Unlike drugs, vitamins and dietary supplements are not required to carry expiration dates on their labels, but many still carry “use by” or “best by” dates on their labels.

But if stored away from heat, light, and humidity, supplements generally last about two years after the date of manufacture before the concentrations fall below 100 percent of the amounts listed on the label, a new study finds, according to The New York Times.

That window is only about a year for probiotics, liquids and oils, which are more fragile.
“If you see some type of expiration date,” said Tod Cooperman, the president of ConsumerLab.com, a popular independent testing company, “the manufacturer is legally required to have stability data demonstrating the product will still have 100 percent of its listed ingredients until that date.”

Most ingredients in supplements decompose gradually over time, which makes them less potent, but not necessarily unsafe — unless, for example, they happen to grow mold.

Cooperman said that to account for the inevitable disintegration, many companies add more than the amounts of ingredients listed on the label, especially vitamins that decompose quickly, like B12 and C.

“If a probiotic label suggests refrigeration, do so,” Cooperman said. “Then return the bottle quickly back to the refrigerator before moisture gets in, as this will activate the organisms, causing them to briefly live and then die.”