You've probably been there. Standing in the supplement aisle, squinting at a plastic bottle of gold-colored pills, wondering if this specific brand of fish oil is going to cover your bases for the winter. It’s a common mix-up. People think fish oil and Vitamin D are basically the same thing because they both come from the ocean and both feel "healthy."
But here is the cold, hard truth: most fish oil capsules actually contain zero Vitamin D.
Wait. Seriously?
Yes. If you are buying standard "Fish Oil" or "Omega-3 Concentrate" made from the body fat of sardines, anchovies, or mackerel, you aren't getting any Vitamin D at all. Unless the manufacturer manually added it back in as a fortifier, that pill is strictly for your heart and brain, not your bones or immune system. It’s a massive distinction that catches people off guard every single year.
The Cod Liver Oil Exception
Now, if we are talking about how much vitamin d is in fish oil capsules specifically labeled as "Cod Liver Oil," the math changes completely. This is where the confusion starts. Regular fish oil comes from the flesh of oily fish. Cod liver oil, as the name suggests, comes from the liver.
✨ Don't miss: Geriatric Case Management Certification: Why Most People Get It All Wrong
Livers are storage organs. In the world of fish, the liver is where Vitamin A and Vitamin D hang out.
A standard teaspoon of liquid cod liver oil usually packs about 400 to 450 IU of Vitamin D. However, when you cram that into a tiny gel capsule, the numbers drop. Most individual cod liver oil capsules only contain about 100 to 150 IU of Vitamin D.
That is not a lot.
If your doctor told you that you're deficient and need 2,000 IU a day, you’d have to swallow nearly 20 capsules of cod liver oil to hit the mark. Nobody wants to do that. It’s gross, and frankly, you’d probably end up with Vitamin A toxicity before you ever fixed your Vitamin D levels.
Why the manufacturing process strips the good stuff
Ever wonder why "refined" fish oil is so clear and doesn't smell like a dead pier? It's because of molecular distillation. This process is great for removing heavy metals like mercury and nasty PCBs, but it's a scorched-earth policy for natural vitamins.
High heat and chemical solvents often strip away the naturally occurring Vitamin D.
Manufacturers then have a choice. They can leave the oil "naked," or they can add synthetic Vitamin D3 (cholecalciferol) back into the mix. If you see "Vitamin D3" listed on the "Other Ingredients" part of the label, it wasn't there to begin with. It was added in a lab. Is that a bad thing? Not necessarily, but it means you're basically taking a multi-vitamin, not a "whole food" supplement.
Real-world numbers: What’s actually in the bottle?
Let's look at some specific brands to see how much vitamin d is in fish oil capsules across the board.
Take Nordic Naturals, a brand most people trust. Their standard "Ultimate Omega" has 0mg of Vitamin D. Zero. If you want the version with D, you have to buy the specific "Ultimate Omega+D3" bottle. In that version, they’ve added 1,000 IU.
Then you have Carlson Cod Liver Oil capsules. These are the old-school choice. Usually, you'll find about 80 IU to 100 IU per softgel.
See the gap?
It's massive. We are talking about the difference between getting a tiny "maintenance" dose and getting a therapeutic dose that actually moves the needle on your blood tests.
The Vitamin A Danger Zone
I mentioned this briefly, but it deserves a deeper look. If you decide to use cod liver oil as your primary source of Vitamin D, you are playing a risky game with Vitamin A.
Fish livers are incredibly high in preformed Vitamin A (retinol). Unlike the beta-carotene in carrots, your body can't easily pee out excess retinol. It builds up in your fat cells. If you start popping 10 fish oil capsules a day to get your "D," you might hit levels of Vitamin A that cause headaches, joint pain, or even liver damage over time.
It’s just inefficient.
Most modern nutritionists, like Dr. Rhonda Patrick or the folks over at the Mayo Clinic, generally suggest keeping your Omega-3s and your Vitamin D separate. It gives you more control. You can take a high-potency D3 drop (like 2,000 or 5,000 IU) and a high-quality fish oil without worrying about the ratios being all out of whack.
💡 You might also like: Linden Oaks Hospital Naperville IL: What Most People Get Wrong About Mental Health Stays
How to read the label like a pro
Don't just look at the front of the bottle. The front is marketing. The back is the law.
- Check the Supplement Facts panel. Look specifically for "Vitamin D." If it’s not listed there with a % Daily Value, it’s not in there.
- Look for the source. "Fish body oil" = No Vitamin D. "Cod liver oil" = Some Vitamin D.
- Check the form. If it says "as Cholecalciferol," it's been added manually.
- The "IU" vs "mcg" trap. New labels use micrograms (mcg). 400 IU is 10 mcg. 1,000 IU is 25 mcg. Don't let the smaller numbers fool you into thinking the dose is lower than it used to be.
Why some people swear by the "natural" D in fish oil
There is a small but vocal group in the keto and carnivore communities who argue that the Vitamin D found naturally in fermented cod liver oil is superior. They claim that because it’s bound to natural co-factors and fats, your body absorbs it better.
While food-based vitamins are generally great, the sheer volume of fish oil you’d need to consume to fix a clinical deficiency is just impractical for most people. Plus, fermented oils can be incredibly expensive and, honestly, taste like something that's been sitting in a sun-drenched tackle box.
Absorption and the "Fat" Factor
If you are taking a fish oil capsule that has Vitamin D added to it, there is one major benefit: absorption.
Vitamin D is fat-soluble. It needs fat to get across the intestinal wall and into your bloodstream. By putting the Vitamin D directly into an oil-filled capsule, the manufacturer has basically built a "delivery vehicle" for the vitamin. This is why many people see their levels rise faster when taking a D3/Fish Oil combo versus taking a dry Vitamin D tablet on an empty stomach.
If you take a dry pill with just a glass of water, you might only absorb half of what’s on the label.
The Verdict on Your Daily Routine
Stop assuming your fish oil is doing double duty.
🔗 Read more: Yoga for a Bigger Bum: Why Most People Are Doing the Wrong Poses
Unless your bottle specifically screams "WITH VITAMIN D" on the label, you are likely just getting EPA and DHA (the fatty acids). Those are amazing for reducing inflammation and keeping your heart ticking, but they won't help you much when the sun goes down at 4:00 PM in December.
Actionable Steps for Your Next Supplement Run
- Check your current bottle tonight. Flip it over. If Vitamin D isn't in the "Supplement Facts" box, it’s not in the pill.
- Decide on your goal. If you want to fix a deficiency, buy a dedicated Vitamin D3 supplement (2,000-5,000 IU) and take it alongside your fish oil.
- Opt for D3, not D2. D3 is the form your body actually makes from sunlight. It's much more effective at raising your blood levels than the plant-based D2 found in some cheap fortified foods.
- Get a blood test. Don't guess. Ask your doctor for a "25-hydroxy vitamin D" test. It’s the only way to know if your current fish oil regimen is actually working.
- Store it right. Both Omega-3s and Vitamin D are sensitive to light and heat. Keep that bottle in a cool, dark cupboard—not on top of the fridge where the compressor generates heat.
Buying supplements is confusing enough without the hidden math. Now that you know exactly how much vitamin d is in fish oil capsules (or isn't), you can stop wasting money on the wrong bottles and actually give your body what it’s asking for.