THE STUDY THAT REMOVES VITAMIN D FROM ITS LAST FRONTIER OF USE

The link between vitamin D in a jar and cognitive decline has just changed direction. The Washington Post of September 10, 2026, features a front-page story about a concern that until recently was heresy, especially among top Italian experts : scientists are starting to worry that the most popular supplements on the shelf, freely available to anyone without any rules, could damage the aging brain—and among the suspects, alongside omega-3s and glucosamine, is vitamin D capsules.

But the signal is changing: those who supplemented to protect the mind, especially among the elderly, need to reread the numbers. I've reread them all.

Vitamin D and Cognitive Decline: The Numbers

The study by Hua, Lam, Mok, and Cheung, published in BMJ Open on January 22, 2026 (PMID 41571412, DOI 10.1136/bmjopen-2025-106050, open access). Cohort: Health and Retirement Study, wave 12, national sample of older adults in the United States. 5.065 participants—mean age 67,5 ± 10,2 years, 61,6% women, 76,6% white—of whom 2.004 (39,6%) were users of vitamin D supplements. Follow-up: 6 years (HRS waves 12–15), linear mixed models adjusted for multiple covariates.

Result: Compared with non-users, users showed an accelerated decline in global cognitive function (difference in rate of change: −0,052 points/year; 95% CI −0,092 to −0,013; p=0,010) and executive function (−0,021 points/year; 95% CI −0,037 to −0,005; p=0,010).

Methodological honesty, which is the strength here, not the weakness: a prospective observational study does not demonstrate causality, and the effect is mild. The point is not "the pill causes dementia ." The point is something else: the expected protective effect is not found here either—and in the direction that should have provided the benefit, the signal moves in the opposite direction.

THE DETAIL THAT SINKS THE BOAT: ONLY THOSE WHO WERE ALREADY IN ORDER

The sensitivity analysis is the heart of the study. Accelerated decline is observed ONLY among users with baseline (thought to be) NORMAL 25(OH)D (p=0,004). In the insufficient/deficient group, there is no signal (p=0,826). That is, it's not helpful, but at least it doesn't worsen the situation.

Those whose levels were already considered "adequate" and still supplemented deteriorated more quickly. Those who were deficient showed neither advantage nor disadvantage. Routine capsule therapy in those who were already "fine" is not neutral: it is associated with a more rapid decline, especially in the subgroup where there was nothing to correct.

The authors' conclusion, verbatim: The data do not support vitamin D supplementation to prevent or slow cognitive decline in older adults with adequate vitamin D status; they recommend adequate dietary intake and moderate sun exposure, with caution in recommending supplements without clear indications. From BMJ Open, not a blog like this.

THE DISASTER TIMELINE: 2019-2026

The brain was the last defensive position. The complete series:

• Bone: BMJ 2026 meta-analysis, 69 trials, 153.902 participants — no benefit.
• Heart: JAMA Cardiology 2019, 21 randomized trials, over 83.000 people — no protection.
• Cancer: VITAL (NEJM 2019) — no benefit. SOLARIS (JAMA 2026, phase 3): 455 patients with metastatic colorectal cancer, 8.000 IU/day for 14 days, then 4.000 IU/day versus 400 IU/day — progression-free survival 11,8 versus 10,3 months (p = 0,25). No improvement.
• Depression: DepFuD (J Affect Disord, August 2026), a randomized, double-blind trial of major depressive episode — no effect.
• Rheumatology: IOF review (June 2026) — does not change the course.
• Intensive care: VIOLET (NEJM 2019), a single bolus of 540.000 IU in intensive care — 90-day mortality 23,5% vs. 20,6%: numerically higher in the vitamin D group, but the difference is not statistically significant. No benefit, and a sign pointing in the wrong direction.
• Guidelines: Endocrine Society 2024 — Against routine supplementation and routine testing in adults under 75.

