Health effects of tea

[1][2] A small number of studies suggests that both green and black tea might have beneficial effects on some cardiovascular disease risk factors, including blood pressure and cholesterol.

[1] The research has limitations though, including how the data were evaluated and differences in study populations, leading to no certain conclusions about health effects.

[6] However, drinking excessive amounts of black tea may inhibit the absorption of iron, and may harm people with anaemia.

[7] Concerns have been raised about the traditional method of over-boiling tea to produce a decoction, which may increase the amount of environmental contaminants released and consumed.

[1] In 2011, the US Food and Drug Administration reported that there was little evidence to support the claim that green tea consumption may reduce the risk of breast and prostate cancer.

"[24] Though there is some positive evidence for risk reduction of breast, prostate, ovarian, and endometrial cancers with green tea, it is weak and inconclusive.

[35] Two reviews of randomized controlled trials concluded that long-term consumption of black tea slightly lowers systolic and diastolic blood pressures (about 1–2 mmHg), a finding based on limited evidence.

[36][37] A 2013 Cochrane review found some evidence of benefit from tea consumption on cardiovascular markers (total and LDL cholesterol), though more research is needed.

[39][40] Use of green tea for attempted weight loss carries a small risk of adverse effects, such as nausea, constipation, and stomach discomfort.