People who drink five cups of tea daily are not only likely to improve their cholesterol levels but may also protect against damage from smoking, suggests new research out tomorrow.
The findings are to be published in a supplement devoted to a recent conference on tea in October's issue of the Journal of Nutrition.
"This collection of research calls attention, once again, to the potential for tea and possibly other flavonoid-rich beverages to contribute to healthful dietary patterns in a significant way," said guest editor of the supplement Dr Jeffrey Blumberg, a professor at the Friedman School of Nutrition Science and Policy and chief of the Antioxidants Research Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston.
"As scientific discoveries in this area continue, we hope to see new dietary recommendations reflect data about phytochemicals, including the flavonoids that are found in high concentration in tea," he added.
A new study published in the supplement showed that five servings of black tea per day reduced LDL cholesterol by 11.1 per cent and total cholesterol by 6.5 per cent in mildly hypercholesterolemic adult study participants. The study is the first of its kind to examine the effect of black tea on blood lipids while all other components of the diet were kept constant, said the researchers at the United States Department of Agriculture (USDA) Beltsville Human Nutrition Research Center in Maryland, US.
The team investigated tea's benefits by comparing the effect of five six-ounce servings per day of either black tea, a caffeine-free placebo or caffeinated placebo beverage in 15 mildly hypercholesterolemic adults for three weeks. The volunteers followed a diet moderately low in fat and cholesterol to eliminate potentially confounding factors.
After three weeks, the researchers examined total cholesterol, LDL cholesterol, and two emerging biomarkers for cardiovascular health which some scientists argue could provide more in-depth measures of individual cardiovascular disease risk than LDL and total cholesterol alone: Apolipoprotein B (ApoB) and Lipoprotein(a) [Lp(a)].
Levels of ApoB decreased by 5 per cent and levels of Lp(a) fell by 16.4 per cent. ApoB concentrations reflect the number of LDL 'particles' in the arteries, providing a more specific measure of LDL cholesterol levels. Lp(a) are lipoprotein particles that contain a particular protein which could potentially interfere with the body's ability to dissolve blood clots. Some scientists believe that a reduction in Lp(a) levels suggests a benefit to cardiovascular health.
This reduction in Lp(a) could be important because most standard cholesterol treatments have little effect on this lipoprotein, reported the researchers. The emerging biomarker may become an important risk factor not reflected in LDL or total cholesterol measures, because of the role blood clots play in the risk of stroke and myocardial infarction.
One possible mechanism for this effect is tea's potential ability to limit cholesterol absorption in the intestines.
"These study results indicate that drinking tea regularly has the potential to lower levels of LDL cholesterol, reducing risk factors of cardiovascular disease," said Dr Joseph Judd, research chemist at the Beltsville Human Nutrition Research Center, USDA.
A second study, led by Arizona College of Public Health, University of Arizona and Arizona Cancer Center in Tucson, studied the effect on 143 heavy smokers of consuming four eight-ounce servings per day of either decaffeinated green tea, decaffeinated black tea or water for four months. The results showed that the levels of 8-OHdG, an indicator of oxidative DNA damage, dropped by a significant 31 per cent after four months in those in the green tea group, but not in the other two groups. Oxidative DNA damage is implicated as a contributor to cancer development as well as cardiovascular disease.
"Tea polyphenols are not only powerful antioxidants but also inducers of phase-2 detoxification enzymes, resulting in the body's ability to quench more oxidative DNA damage, reducing cancer risk," said Dr Iman A. Hakim, the division director of Health Promotional Sciences at the Arizona Cancer Center and research associate professor of Public Health at the College of Public Health, University of Arizona.
Smokers were selected as participants due to the high levels of oxidative DNA damage cigarette smoking causes, making changes in those levels easy to detect. Researchers believe that the process of decaffeination affects black tea much more than green tea, thus the black tea may have been weakened because many of the flavonoids had been removed.
These and other studies, including US government research on emerging biomarkers of cardiovascular health, are included in the supplement titled 'Proceedings of the Third International Scientific Symposium on Tea and Human Health: Role of Flavonoids in the Diet'.
Tea is the second most consumed beverage in the world. Researchers plan to investigate further how tea flavonoids function in the body and their implications and new clinical trials are already underway in the US.