What the research found

Researchers observed that supplementing with vitamin D2 (ergocalciferol)—a common, cheaper form found in many over-the-counter products—appeared to reduce circulating levels of vitamin D3 (cholecalciferol), the form your body synthesizes from sun exposure. The mechanism isn't fully spelled out in this summary, but the implication is competitive suppression rather than simple addition of total vitamin D activity. Prior work cited suggests D3 may confer better antiviral and antibacterial immune responses compared to D2, raising the question of whether D2 supplementation could paradoxically weaken immune readiness.

Why it matters for you

If you're tracking vitamin D as a biomarker—and many MyKine users do, especially those managing testosterone, sleep quality, or immune resilience—the form of supplement you choose may matter more than the dose alone. D2 is ubiquitous in fortified foods and budget supplements because it's cheaper to manufacture and has a longer shelf life. But if this finding holds, you could be taking D2 expecting to raise your 25(OH)D level only to inadvertently lower your D3 pool, which might blunt immune adaptation during heavy training blocks or infection exposure. If you're already deficient or running a winter protocol, choosing D3 (cholecalciferol) over D2 may be the more deliberate choice.

Caveats

• Early/preliminary stage: the source doesn't specify study design, sample size, or effect magnitude
• Mechanism unclear: no detail on why D2 suppresses D3, or whether this occurs at all doses
• Immune claims are suggestive, not proven: prior work is cited but not quantified; clinical relevance to infection risk unknown
• No guidance on dosing: unclear whether lower D2 doses or timing relative to sun exposure would alter the effect