Not all vitamin D is created equal. Some forms work okay, some work great, and one form actually works against you. Here's what you need to know.

We've always known vitamin D2 – the plant-derived vegan form – kinda sucks. And now, thanks to a new study, we know it really sucks. In fact, it may work against you.

As a quick recap, vitamin D3 – the good stuff – is both a nutrient from diet and a compound your body produces when exposed to UVB sunlight (at least when you're younger; natural production declines after 40).

Vitamin D2 is the plant/fungal version of vitamin D. Your body can use D2, but it's less effective at raising and maintaining blood vitamin D levels compared to D3. It also breaks down more quickly in the body. It's often used to "fortify" other foods like plant-based milks, and it's sold as a stand-alone supplement.

Now, thanks to this new study, we know that D2 appears to actually reduce or deplete vitamin D3 levels.

The study

The authors aimed to systematically review and meta-analyze randomized controlled trials to quantify how D2 supplementation affects serum 25(OH)D3 concentrations. Here's what they found:

Between-group end-of-trial difference: D2 supplementation led to a mean reduction in serum 25(OH)D3 of −7.2 ng/mL.

Absolute change over trial: The mean decline was −3.7 ng/mL.

D3, not D2, boosts the type I interferon immune response, which helps fight viruses and bacteria.

How's that happen? One hypothesis is that when total vitamin D concentrations increase via D2, the body might upregulate disposal/metabolic clearance mechanisms – enzymes that degrade 25(OH)D) – which disproportionately reduce D3.

How to use this info

To reap all the physical and mental health benefits of vitamin D, you want your blood levels at 40-70 ng/mL (going by more progressive standards). Taking D2 works against that.

Even taking D3 can be tricky, however. People over 40 have a hard time absorbing and utilizing vitamin D in any form, even from sunlight. Body fat levels and gene variants also affect vitamin D processing.

To guarantee absorption, take microencapsulated D3. This form is manufactured by encapsulating D3 molecules in solid lipid nanoparticles, making it extremely bioavailable. The effects remain constant for up to 14 days, making it superior to conventional D3 supplements.

You can get 5000 IU of microencapsulated D3 in each softgel of D Fix High Absorption Vitamin D (Buy at Amazon).

For more info, check out: Vitamin D: Is there a best time to take It?