It's a beverage that's touted to boost metabolism, prevent cancer, ease arthritis pain, even fight dental cavities. Now, new study findings suggest there's one more reason to drink green tea: It lowers blood cholesterol.
An estimated 40 per cent of Canadians have an unhealthy cholesterol level, a risk factor for heart attack and stroke. Excess LDL (bad) cholesterol in the bloodstream can lead to the development of fatty plaques in blood vessel walls, making it difficult for oxygen-rich blood to flow through them.
According to the new study, antioxidants called catechins - found in high concentrations in green tea - may inhibit the absorption of cholesterol from the intestinal tract and interfere with cholesterol synthesis in the liver.
Green tea is produced from the mature leaves of an evergreen plant called Camellia sinensis that have not been fermented. (Black tea comes from the same plant but the leaves are fermented after they're picked, turning them their characteristic coppery colour - and reducing their catechin concentration.) Earlier research has found that green tea drinkers are less likely to die from heart disease than people who rarely drink it. Studies have also linked green tea catechins to a number of promising outcomes: They've been shown to reduce inflammation in blood vessels and inhibit blood clots. Animal studies have also revealed that green tea catechins can block the action of liver enzymes needed to produce cholesterol.
The current study, published online last week in the American Journal of Clinical Nutrition, combined the results of 14 randomized controlled trials with 1,136 participants to determine the effect of green tea on total cholesterol, LDL cholesterol and HDL (good) cholesterol levels. (Total cholesterol is the combined measure of LDL and HDL cholesterol. HDL cholesterol is considered good because it removes excess cholesterol from the body.) Green tea beverages were tested in half of the trials and a green tea extract capsule was used in the remaining seven trials.
The researchers found that green tea consumption - both drinking green tea and taking a green tea supplement - significantly lowered total and LDL cholesterol but did not affect HDL cholesterol levels.
There are other reasons, too, to add green tea to your diet. Studies suggest that drinking it may lower the risk of breast and ovarian cancers, reduce the severity of arthritis pain and protect the liver from toxins, including alcohol.
But there's no consensus on the optimal intake. Studies have found two to five cups a day to be protective from cancer and heart disease. In the current study, cholesterol levels were significantly reduced in people who consumed both low and high doses (more than five cups) of green tea catechins.
A cup of green tea brewed from loose tea leaves contains more antioxidants than one brewed from a tea bag. That's because tea leaves have more surface area for hot water to extract the antioxidants - and flavour. Tea bags don't have as much surface area for this extraction.
When making green tea, use approximately one teaspoon of loose leaves per six to eight ounces of hot water. (Use a strainer or infuser to hold the leaves.) Warm the pot or cup that you're using with hot water first. Once the water boils, let it cool for one minute before pouring it over the tea leaves to prevent them from burning and producing a bitter taste. Steep for one to two minutes.
One eight-ounce cup of green tea has 30 milligrams of caffeine; one cup of black tea has 45 milligrams and one cup of coffee has 100 to 175 milligrams. Women of childbearing age should limit caffeine intake to 300 milligrams a day; other healthy adults should consume no more than 400 milligrams daily.
Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com.