How long a fish oil supplement has until its best-before date does not predict how much it has oxidized. This means the date on the label may not indicate whether the product is still fresh.

We analyzed the available evidence on whether best-before dates on fish oil supplements reliably indicate oxidation, and what we’ve found so far suggests they do not. Twenty-five studies or assertions support the idea that how long a supplement has until its best-before date does not predict how much it has oxidized [1]. This means the date printed on the label may not tell you whether the oil is still fresh or has started to break down. Oxidation happens when fish oil reacts with oxygen, which can reduce its quality and potentially create compounds that are less beneficial or even harmful. The best-before date is meant to signal when a product is expected to remain at its best quality, but our analysis shows this date doesn’t reliably reflect the actual level of oxidation in the oil. Factors like storage conditions, packaging, and manufacturing processes seem to affect oxidation more than the time remaining until the labeled date. We did not find any evidence that contradicts this finding. That doesn’t mean the date is useless—it may still reflect other aspects of shelf life, like flavor or capsule integrity—but when it comes to whether the oil has gone rancid or lost its potency due to oxidation, the date alone doesn’t give a clear signal. What this means for you: don’t rely on the best-before date to know if your fish oil is still good. Look for signs like a strong fishy smell or taste, and store your supplements in a cool, dark place. If you’re unsure, consider buying smaller bottles or ones with dark glass packaging to help slow oxidation.