These studies have been around now for a while, and I've just looked at them a bit closer...
For those of you who don't know, Harada et al. published a study in 2007 where soy and capsaicin taken together showed an increase in hair growth.
A year later, the same research team published a similar study with raspberry ketone, a compound similar to capsaicin, and found that topical application of this compound increased hair growth as well.
The mechanism was believed to be because of an increase in serum and dermal IGF-1 and blood samples from the treatment group did indeed show an increase in serum IGF-1, thus adding value to the hypothesis that IGF-1 promotes hair growth. This is arguable, because several other studies have shown a correlation between high IGF-1 and vertex balding.
Upon closer reading, the main mechanism seem to be stimulation of sensory neurons, releasing CGRP, wich inhibits TNF, acts as a vasodilator, modulates inflammatory responses, activates endothelial nitric oxide synthase, AND, increases mRNA transcription of IGF-1.
First of all; here are the main problems with those studies:
1. in the raspberry ketone study, there is no placebo group and the inspector isn't blinded. This is a dramatic blow to the credibility of the results. The in vitro results, though, still stands credible.
2. In the soy/capsaicin combo there is both a placebo group, and a blinded inspection. However, while the investigation of IGF-1 in serum is painstakingly measured, how hair growth investigation was done is hardly mentioned. This may suggest that evaluation was based on plain physical inspection, rather than close up photographic inspection or trichometry (wich is standrad in most hair loss research) Although this gives us a clear indication that hair growth indeed happens, a definite measure of how much growth there is (anagen to telogen ratio), is not given.
3. Both publications readily assume that increased IGF-1 is the sole reason for both skin elastisity and hair growht. However, as neurostimulation and CGRP release produces quite a broad biochemical response (as mentioned above) it could very well be that the benefits of soy, capsaicin or raspberry ketone, is due to another biochemical mechanism and that the increase in IGF-1 is merely a side- effect. Although this is mentioned (briefly) in the discussion, no further attempt to investigate this is made.
This is my main issues with these studies.
In addition, this also bugs me...
4. The patient group is extremely diverse, both in terms of age (8 years to 58 years, median of 38) and disease (Androgenetic Alopecia, alopecia areata and alopecia universalis). while proving that IGF-1 is a key player in all of the conditions is quite impressive; the study thus fail to investigate pathophysiology more specific to Androgenetic Alopecia. IGF-1, correlation or causation, this still remains a mystery.
5. The raspberry study fails to mention how the topical preparation is made when tested on humans. They are quite descriptive when they test on mice, but get very vague when they treat humans. This is not good at all, since good publications always include thorough descriptions on materials and methods.
For those of you who don't know, Harada et al. published a study in 2007 where soy and capsaicin taken together showed an increase in hair growth.
A year later, the same research team published a similar study with raspberry ketone, a compound similar to capsaicin, and found that topical application of this compound increased hair growth as well.
The mechanism was believed to be because of an increase in serum and dermal IGF-1 and blood samples from the treatment group did indeed show an increase in serum IGF-1, thus adding value to the hypothesis that IGF-1 promotes hair growth. This is arguable, because several other studies have shown a correlation between high IGF-1 and vertex balding.
Upon closer reading, the main mechanism seem to be stimulation of sensory neurons, releasing CGRP, wich inhibits TNF, acts as a vasodilator, modulates inflammatory responses, activates endothelial nitric oxide synthase, AND, increases mRNA transcription of IGF-1.
First of all; here are the main problems with those studies:
1. in the raspberry ketone study, there is no placebo group and the inspector isn't blinded. This is a dramatic blow to the credibility of the results. The in vitro results, though, still stands credible.
2. In the soy/capsaicin combo there is both a placebo group, and a blinded inspection. However, while the investigation of IGF-1 in serum is painstakingly measured, how hair growth investigation was done is hardly mentioned. This may suggest that evaluation was based on plain physical inspection, rather than close up photographic inspection or trichometry (wich is standrad in most hair loss research) Although this gives us a clear indication that hair growth indeed happens, a definite measure of how much growth there is (anagen to telogen ratio), is not given.
3. Both publications readily assume that increased IGF-1 is the sole reason for both skin elastisity and hair growht. However, as neurostimulation and CGRP release produces quite a broad biochemical response (as mentioned above) it could very well be that the benefits of soy, capsaicin or raspberry ketone, is due to another biochemical mechanism and that the increase in IGF-1 is merely a side- effect. Although this is mentioned (briefly) in the discussion, no further attempt to investigate this is made.
This is my main issues with these studies.
In addition, this also bugs me...
4. The patient group is extremely diverse, both in terms of age (8 years to 58 years, median of 38) and disease (Androgenetic Alopecia, alopecia areata and alopecia universalis). while proving that IGF-1 is a key player in all of the conditions is quite impressive; the study thus fail to investigate pathophysiology more specific to Androgenetic Alopecia. IGF-1, correlation or causation, this still remains a mystery.
5. The raspberry study fails to mention how the topical preparation is made when tested on humans. They are quite descriptive when they test on mice, but get very vague when they treat humans. This is not good at all, since good publications always include thorough descriptions on materials and methods.
