Black Tea

What it is

Black tea is a tea made from the tea plant that supplies caffeine and flavonoids; one cup (236.6 mL) is estimated to provide about 280 mg of total flavonoids [1]. A review judged normal hydration compatible with tea containing under 250 mg of caffeine per cup [2].

What the research says

Blood pressure. A 2021 dose-response meta-analysis of 13 randomized trials (22 arms) found black tea lowered systolic blood pressure by 1.04 mmHg (95% CI 0.03 to 2.05) and diastolic by 0.59 mmHg (0.13 to 1.05), without a significant influence of dose or duration [3]. A 2014 meta-analysis of 11 studies (378 people, 4 to 5 cups a day) found drops of 1.8 mmHg systolic and 1.3 mmHg diastolic [4]. In 5 trials of people with elevated blood pressure (408 people), regular green or black tea lowered systolic pressure by 4.81 mmHg and diastolic by 1.98 mmHg; longer duration (3 months or more) helped, and green tea's effect was stronger than black tea's [5]. A Cochrane review found green and black tea together lowered systolic blood pressure by 2.25 mmHg and diastolic by 2.81 mmHg, but few trials contributed and some were at risk of bias [6]. In a 6-month trial of 111 people, 3 cups a day of black tea solids lowered nighttime blood pressure variation by about 10% versus a caffeine-matched control [7].

Cholesterol. A meta-analysis of 10 trials (411 people) found black tea lowered LDL cholesterol by 4.64 mg/dL (95% CI 0.30 to 8.99), with no change in total or HDL cholesterol [8]. A meta-analysis of 15 trials found no significant effect on total, HDL or (in the random-effects model) LDL cholesterol [9]. In people with high cholesterol, 6 trials found no significant difference in total cholesterol, triglycerides, LDL or HDL [10].

Heart disease and mortality in tea drinkers. A meta-analysis of 22 prospective studies (856,206 people) linked 3 more cups of tea a day to lower risk of coronary heart disease (relative risk 0.73, 95% CI 0.53 to 0.99), stroke (0.82, 0.73 to 0.92), cardiac death (0.74) and total mortality (0.76, 0.63 to 0.91) [11]. For black tea, an analysis of 18 cohorts linked the highest intake to lower all-cause mortality (RR 0.90, 0.83 to 0.98) and lower cancer mortality (0.79, 0.65 to 0.97), with CVD mortality 0.88 (0.77 to 1.01), not significant [12]. A dose-response review found each extra cup a day was linked to 4% lower CVD mortality and 1.5% lower all-cause mortality, with low to moderate strength of evidence [1].

Doses used in studies

Blood pressure trials used 4 to 5 cups of black tea a day [4], or 3 cups a day of black tea solids for 6 months [7]. Cohort analyses used increases of 3 cups a day [11] or one cup (236.6 mL) a day [1]. A review found enough evidence of coronary heart disease risk reduction at 3 or more cups a day [2].

Safety and interactions

Common side effects. None of the five trials in people with elevated blood pressure reported side effects [5]. A review found no credible evidence that black tea in typical amounts was harmful, and normal hydration was consistent with tea when caffeine was under 250 mg per cup [2].

Upper limits and toxic doses. A maximum of eight cups a day was suggested to minimise any risk from excess caffeine [2].

Interactions. There was no evidence that tea drinking harms iron status unless people are already at risk of anaemia [2]. No data on other medicine interactions were found in the studies reviewed.

Pregnancy and breastfeeding. No data on black tea were found in the studies reviewed; see the caffeine page for caffeine and pregnancy.

Relevant conditions. People already at risk of anaemia may need to be careful about iron status [2].

Caveats and open questions

The blood pressure meta-analyses pooled small trials (about 400 people each) with effects of only 1 to 2 mmHg [3][4]. The Cochrane review said only a few trials contributed and the evidence was at risk of bias [6]. Cohort findings are observational, mix tea types and had low strength of evidence in most analyses [11][1].