Researchers urge consumers to look closely at what type of vitamin D theyre taking
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Vitamin D supplements come in two main types: D2 and D3, and a new meta-analysis finds that taking D2 often lowers blood levels of D3.
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The researchers pooled data from randomized controlled trials and used statistical models to compare D2 supplementation against control conditions.
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On average, D2 supplementation was associated with drops in serum 25-hydroxyvitamin D3 of 9 to 18 nmol/L compared to controls.
Many people take vitamin D supplements especially in winter months or in regions with limited sun to support bone health, immune function, and overall well-being.
However, not all vitamin D is created equal. There are two commonly used forms in supplements: vitamin D2 (ergocalciferol), which is often plant-derived, and vitamin D3 (cholecalciferol), which more closely resembles the form our bodies make when exposed to sunlight.
A new study conducted by researchers from the University of Surrey challenges a long-standing assumption: that you can interchangeably take D2 or D3 and expect the same result. The authors report that supplementing with D2 may actually reduce the levels of D3 in your blood a finding with practical implications for how we choose vitamin D products.
Vitamin D supplements are important, especially between October and March, when our bodies cannot make vitamin D from sunlight in the U.K., researcher Emily Brown, Ph.D. said in a news release.
However, we discovered that vitamin D2 supplements can actually decrease levels of vitamin D3 in the body, which is a previously unknown effect of taking these supplements. This study suggests that subject to personal considerations, vitamin D3 supplements may be more beneficial for most individuals over vitamin D2.
The study
The authors searched for well-designed trials that compared D2 supplementation with control conditions and gathered their data. The trials had to report values for serum 25-hydroxyvitamin D3 (abbreviated 25(OH)D3) either before and after treatment or as changes across the trial.
They used random-effects models (a method in meta-analysis that assumes variation among studies) to calculate weighted mean differences comparing those taking D2 versus those not taking it (control).
The results
The results were consistent and somewhat surprising: D2 supplementation was linked to a drop in D3 levels. Specifically:
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In the end-of-trial comparisons, the D2 groups had, on average, 17.99 nmol/L lower D3 compared to controls, which was statistically highly significant.
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For absolute change (how much each persons D3 shifted over time), D2 supplementation corresponded to an average drop of 9.25 nmol/L.
In many of the included trials, the D3 levels in participants taking D2 dropped below those in the non-supplemented control groups.
The authors suggest that this effect might stem from an inverse relationship between D2 and D3 concentrations: perhaps taking D2 accelerates the breakdown or clearance of D3 in the body.
The team is careful to note that these findings dont prove harm, and they call for further research to see whether D2 and D3 have fundamentally different effects on total vitamin D metabolism and whether one type should be preferred.
Tips on Choosing a Vitamin D Supplement
If you take a daily vitamin D supplement, this research might have you rethinking whats in your bottle. Here are a few simple takeaways to help you make an informed choice:
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Check the label for D3 (cholecalciferol). Both D2 and D3 can raise overall vitamin D levels, but this study suggests that D3 may be more effective at maintaining healthy blood concentrations. Look for vitamin D3 or cholecalciferol on the ingredient list.
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Know where your vitamin D comes from. Vitamin D2 is typically plant-based (often made from mushrooms or yeast), while D3 is usually derived from animal sources like lanolin. If you follow a vegan diet, there are now plant-based D3 options made from algae that can offer a good middle ground.
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Dont overdo it. More isnt necessarily better. The right dose depends on your age, diet, and how much sun exposure you get. Most adults need between 600 and 800 IU daily, but some may require more under medical supervision.
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Ask your health care provider about testing. A simple blood test can show whether your vitamin D levels are low or within the healthy range. That information can help you decide whether supplementation and which form makes sense for you.
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Consistency matters. Vitamin D is fat-soluble, so its best absorbed when taken with a meal that contains healthy fats (like avocado, olive oil, or nuts).
Posted: 2025-10-07 16:39:54