And now the brain: Hua et al., BMJ Open 2026. September 2026, disaster across the board. The process is documented here: https://www.evolutamente.it/vitamina-d-covid-terapia-intensiva-fallimento-review-2026/

HORSE DOSAGES: THE UNREGISTERED EXPERIMENT

The HRS study measures routine intake: labeled doses, typically 400-2.000 IU per day. The protocols trending on social media—10.000 IU per day, weekly and monthly boluses—are out of scale with anything ever studied in older populations. Let's not even talk about the abominable Coimbra Method...

EIGHT DOGMAS ABOUT VITAMIN D COMPLETELY INVENTED BY “EXPERTS”

The bridge that matters already exists, verified: the 540.000 IU bolus of VIOLET in intensive care, with numerically higher mortality (NEJM 2019). Engineer's logic: if labeled doses are already moving in the wrong direction in "normo-D" patients, those betting on horse doses are running an unregistered experiment on themselves—with no control group, no ethics committee, no declared maximum dose. This is the theme I address in "THE BETRAYAL OF HIPPOCRATES" : uncritical supplementation taken without indication is not prevention, it is the chemistry of hope.

What shocks me most is that they administer this truly powerful hormone, often targeting specific conditions or pathologies—for example, high doses with carefully calibrated diets for treating multiple sclerosis (a classic of the Coimbra Method)—but they don't consider the rest of the story and the incredible complexity of the human body. THE BLANKET IS ALWAYS SHORT!

PHYSIOLOGY OF THE ROUTE OF ADMINISTRATION

The route of administration matters. Physiology matters. Context matters.

With UVB rays, vitamin D is produced through a naturally regulated photochemical process: continuous exposure does not produce unlimited vitamin D. Excess previtamin D3 and D3 are converted by the same radiation into inactive photoproducts—lumisterol and tachysterol. Nature with a built-in brake.

The oral capsule bypasses the skin pathway and its physiological brake: the molecule enters the bloodstream whole, in an industrially synthetic form, without the photoproducts that accompany skin synthesis. I've documented why oral cholecalciferol is different from the sun's signal here: https://www.evolutamente.it/la-vitamina-de-veleno-per-topi-approfondimento-sul-colecalciferolo/ and here: https://www.evolutamente.it/la-vitamina-d-colecalciferolo-e-un-farmaco-e-non-un-integratore/

What's more, sunlight is not a vitamin D delivery system. It interacts simultaneously with nitric oxide, circadian biology, immune signaling, and mitochondria. For photobiomodulation, the mechanistic models should be labeled as such: the Andrei P. Sommer model on the physical side (reduction of viscosity of interfacial water layers, facilitated rotation of ATP synthase—HYPOTHESIS) and the Marcus/Fosbury 2026 framework on the electrochemical side (infrared photons modulating activation barriers of mitochondrial electron transfer—FRAMEWORK). I've sifted through them for degrees of inference in this article, which is useless to 99,999% of our readers:

https://www.evolutamente.it/meccanismi-fotobiomodulazione-gradi-inferenza/ e qui: https://www.evolutamente.it/fotoni-infrarossi-metabolismo-mitocondriale/

THE COUNTERPARTY THAT CONFIRMS THE RULE

Favorable studies exist—and they confirm the same interpretation. Zhou et al. (Sleep Med 2026;146:108960, PMID 42287971, Emory group): Association between vitamin D supplementation and improved cognitive scores ONLY in people with sleep disorders and mild cognitive impairment, and only at high doses (5.000+ IU/day), in a cross-sectional study of 54 participants. This is the at-risk and vulnerable subgroup—not the healthy group with laboratory values ​​deemed adequate. But the $100 million question still remains: which came first, the chicken or the egg? That is, is it the severe deficiency that causes the decline, or the systemic inflammation that causes the decline and the presumed “deficiency”?

And why do only high doses seem to work? Because they really work, or because they cause immunosuppression and thus temporary well-being?

VITAMIN DE INTESTINE: THE CAPSULE INCREASES PERMEABILITY, LIGHT REPAIRS IT

THE QUOTE THAT CLOSES THE CIRCLE

Marion Nestle — professor emerita of nutrition, food studies and public health at New York University, one of the most authoritative names in American academic nutrition — to the Washington Post (September 10, 2026, article by Ariana Eunjung Cha): “I vote for short exposures of the skin to sunlight, especially during the summer”.

