Tea and Cardiovascular Health
In Canada, cardiovascular disease kills more people than any other disease. According to Statistics Canada’s latest figures, in 2003 cardiovascular disease accounted for 74,255 Canadian deaths.
Based on Heart and Stroke Foundation data, 54 percent of all cardiovascular deaths are due to coronary artery disease; 21 percent due to stroke; 16 percent the result of other forms of heart disease including problems with the electrical system of the heart, heart muscle disease, and viral heart infections; and the remaining nine percent are due to vascular problems such as high blood pressure and hardening of the arteries.
Tea and Reduced Risk for Cardiovascular Disease
Drinking tea regularly as part of a healthy lifestyle may help maintain a healthy heart. Numerous population health studies conducted around the world have demonstrated that drinking tea is linked to a reduced risk of cardiovascular disease.
Two recent meta-analyses, which examined results from all previous population studies, concluded that the regular consumption of black tea had beneficial effects.
One of these studies, published in 2003 in the European Journal of Clinical Nutrition, evaluated the relationship between the consumption of dietary flavonoids and death from heart disease. Tea is a major source of flavonoids, which act as potent antioxidants that neutralize the body’s naturally occurring but cell-damaging free radical molecules.
Using results from seven previous studies, researchers found that individuals in the top third of dietary flavonoids intake had a 20 percent lower risk of death from coronary heart disease, compared to those in the bottom third.
The other meta-analysis reviewed 17 existing population health studies, dating from 1966 to 2000, which had investigated the relationship between drinking tea and cardiovascular disease. Published in the American Journal of Epidemiology in 2001, the study found that the rate of heart attack decreased by 11 percent among those who drank three cups of tea a day.
While much of the strongest research support for tea’s potential to contribute to heart health has focused on black tea, new research has shown that green tea also offers cardiovascular benefits.
A study by Japanese researchers, published in the Sept. 13th 2006 issue of the Journal of the American Medical Association, found that individuals who consumed five or more cups of green tea per day had a 26 percent lower risk of death due to cardiovascular disease than participants who consumed less than one cup of tea per day. For the study, researchers followed 40,530 Japanese adults, aged 40 to 79 years with no previous history of major disease, for up to 11 years for death from all causes and for up to seven years for death from a specific cause.
Cardiovascular disease is very complex and scientists are still exploring possible explanations for how regular consumption of tea reduces the risk of the disease. Some studies suggest that tea flavonoids provide several mechanisms that work in tandem to collectively improve markers for cardiovascular health. Research has shown that tea flavonoids may help promote heart health by improving blood vessel and endothelial function, and by improving cholesterol levels.
Tea and Cholesterol
Recent studies have found that in people at risk for coronary disease, tea and its flavonoids can have a significant cholesterol lowering effect. High blood cholesterol is a major risk factor for heart disease and stroke. High cholesterol can lead to a build up of plaque in the artery walls and narrow the arteries.
Researchers from the United States Department of Agriculture found that for adults with mildly elevated levels of cholesterol, consuming five servings of black tea per day reduced “bad” LDL cholesterol by 11.1 percent and total cholesterol by 6.5 percent. The research was published in 2003 in the Journal of Nutrition.
In another study, published in 2003 in the Archives of Internal Medicine, researchers found that green tea had a similar cholesterol lowering effect. In the study of 240 men and women with mildly elevated cholesterol levels, LDL cholesterol was reduced by 16.4 percent and total cholesterol by 11.3 percent among the participants who consumer green tea extract compared to those who consumed a placebo.
Tea and Endothelial Function
Results from recent scientific studies suggest that black tea may help reduce the risk of heart disease by helping maintain healthy function of the endothelium, the inner lining of blood vessels. Phytochemicals in tea may increase the arteries ability to dilate.
A double-blind controlled study of healthy males, published in the 2004 in the Journal of Cardiology, found that drinking a cup of black tea improved coronary vessel function.
An earlier study of patients with coronary heart disease showed that drinking black tea restored endothelial and blood vessel function to levels similar to those of healthy subjects. Published in 2001 in Circulation, the study measured both the short-term effect of drinking two cups of black tea and the longer term impact of drinking four cups of black tea daily for four weeks.
Both short and long-term tea consumption improved blood vessel function, while drinking water had no effect.
Tea and Hypertension
Drinking tea regularly may help prevent hypertension. According to the Heart and Stroke Foundation of Canada, hypertension affects one in five Canadians and is the number one risk factor for stroke and a major risk factor for heart disease.
Research published in the Archives of Internal Medicine in 2004, found that regular consumption of moderate strength green or oolong tea for one year reduced the risk of developing hypertension. The study examined the effect of drinking tea on the risk of developing hypertension in 1507 subjects with no previous history of the condition.
Researchers found that the risk of hypertension decreased by 46 percent for the 600 subjects in the study who consumed 120 ml or more of tea per day for at least a year.
Tea and Heart Attacks
Daily tea consumption has been shown to lower the risk of having a heart attack and to improve the likelihood of surviving after having a heart attack.
Researchers at Harvard examined 340 women and men who had suffered heart attacks and compared them to matched control subjects. The study, published in the American Journal of Clinical Epidemiology in 1999, found a 44 percent reduction in the risk of heart attack among those who drank a cup of black tea or more daily compared to the non-tea drinkers.
Another Harvard study examined 1,900 people and found that those who consumed tea during the year prior to having a heart attack fared far better in the three to four years following the attack. Individuals who drank more than 14 cups of tea per week had a 44 percent reduced death rate compared to non-tea drinkers, and those who consumed tea but less than 14 cups per week had a 28 percent reduced death rate. The study was published in Circulation in 2002.
A Dutch study published in 2002 in the American Journal of Clinical Nutrition also found that an increased intake of tea and flavonoids lowered the risk of a fatal heart attack. Researchers followed 4807 men and women with no history of myocardial infraction, for five years.
Tea drinkers who consumed more than 375 ml of tea daily had a lower relative risk of incident myocardial infraction than non-tea drinkers. The inverse association with tea drinking was stronger for fatal events than for nonfatal events.