Black tea can dilute the gastric juices, making it difficult to digest food normally. Worse effects can include dyspepsia, abdominal distension and stomach-ache or duodenal ulcer.
Drinking black tea can reduce the body’s absorption of iron. The stronger the tea you drink, the greater the resistance to iron absorption in your body. This may be especially harmful to women during their period.
There is much more tannic acid contained in strong than in weak black tea, which may aggravate symptoms of constipation. This is because tannic acid can slow bowel peristalsis.
Too much caffeine intake will increase heart rate and elevate blood pressure. It can also cause chest tightness and palpitation, which may exacerbate the risk of heart failure. Patients who are recovering from heart attacks or acute cardiovascular disorders should restrict their intake of black tea.
Women should avoid excessive consumption of black tea during pregnancy because it normally contains more caffeine than other kinds of tea; however, there is no harm in enjoying one or two cups now and again.
People who are sensitive to caffeine should avoid black tea because it may increase their risk of developing insomnia, anxiety, irritability, nausea or stomach upset.
People who should avoid drinking black tea:
People with a fever. the caffeine in black tea can not only increase body temperature but also reduce the effect of anti-fever drugs.
Patients with liver disease. The caffeine in tea needs to be metabolised by the liver. If the liver is not properly functioning, drinking tea will increase metabolic pressure and may damage the liver itself.
Patients with neurasthenia. Tea increases nervous excitement, and if taken at night can degrade the quality of sleep or cause insomnia.
Pregnant women should avoid drinking too much black tea because it has more caffeine than other types of teas.
Breastfeeding mothers. If a mother drinks too much tea while breastfeeding, this may have an indirect effect on the neural excitation of the baby, potentially leading to morbid night crying or reduced sleep quality of babies.
People who are taking any medicine should drink black tea with care and ideally seek their doctor’s advice.