Micronutrients I: Fat-Soluble Vitamins & Major Minerals

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1. Introduction

Fat-soluble vitamins (A, D, E, K) and the major minerals (calcium, magnesium, phosphorus) share a biology that distinguishes them sharply from the water-soluble vitamins covered elsewhere in this course: they are absorbed with dietary lipid, transported in lipoproteins or bound proteins, stored in adipose tissue, liver, and bone in quantities that can last weeks to years, and cleared slowly. This storage capacity is a double-edged pharmacologic property. It buffers against transient dietary shortfall, but it also means toxicity is a real and recurring clinical concern — unlike vitamin C or the B-complex, one cannot simply "flush out" excess vitamin A or D in the urine.

This module is also a case study in one of the central lessons of Module 01: the frequent failure of large, well-conducted supplementation RCTs to reproduce the benefits suggested by observational cohorts. Low vitamin D predicts fracture, cancer, and cardiovascular death in cohort after cohort — yet the VITAL and D-Health mega-trials found no significant reduction in these hard endpoints from supplementing generally replete adults [5][7]. Vitamin E looked like a cardioprotective antioxidant in the 1990s; large RCTs instead showed no cardiovascular benefit and, in some analyses, harm signals. Calcium supplements build bone mineral density on a DEXA scan but carry an unresolved signal for excess cardiovascular events [9][23]. Students should leave this module able to explain why the mechanistic story and the trial data diverge for these nutrients, and to counsel patients accordingly — with calibrated confidence, not reflexive supplementation.

2. Learning Objectives

By the end of this module, the learner will be able to:

1. Describe the molecular mechanisms by which retinoic acid, calcitriol, and vitamin K–dependent γ-carboxylation regulate gene transcription, immune function, coagulation, and mineral metabolism.
2. Explain the hormonal loop (PTH–calcitriol–FGF23–calcitonin) that maintains calcium and phosphate homeostasis, and identify the causes and clinical features of hypo- and hypercalcemia.
3. Summarize the deficiency syndromes (xerophthalmia, rickets/osteomalacia, vitamin K deficiency bleeding, hypomagnesemia) and the toxicity syndromes (hypervitaminosis A, hypervitaminosis D, vitamin K–warfarin interaction) associated with each nutrient.
4. Critically appraise the major supplementation RCTs (VITAL, D-Health, ATBC/SELECT/HOPE-type vitamin E trials, calcium/vitamin D fracture trials) and explain why they frequently fail to replicate observational associations.
5. Apply current, contested thresholds for vitamin D sufficiency and the rationale for targeted rather than universal screening.
6. Formulate practical clinical recommendations — dosing, monitoring, and drug interactions (notably warfarin–vitamin K) — for each nutrient, including when supplementation is not indicated.

3. Scientific Foundations

3.1 Vitamin A: retinoid signaling, vision, immunity, and toxicity

Vitamin A's active metabolite, all-trans retinoic acid (ATRA), functions as a hormone-like transcriptional regulator. It binds nuclear retinoic acid receptors (RARα/β/γ), which heterodimerize with retinoid X receptors (RXR) and bind retinoic acid response elements (RAREs) in target-gene promoters, remodeling chromatin by displacing histone deacetylases and increasing activating H3K27 acetylation marks [1]. Cellular uptake is self-regulated through the receptor STRA6, which is up- or down-regulated by retinoic acid signaling itself — a homeostatic "rheostat" that buffers against both deficiency and toxicity at the cellular level [3].

In vision, 11-cis-retinal complexes with opsin to form rhodopsin in retinal rod cells; light-induced isomerization to all-trans-retinal triggers the phototransduction cascade underlying low-light (scotopic) vision — the physiological basis of the classic finding that deficiency first manifests as night blindness.

In immunity, ATRA is central to mucosal tolerance and antimicrobial defense: it promotes differentiation of Foxp3⁺ regulatory T cells while antagonizing pro-inflammatory Th17 cells, induces gut-homing receptors (CCR9, α4β7 integrin) that direct lymphocytes to intestinal mucosa, drives IgA class-switching in B cells, and stimulates IL-22/IL-17–mediated epithelial barrier repair [1][2]. This explains the clinical link between vitamin A deficiency and increased severity of measles, diarrheal disease, and pneumonia in children [4].

