Category: Safety & Interactions

Almost none, and far less than the fish most people eat. Antarctic krill feed on phytoplankton and live two to six years, so they never accumulate the mercury that builds up in long-lived predator fish — measured concentrations in wild Antarctic krill run around 0.006 to 0.071 parts per million, against the roughly 1.0 ppm that puts swordfish and shark on the FDA’s avoid list. The heavy metal actually worth asking a krill oil company about is not mercury. It is lead, and we will get to why.

Why krill are a bad place for mercury to end up

Mercury does not become dangerous because it exists in seawater. It becomes dangerous because it biomagnifies — each step up the food chain concentrates what the step below already carried, and each extra year of life adds to the total. A swordfish is a big predator that eats other predators for a decade or more. That is the whole mechanism.

Antarctic krill (Euphausia superba) break that mechanism in both directions: they eat phytoplankton and small protists, near the base of the food web rather than the top, and they are short-lived, so there is not much time on the clock for anything to build up.

The measurements bear this out. Seco and colleagues, writing in Environmental Pollution in 2019, sampled krill across three locations in the Scotia Sea and reported total mercury of roughly 0.006 to 0.071 µg/g — lowest in adult males from South Georgia, highest in juveniles from the South Orkney Islands. Krill from the South Orkneys carried five to seven times more than krill from South Georgia, which is a useful reminder that “krill” is not one uniform thing; where the boat is matters.

A parallel finding from Sontag, Steinberg and Reinfelder in Science of the Total Environment (2019, vol. 688) is that juvenile krill consistently carried more methylmercury than adults — the opposite of the pattern in fish, and further evidence that krill are not accumulating over a lifetime the way a tuna does.

One honest caveat on the comparison, because nobody else will give it to you: those krill figures are reported on a dry-weight basis, while the FDA’s fish numbers are wet weight. Krill is mostly water. Corrected properly, the gap is wider than the raw numbers suggest, not narrower. We are pointing that out against our own interest in keeping the math simple.

What actually shows up in the finished bottle

Wild krill is one thing. The oil in a capsule is another — it has been through a factory, a supply chain and a bottling line, and that is where contamination usually enters.

The reassuring result: when ConsumerLab tested fish, krill and algal oil supplements using a cold-vapor method, no detectable mercury turned up in any product tested. Their own summary was blunt — you will get more contamination from eating fish than from these capsules.

The unflattering finding, and the reason this article exists: a 2021 study in the Kocatepe Veterinary Journal (Erden Kızılırmak et al., 14(4):408–414) bought 11 krill oil brands off pharmacy shelves and sent them to an accredited lab. Mercury and cadmium came back inside Codex Alimentarius limits in every sample. But all 11 exceeded the EU tolerable limit for lead (0.08 mg/kg), and only one of the 11 came in under the arsenic limit (0.1 mg/kg). Peroxide values — a freshness measure — ranged from 10 to 30 meq O₂/kg.

Read that carefully, because the headline and the finding point in different directions. The metal people worry about is fine. The metals nobody asks about are the ones that failed.

The limits of that study, stated plainly

It was 11 brands from Turkish pharmacies, not a global survey, and it is a single small paper. It also measured total arsenic. Most arsenic in marine organisms is arsenobetaine, an organic form the body largely passes through unchanged, and a total-arsenic test cannot tell that apart from the toxic inorganic form. So the arsenic column is much weaker evidence than the lead column. The lead result is the one that should make you ask a question, and it is the one we would want asked of us.

What “heavy metal tested” on a label actually means

Scan any krill oil listing and you will see it: lab tested, heavy-metal tested, mercury-free. Those phrases are not regulated and mostly mean the company ran a test at some point. Two questions separate a real answer from a sticker.

Tested for what, exactly? Mercury is the cheap, easy, reassuring one — and, as the Kocatepe data shows, the one least likely to fail. A panel that stops at mercury is testing for marketing. Lead, cadmium and arsenic are where the interesting answers live.

Will they show you the paperwork? “Documentation available on request” only counts if the documentation actually arrives when you request it.

How we handle it, and what we will not claim

Captains Krill Oil™ is pressed mechanically from fresh-caught Antarctic krill, on the boat, in the Southern Ocean. No hexane. No chemical solvents. That matters here for a plain reason: every processing step and every added chemical is another opportunity for something to enter the oil, and we removed most of the steps by doing the extraction where the krill is caught rather than shipping meal halfway around the world first. If you want the long version, we wrote it up in is krill oil extracted with hexane.

We test lots at random, and they come back strong. Documentation is available on request — ask and we will send it. What we will not tell you is that we document every single lot, because we do not, and a company claiming a paper trail that complete is either a much bigger operation than ours or is telling you a story. It is a natural catch from a small family business that has been doing this for twenty years, and it varies a little lot to lot. That is what a real product looks like.

