Should You Take a Fish Oil Supplement?

The Confusing Science on Fish Oil Supplements

When people talk about the health benefits of fish oil, they’re really talking about the health benefits of omega-3s. These fats are most prevalent in oily seafood but can also be found in some plant-based foods, particularly algae and certain nuts and seeds.

Consuming adequate amounts of these fats appears to protect overall health by reducing inflammation, slowing cellular aging, and lowering blood pressure and triglycerides.³^,⁴

However, the research can be confusing on whether supplemental omega-3s lead to the same health benefits. Let’s look at some examples.

Brain protection

The membranes of brain cells require DHA to function properly. In addition, people with Alzheimer’s disease tend to have lower levels of DHA in their blood.⁵ Those lower blood DHA levels are associated with a greater accumulation of amyloid, which can collect in the brain and raise risk for Alzheimer’s disease.⁶ 

Evidence from population studies supports this connection. When researchers analyzed the data from 35 studies involving 849,263 people, people who consumed the most fish—around 5.2 ounces a day—were up to 30% less likely to develop any form of cognitive impairment.⁷

Research on supplements is more complicated. For example, in one trial of 485 healthy older adults, taking 900 milligrams of DHA daily for six months slowed cognitive decline compared to placebo.⁸

But in people already living with mild to moderate Alzheimer’s, supplementing with 2 grams of DHA daily for 18 months didn’t alter the progression of the disease—even though blood levels of DHA increased by more than 200%.⁹

The researchers speculate that DHA supplementation may be more effective when started earlier, before dementia is established.

All that’s one way you end up with headlines like: “Fish Oil Supplementation Slows Cognitive Decline!” and “Fish Oil Doesn’t Slow Cognitive Decline!”

Mood

In an analysis of 26 studies, people who consumed the most fish experienced a 17% lower risk of developing depression compared to people with lower fish intakes.¹¹

And while some studies report that fish oil supplementation significantly decreases symptoms of depression, other studies show little to no effect.¹¹^,¹²^,¹³^,¹⁴

Remember: Studies aren’t perfect. They may focus on one main result—like how people rate their mood—while other improvements, such as lower inflammation or changes in brain function, might not make the headlines.

Heart attack and stroke 

The research on omega-3 supplements and major cardiovascular events—like heart attack and stroke—is mixed, with some trials and meta-analyses pointing to a benefit but many others showing no effect.²^,¹⁵^,¹⁶^,¹⁷^,¹⁸^,¹⁹^,²⁰^,²¹^,²²

One systematic review noted that when you look at the highest-quality studies, omega-3 supplements showed little to no effect on overall mortality or major cardiovascular events, while smaller or more biased studies sometimes reported benefits.21 

Other experts have suggested that differences in dose or in people’s baseline balance of omega-3s and other fats in the blood may explain the conflicting results.²³

Another possibility: Even multi-year supplement trials may be too short to show an effect on heart attacks or strokes—especially compared to a lifetime of eating fish. And because most trials are done in middle-aged or older adults with existing risks, they may miss benefits that would show up if supplementation started earlier.

Regardless, the bottom line is that the results often seem conflicting. And it’s led some experts to conclude that fish is heart health-promoting, but fish oil supplements are “worthless” (even though it’s well-established they consistently improve triglycerides, a risk factor for heart disease⁴^,²⁴).

No wonder people are confused. But hopefully, what I’m about to tell you will help. 

The Nuanced Truth About Fish Oil Supplements

So, what should you make of these inconsistent findings?

My take…

The benefits of fish oil supplements are most noticeable if you’re deficient in omega-3s. 

And most people are deficient. In fact, it’s one of the most common nutritional deficiencies I see. 

I’ve tested levels of essential fatty acids, including omega-3s, in thousands of individuals. You’d be surprised by how many people are walking around with significant deficiencies and don’t know it.

For individuals who are deficient, fish oil supplementation works similarly to any other therapeutic approach. If you have a headache, a pain reliever will help alleviate the discomfort. In contrast, if you don’t have a headache, taking a painkiller won’t result in any improvement. 

It’s the same with fish oil supplements.

If your blood levels of omega-3s are already optimal, you may not see much of an added benefit from supplements. On the other hand, if you don’t consume fish very often, a supplement may be in order. 

