How Long Does It Take for Fish Oil to Work?

Fish oil is the primary source of two omega-3 fatty acids – eicosapentaenoic acid, or EPA, and docosahexaenoic acid, or DHA – which prevent inflammation and lower the risk of cardiovascular disease. The amount of time it takes for fish oil supplements to take effect depends on a variety of factors, from your overall health to the dose and type of fish oil consumed, but your body should attain optimal levels within three months. Large doses of fish oil can cause side effects and interact with medications, so talk to your doctor before taking supplements.

Blood levels of omega-3 fatty acids increase in proportion to the dose of fish oil. In large doses, optimal blood levels may be reached in about one month, but it will take longer for levels to improve in the brain and heart, reported the American Journal of Clinical Nutrition. In lab rats, levels of omega-3s in the brain, heart and liver reached equilibrium after three months.

One producer of omega-3 supplements advises that most people experience benefits within two to three months. To reach and sustain levels of EPA and DHA, it's important to consistently consume the recommended amount of fish oil each day.

With fish oil, the time to take effect can be impacted by your overall health. If you're deficient in EPA and DHA, the severity of the deficiency will influence how soon levels get back to normal. If you're pregnant, some of the omega-3 fatty acids you consume will go to your baby.

The chemical form of the fish oil also makes a difference. Research is ongoing, and larger studies may produce different results, but one study published in Lipids in Health and Disease reported that blood levels of EPA and DHA increased more in study subjects taking krill oil, compared to those who took other forms of fish oil.

The Linus Pauling Institute of Medicine may develop new guidelines, but for now it only recommends a daily intake for the plant-based form of omega-3 called alpha-linolenic acid, or ALA. While your body converts some ALA into EPA and DHA, you can't count on ALA to meet your body's needs.

The Academy of Nutrition and Dietetics suggests consuming 500 milligrams of combined EPA and DHA daily, which you can get from food. Eating a 3.5-ounce serving of fish twice a week is recommended by the American Heart Association for healthy people. An excellent source is salmon; other good sources include mackerel, trout, sardines, canned light tuna and flounder.

If you take too much fish oil side effects are possible, such as bleeding and a weakened immune system. If you take medications to treat diabetes or thin blood, don't take any fish oil supplements until you consult your physician.

Some people experience minor side effects, such as gas, bloating and diarrhea. Taking several smaller doses during the day or using time-release supplements may prevent these problems.

If you eat foods that are fortified with fish oil, be sure to include the amount in your daily tally. Combining supplements with fortified foods makes it easy to exceed 3 grams, warns a study in the medical journal Prostaglandins, Leukotrienes and Essential Fatty Acids.