You might not need us

If mercury is your only reason for considering krill over fish oil, the honest answer is that you are solving a problem you probably do not have. Good fish oil from a reputable brand also tests clean for mercury — ConsumerLab found the same thing across the whole category. Mercury is not a reason to pay more for krill.

And if you eat fatty fish twice a week, you do not need a supplement at all, from us or anyone. The FDA’s own guidance is to eat fish, choosing lower-mercury species like salmon, sardines and pollock over swordfish and tilefish. That advice is free and it works. If you are pregnant, mercury exposure is worth real attention — and that is a conversation for your doctor, not a supplement company’s blog post.

The better reasons to choose a krill oil are the phospholipid form the omega-3 arrives in and how the oil was made and kept. Freshness is a bigger practical risk than any metal: rancid oil is far more common than contaminated oil, and you can often taste it. We covered that in does krill oil expire. On the sourcing question that usually comes next, see is krill endangered.

Frequently asked questions

Does krill oil have less mercury than fish oil?

In the raw material, yes, and by a wide margin — krill sit far lower on the food chain than the fish used for most fish oil. In the finished capsule the difference largely disappears, because refining removes mercury from fish oil too. ConsumerLab found no detectable mercury in either category.

Is krill oil safe during pregnancy?

Mercury is not the concern with krill that it is with predator fish, and unlike cod liver oil, krill carries no preformed vitamin A load. That said, pregnancy is exactly the situation where you should ask your OB or midwife rather than a supplement label, and we would rather you did.

What about lead, cadmium and arsenic in krill oil?

Cadmium has consistently tested within Codex limits. Lead is the one with a real finding against it — all 11 brands in the 2021 Kocatepe study exceeded the EU tolerable limit of 0.08 mg/kg. Ask any brand you are considering for lead results specifically, not a general “heavy metal tested” claim.

Do I need a certificate of analysis before buying krill oil?

It is a fair thing to ask for, and any brand should be able to produce testing documentation on request. Be skeptical of a company that will not, and equally skeptical of one promising a level of documentation that no small natural-product operation could actually maintain.

Can you taste or smell contamination in krill oil?

No. Metals have no taste at these concentrations. What you can taste is rancidity — a sharp, paint-like, old-fish note that means the oil has oxidized. That is the far more common defect, and your nose is a genuinely useful instrument for it.

Honest answer, not a pitch. — captainskrilloil.com

Fish oil makes you burp for two reasons, and only one of them is about fish. Omega-3 oil is lighter than the liquid already in your stomach, so a dissolved capsule floats to the top and rides up with any reflux — and if that oil has oxidized on a warehouse shelf, what comes back up smells far worse than fish ever did.

Krill oil has a real mechanical reason to do this less often. It is not a guarantee, and we’ll show you the trial that says so.

Reason one: the oil floats

A softgel is a shell around liquid fat. Your stomach breaks the shell, and the oil — less dense than gastric fluid — separates and sits on top like unshaken salad dressing. Anything pushing stomach gas upward carries a little of that surface oil with it. That’s the burp: a density problem, not a digestion problem.

This is why the oldest advice still works best: take it mid-meal, with some fat, and not right before bed. Food gives the oil something to disperse into.

Reason two: the oil already went bad — and this is the one people miss

Fresh omega-3 oil tastes like almost nothing. If your burp tastes like a dock in August, the oil has probably oxidized. Long-chain omega-3s are polyunsaturated — a lot of places for oxygen to grab on. Heat, light, and time turn them into aldehydes and ketones, and those are the compounds behind the smell.

How common is that? More common than the shelf suggests. Jackowski and colleagues tested 171 over-the-counter omega-3 supplements from 49 North American brands and found 50% exceeded a voluntary industry oxidation limit on at least one measure, and 39% exceeded the recommended TOTOX ceiling (Jackowski et al., Journal of Nutritional Science, 2015; 4:e30). A separate New Zealand survey published in Scientific Reports found roughly a quarter of products over the peroxide-value limit and about the same share over TOTOX (Albert et al., 2017).

The reference numbers those studies measure against come from the trade body GOED: peroxide value at or under 5 mEq/kg, anisidine value at or under 20, TOTOX at or under 26. Nobody prints those on a box. You are meant to take freshness on faith.

So before you blame the fish, run the free test: bite one capsule. Fresh oil is bland and faintly marine. Rancid oil is sharp, paint-like, and it lingers. If it fails, that bottle is done — whoever sold it to you. More on that in what “rancid” actually means in an omega-3 bottle.

Does krill oil actually fix the burping?

Here is the honest version, which is not the version most krill brands print.