Deficiency remains a major global health problem. Cross-sectional data show marginal or frank deficiency in up to 38.9% of young children in some populations (65.9% in infants specifically), and deficiency is a strong predictor of childhood mortality, chiefly through immune compromise [4]. The classic ocular progression is night blindness → conjunctival/corneal xerosis (xerophthalmia) → Bitot's spots → corneal ulceration → irreversible blindness; in high-resource settings, deficiency is now more often secondary to cirrhosis, malabsorption/bariatric surgery, or pancreatic insufficiency, and is frequently underdiagnosed [4].

Toxicity is equally important to teach because preformed vitamin A (retinyl esters, found in animal liver and many supplements) is stored efficiently and toxicity thresholds are far lower than commonly assumed. Chronic intake above the tolerable upper intake level (roughly 3,000 µg RAE/day in adults) causes hepatotoxicity and hepatosplenomegaly, and patients with pre-existing hepatitis or those on dialysis can develop toxicity at doses as low as ~7,500 µg RAE/day [11]. Excess retinoic acid signaling stimulates osteoclastic bone resorption while suppressing osteoblastogenesis, producing cortical thinning and increased fracture risk [11]. Most critically, vitamin A is teratogenic: intake above roughly 3,000 µg RAE/day in pregnancy is linked to cranial–neural crest and urogenital/renal malformations, and topical retinoids are contraindicated in pregnancy [6].

3.2 Vitamin D: synthesis, VDR signaling, and the mega-trial era

Vitamin D3 (cholecalciferol) is synthesized in skin keratinocytes from 7-dehydrocholesterol under UVB radiation, or obtained from diet as D3 or D2 (ergocalciferol) [8]. It is a prohormone requiring two sequential hydroxylations: hepatic CYP2R1/CYP27A1 converts it to 25-hydroxyvitamin D [25(OH)D] — the long-half-life storage form used clinically to assess status — and renal CYP27B1 (1α-hydroxylase) converts this to the active hormone calcitriol [1,25(OH)2D], a step tightly controlled by PTH, FGF23, and serum calcium/phosphate [8]. Calcitriol binds the nuclear vitamin D receptor (VDR), heterodimerizes with RXR, and regulates over 1,000 target genes via vitamin D response elements, chiefly increasing intestinal calcium and phosphate absorption and enabling bone mineralization [8]. CYP24A1 catabolizes active vitamin D to water-soluble calcitroic acid, preventing toxic accumulation; loss-of-function CYP24A1 mutations cause a rare hypercalcemic syndrome [12].

Beyond the skeleton, essentially all immune cells express VDR and CYP27B1, allowing local, autocrine activation of vitamin D that induces antimicrobial peptides (cathelicidin, defensins), promotes autophagy-mediated pathogen clearance, and shifts adaptive immunity toward a Treg-dominant, tolerogenic phenotype while suppressing Th1/Th17 responses [24][25]. This mechanistic plausibility underlies decades of observational association between low vitamin D and autoimmune disease, respiratory infection, and severe COVID-19 outcomes [26].

The single most important teaching point of this section is the mega-trial disconnect. The VITAL trial (25,871 US adults, 2,000 IU/day D3) found no significant reduction in overall cancer incidence, cardiovascular events, falls, or fractures, though a secondary analysis suggested reduced advanced cancer incidence in normal-weight participants [13][14][19]. D-Health and DO-HEALTH similarly found no fracture benefit, even in participants with low baseline 25(OH)D — supporting a "threshold" model in which vitamin D is permissive for bone mineralization up to roughly 20 ng/mL but confers no additional skeletal benefit above it [7][16]. All-cause mortality was unaffected in VITAL and D-Health, but UK Biobank–based trial emulation restricted to participants with genuinely low baseline 25(OH)D found substantial mortality reduction, suggesting these mega-trials were underpowered because most enrollees were already replete [15].

3.3 Vitamin E: antioxidant chemistry and the prevention-trial disappointment

α-Tocopherol is the biologically dominant form of vitamin E and functions as a lipid-soluble, chain-breaking antioxidant embedded in cell membrane phospholipid bilayers, donating electrons to lipid peroxyl radicals to terminate the propagation phase of lipid peroxidation [17][18]. Recent biophysical work suggests α-tocopherol's low membrane concentration is compensated by aromatic amino acid side chains on membrane proteins, which scavenge peroxyl radicals and are then regenerated by tocopherol — an antioxidant relay rather than a simple stoichiometric scavenger [20]. Vitamin E is regenerated in turn by vitamin C, linking the two antioxidant systems [17].

