Power Of Oolong Tea!

In my blog post last week, I mentioned that during the oxidation of tea leaves, which is the main process involved in the production of black tea, over 75% of a tea leaf’s catechins (a type of polyphenol I discussed in an earlier blog post) are transformed into ‘polyphenol derivatives’. These include: theaflavins, thearubigins and theasinensins. Theaflavins and thearubigins are predominantly found in black tea, while theasinensins are predominantly found in oolong tea. 

There have been studies into the specific health benefits of oolong teas, which have been either partly or wholly attributed to their theasinensin content. I have summarised these benefits below. By the end, you may find yourself wanting to start including more oolong tea into your diet. 

Antioxidant Activity

One study has found that the consumption of oolong tea temporarily increases the antioxidant capacity of human plasma and reduces oxidative stress and DNA damage caused by free radicals (Higdon and Frei 2003), a key to youthfulness and longevity. 

Another study performed on athletes has revealed that the consumption of oolong tea for 30 days significantly reduces ‘lipid peroxidation’ after exercise (Tsai et al. 2005). Lipid peroxidation is the process name for damage to lipid cell membranes by free radicals produced by high intensity exercise. 

Anti-Inflammatory Activity

There have been many studies on the anti-inflammation activity of oolong teas. Some findings include:

• Increase in angiogenesis (the forming of new blood vessels) and increase in adiponectin secretion (a protein involved in regulating glucose levels as well as fatty acid breakdown), which are both considered to have anti-inflammatory effects (Weerawatanakorn et al. 2015).
• Reduction in obstructive nephropathy (one of the most common kidney diseases) (Hou et al. 2010).
• Increase in immunomodulating agents (substances in the body that can either stimulate or suppress antibody formation), which, in turn, has been found to decrease the body’s inflammatory responses (Chen et al. 2011; Weerawatanakorn et al. 2015). 

 Anti-Obesity Activity

A study on mice has found that oolong tea could help in weight reduction through the inhibition of pancreatic amylase (an enzyme that helps digest carbohydrates), which results in significantly decreasing lipid absorption and increasing lipid excretion into faeces (Weerawatanakorn et al. 2015). 

Another study demonstrated that oolong tea could reduce LDL-cholesterol, total cholesterol and triacylglycerols in rats and decrease their weight (Weerawatanakorn et al. 2015). (LDL-cholesterol, total cholesterol and triacylgylcerols are bad fats, which, when in excess in the bloodstream, are linked to obesity.) 

Also, a human study found that oolong tea consumption in general increases energy expenditure, which can help in maintaining low body weight (Rumpler et al. 2001). 

Anti-Cancer Activity

There have been a couple of studies directly connecting theasinensins with cancer prevention, including apoptosis (cell death) in lymphoma and leukemia cancer cells in humans (Pan et al. 2000).

Anti-Microbial Activity

In vitro studies have reported oolong tea extracts and theasinensins can inhibit pathogen growth, including: Streptococcus sobrinus 6715, Bacillus subtilis, Escherichia coli, Proteus vulgaris, Pseudomonas fluorescens, Salmonella sp., and Staphylococcus aureus (Weerawatanakorn et al. 2015). 

Anti-Diabetic Activity

A study of 20 people with diabetes found that combining oolong tea with hypoglycaemic drugs (used to treat diabetes) can bring about stronger effects in reducing blood glucose than taking hypoglycaemic drugs alone because of the theasinensin content (Hosoda et al. 2003). 

Mice and rat studies have shown that theasinensin A reduces blood glucose levels by over 30%, and inhibits glucose production and absorption in the intestine. Other studies have shown that theasinensins A and B can promote glucose uptake in cells and improve insulin resistance (Weerawatanakorn et al. 2015). 

Cardiovascular Effects

There are epidemiological studies (population studies) which have shown beneficial effects of oolong tea consumption for the cardiovascular system. One study performed on 1507 subjects from Taiwan found that those who drank between 120-599 ml of green tea or oolong tea a day reduced their risk of developing hypertension (high blood pressure) by 46%, and was further reduced by 65% for those who drank 600 ml or more a day (Yang et al. 2004).

Jaq James has a botany diploma and has studied tea culture and tea science in the birthplace of black tea and oolong tea - Mount Wuyi in China.