Black, green and white tea all originate at the same source, the Camellia sinesis plant. The differences between them come from the part of the plant they come from and how long they’re aged. Black tea leaves are aged longer than green tea leaves; black tea has a darker color and stronger flavor. Black tea also has higher caffeine content than other teas, which can cause problems for some people. Around 90 percent of tea drinkers in the Western world drink black tea, according to Robin Bagwell of the University of Illinois Extension.

High Caffeine Content

The high caffeine content of black tea has both benefits and disadvantages. The increased mental alertness and energy can work to your benefit, but the jitteriness, irritability, irregular heartbeat and potential increase in blood pressure may not. While black tea contains more caffeine than other types of tea, it still contains only around half as much caffeine as coffee. Caffeine can also raise the pressure inside your eye, which could worsen glaucoma.

Estrogen-Like Effects

Black tea may have estrogen-like effects, which could have negative health implications for people with hormone-dependent tumors such as breast, uterine or prostate cancer, according to MedlinePlus. Ask your doctor if you should avoid black tea if you suffer from any of these conditions. If you have endometriosis, growth of uterine tissue outside the uterus or uterine fibroids, which can also worsen in response to estrogen, you may want to avoid black tea in large quantities.

Decreased Catechins

Compared to white, green and oolong tea, black tea has fewer polyphenols called catechins. Catechins act as antioxidants, substances that scavenge and destroy molecules called free radicals. Free radicals can damage cell DNA, which can increase your risk of developing heart disease, cancer or complications from diabetes, among other diseases. Because of this, black tea may have fewer health benefits than green tea.

Iron Absorption

Black tea may decrease iron absorption, which could cause anemia if you already have low iron levels. Iron comes in two forms, heme iron, obtained from animal sources and non-heme iron, obtained from plants. A cup of tea can decrease non-heme iron absorption by as much as 70 percent, according to the Linus Pauling Institute. Don’t drink black tea at the same time when you eat meals high in non-heme iron, particularly if you’re anemic.