Supplement Comparison
Vitamin D3 vs D2: Does the Form Actually Matter?
We analyzed what 5 longevity experts — Huberman, Attia, Patrick, Johnson, and Hyman — actually say about vitamin d3 (cholecalciferol) vs vitamin d2 (ergocalciferol). Here is where they agree and where they don't.
Strong Consensus
on Vitamin D overall
TL;DR — Vitamin D3 — near-unanimous
Take D3, not D2. Four of 5 experts specifically recommend D3 (cholecalciferol). Hyman goes further: always pair D3 with K2 for proper calcium metabolism. Fortified foods often use the less effective D2.
What Each Expert Actually Takes
Vitamin D3
Includes D3 in his foundational supplementation protocol. Discusses UVB exposure for natural D3 production. Covers vitamin D's role in immune function and circadian rhythm.
Vitamin D3 (with blood monitoring)
Specifically says 'when I say vitamin D, I mean D3' in his bone health episode. Includes D3 in his personal supplement stack, dosed based on blood levels. Most cautious about oversupplementation.
Vitamin D3 (strong advocate)
Most data-driven advocate. Cites study showing 40% lower dementia risk with D3 supplementation. Links deficiency to 5 years of accelerated biological aging. Recommends supplementation for most people.
Vitamin D (included in protocol)
Includes vitamin D in his comprehensive longevity protocol. Addresses it in the context of bone health alongside calcium, protein, and phosphorus.
Vitamin D3 + K2 (always together)
Specifically recommends D3 with K2 for optimal calcium metabolism. Warns that fortified foods use the less effective D2 form. Targets blood levels of 50-80 ng/mL. Has dedicated videos on D3+K2 synergy.
Key Differences
Source
Vitamin D3 (Cholecalciferol)
Animal-derived (lanolin, fish oil) — same form your skin makes from sunlight
Vitamin D2 (Ergocalciferol)
Plant/fungal-derived (irradiated mushrooms, yeast)
Potency
Vitamin D3 (Cholecalciferol)
Raises blood levels more effectively and maintains them longer
Vitamin D2 (Ergocalciferol)
Less effective at raising 25(OH)D levels — shorter half-life
Expert Support
Vitamin D3 (Cholecalciferol)
4 of 5 experts specifically recommend D3. Attia says 'I mean D3'
Vitamin D2 (Ergocalciferol)
No expert recommends D2 over D3. Hyman warns fortified foods use inferior D2
Blood Level Impact
Vitamin D3 (Cholecalciferol)
Sustains blood levels for weeks. Better at achieving target range
Vitamin D2 (Ergocalciferol)
Blood levels drop faster. Less reliable for maintaining optimal range
K2 Pairing
Vitamin D3 (Cholecalciferol)
Hyman recommends always pairing D3 with K2 to direct calcium to bones
Vitamin D2 (Ergocalciferol)
K2 pairing less discussed with D2 since it's not the recommended form
Availability
Vitamin D3 (Cholecalciferol)
Widely available as standalone supplement
Vitamin D2 (Ergocalciferol)
Often used in fortified foods and prescription-strength supplements
What the Experts Said (Direct Quotes)
"Vitamin D is presented as a steroid hormone that regulates a significant portion of the human genome. It plays a role in immune function, blood pressure, and even serotonin production by activating the tryptophan hydroxylase gene."
Essentials: Micronutrients for Health & Longevity | Dr. Rhonda Patrick at 06:13
"Dr. Patrick discusses the critical role of vitamin D as a steroid hormone and the importance of magnesium for DNA repair and cellular energy, noting that many people are deficient in both."
Micronutrients for Health & Longevity | Dr. Rhonda Patrick at 35:45
"The health benefits attributed to high vitamin D levels may actually stem from the active, outdoor lifestyle required to achieve them naturally rather than the supplement itself."
Balancing the benefits and risks of sun exposure at 00:36
"There is debate regarding optimal Vitamin D levels, with cut-offs for deficiency and sufficiency ranging between 30 and 75 nmol/L. Due to the risks of hypervitaminosis and the unreliability of assays, the speakers recommend prioritizing dietary intake and safe sun exposure."
How to optimize your children's bone health through diet, sunlight exposure, and physical activity at 05:36
"A recent study involving over 12,000 people found that vitamin D supplementation was associated with a 40% lower risk of dementia over a decade. After five years, 84% of vitamin D users were dementia-free compared to 68% of non-users."
This Supplement Could Cut Your Dementia Risk By 40% at 00:00
"Trials on individuals with Alzheimer's disease or mild cognitive impairment show that vitamin D supplementation improved cognition, memory, and attention. It also reduced blood biomarkers of amyloid beta pathology."
This Supplement Could Cut Your Dementia Risk By 40% at 03:09
"The first key pillar of bone health is nutrition. Minerals like calcium, phosphorus, magnesium, and vitamin D are essential building blocks."
How Weak Are Your Bones? (Test & Fix) at 01:24
"While sun exposure is beneficial for vitamin D, mood, and circadian rhythm, excessive exposure can damage collagen and elastin, leading to wrinkles and sagging skin."
How To Not Look Old at 00:36
"Optimizing vitamin D can be achieved through diet, sensible sun exposure, or supplementation. While fortified foods exist, they often use the less effective D2 form. Supplementation with D3, ideally with K2, is recommended."
The Truth About Vitamin D & Warning Signs Your Body Is Deficient | Dr. Mark Hyman at 10:07
"Individuals with darker skin tones, those living in northern latitudes, the elderly, obese individuals, and those with chronic illnesses are at higher risk. Most people are advised to consider vitamin D supplementation."
Vitamin D Deficiency? Here's What's Really Happening at 10:45
Bottom Line
Take vitamin D3, not D2. This is one of the clearer form distinctions in supplementation. D3 is the same form your skin produces from sunlight, it raises blood levels more effectively, and it maintains those levels longer than D2. Four of 5 experts explicitly recommend D3. Hyman adds an important nuance: always pair D3 with K2, which directs calcium to your bones rather than allowing it to deposit in your arteries. The common pitfall is relying on fortified foods (milk, cereal), which typically use the less effective D2 form. Get a 25-hydroxy vitamin D blood test, target 50-80 ng/mL (per Patrick and Hyman), and supplement with D3+K2 to fill the gap. Almost everyone living above 35 degrees latitude needs to supplement, especially in winter.
Consensus Protocol — Vitamin D
Dosage
1,000-5,000 IU daily of vitamin D3 depending on baseline levels and body weight. Hyman recommends testing levels and targeting 50-80 ng/mL. Patrick suggests most people need supplementation given widespread deficiency.
Form
Vitamin D3 (cholecalciferol), NOT D2. Hyman specifically recommends D3 with K2 for proper calcium metabolism. Fortified foods often use the less effective D2 form.
Timing
Take with a fat-containing meal for better absorption. Morning or midday preferred — some evidence that evening doses can interfere with melatonin production.
Notes
Get a 25-hydroxy vitamin D blood test before supplementing to establish baseline. Retest after 3 months. Body fat sequesters vitamin D, so higher BMI individuals may need higher doses. Sensible sun exposure (UV index below 3, early morning or late afternoon) is the most efficient way to produce vitamin D but isn't sufficient for most people year-round.
Now you know which form. Get the full protocol.
Exact dosages — what each expert recommends, not just which form
Daily schedule — morning vs evening, what to pair with food, what to separate
Expert watchdog — get alerted when an expert changes their recommendation
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