Krill oil has become a popular alternative to fish oil in recent years. It’s extracted from Antarctic krill, small crustaceans that sit near the bottom of the food chain. Because krill eat algae rather than other fish, they tend to accumulate fewer heavy metals and environmental pollutants than larger fish species. This is one of the main reasons people give for choosing krill oil over traditional fish oil.

What makes krill oil different from fish oil?

The main difference is in the chemical structure. In krill oil, roughly 30% to 65% of the omega-3 fatty acids are attached to phospholipids, mainly phosphatidylcholine (also known as lecithin). Fish oil, by contrast, delivers its omega-3s primarily as triglycerides.

Why does this matter? Phospholipids are the building blocks of cell membranes, and they’re amphiphilic, meaning they have both water-soluble and fat-soluble portions. The theory is that this structure makes krill oil easier for the body to absorb.

The honest truth, though: the evidence on whether krill oil is actually more bioavailable than fish oil remains inconclusive. A 2015 review in the journal Lipids in Health and Disease found that study results were too mixed to draw firm conclusions. Some trials showed better absorption with krill oil, others showed no difference [1]. We need larger, better-designed studies before anyone can definitively claim one is superior to the other.

Krill oil also contains astaxanthin, a red-orange pigment that acts as an antioxidant. Fish oil doesn’t naturally contain this compound. Whether the amount of astaxanthin in krill oil is enough to provide meaningful benefits is another open question, but it does help prevent the oil from going rancid.

Five potential benefits of krill oil

I’ve gone through the clinical research on krill oil. Here’s what the evidence actually shows, along with my honest assessment of how strong that evidence is.

1. May reduce knee pain from mild osteoarthritis

This is probably the most interesting finding in the krill oil literature, and it’s why I listed it first.

Knee pain is extremely common as people age. Estimates suggest over 50% of people over 50 experience it to some degree, with rates higher in women (around 58%) than men (about 32%) [2]. It’s almost unavoidable if you live long enough.

A 30-day double-blind trial published in 2016 tested krill oil against placebo in 50 people with mild knee pain [3]. The participants taking krill oil showed improvements in pain, stiffness, and range of motion in both knees, as measured by the Japanese Knee Osteoarthritis Scale and the Japanese Orthopaedic Association scoring system.

The researchers also found that blood omega-3 levels increased in the krill oil group, while the ratio of omega-6 to omega-3 fatty acids decreased. This shift in fatty acid balance is thought to reduce the production of pro-inflammatory compounds.

My honest assessment: the study is small, and 30 days is a short follow-up period. But the results are encouraging enough that it’s reasonable to try krill oil for mild joint discomfort. I wouldn’t expect dramatic results, and it’s certainly not a substitute for proper medical evaluation if you have significant joint pain or arthritis.

2. May help immune function after intense exercise

Regular moderate exercise is good for the immune system. But there’s a catch: prolonged, intense exercise like marathons or long-distance cycling can temporarily suppress immune function for 3 to 24 hours afterward [4]. During this window, athletes are more susceptible to upper respiratory tract infections.

A 2015 randomised, double-blind trial gave 37 healthy adults either krill oil or placebo for six weeks [5]. After intense endurance exercise, the krill oil group showed better immune markers, specifically improved activity of peripheral blood mononuclear cells and natural killer cells.

One thing to note: krill oil didn’t improve exercise performance itself. The participants taking krill oil didn’t run faster or cycle longer. It just seemed to help their immune systems recover better afterward.

The catch? This is one study with 37 people. I’d want to see this replicated before drawing strong conclusions. But for serious endurance athletes who find themselves getting sick after big events, it might be worth trying.

3. May help regulate blood lipid levels

Dyslipidaemia, or abnormal blood lipid levels, affects roughly one in three adults in developed countries [6]. The most common form is high LDL cholesterol, though high triglycerides and low HDL cholesterol are also concerns. Over time, these abnormalities increase cardiovascular disease risk.

A 2017 systematic review and meta-analysis looked at seven studies involving 662 participants [7]. The analysis found that krill oil reduced LDL cholesterol and triglycerides compared to placebo.

The proposed mechanism involves effects on mitochondrial function and the inhibition of fat and cholesterol synthesis in the liver.

My honest take: the effect sizes were modest, and the studies included in the review were quite heterogeneous, meaning they used different doses, durations, and patient populations. Krill oil might be useful as one component of a broader approach to managing high cholesterol, but it’s not going to replace proper diet, exercise, and medication if those are indicated.

4. May support cognitive function in older adults

As we age, cognitive decline becomes increasingly common. Memory, processing speed, and attention all tend to slow down. The question is whether we can do anything about it.

A 12-week randomised, double-blind trial from 2013 compared krill oil and sardine oil in 45 elderly men [8]. Both supplements seemed to activate the prefrontal cortex of the brain and improve working memory. However, krill oil showed a slightly better effect on computational ability specifically.

The researchers suggested that the phospholipid form of omega-3s in krill oil might cross the blood-brain barrier more readily than the triglyceride form in regular fish oil.

