Vitamin D is fat-soluble, so every liquid vitamin D product needs an oil to carry it. The oil is not packaging. It is roughly 99% of what is in the bottle, and it is the ingredient you consume the most of.
Most brands use refined sunflower oil or fractionated MCT because both are cheap and taste of nothing. Olive oil costs more. Here is what actually separates them.
DOES THE TYPE OF OIL AFFECT VITAMIN D ABSORPTION?
Being honest about the evidence: the presence of fat clearly matters, and the specific type of fat is not well established.
The fat effect is solid. A 2010 study in the Journal of Bone and Mineral Research found that taking vitamin D with the largest meal of the day raised blood levels by about 50% compared with taking it on an empty stomach. That is why an oil-based form has a real advantage over a dry tablet, which is why vitamin D needs fat to be absorbed.
Direct head-to-head trials between carrier oils are thin. Any brand claiming their particular oil absorbs meaningfully better than another is ahead of the data. So the question worth asking is not which oil absorbs best. It is which oil is best to be swallowing every day for years.
| Extra virgin olive oil | MCT oil | Refined sunflower oil | |
|---|---|---|---|
| Processing | Cold-pressed, unrefined | Fractionated from coconut or palm | Chemically refined, often deodorised |
| Dominant fat | Oleic acid, monounsaturated | Medium-chain saturated | Linoleic acid, polyunsaturated |
| Oxidative stability | High, protected by natural polyphenols and vitamin E | High, little to oxidise | Lower, polyunsaturated fats oxidise more readily |
| Anything else in it | Polyphenols, vitamin E, oleocanthal | Essentially nothing | Essentially nothing |
| Cost | Highest | Moderate | Lowest |
WHY IS OLIVE OIL USED IN SUPPLEMENTS?
Because it does two jobs at once, and the second one is the reason it is worth the cost.
The first job is carrying the vitamin, which any fat can do. The second is protecting it. Extra virgin olive oil contains naturally occurring polyphenols and vitamin E, which are antioxidants. They are why olive oil resists going rancid better than most seed oils, and that same antioxidant capacity works inside the bottle.
Vitamin D degrades with exposure to oxygen and light. An oil that is naturally resistant to oxidation is not just a nicer carrier, it helps keep the thing it is carrying intact. Refined oils have had most of those protective compounds stripped out during processing, which is why they often need synthetic stabilisers added back in.
The oil is 99% of what is in the bottle. It is worth knowing which one.
IS DRINKING OLIVE OIL ACTUALLY GOOD FOR YOU?
The morning olive oil shot is having a moment, and unlike most wellness trends there is a real body of research behind olive oil itself.
Extra virgin olive oil is the defining fat of the Mediterranean diet, which is among the most studied dietary patterns in existence. Its polyphenols, particularly oleocanthal and hydroxytyrosol, are the compounds most of that research focuses on.
A dropper of oil is not a shot, and nobody should buy a vitamin D supplement for its olive oil content. But if you are going to swallow a fat every morning for years, there is a difference between one with a research literature behind it and one that was fractionated in a factory because it was cheap and tasteless.
WHAT ABOUT MCT OIL?
MCT is a reasonable carrier. It is stable, neutral, and absorbs readily.
The trade-off is that it is a highly processed isolate. MCT oil is fractionated from coconut or palm oil, meaning specific fat chains are separated out and everything else is discarded. That is why it is colourless and tasteless, and it is also why there is nothing else in it. No polyphenols, no vitamin E, no antioxidant capacity of its own.
Some people also find larger amounts of MCT cause digestive upset. At dropper-sized doses this is unlikely to matter.
WHAT ABOUT SUNFLOWER OIL?
It is the most common carrier in cheap vitamin D products, and the least interesting.
Standard sunflower oil is high in linoleic acid, a polyunsaturated fat that is more prone to oxidation than the monounsaturated fat that dominates olive oil. It is almost always refined, meaning heat and solvents have removed the colour, smell, and most of the naturally occurring compounds.
It works as a carrier. It brings nothing else, and it is the least stable of the three.
HOW TO CHECK WHAT IS IN YOUR BOTTLE
Read the other ingredients line. If it says sunflower oil, that is almost certainly refined. If it says olive oil without specifying, it may be refined olive oil rather than extra virgin, which is a meaningfully different product with most of the polyphenols removed.
Also check for what should not be there. Flavourings, sweeteners, colourings, and synthetic preservatives are all common in liquid supplements and all unnecessary in an oil that is stable on its own.
D3X uses organic cold-pressed extra virgin olive oil, and there are three ingredients in the bottle: D3, K2 as MK-7, and the oil. No flavourings, no sweeteners, no added preservatives, because the oil does not need them.* It is in glass rather than plastic for the same reason, since light and oxygen are what degrade both the oil and the vitamin.
If you are comparing liquid vitamin D products, the oil is the ingredient you will consume the most of. It is worth more than a glance.
Sources
Mulligan GB, Licata A. "Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D." Journal of Bone and Mineral Research, 2010.
Dawson-Hughes B, et al. "Dietary fat increases vitamin D-3 absorption." Journal of the Academy of Nutrition and Dietetics, 2015.
Frequently Asked
What is the best carrier oil for vitamin D?
Extra virgin olive oil is the strongest option on the factors that can actually be compared. It is cold-pressed rather than chemically refined, high in monounsaturated oleic acid, and contains natural polyphenols and vitamin E that resist oxidation. MCT and refined sunflower oil work as carriers but contain nothing beyond the fat itself.
Does the type of oil affect vitamin D absorption?
The presence of fat clearly matters. A 2010 study found taking vitamin D with the largest meal raised blood levels by about 50% versus an empty stomach. Direct head-to-head comparisons between specific carrier oils are thin, so claims that one oil absorbs meaningfully better than another are ahead of the evidence.
Why is olive oil used in vitamin D supplements?
It does two jobs. It supplies the fat vitamin D needs to absorb, and its natural polyphenols and vitamin E act as antioxidants that resist oxidation. Vitamin D degrades with exposure to oxygen and light, so a naturally stable oil helps protect what it is carrying.
Is MCT oil or olive oil better for vitamin D?
Both work as carriers. MCT is stable and neutral but is a fractionated isolate with no polyphenols or antioxidant capacity of its own. Extra virgin olive oil is unrefined and retains those compounds, which is the practical difference between the two.
Is sunflower oil bad in supplements?
It is not harmful, it is just the least interesting option. Standard sunflower oil is high in polyunsaturated linoleic acid, which oxidises more readily than the monounsaturated fat in olive oil, and it is almost always refined, removing most naturally occurring compounds.
Is taking a shot of olive oil good for you?
Extra virgin olive oil is the defining fat of the Mediterranean diet and has a substantial research literature behind its polyphenols, particularly oleocanthal and hydroxytyrosol. A dropper of supplement oil is not a shot, but it is a difference worth knowing about when choosing what you swallow daily.
How can you tell if a supplement uses refined or extra virgin olive oil?
Check the other ingredients line. A label saying only olive oil may mean refined olive oil, which has had most polyphenols removed. Extra virgin or cold-pressed should be stated explicitly. Also check for flavourings, sweeteners and synthetic preservatives, which a stable oil does not need.
