Medical science has learned a great deal about cholesterol in the last five years. For decades, the whole conversation revolved around drugs like statins to reduce your LDL cholesterol. Now, researchers have found that the amount of cholesterol in your bloodstream is not nearly as important as the type—large or small—and what happens to it while it’s in your arteries.
New evidence suggests cholesterol becomes particularly harmful when it is oxidized in your bloodstream, but that these harmful effects may be partially neutralized with powerful antioxidants.
Green tea is known to possess some of the most powerful natural antioxidants known to man. Let’s take a look at the science behind using green tea to “neutralize” your cholesterol and why it might be an important addition to your heart disease prevention diet and lifestyle.
What exactly is green tea?
True teas (not the various herbal and spice teas that proliferate the store shelves) all come from the leaves of the Camelia sinensis plant. What differentiates the various teas is how the plant is processed after harvesting.
Like most plants, tea leaves are naturally green. However, the common black teas are dried and subjected to processes that essentially oxidizes the leaves and turns them “black.” For example, Oolong tea is a popular type of black tea often associated with Chinese or Japanese restaurants.
Unfortunately, this oxidation process radically changes the natural chemical make-up of the tea. Green teas are prepared by heating or steaming the leaves in order to inactivate the enzyme responsible for oxidizing them.
What is so special about green tea?
The health effects of green tea are from a special group of natural substances called flavonoids. Flavonoids have been shown to exhibit numerous healthful qualities such as anti-allergic, anti-inflammatory, anti-microbial, anti-cancer, and anti-diarrheal properties. But perhaps its most powerful effect in humans is due to its antioxidant properties. Flavonoids exhibit anti-oxidant capabilities far greater than more well-known natural antioxidants such as vitamin C.
But what makes green tea so special is that it is especially rich in catechins—the most powerful antioxidant of all the flavonoid compounds. Catechins are also the most readily absorbed flavonoid and account for approximately one-third of the dry weight of green tea leaves. Compare the total flavonoid content per 100-gram serving of green tea versus many other popular natural sources:
- Blueberries: 224 mg
- Red wine: 28 mg
- Green tea: 133 mg
But, consider that a typical eight-ounce “serving” of green tea contains 227 g of tea that yields a whopping 302 mg per cup of brewed product. Green tea does contain caffeine—about 25 mg per eight-ounce cup, or roughly 25 percent that of coffee. It should be noted that flavonoid content for decaffeinated green tea is less than half this amount as many flavonoids are lost in the decaffeinating process. An alternative for those who want a lower caffeine product but still want to benefit from catechins, is white teas. White teas contain nearly the same catechin content but are much lower in caffeine.
Heart health benefits of green tea
There are numerous studies that tout the benefits of tea consumption of any kind.
One 2001 study associated an 11 percent reduction in risk for cardiovascular mortality over 11 years of consumption.
A study of 40,530 Japanese found that those who drank five 3- to 4-ounce servings of green tea per day had a 31 percent reduced risk for cardiovascular mortality compared to those who did not.
A recent combined analysis of multiple clinical studies suggests that those who consume five cups per day or more of green tea reduce their risk for cardiovascular events by 28 percent with those who drank the most enjoying the greatest benefit. No such effect was seen with black tea.
I asked my friend and cardiologist Dr. William R. Davis if he could help explain some of the science behind why green tea seems to provide such an outsized cardiovascular benefit. He provided the following observations from several studies he was familiar with. Warning: lots of science ahead.
500 mg per day of green tea catechins can reduce oxidized LDL by 18 percent. Interestingly, after reaction with oxidative free radicals, the antioxidative properties of the phenolic ring structures in catechins yield an anthocyanin-like class of compounds.
Green tea extract has been shown to reduce LDL (calculated), triglycerides, and increase HDL, though effects are modest. There may be a more prominent effect in reducing postprandial lipoproteins; one small study demonstrated a 28.7 percent reduction in postprandial triglycerides after 674 mg total green tea catechins. These effects likely derive from green tea catechins’ capacity to inhibit micellization in the intestinal tract (i.e. formation of absorbable forms of dietary fats, and bind cholesterol and increase liver uptake of LDL particles).
Green tea catechins, 455 mg per day, have been shown to reduce expression of multiple inflammatory markers such as phosphatidylcholine hydroperoxide (oxidation of phosphatidylcholine leads to oxidized LDL particles), CRP, sICAM-1, MCP-1, and TNF-α. Green tea has been associated with reduced urinary and serum measures of oxidative phenomena.
Green tea has been associated with reduced body weight and visceral fat, both of which can result in improved insulin responsiveness and lipoprotein patterns.
Green tea improves endothelial function (i.e., increased dilation of the brachial artery) at doses equivalent to two eight-ounce cups per day.
Green tea inhibits the action of inflammatory enzymes, metalloproteinase-2 and metalloproteinase-9 that erode atherosclerotic plaque supportive tissue and are believed to lead to the plaque ruptures of heart attack. Blocking metalloproteinase enzymes may also reduce the growth of smooth muscle cells that underlie plaque growth.
Green tea modestly reduces blood glucose and hemoglobin A1c (a reflection of prior 60 to 90 days blood glucose).
Green tea inhibits platelet aggregation via reduced arachidonic acid and thromboxane release.
Weight loss can result with green tea. Pooled data from seven trials demonstrated modest effects, including reduction in BMI of 0.38, reduction in body weight of 0.44 kg (1 lb.), and reduction in waist circumference of 0.49 cm. Total green tea catechin doses ranged from 583 to 714 mg/day administered over 12 weeks, usually with caffeine of 21to 23 mg. Green tea without caffeine showed no effect on any measure.
Green tea has been shown to increase energy expenditure. A carefully conducted study of energy usage in young slender males demonstrated that 150 mg caffeine and 375 mg green tea catechins. Again it was noted that caffeinated green tea was necessary for full effect. Neither green tea nor caffeine by itself was as effective.
Beyond increased energy expenditure, there may be effects on satiety that contribute to the weight loss effect. The protective cytokine adiponectin has been shown to increase modestly with consumption of green tea extract. The activity of fat-digesting enzymes, pancreatic lipase and phospholipase A2, are reduced by the high concentrations of green tea catechins in the intestinal tract, slowing or reducing fat digestion. Carbohydrate absorption is also reduced 25 percent by 400 mg of tea catechins.
Whew, that certainly is a mouthful, and I’ll leave it to those who want to really dig in to look up all the three-letter acronyms and six-syllable words! But, it is safe to say there is plenty of hard science to back up the health benefit claims of green tea.