Black Tea: Caffeine, Health Benefits & How It Compares to Green Tea

Black tea is the same plant as green tea — Camellia sinensis. The difference is processing: black tea leaves are fully oxidized before drying, which produces the dark colour, the brisk astringent flavour, and a meaningfully different polyphenol profile. The health-benefit headlines are mostly real, but smaller than the marketing suggests.

How much caffeine is in black tea?

A standard 240 mL (8 oz) cup of brewed black tea contains 40–70 mg of caffeine, depending on tea type and steep time. English Breakfast and Assam blends are at the higher end (60–70 mg); Darjeeling and lighter Ceylon teas are around 40–50 mg. Compare to a cup of brewed coffee at 95–165 mg.

Decaf black tea retains 2–5 mg per cup — not zero, but low enough to be irrelevant for most adults. Iced tea from a bottle (Lipton, Nestea, Tetley iced) typically has 25–40 mg per 355 mL can, less than fresh-brewed.

Health Canada’s caffeine ceiling for healthy adults is 400 mg/day. That works out to ~6 cups of typical black tea, or 4 strong cups, or 3 cups of coffee + 2 cups of tea.

What the trials actually show

The strongest evidence is for cardiovascular risk: a 2022 Lancet meta-analysis of 39 cohort studies (~1.7M participants) found a 9% reduction in cardiovascular mortality at 2–3 cups/day, plateauing above 3 cups. The mechanism is thought to be flavonoid-mediated improvements in endothelial function and a small reduction in LDL cholesterol.

For type 2 diabetes prevention, evidence is weaker but consistent: 2–4 cups/day is associated with a 4–8% lower risk in cohort studies. The effect is similar across black, green and oolong teas — not unique to any one type.

For weight loss, cancer prevention, and cognitive enhancement, the evidence is much weaker. Don’t drink black tea expecting any of those.

Black tea vs green tea

Both come from Camellia sinensis. Green tea is steamed/pan-fired immediately after picking to halt oxidation, preserving more catechins (EGCG). Black tea is fully oxidized, converting catechins into theaflavins and thearubigins.

Net antioxidant content is similar — just different molecules. EGCG is more studied for cancer-prevention claims; theaflavins are more studied for cardiovascular endpoints. Both teas have nearly identical effects on cardiovascular mortality.

Caffeine: black tea typically has more (60 mg vs 30 mg per cup). Iron absorption: both can reduce non-heme iron absorption by 50–60% if drunk with meals — an important consideration for vegetarians and people with iron-deficiency anemia.

The bottom line

Black tea is a healthy beverage with real but modest cardiovascular benefits at 2–3 cups/day. Choose loose-leaf or pyramid bags over standard tea bags for better flavour, and brew 3–5 minutes to extract the polyphenols. If you’re iron-deficient, drink tea between meals, not with them.

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