Black Tea, Chronic Stress, and Heart Health
Posted by Susan Lutfallah on June 6, 2009
Drinking black tea has been linked with reduced risk of heart disease in several studies – in fact, a number of these studies suggest that this benefit may be due to lowering of blood levels of low density lipoprotein (LDL) cholesterol (bad cholesterol). Unfortunately, elevated levels of LDL cholesterol are linked with heart disease.
However, the mechanism behind the beneficial effect of black tea in lowering LDL cholesterol levels was unclear – only recently have studies began to demonstrate that it is theaflavins, one of the complex flavonoids in black tea, which is responsible for this LDL-reducing effect.
Recently, researchers at the University College London and Unilever Research Colworth conducted the first randomized clinical trial on the effects of black tea on stress – overall, their results found that drinking black tea may reduce stress hormone levels (cortisol) and ease the burden of heart disease.
During the study, the researchers recruited 75 healthy young males and put them through a four-week “washout” period during which they were not allowed to consume tea, coffee, caffeinated beverages, dietary supplements, and many other substances. Subsequently, 37 of the men were given four cups of black tea per day for six weeks while the 38 members of the placebo group were given an identical-tasting caffeinated drink, with no active tea ingredients, for the same time period.
Afterwards, both groups were asked to perform stressful tasks – these included verbally responding to threats of unemployment and accusations of shoplifting while sitting in front of a camera. During the procedure, the researchers measured the cortisol, blood pressure and blood platelet levels of the subject, and also asked them to self-rate their stress levels.
According to the results, both groups showed significant increases in blood pressure, heart rate and subjective stress levels during the tasks.
However, 50 minutes after the tasks were complete, cortisol levels in the tea-drinking group had dropped by 47 percent compared to only 27 percent in the placebo group!
Additionally, the black tea drinkers showed lower blood platelet activation — which has been linked to blood clotting and subsequent heart attack risk — and a greater degree of relaxation after the tasks.