We’ve all got bottles of supplements sitting around. Usually vitamin D. Especially if you live in a place where the sun is basically a rumor between October and March. Like the UK.
Here’s the thing though.
Not all Vitamin D is created equal.
Researchers at the University of Surrey dug into the data. Randomized controlled trials. The good stuff. What they found was… awkward. If you’re popping vitamin D2, you might actually be tanking your vitamin D3 levels.
Yes. It drops.
Lower than if you hadn’t taken the pill at all. In many studies, D3 levels in people taking D2 went below the control group. You take the supplement, you lose the natural stuff your skin makes when you catch a few rays. That seems counterintuitive. It feels like drinking saltwater when you’re thirsty.
“This is a previously unknown effect,” Emily Brown, a research fellow at Surrey, told Nutrition Reviews. She didn’t sugarcoat it. D2 reduces D3. So why are we taking D2?
Brown’s advice is practical. Subject to your own gut feelings or specific medical needs, D3 wins. It’s what the body knows. It’s the form sunlight provides. It works.
But it’s not just about levels in the blood.
There’s immune function. A whole different ballgame.
Professor Colin Smith from the same university found something even more specific earlier. D2 and D3 aren’t twins. They don’t do the same job in the same way. Specifically, type I interferon signalling. Sounds like a tech error. It’s not. It’s your body’s first line of defense. The alarm system against viruses and bacteria.
Only D3 triggers it.
“A healthy vitamin D3 status helps prevent viruses from gaining a foothold.”
D2? Not so much. It sits there. Maybe does some other minor thing. But it doesn’t slam that alarm button the way D3 does. Which matters. Because when winter hits, we need every edge we can get.
Professors Cathie Martin from the John Innes Centre points out another wrangle. Access.
If D3 is the better option… well, it’s often derived from animal sources. Lanolin, mostly. From sheep wool. That leaves a lot of people out in the cold. Or at least, the plant-based crowd. Martin stresses the need for plant-based D3 options. We need the supplement that works. Without the ethical compromise.
“Ensuring plant-based vitamin D3 is accessible… is key.”
The Quadram Institute agrees. Professor Martin Warren sees this as a public health emergency. Deficiency is massive across the UK right now. The food we eat isn’t packing the nutrient punch it should be. Fixing it requires better fortification. But also… choosing the right molecule to add.
Using D2 is like bringing a knife to a gunfight.
You’re supplementing. You’re trying to help. But the evidence says you might be undermining the very system you’re trying to support.
So look at your bottle. What does it say? D2? D3?
The science suggests ditching the former. At least for now. Unless you have a specific reason to do otherwise. Otherwise, you’re just moving numbers on a graph in the wrong direction.
Why settle for less effective protection when the better tool is right there?
Maybe we don’t have all the answers yet. Further research is needed. Always. But for now…
Read the label.
