Tea has been touted for a myriad of beneficial health effects for as long as people have been drinking it. But concerns over soil contamination affecting tea plants has piqued in recent years. Overall, it seems that tea may potentially proffer both positive and negative effects.
In China, people were drinking tea more than 3,000 years ago, where the beverage likely originated as a medicinal drink during the Shang dynasty. The introduction of tea to the West has been more recent—starting in the 16th century when Portuguese traders brought it back from the Orient and it became the drink of choice among the very wealthy. Raised in Portugal, Catherine of Braganza, queen-consort of King Charles II, popularized tea as a recreational drink rather than a health tonic in 17th-century European society. The use of tea bags, which is how tea is mostly prepared nowadays, became popular after World War II.
Heavy metals found in acidic or alkaline soil can leach into tea. Furthermore, environmental pollutants, such as fluoride and aluminum, also pose health risks. And air contaminants, which come from the burning of fossil fuels, can boost levels of lead, arsenic, and cadmium in tea. This is especially concerning in China—one of the world’s top producers of tea—where 47% of the world’s coal is burned.
Although tea comes in various forms—including white, green, black, yellow, and oolong—most research on its potential benefits and harms has been done on green tea. Let’s take a look at some of the positive and possibly detrimental health effects of tea consumption.
Various reports in the literature suggest that green tea might lower total and low-density lipoprotein cholesterol levels, reduce the risk of coronary artery disease, lower blood pressure levels, help with inflammation, and mitigate insulin resistance. Black tea, on the other hand, has not been linked to a decreased risk of coronary artery disease.
Green and white teas contain antioxidants called catechins. Due to processing, black and oolong teas contain lower concentrations of these antioxidants. Overall, the data on whether tea prevents cancer are mixed. It seems that tea might exert beneficial effects with respect to some cancer types but not others.
For instance, green tea might decrease the risk of breast cancer. This effect is possibly due to phytochemicals that interfere with the metabolism of estrogens. However, green tea likely has no effect on prostate cancer, and black tea might actually increase this risk. Similarly, green tea and coffee might decrease the risk of esophageal cancer, whereas black tea does not.
In obese and overweight adults, green tea might result in a little weight loss, according to findings of a Cochrane review. The amount of weight loss brought on by green tea, however, was found to be nonsignificant and is likely negligible.
Green tea might decrease fasting glucose levels but not enough to budge HbA1c levels. However, researchers have shown that the antioxidant properties of green tea might improve insulin resistance and protect against retinopathy and neuropathy.
Epigallocatechin gallate—the most active ingredient in green tea—has antiviral, antibacterial, and antifungal properties. In fact, green tea extract could make a good mouthwash to prevent cavities and periodontal disease.
A cup of tea contains between 30 and 90 mg of caffeine. Drinking four or more cups a day may help with depression. In a cross-sectional study involving over 500 men and women aged 20-68 years, researchers found that greater consumption of green tea was linked to a lower prevalence of depressive symptoms.
Heavy metal exposure
Heavy metals and metalloids found in tea can interfere with metabolism in multifarious ways, including cytotoxicity, endocrine disruption, mitochondrial dysfunction, and oxidative stress. These heavy metals accumulate in the body over time and are recycled via bile. Of note, lead found in tea could interfere with neurological development in children. (No iced tea for kids.)
In a recent study published in the Journal of Toxicology, researchers used common, off-the-shelf varieties of black, green, white, and oolong teas in tea bags. They found that all brewed teas contained lead. Further, 73% of teas brewed for 3 minutes, and 83% of those brewed for 15 minutes had lead levels that considered unsafe for consumption by women who were pregnant or lactating.
In addition, they found that in 20% of brewed teas, aluminum levels were above levels set by recommended guidelines. No mercury was detectable in the samples, and researchers also found that beneficial elements were present in tea including magnesium, calcium, potassium, and phosphorus. Only black teas had excessive manganese levels.
Please keep in mind that tea is not regulated in any way. It may be a good idea for public health agencies to issue possible warnings about tea—especially black teas, which seem to harbor higher concentrations of heavy metals. In the meantime, you may want to limit your consumption of green tea to a few cups at most each day and avoid steeping your tea bags for too long (no more than 15 minutes).