The mechanism is real. In fish oil, EPA and DHA ride on triglycerides, which don’t mix with water and float. In krill, most of that same EPA and DHA is attached to phospholipids — the molecule your own cell membranes are built from, and the same class of molecule that makes egg yolk hold a vinaigrette together. Phospholipids are amphiphilic: one end likes water, one end likes fat. They emulsify into stomach contents instead of pooling on top. Less oil on the surface, less oil in the burp. We wrote up the underlying chemistry in same molecule, different vehicle.

The human data is not as tidy as the mechanism. In a four-week randomized trial comparing krill oil, fish oil, and a corn oil placebo, the placebo and fish oil arms each logged one incidence of burping — and the krill oil arms logged four and three. Aftertaste was reported mild on three occasions in the fish oil arm and six times in the krill arm, with one rated moderate (Ramprasath et al., Lipids in Health and Disease, 2013; the tolerability breakdown is laid out in the published commentary on that trial). The study still concluded krill oil was well tolerated, and it was — these were minor complaints in a small group. But it is not the result you’d predict from the marketing.

Across omega-3 trials generally, total gastrointestinal complaints — belching, aftertaste, loose stools, indigestion — run around 1.4% to 4.9% of participants. Most people never burp at all. The ones who do tend to be taking a big dose, on an empty stomach, from a bottle that’s been open a while.

Our read after twenty years of selling this stuff: the phospholipid form helps some people and does nothing for others, and freshness matters more than form. A fresh triglyceride fish oil will beat a stale phospholipid krill oil on burps every time.

Five things to try before you switch brands

1. Take it mid-meal, with fat. Not before eating, not after — in the middle. This is the single biggest lever and it costs nothing.
2. Freeze the capsules. A frozen softgel takes longer to break open, so the oil is released further along and gets less chance to pool. Cold storage also slows oxidation. See how to store it.
3. Split the dose. Two capsules at breakfast and dinner instead of four at once. Gastrointestinal complaints with omega-3s are dose-dependent.
4. Do the smell test on the bottle you already own. If it reeks, none of the other four tips will save it.
5. Be careful with enteric coatings. They genuinely move the release past the stomach and they do stop burps. They also hide the taste of oil that has gone off — which removes your only free freshness sensor. A coated capsule can be rancid and you would never know.

What we do about it on our end

Captains Krill Oil™ is pressed mechanically on the boat, right after the catch — no solvents, no chemical processing, no shipping raw krill meal across the world to be reprocessed months later. That isn’t romance. Oxidation is a clock that starts the moment the krill leaves the water, and every extra step is time on that clock.

We are a natural catch, not a factory line, so the oil varies a little from lot to lot — that is what an unstandardized product looks like when nobody is adjusting it to hit a number. We test lots at random, and they come back strong. Documentation is available on request.

And the honest part: some people still burp on ours. Fewer than on the fish oil they came from, customers tell us — but “fewer” is not “none,” and anyone promising none is selling.

You might not need us for this

If your burps started recently on a bottle you have had open for six months, you do not have a brand problem. You have a rancidity problem, and the fix is a fresh bottle of anything — ours, theirs, whoever’s — kept cold and used inside a couple of months.

If you eat oily fish twice a week, you don’t need a capsule at all, and this whole question goes away.

And if you’ve tried the meal timing, the freezing, and a fresh bottle and it still comes up, softgel omega-3s may not be for you. Sardines, mackerel, and canned salmon deliver the same molecules with no burp. We’d rather tell you that than sell you a bottle you’ll quit in three weeks.

Honest answer, not a pitch. — captainskrilloil.com

Frequently asked questions

Do fish oil burps mean the oil has gone bad?

Often, but not always. A faint fishy note can happen with perfectly fresh oil purely because the oil floats on stomach contents. A strong, sharp, paint-like taste that lingers is a rancidity signal — bite a capsule and smell it, and throw the bottle out if it reeks.

Does krill oil cause fewer burps than fish oil?

Mechanically it should, because krill’s omega-3s are carried on phospholipids that emulsify into stomach contents rather than floating on top. But the head-to-head trial data doesn’t confirm it — one four-week randomized trial logged more burping and aftertaste reports in the krill arm than the fish oil arm. Treat it as likely to help, not certain to.

Does freezing krill oil capsules stop the burping?

It helps a lot of people. A frozen softgel dissolves more slowly, so the oil is released further down and has less opportunity to pool at the top of the stomach. Freezing also slows oxidation, which addresses the other half of the problem at the same time.

Are enteric-coated omega-3 capsules the answer?

They reliably stop burps, because the capsule opens past the stomach. The trade-off is that the coating also masks the taste and smell of oil that has already oxidized, so you lose the one free freshness test you had. If you use coated capsules, buy small bottles and keep them cold.

How long before the burping settles down?

If it’s a timing issue, changing when you take it usually works within a day or two. If it’s a freshness issue, nothing improves until you open a new bottle. If you’ve fixed both and two weeks bring no change, softgels probably aren’t your delivery method.