Hair Health Correlations
Erythropoietin Promotes Hair Growth in Cultured Human Hair Follicles
So you might be wondering, what exactly is erythropoietin? Erythropoietin (EPO) is a glycoprotein (sugar bound amino acid) which stimulates red blood cell production.
In conventional medicine, erythropoietin is injected to help treat anemia, so that blood transfusions can be reduced. Ultimately, for
an anemia patient, an EPO treatment can result in more energy.
So what does erythropoietin have to do with hair? Simply put, if EPO levels are low, hair will not grow--at least not very well.
Research has shown that erythropoietin (EPO) and/or erythropoietin receptor (EPOR) signaling exists in human hair follicles.
When erythropoietin is abundant, hair growth is likely to be robust assuming everything else is in proper order. When levels of EPO are restored in deficient animals, the growth phase of the hair cycle (anagen) is stimulated from its resting phase (telogen) and also prolongs the anagen/growth phase of the hair cycle. 
Reasons for Erythropoietin Deficiency?
The exact cause is unknown, however based on the current research available, it would appear that vitamin D levels
have a lot to do with EPO levels. , 
Not having optimal kidney health is probably the main culprit if you want my opinion.
If you're low on vitamin D, consider supplementing with 5,000 IU per day and look for changes over several months.
If vitamin D doesn't work, research suggests that oral echinacea supplementation will yield significant increases in EPO. , 
Based upon the dosage used in the study, it was rather large. Echinacea was taken four times per day at a dosage of 2000 mg for a period of 28 days.
. J Dermatol Sci. 2010 Aug;59(2):86-90. doi: 10.1016/j.jdermsci.2010.04.015.
. J Nephrol. 2011 Jan-Feb;24(1):98-105.
. Diabetes Care. 2001 Mar;24(3):495-9.
. J Strength Cond Res. 2012 Jul;26(7):1928-33.
. Int J Sport Nutr Exerc Metab. 2007 Aug;17(4):378-90.