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The Biochemical and Medicinal Applications of the Sourwood Tree

Justin May

            I have always considered myself to have a strong background in traditional human biology, medicine and therapies used in modern medicine, but I tend to shy away from the ecological based sciences. My apprehension with ecological based sciences most likely arises from two particular biology classes that are a requirement in order to receive a BS-Biology degree and the fact that I have always been drawn to the medical realm. This class however, has allowed me to step outside my narrowly defined version of biology solely on medicine and human physiology to include ecological sciences. Perhaps the most interesting thing that I encountered this semester is the Sourwood tree and the fact that if you chew a sourwood leaf, you will experience a sour taste in your mouth followed by the production of saliva that quenches a dry mouth or cottonmouth quite efficiently. This particular quality is fascinating to me and therefore I wanted to investigate the sourwood tree in general but really delve into the biochemical reason behind this reaction and the potential uses of the Sourwood tree in sports and medicine.

            Throughout the semester my group had the opportunity to study and take observations on the Sourwood tree within our plot in Battle Park. The Sourwood tree also known by its binomial nomenclature name Oxydendrum arboreum and is a tree that is found in the Eastern and Southeastern United States. The scientific name comes from the Greek word Oxys (acid) and Dendron (tree) that refers to the sour taste of its leaves.[1]  Oxys also refers to the optimal growing conditions for the Sourwood tree, which is in acidic soil with a pH from 3.7 to 6.5. Another interesting characteristic is that the sourwood is usually found as a single tree growing on a slope and is rarely clustered with other sourwoods because it requires full to partial sun and becomes less tolerant of stress as it ages.[2] This particular characteristic can be noted in the High Elevation plot of Battle Park where there was a single, isolated sourwood tree that reached a certain height and then immediately shunted its growth sideways to capture direct sunlight. It is important to note that a canopy created by the numerous white oaks in our plot covered this particular sourwood. Therefore it is reasonable to assume that by growing sideways the sourwood was branching out towards direct sunlight to successfully fulfill its photosynthetic needs.

            The sourwood tree is a bit of an oxymoron it produces sour leaves but has small summer flowers containing sweet nectar both of which have medical applications. The leaf tissues contain oxalic acid, which when chewed is responsible for the sour taste. The sourness produced by chewing the leave stimulates the salivary glands into over producing saliva to help quench thirst and has been historically used by hikers for this thirst quenching quality.  A similar application involves collecting the sourwood tree sap, evaporating the sap into syrup that results in a gummy residue that when chewed alleviates thirst. It is very important to note that oxalic acid is considered inedible but is not considered to be nephro- or hepatotoxic. Something that is nephrotoxic is a substance that is toxic to the kidney that usually causes kidney damage. Similarly a substance that is hepatotoxic is any agent that is toxic and causes damage to the liver. It is important to note that this damage could be acute or permanent, which if the latter is the case can lead to permanent organ failure. This is due to the large amount of oxalic acid one would have to ingest orally, fifteen to thirty grams, to cause tissue destruction.[3] Furthermore, the lowest published oral LDLO (Lowest Lethal Oral Dose) is 600 milligrams of oxalic acid per kilogram of body mass, which when considering the average body weight of an American male is approximately 70 kilograms[4] one would have to ingest 42 grams of oxalic acid to produce a lethal effect. Therefore, one can conclude that chewing the leaf or ingestion of a small concentration of oxalic acid in the form of honey or sap would not have any adverse medical effects.

            Sourwood sap and tonic has been historically used to treat a variety of conditions. For example, Native Americans topically applied the sap to reduce skin irritation or chewed the bark to treat mouth sores. European Americans used sourwood tincture to treat urinary problems due to its ability to act as a natural diuretic[5], increasing urinary output by increasing efferent capillary pressure. Increasing glomerular capillary pressure, one increases the glomerular filtration rate. Increasing the glomerular filtration rate, increases the amount of urine filtration by the kidney, thus producing a higher volume of urine that will be voided. [6]  This is beneficial for treating urinary retention problems arising from an enlarged prostate as seen in Benign Prostate Hypertrophy or Prostate Cancer. Sourwood tincture’s ability to act as a potent diuretic, agent that increases urinary output, was also beneficial for treating constipation, edema, and congestive heart failure.II As better agents became available throughout the evolution of modern medicine in the early 20th century, sourwood tincture use declined. Furthermore, following years of academic research it was found that the mechanism the human body possess to metabolize oxalic acid lead to the formation of kidney stones, which is actually counterintuitive and can actually exacerbate renal dysfunction and urinary retention. However, recent medical research focuses on the antioxidant potential found in Sourwood honey. It has been shown that the high amounts of phenolic content produced in Sourwood honey is correlated with higher antioxidant activity within the body.[7] Antioxidant activity is important because antioxidants inhibit the oxidation of molecules within the body. Oxidation or oxidative stress put on the molecules that make up the various human body tissues can cause brain cell apoptosis, neurological damage, and even cardiovascular disease and thus demonstrates positive health benefits to consuming Sourwood honey again making sure not to reach nephrotoxic levels of oxalic acid.

            Overall this class has broadened my biological horizons and while I do not think I will ever use Sourwood honey as a nurse anesthetist, I have grown to respect the importance of ecological principles in human biology and physiology. Some of the greatest medical innovations have come through the incorporation of ecological principles into human biology, such as the discovery of penicillin, from studying mold or the eradication of certain diseases based on the ecological environment surrounding the disease epicenter, such as poliovirus, diphtheria, and small-pox. Therefore, it would be in the best interest of every student studying biology or chemistry to keep in mind the importance of incorporating all branches of biology such as ecology, herbalism, and dendrology when approaching biological research and development in the future. 

 

Class of 2013

Biology

Charlotte, NC

 

Literature Bibliography


[1]University of Kentucky Department of Agriculture. “Sourwood.” Department of Agriculture. University of Kentucky, 2013 Web. 20 Nov. 2013. <http://www.uky.edu/hort/Sourwood>.

[2]Coder, Kim D. “Sourwood Oxydendrum Arboreum: The Honey Tree.” Ed. University of Georgia School of Forestry and Natural Resources. Native Tree Series (2011): 1–14. Web. 20-11-13. <http://www.warnell.uga.edu/outreach/pubs/pdf/forestry/sourwood%20pub%2011-13.pdf>.

[3]Sigma-Aldrich. “Oxalic Acid Dihydrate MSDS.” Sigma-Aldrich, 10–23 2012. Web. 20 Nov. 2013. <http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=US&language=en&productNumber=247537&brand=SIAL&PageToGoToURL=http%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fproduct%2Fsial%2F247537%3Flang%3Den>.

[4]Environmental Protection Agency. “Body Weight Studies.” Exposure Factures Handbook. Washington, DC: EPA, 2011. 2. Print.

[5] Felter, Harvey W, and John  U Lloyd. “Oxydendron--Sourwood Tree.” King’s American Dispensatory. Henriette Kress, Web. 20 Nov. 2013. <http://www.henriettesherbal.com/eclectic/kings/oxydendron.html>.

[6]Marieb, Elaine N, and Katja Hoehn. “The Urinary System.” Anatomy and Physiology Third Edition. San Francisco, CA: Pearson Benjamin Cummings, 2008. 876–99. Print.

[7]Moniruzzaman, Mohammed. “Evaluation of Physicochemical and Antioxidant Properties of Sourwood and Other Malaysian Honeys: a Comparison with Manuka Honey.” Chemistry Central Journal 7.138 (2013): n. pag. Chemistry Central Journal. Web. 20 Nov. 2013. <http://journal.chemistrycentral.com/content/7/1/138>.