McKay and her colleagues studied the scientific literature related to two popular herbal teas: chamomile and peppermint. Although the group found no human trials on the calming effects of chamomile, they did discover studies suggesting antimicrobial and antioxidant benefits from the tea, as well as signs of lowering cholesterol. Peppermint has been shown to possess antioxidant and anti-tumor potential. A relaxation effect was recorded in the gastrointestinal tissue of animals that were given peppermint leaves or plant extracts. These tests were conducted on animals or in test-tube conditions, McKay says, and human clinical studies may produce different results. The findings are compelling enough to warrant human testing, she says.
Another common type of herbal tea shows promise in regulating blood pressure. In human clinical studies at Tufts, McKay found that tea brewed from flowers of the tropical roselle plant, Hibiscus sabdariffa, lowered the blood pressure of research subjects. Three cups daily of this hibiscus tea lowered both systolic and diastolic blood pressures over a course of 6 weeks. Subjects whose blood pressures were highest at the beginning of the study registered the greatest drops.
McKay cautions against self-treatment of serious medical conditions based on these limited studies. Still, the results are encouraging, and the beneficial phytochemicals in herbal teas make them a natural, healthy alternative to sugary refreshments. “Plant-based foods in the diet do benefit the body. They lower the risk of chronic diseases,” she says. “There is no guarantee that chamomile will help you sleep, but a majority of herbals are caffeine free.”