Caffeine is in coffee, tea, soft drinks, chocolate and some nuts. Whether high caffeine intake increases the risk of coronary heart disease is still under study. Many studies have been done to see if there's a direct link between caffeine, coffee drinking and coronary heart disease. The results are conflicting.

One study finds a strong link between drinking very high concentrations of black tea and healthy arteries in individuals who have heart disease, according to a report in today's Circulation: Journal of the American Heart Association.

Black tea can offer some of the same benefits as other foods rich in the antioxidants known as flavonoids, such as purple grape juice, onions and red wine. Flavonoids, the major antioxidants found in tea, have been shown to prevent the oxidation of low-density lipoproteins or "bad" cholesterol that leads to the formation of plaque in artery walls. The new study shows that flavonoids improve the function of the vascular endothelium, which forms the inner lining of cells in all blood vessels. It responds to minute to minute changes in the body's oxygen and blood flow needs, by causing blood vessels to expand (dilate) or contract. The vessels expand when the need for blood flow is higher, as occurs during exercise, and the vessels return to original size when the individual is at rest. Black tea also inhibits the formation of blood clots and the development of inflammation in the vessel wall, which can help prevent heart attacks and stroke.

Researchers measured the immediate and longer-term effects of black tea vs. water consumption on the arteries of 50 individuals who had coronary artery disease. They found that tea improved endothelial-dependent dilation in their arteries, while water had no effect.

Some people think that caffeine can help them lose weight. Caffeine is a diuretic so it increases water loss from the body via urine. Water loss decreases body weight, but the weight lost is not body fat .Caffeine can suppress appetite, but these effects don't last long enough to cause significant weight loss. A few studies have indicated that for people who exercise and maintain a low-fat diet, consuming large amounts of caffeine and other stimulants may slightly enhance weight loss. However , large amounts of caffeine can also cause jitters, irritability, insomnia and elevated blood pressure. It stimulates the central nervous system by increasing heart rate and releasing free fatty acids from fatty tissue, although it doesn't seem to boost the metabolic rate or promote loss of body fat. On the contrary, many caffeinated beverages contain sugar, which can add calories.

Moderate coffee drinking (1-2 cups per day) doesn't seem to be harmful. However, caffeine-habituated individuals can experience "caffeine withdrawal" 12 to 24 hours after the last dose of caffeine. It resolves within 24-48 hours. The most prominent symptom is headache. They can also feel anxiety, fatigue, drowsiness and depression.