lengthen the anagen stage, or whether it works through other mechanisms.

Clinical Data

Unfortunately, no clinical data suggests that Japanese knotweed alone or the compounds it contains have any actual effects on hair growth. 

Is Japanese Knotweed Supplementation Safe?

At this point in time, there does not appear to be any published safety data for the use of Japanese knotweed as a whole, administered orally or topically. However, some clinical studies have shown that resveratrol (which can be extracted from Japanese knotweed) can be well-tolerated and pharmacologically safe at concentrations of up to 5 g/day.^[16]Zhang, L.X., Li, C.X., Kakar, M.U., Khan, M.S., Wu, P.F., Amir, R.M., Dai, D.F., Naveed, M., Li, Q.Y., Saeed, M., Shen, J.Q., Rajput, S.A., Li, J.H. (2021). Resveratrol (RV): A pharmacological review … Continue reading 

Who might benefit from Japanese Knotweed Supplementation?

There is very limited data supporting the use of Japanese knotweed for any type of hair loss. However, based on the information that we do have, we could speculate that isolating apigenin from it might be beneficial for people with androgenetic alopecia. Additionally, due to resveratrol’s potential to induce anagen, it may be helpful for those with telogen effluvium. It is important to reiterate however that with the lack of data, we do not presently recommend that Japanese knotweed is used to treat hair loss disorders.