Neither krill oil nor cod liver oil is universally better. They are different supplements that serve different purposes, and the right choice depends on what you’re trying to get out of it. Krill oil is primarily an omega-3 supplement with added antioxidant benefits, while cod liver oil is a combined source of omega-3s, vitamin A, and vitamin D. Here’s how they compare on the details that actually matter.
What Each Oil Actually Contains
Both oils deliver EPA and DHA, the two omega-3 fatty acids linked to heart and brain health. But the ratios differ. Fish oils (including cod liver oil) typically contain EPA and DHA in roughly a 1:1 ratio, while krill oil skews toward a 2:1 ratio favoring EPA. This means krill oil delivers proportionally more EPA per serving, which is the omega-3 more closely associated with reducing inflammation.
The defining feature of cod liver oil is its vitamin content. One tablespoon provides about 4,080 micrograms of vitamin A and 1,360 IU of vitamin D. That’s a significant amount of both, enough to cover daily needs for most adults and then some. If you’re looking to address a vitamin D deficiency or support bone health through a single supplement, cod liver oil does double duty that krill oil simply can’t match. Krill oil contains negligible amounts of these vitamins.
Krill oil, on the other hand, contains astaxanthin, a pigment that gives it its red color and acts as a powerful antioxidant. Astaxanthin helps neutralize free radicals and activates the body’s own antioxidant defense systems, reducing oxidative stress at a cellular level. It may also help with insulin sensitivity by lowering the oxidative damage that contributes to insulin resistance. Cod liver oil has no astaxanthin.
How Well Your Body Absorbs Each One
This is where krill oil gets most of its marketing buzz, and the science is more nuanced than the labels suggest. The omega-3s in krill oil are bound to phospholipids, which are the same type of fat that makes up your cell membranes. In cod liver oil and other fish oils, the omega-3s are bound to triglycerides. The theory is that phospholipid-bound omega-3s pass through the intestinal wall more easily, giving krill oil a bioavailability advantage.
A 2025 network meta-analysis found that at dosages under 2,000 mg per day, krill oil does appear to raise the omega-3 index (a measure of omega-3 levels in red blood cells) more effectively than fish oil at the same dose. However, head-to-head studies comparing blood levels of EPA have found that when people take similar amounts of EPA from krill oil and fish oil, the actual increase in blood EPA is almost identical. So while there may be a modest absorption edge for krill oil at lower doses, it’s not the dramatic difference that marketing often implies.
In practical terms, this means you could potentially take a smaller dose of krill oil and get comparable omega-3 levels to a larger dose of fish oil. But krill oil hasn’t been studied at doses above 1,900 mg per day, so for people who need high-dose omega-3 therapy, fish oils (including cod liver oil) remain the better-studied option.
Effects on Heart Health
Both oils lower triglycerides, a key blood fat linked to cardiovascular risk. A network meta-analysis comparing krill oil and fish oil found that per gram of omega-3s, they reduced triglycerides by nearly identical amounts: about 9 mg/dL for fish oil and about 10 mg/dL for krill oil. The differences in LDL cholesterol, HDL cholesterol, and total cholesterol between the two were not statistically significant either. In short, for lipid management, they perform the same.
Where krill oil may have a slight edge is in reducing C-reactive protein (CRP), a marker of inflammation throughout the body. One clinical trial found that while both krill oil and omega-3 supplements lowered CRP from baseline, krill oil reduced it more effectively. This could matter for people whose cardiovascular risk is driven more by chronic inflammation than by cholesterol numbers alone, though more research is needed to confirm the size of this benefit.
Inflammation and Joint Health
Omega-3 fatty acids in general help dial down inflammation, and both oils deliver on this front. Krill oil’s combination of phospholipid-bound omega-3s, a higher EPA ratio, and astaxanthin may give it a stronger anti-inflammatory profile overall. The CRP reduction data supports this, and astaxanthin independently reduces oxidative stress, which is a driver of chronic inflammatory conditions.
Cod liver oil’s high vitamin D content is also relevant here. Vitamin D plays a role in immune regulation and has been linked to reduced inflammation in people who are deficient. If your vitamin D levels are low, cod liver oil addresses both omega-3 and vitamin D gaps simultaneously, which could indirectly support joint health and immune function.
Side Effects and Tolerance
Fishy aftertaste and “fish burps” are the most common complaints with any omega-3 supplement. Krill oil is often marketed as easier on the stomach, and some users do report less reflux, but it’s not a guarantee. The Cleveland Clinic notes that some people still experience a fishy taste with krill oil, along with occasional diarrhea, headaches, heartburn, or upset stomach.
Cod liver oil carries a unique risk: vitamin A toxicity. Because one tablespoon contains over 4,000 micrograms of vitamin A, taking it alongside a multivitamin or other vitamin A sources can push you past safe upper limits. Chronic excess vitamin A can cause liver damage, bone loss, and birth defects during pregnancy. This is not a concern with krill oil, which contains no meaningful vitamin A. If you already get plenty of vitamin A from your diet or other supplements, cod liver oil requires more careful dosing.
Contaminant Concerns
Krill sit at the very bottom of the ocean food chain, which means they accumulate far less mercury and other heavy metals than larger fish like cod. That said, the NIH notes that omega-3 supplements in general, including fish oil products, have mercury removed during processing and purification. Both supplements are considered safe from a contaminant standpoint when purchased from reputable manufacturers, but krill oil starts with a cleaner raw material.
Which One to Choose
Choose cod liver oil if your primary goal is getting omega-3s along with vitamins A and D in a single supplement, especially during winter months or if you’ve been told your vitamin D is low. It’s also the more affordable option per serving and has decades of research behind it.
Choose krill oil if you want a focused omega-3 supplement with added antioxidant benefits, prefer a potentially smaller pill for comparable omega-3 absorption, or are concerned about getting too much vitamin A from other sources. Krill oil’s phospholipid structure and astaxanthin content give it a distinct biochemical profile, even if the end result on blood lipids is similar to fish oil.
For people who simply want to raise their omega-3 levels and have no strong preference either way, the two oils produce comparable results on the measures that matter most: blood omega-3 levels, triglyceride reduction, and cholesterol balance. The differences are real but modest, and consistency matters more than which bottle you pick.