Despite this coherent mechanism, and an early signal from the ATBC study suggesting reduced prostate cancer incidence with vitamin E in male smokers, the confirmatory SELECT trial found no significant protective effect of vitamin E (or selenium) on prostate cancer incidence, and other RCT and cohort data in the same review found no significant effect of vitamin E on prostate cancer risk [21]. HOPE and HOPE-TOO–type cardiovascular prevention trials likewise failed to show reduced myocardial infarction or stroke with vitamin E supplementation. High-dose supplementation (typically >400 IU/day) has been linked in some meta-analyses to increased all-cause mortality and hemorrhagic stroke, plausibly related to vitamin E's antiplatelet effect, which also raises bleeding risk when combined with anticoagulants [18].

3.4 Vitamin K: K1 versus K2, coagulation, and the calcification hypothesis

Vitamin K exists mainly as phylloquinone (K1), from green leafy vegetables, and menaquinones (K2, e.g., MK-7), from fermented foods and bacterial synthesis. Both are essential cofactors for the enzyme γ-glutamyl carboxylase, which carboxylates glutamate residues on vitamin K–dependent proteins, enabling calcium binding [10]. In the liver, this activates the pro-coagulant clotting factors II (prothrombin), VII, IX, and X, as well as the anticoagulant regulators protein C and protein S [10]. Warfarin is a vitamin K antagonist: it inhibits vitamin K epoxide reductase complex 1 (VKORC1), blocking the recycling of vitamin K epoxide back to its active reduced form and thereby depleting functional clotting factors; roughly 30–40% of inter-patient variability in warfarin dosing is explained by CYP2C9 and VKORC1 genetic polymorphisms [10]. Dietary vitamin K spikes (leafy greens, fortified nutritional shakes) or herbal interactions (e.g., hibiscus tea) can destabilize INR control in either direction [10].

Outside the liver, γ-carboxylation activates two extrahepatic proteins central to the bone–vascular calcification hypothesis: osteocalcin, produced by osteoblasts, which requires carboxylation to bind bone mineral and promote proper mineralization; and matrix Gla protein (MGP), which inhibits ectopic calcium-phosphate deposition in blood vessels and requires carboxylation to prevent vascular and lung elastin calcification [22][27]. This mechanistic link — undercarboxylated MGP correlating with lower vitamin K status, more severe arterial and lung calcification — has motivated the hypothesis that vitamin K2 supplementation could simultaneously improve bone density and slow vascular calcification, and observational data support the association [27][28]. Clinical outcome trial evidence for K2 supplementation, however, remains preliminary and heterogeneous.

3.5 Calcium homeostasis and dysregulation

Serum ionized calcium is defended within a narrow range by a three-hormone system. Falling calcium triggers PTH release, which mobilizes calcium from bone via osteoclast activation, increases renal calcium reabsorption, decreases renal phosphate reabsorption, and upregulates renal CYP27B1 to generate more calcitriol [30]. Calcitriol increases intestinal calcium and phosphate absorption and provides negative feedback on PTH secretion [30]. Calcitonin, from thyroid C-cells, is a minor counter-regulatory hormone released in response to hypercalcemia that inhibits osteoclastic resorption [30]. Hypocalcemia commonly results from vitamin D deficiency (rickets in children, osteomalacia in adults), hypoparathyroidism (post-surgical being most common), CKD, or hypomagnesemia, and presents with neuromuscular irritability, tetany, and in children, skeletal deformity [30]. Hypercalcemia most often reflects primary hyperparathyroidism or malignancy, but granulomatous disease (sarcoidosis) and rare CYP24A1 loss-of-function mutations cause vitamin D–mediated hypercalcemia through unregulated calcitriol production; clinical features include nephrolithiasis, nephrocalcinosis, polyuria, and — with sustained elevation — vascular and basal ganglia calcification [12][30].