I should be clear: this is preliminary evidence from a single small study. I wouldn’t take krill oil expecting it to prevent dementia or reverse cognitive decline. But the findings are interesting enough that continued research seems worthwhile.

5. May improve premenstrual syndrome symptoms

Premenstrual syndrome (PMS) affects a substantial proportion of women during the luteal phase of their menstrual cycle, the period between ovulation and menstruation. Symptoms vary widely but can include physical discomfort (bloating, breast tenderness, headaches), mood changes (irritability, anxiety, depression), and fatigue.

A 90-day double-blind study compared krill oil to fish oil in 70 women with PMS [9]. Both supplements improved psychosomatic symptoms like abdominal pain, bloating, and water retention.

However, krill oil outperformed fish oil on several secondary measures: participants reported less need for painkillers, better mood, less breast tenderness, and less joint pain.

The difference might be due to the phospholipid structure of krill oil omega-3s, which some researchers believe the body handles differently than triglyceride-based omega-3s.

This is one of the stronger studies in the krill oil literature. If you’ve tried fish oil for PMS symptoms without much success, switching to krill oil might be worth considering.

Side effects and safety

In short-term studies lasting three months or less, krill oil appears quite safe. However, it can cause side effects similar to those of fish oil and other omega-3 supplements:

Heartburn or acid reflux
Unpleasant fishy taste or breath
Stomach upset, nausea, or diarrhoea
Bloating

These side effects are usually mild and often improve if you take the supplement with food.

Who should avoid krill oil

Pregnant and breastfeeding women: There isn’t enough safety data on krill oil use during pregnancy or breastfeeding. It’s best to avoid it or consult your doctor first.

People with seafood allergies: Krill are crustaceans. If you’re allergic to shellfish, shrimp, or other seafood, krill oil could trigger an allergic reaction. This isn’t theoretical; there have been reported cases.

People with bleeding disorders or on anticoagulant medication: Omega-3 fatty acids have anticoagulant (blood-thinning) properties. If you’re taking warfarin, aspirin, or other anticoagulant or antiplatelet drugs, adding krill oil could increase bleeding risk. Talk to your doctor before combining them.

Before surgery: Because of the blood-thinning effect, stop taking krill oil at least two weeks before any scheduled surgery.

People with liver or kidney problems: The safety of krill oil in people with impaired liver or kidney function hasn’t been established. Exercise caution.

How much to take

Most studies have used doses between 500mg and 3g of krill oil daily. The higher end of this range was typically used in studies looking at blood lipid effects.

If you’re trying krill oil for the first time, starting with a lower dose (around 500mg daily) and seeing how you tolerate it makes sense.

The bottom line

Krill oil is a reasonable alternative to fish oil for people who want omega-3 supplementation. The evidence for specific benefits is not overwhelming, but there are promising findings for joint pain, blood lipid management, and PMS symptoms.

The main advantages over fish oil are potentially better absorption due to the phospholipid structure, lower risk of heavy metal contamination, and the presence of astaxanthin as an antioxidant. The main disadvantage is cost; krill oil is typically more expensive than fish oil per milligram of omega-3s.

Whether those potential advantages are worth the extra expense is a personal decision that depends on your budget and your specific health goals.

References

Ulven SM, Holven KB. Comparison of bioavailability of krill oil versus fish oil and health effect. Vasc Health Risk Manag. 2015;11:511-524. PubMed
Cross M, Smith E, Hoy D, et al. The global burden of hip and knee osteoarthritis: estimates from the global burden of disease 2010 study. Ann Rheum Dis. 2014;73(7):1323-1330.
Suzuki Y, Fukushima M, Sakuraba K, et al. Krill oil improves mild knee joint pain: a randomised controlled trial. PLoS One. 2016;11(10):e0162769. PubMed
Nieman DC. Exercise, infection, and immunity. Int J Sports Med. 1994;15 Suppl 3:S131-S141. PubMed
Da Boit M, Mastalber BA, Sherida S, et al. The effect of krill oil supplementation on exercise performance and markers of immune function. PLoS One. 2015;10(9):e0139174. PubMed
Carroll MD, Kit BK, Lacher DA, Shero ST, Mussolino ME. Trends in lipids and lipoproteins in US adults, 1988-2010. JAMA. 2012;308(15):1545-1554.
Bunea R, El Farrah K, Deutsch L. Evaluation of the effects of Neptune Krill Oil on the clinical course of hyperlipidemia. Altern Med Rev. 2004;9(4):420-428.
Konagai C, Yanagimoto K, Hayamizu K, et al. Effects of krill oil containing n-3 polyunsaturated fatty acids in phospholipid form on human brain function: a randomised controlled trial in healthy elderly volunteers. Clin Interv Aging. 2013;8:1247-1257. PubMed
Sampalis F, Bunea R, Pelland MF, et al. Evaluation of the effects of Neptune Krill Oil on the management of premenstrual syndrome and dysmenorrhea. Altern Med Rev. 2003;8(2):171-179. PubMed