Intake of Dietary Catechins May Reduce Risk of Death from Ischemic Heart Disease

Reviewed: Arts ICW, Hollman PCH, Feskens EJM, deMesquita HBB, Kromhout D. Catechin intake might explain the inverse relationship between tea consumption and ischemic heart disease: The Zutphen Elderly Study. American Journal of Clinical Nutrition 2001;74:227-32.

Some epidemiological studies have found evidence that drinking tea (Camellia sinensis (L.) Kuntze, Theaceae) may protect against cardiovascular and cerebrovascular diseases. However, other studies found either no effect or a slightly higher risk of ischemic heart disease (IHD, inadequate blood circulation to the heart, usually as a result of coronary artery disease) with greater tea consumption. Tea contains flavonoids, natural plant chemicals that appear to be responsible for any protective effects of tea. Scientists have identified over 4,000 different flavonoids, which are found in numerous plants. One subgroup of the flavonoid family is known as the catechins.

Catechins are the main components of tea, accounting for approximately 30 percent of the dry weight of green tea and 9 percent of the dry weight of black tea (black tea is fermented green tea). Researchers have identified several possible mechanisms by which catechins could inhibit the development of cardiovascular disease. Catechins may prevent oxidative damage to low-density lipoprotein cholesterol by scavenging free radicals, and inhibit inflammatory processes involved in atherosclerosis. Other potential mechanisms have been proposed, but in vivo studies have not yet confirmed any of these theories.

Tea is not the only source of catechins in human diets — apples and chocolate are two other examples of dietary sources. Catechin intakes from other foods may have confounded the results of previous studies that attempted to link tea consumption to risk of cardiovascular disease. Also, reliable data on the catechin contents of various foods were not available until recently, when the authors developed a method for measuring the six major catechins in foods.

This article describes the authors' evaluation of the possible link between catechin intake and incidence of and mortality from IHD and stroke. They used data from the Zutphen Elderly Study, a prospective cohort study of Dutch men who were 65 to 84 years old at study entry in 1985. Complete data were available from 806 men.

The results showed that the mean catechin intake of the 806 subjects was 72 ± 47.8 mg/day (range: 0-355.4 mg/day) at baseline in 1985. Black tea accounted for 87 percent of catechin intake, and apples and chocolate contributed 8 percent and 3 percent, respectively. Legumes and fruits other than apples were minor sources of catechins, whereas vegetables did nor contribute any catechins. The authors write, "Because tea was the most important source of catechins in this population, tea consumption increased dose-dependently with catechin intake." However, it would seem that the reverse would be the case (i.e., catechin intake increasing with tea consumption).

The subject population was followed for 10 years, during which rime 374 men (46 percent) had died. The cause of death was stroke for 47 men and IHD (as either the primary or secondary cause) for 90 men. A significant inverse association was found between total catechin intake and risk of death from IHD; the adjusted risk ratio was 0.49 in the highest category of catechin intake. Thus, IHD mortality risk was reduced by 51 percent in the highest third of catechin intake. The three groups of total catechin intake were defined as low (0-49.0 mg/day), middle (49.1-85.8 mg/day), and high (85.9-355.4 mg/day). The authors also found that a 50-mg increase in catechin intake was linked to a 25 percent decrease in risk; 50 mg is found in 1 cup of black tea plus a small piece of dark chocolate or in two large apples.

The association between total catechin intake and risk of death from IHD remained essentially unaltered after adjustment for other variables, including prevalence of myocardial infarction or angina pectoris at baseline, physical activity, age, body mass intake, alcohol intake, smoking, dietary factors, prevalent hypertension or diabetes, serum total or HDL cholesterol, and systolic blood pressure. The authors note that prevalent myocardial infarction (heart attack) or angina at baseline had an important influence on mortality. However, "catechin intake was inversely associated with IHD mortality both in subjects free of disease at baseline and in subjects with prevalent disease at baseline."

The data were also analyzed to identify possible associations between catechin intake and both myocardial infarction and stroke. For incidence of fatal and nonfatal myocardial infarction, the age-adjusted reduction in risk with higher catechin intake was not as large as that for IHD mortality. The risk ratio for incidence of myocardial infarction was 0.70 for the highest category of catechin intake, but this was no longer statistically significant after adjustment for possible confounders. For stroke incidence and mortality, there was no relationship with catechin intake.

The authors conclude, "in our study of elderly men in the Netherlands, catechin intake was inversely associated with IHD mortality but not with [heart attack] incidence or stroke." Their study was the first to evaluate links between cardiovascular diseases and catechin intake. However, the study was limited in its ability to distinguish between the effects of tea, catechins from all sources, and dietary flavonols. Future research should attempt to confirm these results and also investigate whether catechins or other substances in tea have protective effects against IHD.

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By Christina Chase, MS, RD

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