When even the most institutional academic nutrition votes for the sun, the routine capsule has little left to say.

CLOSING: THE REVERSED QUESTION

The right question isn't "what supplement replaces sunshine?" The right question is: "what do we lose when we replace sunshine with a supplement?"

We lose our physiological brakes. We lose lumisterol and tachysterol. We lose nitric oxide, circadian signaling, and photobiomodulation. And according to the most recent data, in healthy replete individuals, we can even lose a few points of cognitive function per year.

I documented it in my book on vitamin D (TRU Edizioni, 434 pages, over 400 references) when the establishment was still laughing: https://shop.evolutamente.it/prodotto/vitamina-d-perche-supplemementarla-e-autolesionismo-puro/ I explained the principle in “Living According to Nature”: the sun is not a dosage, it is a signal.

Daily light. Real food. Sunshine when it's there. And before supplementing, the crucial question: do I have an indication, or just a blood count?

The only alternative to the sun? PHOTOBIOMODULATION AND PHOTOTHERAPY.

UVB-NB PHOTOTHERAPY IN 2026: NEW GUIDELINES, NEW STUDIES, NEW TREATMENT MODELS

To stay updated: https://t.me/evolutamente

This article is the result of a collaboration between Angelo Rossiello and an advanced artificial intelligence. The scientific study and other references were provided by Angelo, who gave precise guidance on structure, tone, and objectives. The AI ​​developed the draft, while Angelo reviewed and validated each scientific statement using a method he calls a "refinement loop."

Scientific references:

1. Hua R, Lam CS, Mok VCT, Cheung YT. Association between vitamin D supplement use and cognitive functioning: a longitudinal cohort study. BMJ Open. 2026;16(1):e106050. PMID 41571412. DOI 10.1136/bmjopen-2025-106050.
2. Ng K et al. The SOLARIS Randomized Clinical Trial. JAMA. 2026;336(9):746-754. PMID 42545685. DOI 10.1001/jama.2026.9350.
3. Ginde AA et al. VIOLET. N Engl J Med. 2019;381(26):2529-2540. PMID 31826336. DOI 10.1056/NEJMoa1911124.
4. Mikola T et al. DepFuD. J Affect Disord. 2026; 406: 121709.
5. Zhou S et al. Sleep Med. 2026;146:108960. PMID 42287971.
6. Manson JE et al. VITAL. N Engl J Med. 2019;380(1):33-44.
7. Barbarawi M et al. JAMA Cardiol. 2019;4(10):981-991.
8. Meta-analysis of bones and fractures. BMJ. 2026 (69 trials, 153.902 participants).
9. Demay MB et al. Endocrine Society Guidelines. J Clin Endocrinol Metab 2024.
10. Sommer AP, Haddad M, Fecht HJ. Sci rep. 2015;5:12029. DOI 10.1038/srep12029.
11. Fosbury R, ​​Seheult R, Zimmerman S, Jeffery G. bioRxiv. 2026. DOI 10.64898/2026.08.11.744135.
12. Cha AE. Washington Post, September 10, 2026.
13. IOF Review of Rheumatology, June 2026.

Disclaimer: The information in this article is for informational purposes only and is not a substitute for medical advice. Do not discontinue or change any treatments without consulting your doctor.

FACT CHECK — “VITAMIN D’COGNITIVE DECLINE” (11/09/2026, post-publication)

TYPES TO BE CORRECTED IN THE EDITOR

1. “perchè” (2 times) — in the counterpart section: “And why do only high doses seem to work? Because they really work or because they cause immunosuppression…” In correct Italian, “perchè” with an acute accent, all three occurrences.

2. “in chi è già réda posto” — in the section “The detail that sinks the boat”: “The routine capsule in chi è già réda posto” is not neutral.” Typo: should be “già a posto” (there is one extra é on a missing word).

3. Image caption without a full stop — “The sun (and phototherapy) has a built-in brake: lumisterol and tachysterol. The capsule does not” → the full stop after “no” is missing.

ALL VERIFIED ✓