Does Green Tea Lower Cholesterol?
All right, this green tea article has been hanging over my head for at least a month now. I just couldn't get motivated to wade through all the research to determine if yes, this is an effective way to lower cholesterol and prevent heart disease, or no, it's just a lot of hype.
Well, I sat down and sorted it all out today and here's what I found.
The proposed health claim for green tea is that drinking at least 5 fluid ounces as a source of catechins may reduce risk factors associated with cardiovascular disease.
What are catchins?
Green tea contains catechins, which are a type of flavenoid with antioxidant properties. Antioxidants slow the oxidation process. The oxidation of LDL molecules is what results in plaque formation. Therefore, increasing antioxidant intake should slow oxidation of LDL, resulting in less arterial plaque formation.
Also, when molecules are oxidized, free radicals are released that damage cells. These free radicals can increase inflammatory issues associated with cardiovascular disease.
How flavenoids work
The body recognizes flavenoids as foreign particles and works to eliminate them from the body. Flavenoids themselves do not act as an antioxidant and they are poorly absorbed by the body. However, the proposed benefit of extra flavenoids is that as the body eliminates the unwanted flavenoids, damaging free radicals are also eliminated.
The various types of tea are produced differently. The leaves of oolong tea and black tea are allowed to oxidize (enzymes in the tea change catechins to larger molecules). Green tea is not oxidized, but produced by steaming fresh-cut leaves whereby enzymes are inactivated and little oxidation occurs. The least processed tea is white tea, which contains the highest levels of catechins. Green tea contains the second highest catechin level, approximately 125 mg catechins per serving (or ~25% dry weight of fresh tea leaves).
Here's a little breakdown on tea oxidation:
Black tea - Highest oxidation; also, highest caffeine content and strongest flavor; 90% of all tea served in the West is black tea
Oolong tea - 10-70% oxidized
Green tea - Low oxidation
White tea - Minimal oxidation; Uncured, unfermented; Lower caffeine content that other teas
In 2005, the FDA did not approve the health claim for green tea, because the link between green tea and reduced cardiovascular disease risk was too weak and more conclusive evidence was needed.
This past June, 2008, a study was published that links green tea to reduced flow-mediated dilation of brachial arteries (major blood vessels in the upper arms). Flow-mediated dilation is related to coronary endothelial function and is an indicator for cardiovascular disease risk. Increased dilation is good. It means the heart has to do less work to move blood throughout circulation. (The endothelium is the inner layer of an artery, which blood flows against.)