This 1998 study tested whether piperine, from black pepper, changes how curcumin is absorbed. In rats it raised curcumin bioavailability by 154%. In healthy human volunteers, 2 g of curcumin alone gave undetectable or very low blood levels, and adding 20 mg of piperine raised bioavailability by 2000%.
Researchers gave curcumin with and without piperine, which blocks glucuronidation, a liver and gut process that clears curcumin, to rats and to healthy human volunteers. Rats received curcumin at 2 g/kg with or without piperine at 20 mg/kg. Volunteers received 2 g of curcumin with or without 20 mg of piperine. Curcumin in the blood was measured over the following hours.
In rats, curcumin alone reached moderate blood levels over four hours. Piperine raised blood levels for one to two hours, lengthened the time to peak, lowered elimination half-life and clearance, and raised bioavailability by 154%. In humans, curcumin alone gave blood levels that were undetectable or very low. With piperine, levels were much higher from 15 minutes to one hour after the dose, and bioavailability rose by 2000%. No adverse effects were seen.
This measured curcumin in the blood after a dose, not in cartilage, and not over weeks of use. The abstract does not give the number of volunteers. The 2000% rise was measured against very low starting levels, at a 2 g curcumin dose, so it describes this pairing at these doses, not every curcumin and pepper combination. It says nothing about MMP13.
Lab studies show curcumin can turn down MMP13 in cells, but a compound has to reach the body to matter. This is the study behind the common pairing of curcumin with black pepper: on its own, very little curcumin reached the blood of the volunteers.