How Long Will Sealed Fish Oil Keep?

Fish oil, in pure or capsule form, contains essential omega-3 fatty acids that have grown immensely in popularity in recent years because of their far-reaching health benefits. Like any animal product, fish oil eventually goes bad, and it's usually easy to tell when it does. Consuming rancid fish oil not only negates the positive effects of the omega-3 fatty acids, it can also be harmful to your health.

Shelf Life

• The shelf life of fish oil depends on the brand, how it is packaged and how you store it. A bottle of capsules or pure oil usually indicates the shelf life on the exterior of the bottle. This can be anywhere from 12 months to several years, depending on the brand and storage methods.

Why Fish Oil Goes Rancid

• Fish oil goes rancid because it eventually oxidizes. The more unsaturated the oil is, the more likely it is to go rancid. The oxidative byproducts in many fish oils cause them to go rancid faster. Fish oil is unstable and tends to go rancid when exposed to light, heat, oxygen and metals. Antioxidants such as vitamin E help block the oxidation, though these are not always used in capsules because they are expensive in their rich gamma and delta forms. When oxygen is replaced by nitrogen, as is the case with Carlson's cod liver oil, the oil lasts longer.

Signs Fish Oil is Rancid

• The easiest way to tell if fish oil is rancid is to smell and taste it. Fresh fish oil should taste slightly of fish but should not have a strong or rotten scent. With capsules, the best way is to bite in and chew a pill once in a while to make sure the rest are not rancid.

Dangers of Rancid Fish Oil

• Rancid fish oil contains lipid peroxides that are harmful to human health. They cause the formation of free radicals that damage cell membranes. They also consume vitamin E and other important antioxidants that are important in a healthy immune system. According to Rufus Turner, a fish oil expert at the University of Reading, oxidized fats increase the risk of atherosclerosis and blood clots.

Preventing Rancidity

• There are a number of ways to decrease the risk of rancidity in fish oil. First, don't buy the cheapest brands, because they are more risky. Refrigerating fish oil increases its shelf life and helps ensure freshness. Also, store fish oil in glass bottles instead of plastic, because air is more likely to penetrate plastic than glass.