How to Know if You’re Deficient 

To maintain adequate levels of omega-3s, I recommend consuming three weekly servings of oily fish. Good sources include wild salmon, mussels, anchovies, sardines, and herring. 

Note that several varieties of oily fish—including king mackerel and ahi tuna—have been contaminated with mercury and should be limited or avoided. 

Now, most people don’t consume oily fish three times a week. That’s why I believe supplemental fish oil is so important. It fills in the gaps. 

If you rarely or never eat fish, you probably need one. And this is particularly true if you have any of the following signs of deficiency:

• Dry, itchy skin or dandruff
  
  
• Soft, brittle nails
  
  
• Chicken skin (keratosis pilaris), which looks like tiny, rough bumps on the backs of your arms or thighs
  
  
• Mood issues, such as feeling down, anxious, or having trouble focusing
  
  
• Joint pain or stiffness

How can you know for sure if you need fish oil? Consider getting your Omega-3 blood levels tested through Function Health. 

Included in your one year membership (which tests for over 100 health biomarkers): a measure of your total amount of Omega-3s, plus a breakdown of three different types of Omega 3s—EPA, DHA, and DPA—and how they compare to your overall fatty acid profile. 

This way, you can get a comprehensive view of your body’s fatty acid profile—Are your markers out of range? Are they optimized?—and also be able to track changes to your status over time. 

How Much Fish Oil Do You Need?

If you’re deficient, work with your doctor to determine the best supplemental dose for you. 

Generally, a typical recommendation is 1,000–2,000 milligrams of combined EPA and DHA per day. However, for specific conditions like inflammation, heart health, or brain support, higher doses—up to 3,000 mg of EPA and DHA daily—may be beneficial.

Know that taking too much fish oil can thin your blood, which might not be ideal if you’re on blood thinners or preparing for surgery. That’s why it’s important to work closely with a healthcare professional who can keep tabs on your blood work and alter your dosage as needed.

Keep in mind, not all fish oil supplements are created equal. 

Some products are poorly sourced, oxidized, or contaminated with heavy metals and toxins. So it’s crucial to choose a high-quality, purified fish oil such as Omega-3 Rejuvenate blend from Big Bold Health. That’s the one I take every day, and what I recommend to my patients.

References

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2. Nissen SE, Lincoff AM, Wolski K, Ballantyne CM, Kastelein JJP, Ridker PM, et al. Association between achieved ω-3 fatty acid levels and major adverse cardiovascular outcomes in patients with high cardiovascular risk: A secondary analysis of the STRENGTH trial: A secondary analysis of the STRENGTH trial. JAMA Cardiol. 2021 Aug 1;6(8):910–7.    

3. Madison AA, Belury MA, Andridge R, Renna ME, Rosie Shrout M, Malarkey WB, et al. Omega-3 supplementation and stress reactivity of cellular aging biomarkers: an ancillary substudy of a randomized, controlled trial in midlife adults. Mol Psychiatry. 2021 Jul;26(7):3034–42. 

4. Skulas-Ray AC, Wilson PWF, Harris WS, Brinton EA, Kris-Etherton PM, Richter CK, et al. Omega-3 Fatty Acids for the Management of Hypertriglyceridemia: A Science Advisory From the American Heart Association. Circulation. 2019 Sep 17;140(12):e673–91.    

5. Chew EY, Clemons TE, Agrón E, Launer LJ, Grodstein F, Bernstein PS, et al. Effect of omega-3 fatty acids, lutein/zeaxanthin, or other nutrient supplementation on cognitive function: The AREDS2 randomized clinical trial. JAMA. 2015 Aug 25;314(8):791–801.    

6. Yassine HN, Feng Q, Azizkhanian I, Rawat V, Castor K, Fonteh AN, et al. Association of serum docosahexaenoic acid with cerebral amyloidosis. JAMA Neurol. 2016 Oct 1;73(10):1208–16.    

7. Godos J, Micek A, Currenti W, Franchi C, Poli A, Battino M, et al. Fish consumption, cognitive impairment and dementia: an updated dose-response meta-analysis of observational studies. Aging Clin Exp Res. 2024 Aug 20;36(1):171.     

