A teaspoon of black pepper contains between 50-100 mg of piperine. (Photo by tokyofoodcast)
I've written quite a bit about green tea and its polyphenols on this blog. By now, it's pretty clear that they have a wide range of health benefits.
The one green tea polyphenol that seems to be especially healthy is epigallocatechin gallate (EGCg). It is one of the main catechins of green tea. Catechins are a type of flavonoids, which in turn are a a type of polyphenols.
As beneficial as EGCg is, it's not very well absorbed. In mice, the bioavailability is 26.5%; in rats, it's as low as 1.6%. We don't know how well humans absorb green tea catechins, but if these numbers are anything to go by, finding ways to improve the bioavailability seems like a good idea.
Fortunately, Lambert et al. have done just that. Apparently piperine, the black pepper alkaloid responsible for the pungent taste, increases the absorption in mice.
Black pepper has the ability to inhibit glucuronidation, which is a process that the body uses to make substances more water-soluble. This allows them to be eliminated from the body through urination. When this process is inhibited, it seems that the bioavailability of some substances is increased.
The important results from the study are listed below.
Piperine inhibits small intestinal glucuronidation. The small intestinal and hepatic microsomes of the mice glucuronidated EGCg rapidly. However, when piperine was administered with the catechin, glucuronidation in the small intestine was reduced by 40-60%, depending on the dose. The more piperine, the more inhibition.
The above figure shows that even the larger doses of piperine didn't have a significant on hepatic glucuronidation. On the other hand, small intestinal glucuronidation was significantly reduced.
Piperine increases plasma EGCg concentration. When piperine was administered to the mice along with epigallocatechin gallate, plasma levels of EGCg increased substantially.
The graph shows plasma levels of epigallocatechin gallate with and without piperine. The word "free" in the graph refers to unconjugated EGCg, while "total" refers to the total plasma level of EGCg. The bottom row of numbers represents time in minutes.
Piperine decreases excretion of EGCg. Another sign of better bioavailability with piperine is the fact that the mice administered both EGCg and piperine excreted less of the EGCg in their feces.
As you can see, here the effect of piperine is clear. Compared to the control group, the piperine group excreted less than half of the EGCg after 5 hours.
Implications for humans
As is usual with mouse studies and highly concentrated extracts, the amounts used and effects observed are not easily translated into human equivalents. The authors note that they used a 100% extract of EGCg, and that the amount of piperine used was about 40% of the EGCg amount (micromoles per kg).
One cup of green tea has about 180 mg of EGCg on average (the actual amount depends on quality and brewing time, among other things) and black pepper contains between 5-10% piperine.
If we take the cautious estimate of a 5% piperine content, then using the above-mentioned 40% number as is means that for each cup of green tea (containing 180 mg of EGCg), 1.44 g of black pepper (containing 72 mg of piperine) is needed. That's about one and a half teaspoon.
Keep in mind that this is a very rough calculation (and quite possibly even wrong). First, we don't know how well humans absorb EGCg. Even between mice and rats the differences were very big. Second, we don't know how much piperine affects the bioavailability of EGCg in humans. For now, we only know how it affects it in mice.
EGCg is perhaps the most important and healthy polyphenol of green tea. Though many studies have shown its benefits, the downside is EGCg is not well absorbed, at least not in rodents.
Piperine, a component of black pepper, increases the bioavailability of epigallocatechin gallate in mice. The more piperine was given, the more EGCg was found in plasma. Accordingly, the excretion of EGCg in feces was significantly reduced.
This improvement in bioavailability is likely due to piperine's ability to inhibit the glucuronidation of epigallocatechin gallate. Piperine will likely improve the bioavailability of epigallocatechin gallate even in humans. The exact numbers, however, are a big unknown.
Still, don't let that keep you from adding a teaspoon of black pepper the next time you brew a cup of green tea.
For more information on green tea, see these posts:
Drinking 10 Cups of Green Tea Daily and Not Smoking Could Add 12 Years to Your Life
Green Tea, Black Tea & Oolong Tea Increase Insulin Activity by More than 1500%
Green Tea Grows Hair in Vitro, Might Work in Vivo
Green Tea Reduces the Formation of AGEs