China burns about half of the world’s coal, spewing heavy metals such as mercury and lead into the atmosphere that affect the development of neighboring children. What if you don’t live in China or eat anything produced there? You could still be exposed to the mercury that settles in the oceans if you eat fish and other seafood. What if you drink something from China? Tea. China is one of the world’s biggest tea exporters, but their rapid industrialization has raised concerns about contamination with lead, a toxin that can affect almost every organ in the body. The more lead there is in the soil, the more lead there is that ends up in the tea leaves. And, the closer to the highway the tea is grown, the higher the lead levels. This suggests that leaded gas, which wasn’t banned in China until the year 2000, may be playing a role in the contamination of tea grown there.

Just like larger and longer-living fish accumulate more mercury, longer-living tea leaves accumulate more lead. Young tea leaves appear to have two to six times less lead than mature leaves, so the young leaves that are used to make green and white tea have significantly less lead than the older leaves used to make black and oolong tea. As well, the lead in black and oolong tea appears to be released much more readily into the tea water when brewed. This means the health risk from lead may be 100 times lower for green tea compared to oolong and black.

Because certain fungicides may have heavy metal impurities, one might assume organic teas would be less contaminated. However, a study of 30 common teas taken from North American store shelves showed no less toxic element contamination in organic teas than regular teas, though, organic teas would presumably have much less pesticide contamination. In terms of lead, the source of the tea—that is, the country of origin—appears to be the most important factor.

So, how much tea is safe to drink? Based on the most stringent safety limits in the world, such as California’s Prop 65 parameters, and the largest studies of tea lead contamination from around the world, I was able to come up with guidelines I outline in my video Lead Contamination of Tea.

If you’re not pregnant and drinking only green tea, it doesn’t matter where you get your tea. You can drink as much as you want, as long as you’re drinking the green tea and throwing away the leaves or bags. Given the average levels of lead in Chinese black tea samples, however, more than three cups a day would exceed the daily safety limit for lead. What if you’re eating tea leaves—for example, drinking matcha tea, which is powdered green tea—or throwing tea leaves into your smoothie like I do? In that case, two or three heaping teaspoons is the limit. The exception is Japanese green tea, which is so low in lead that you can safely eat 15 spoonfuls per day, but I caution consuming more than 8 teaspoons given the risk of exceeding the daily recommended limit for caffeine intake for adults.

What about children? For a 70-pound 10-year-old, lead isn’t a problem if they’re drinking green tea. But the safe caffeine intake for children is probably around three milligrams per kilogram, which would limit a child to about four cups of green tea per day. For caffeine reasons, I recommend adding no more than two spoonfuls of Japanese green tea to a child’s smoothie. And for lead reasons, children should have no more than one teaspoon of Chinese green tea leaves. When it comes to black tea, children shouldn’t drink more than one cup per day and should not eat the tea leaves at all.

Pregnant women should be able to drink one cup of green tea per day throughout pregnancy, regardless of source. The limit for Japanese green tea is really just the caffeine limit of about four cups per day. I do not recommend drinking black tea during pregnancy or eating any kind of tea leaves, unless you know you’re getting tea from a low lead source.

I’ve long been an advocate of teas, but the information I’ve shared with you here has led me to change my daily diet. If you look at my smoothie recipe in A Better Breakfast, for example, you’ll see I’ve recommended throwing in tea leaves, and Is Matcha Good for You? doesn’t hide the fact that I’ve been a big fan of matcha. I still enjoy both, but am now more careful about where my tea is sourced. As soon as I learned of this, I made announcements on Facebook, Twitter, and Google+ to inform everyone. So, if you closely follow my recommendations (which I elaborate on extensively in my book, How Not to Die), please make sure to keep an eye on our social media where I can post updates within minutes of learning about the latest news.

I’ve got a whole slew of tea videos, including:

Where else might you find heavy metal risk (besides my music collection :)?

In health,

Michael Greger, M.D.