8. Yurko-Mauro K, McCarthy D, Rom D, Nelson EB, Ryan AS, Blackwell A, et al. Beneficial effects of docosahexaenoic acid on cognition in age-related cognitive decline. Alzheimers Dement. 2010 Nov;6(6):456–64. 

9. Quinn JF, Raman R, Thomas RG, Yurko-Mauro K, Nelson EB, Van Dyck C, et al. Docosahexaenoic acid supplementation and cognitive decline in Alzheimer disease: a randomized trial: A randomized trial. JAMA. 2010 Nov 3;304(17):1903–11.    

10. Li F, Liu X, Zhang D. Fish consumption and risk of depression: a meta-analysis. J Epidemiol Community Health. 2016 Mar;70(3):299–304.    

11. Su K-P, Huang S-Y, Chiu T-H, Huang K-C, Huang C-L, Chang H-C, et al. Omega-3 fatty acids for major depressive disorder during pregnancy: results from a randomized, double-blind, placebo-controlled trial. J Clin Psychiatry . 2008 Apr;69(4):644–51. 

12. Su K-P, Huang S-Y, Chiu C-C, Shen WW. Omega-3 fatty acids in major depressive disorder. A preliminary double-blind, placebo-controlled trial. Eur Neuropsychopharmacol . 2003 Aug;13(4):267–71. 

13. Peet M, Horrobin DF. A dose-ranging study of the effects of ethyl-eicosapentaenoate in patients with ongoing depression despite apparently adequate treatment with standard drugs. Arch Gen Psychiatry . 2002 Oct;59(10):913–9. 

14. Grenyer BFS, Crowe T, Meyer B, Owen AJ, Grigonis-Deane EM, Caputi P, et al. Fish oil supplementation in the treatment of major depression: a randomised double-blind placebo-controlled trial. Prog Neuropsychopharmacol Biol Psychiatry . 2007 Oct 1;31(7):1393–6. 

15. Yokoyama M, Origasa H, Matsuzaki M, Matsuzawa Y, Saito Y, Ishikawa Y, et al. Effects of eicosapentaenoic acid on major coronary events in hypercholesterolaemic patients (JELIS): a randomised open-label, blinded endpoint analysis. Lancet. 2007 Mar 31;369(9567):1090–8.    

16. Risk and Prevention Study Collaborative Group, Roncaglioni MC, Tombesi M, Avanzini F, Barlera S, Caimi V, et al. N-3 fatty acids in patients with multiple cardiovascular risk factors. N Engl J Med. 2013 May 9;368(19):1800–8.    

17. Aung T, Halsey J, Kromhout D, Gerstein HC, Marchioli R, Tavazzi L, et al. Associations of Omega-3 Fatty Acid Supplement Use With Cardiovascular Disease Risks: Meta-analysis of 10 Trials Involving 77 917 Individuals. JAMA Cardiol. 2018 Mar 1;3(3):225–34. 

18. Tseng P-T, Zeng B-Y, Hsu C-W, Liang C-S, Stubbs B, Chen Y-W, et al. The optimal dosage and duration of ω-3 PUFA supplementation in heart failure management: Evidence from a network meta-analysis. Adv Nutr . 2025 Feb;16(2):100366. 

19. Dinu M, Sofi F, Lotti S, Colombini B, Mattioli AV, Catapano AL, et al. Effects of omega-3 fatty acids on coronary revascularization and cardiovascular events: a meta-analysis. Eur J Prev Cardiol . 2024 Nov 11;31(15):1863–75. 

20. Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, Moore HJ, et al. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev . 2018 Jul 18;7:CD003177. 

21. Yan J, Liu M, Yang D, Zhang Y, An F. Efficacy and safety of omega-3 fatty acids in the prevention of cardiovascular disease: A systematic review and meta-analysis. Cardiovasc Drugs Ther . 2024 Aug;38(4):799–817. 

22. Manson JE, Cook NR, Lee I-M, Christen W, Bassuk SS, Mora S, et al. Marine n-3 fatty acids and prevention of cardiovascular disease and cancer. N Engl J Med. 2019 Jan 3;380(1):23–32. 

23. Nishizaki Y, Daida H. Optimal dose of n-3 polyunsaturated fatty acids for cardiovascular event prevention. Circ Rep. 2020 Mar 28;2(4):260–4.