Tea for Two

In the quest for non-pharmacological interventions to prevent myocardial infarction (MI), it seems an old weapon in our arsenal may have been under-appreciated. Two recent studies have suggested a cardiovascular benefit of drinking black tea.

As part of the Determinants of Myocardial Infarction Onset Study, researchers performed a prospective cohort study of 1900 patients hospitalized with a confirmed acute MI between 1989 and 1994, with a median follow-up of 3.8 years.¹ Tea consumption was determined based on a self-reported standardized questionnaire. Patients were separated into three groups based on the results: non-drinkers, moderate users (fewer than 14 cups a week) and heavy users (14 or more cups per week). Long-term mortality according to tea consumption was compared using Cox proportional hazards regression.

A total of 1,019 patients drank no tea in the year before their heart attack; 615 were moderate drinkers and 266 were heavy drinkers. Compared with non-drinkers, age- and sex-adjusted mortality was lower among the moderate tea drinkers (hazard ratio 0.69; 95% CI, 0.53 to 0.89) and heavy tea drinkers (hazard ratio 0.61; 95% CI, 0.42 to 0.86). Additional adjustment for clinical and sociodemographic characteristics--age, gender, smoking status, obesity, hypertension, diabetes or previous heart attack--did not appreciably alter the association.

In a related study, researchers in The Netherlands found that tea may protect against MI.² A longitudinal analysis, performed with data from the Rotterdam study, examined the association between tea and flavonoid intake and incident MI. Tea contains high levels of flavonoids, which are antioxidants found naturally in various plant-derived foods. The analysis included 4,807 subjects with no history of MI, who were followed from 1990-93 until 1997. Data were analyzed in a Cox regression model, with adjustment for age, sex, body mass index, smoking status, pack-years of cigarette smoking, education level and daily intake levels of alcohol, coffee, polyunsaturated fat, saturated fat, fibre, vitamin E and total energy. During the 5.6-year follow-up, a total of 146 MIs occurred, 30 of which were fatal. The relative risk of incident MI was lower in tea drinkers with a daily intake of >375 mL (RR:0.57; 95% CI, 0.33 to 0.98) than in non-tea drinkers. The intake of dietary flavonoids was significantly inversely associated with fatal MI (0.35; 95% CI 0.13 to 0.98) in upper compared with lower tertiles of intake. This inverse association was stronger for fatal events (0.30; 0.09 to 0.94) than for non-fatal events (0.68; 0.37 to 1.26).

Researchers suspect the findings of both studies are linked to the high levels of flavonoids in tea. Short and long-term tea consumption has been shown to reverse endothelial dysfunction in patients with coronary artery disease.³ In addition, flavonoids may inhibit the oxidation of low-density lipoprotein (LDL)--oxidized LDL may promote atherosclerosis.⁴

Of course, it is always possible that some other aspect of the participants' diets contributed to the findings. Further research will be required to confirm the results of these studies. In the meantime, drink up!

Source

1. Mukamal KJ, Maclure M, Muller JE et al. Tea consumption and mortality after acute myocardial infarction. Circulation 2002;
2. Geleijnse JM, Launer LJ, Van der Kuip DA et al. Inverse association of tea and flavonoid intakes with incident myocardial infarction: the Rotterdam study. Am J Clin Nutr 2002; 75:880-6.
3. Duffy SJ, Keaney JF, Holbrook M et al. Short- and long-term black tea consumption reverses endothelial dysfunction in patients with coronary artery disease. Circulation 2001; 104:151-6.
4. Yoshida H, Ishikawa T, Hosoai H et al. Inhibitory effects of tea flavonoids on the ability of cells to oxidize low density lipoprotein. Biochem Pharmacol 1999; 58:1695-703.