3.6 Magnesium

Magnesium is a cofactor for hundreds of enzymatic reactions, including ATP-dependent processes and the activation of vitamin D itself. Chronic latent magnesium deficiency is common and under-recognized — NHANES-based reference data suggest a substantial fraction of US adults, particularly those with diabetes, hypertension, or CKD, run below optimal serum magnesium [31][32]. Deficiency is mechanistically linked to endothelial dysfunction, coronary vasospasm, insulin resistance, and arrhythmia, and observational cohorts associate low magnesium with heart failure, stroke, and mortality [29][33].

3.7 Phosphorus and the CKD–mineral bone disorder axis

Phosphorus, stored predominantly in bone as hydroxyapatite, is essential for skeletal structure and cellular energy metabolism, but its homeostasis is intimately coupled to calcium, PTH, FGF23, and vitamin D [35]. In health, the kidney excretes excess dietary phosphate; in chronic kidney disease, this "gatekeeper" function fails, producing hyperphosphatemia that drives compensatory FGF23 and PTH elevation, suppresses calcitriol synthesis, promotes secondary hyperparathyroidism, and triggers osteogenic reprogramming of vascular smooth muscle cells — the pathophysiologic core of CKD-mineral and bone disorder (CKD-MBD), which links renal failure to both fracture and cardiovascular calcification [35][38]. Modern diets, dominated by inorganic phosphate food additives that are nearly 100% bioavailable (versus ~40–60% for organic phosphate in whole foods), have increased population phosphate exposure independent of protein intake [37].

4. Clinical Relevance

Fat-soluble vitamin and major mineral disorders are common across every specialty a medical student will enter: rickets and vitamin D–deficiency myopathy in pediatrics, warfarin–vitamin K interactions in cardiology and anticoagulation clinics, hypercalcemia workups in endocrinology and oncology, CKD-MBD in nephrology, and vitamin A deficiency in patients with malabsorptive disease or after bariatric surgery. Just as importantly, this is the nutrient class most heavily marketed for supplementation despite the weakest RCT support for hard outcomes in replete, healthy populations — physicians are frequently asked to interpret a patient's "low-normal vitamin D" or defend against unsolicited high-dose vitamin A or E regimens. The capacity to distinguish nutrients with genuine deficiency-driven disease (where repletion clearly helps) from nutrients where population-wide supplementation has been tested and found wanting (vitamin D and CVD/cancer; vitamin E and CVD/cancer; calcium and CVD) is a core clinical competency this module builds.

5. Evidence Review

Established (high confidence):

• Vitamin A deficiency causes xerophthalmia and increases childhood infectious mortality; deficiency remains globally prevalent. AllNutrition evidence_strength: strong, consensus_level: moderate [4].
• Vitamin D undergoes hepatic 25-hydroxylation and renal 1α-hydroxylation to calcitriol, which acts via VDR to govern intestinal calcium/phosphate absorption; this mechanism is well characterized though overall answer confidence was tempered by breadth of extrapolation. evidence_strength: limited, consensus: moderate [8].
• Warfarin antagonizes vitamin K by inhibiting VKORC1, and dietary/herbal vitamin K fluctuations materially affect INR control. evidence_strength: moderate, consensus: mixed [10].
• Chronic excess preformed vitamin A causes hepatotoxicity and increases fracture risk via osteoclast stimulation; vitamin A is teratogenic above ~3,000 µg RAE/day in pregnancy. evidence_strength: strong, consensus: mixed [11][6].
• CKD-MBD guideline-level evidence supports individualized dietary phosphorus/calcium targets and phosphate-binder therapy in pediatric and adult CKD. (guideline, trust 0.912) [38].

Probable:

• Calcium plus vitamin D supplementation produces a statistically significant but clinically small reduction in fracture risk, driven substantially by a single high-risk-population trial; benefit is not clinically meaningful for the general population. evidence_strength (BMJ systematic review): high-trust systematic review, trust 0.892 [9].
• Vitamin D deficiency is associated with increased respiratory infection risk and severity, with supplementation showing benefit concentrated in the severely deficient. evidence_strength: limited, consensus: moderate [26].
• Magnesium repletion modestly lowers blood pressure, particularly in hypomagnesemic or high-cardiometabolic-risk individuals, though hard cardiovascular-event RCT data remain immature. evidence_strength: strong, consensus: moderate [33].

Emerging:

• Vitamin K2/menaquinone effects on vascular calcification and bone quality via matrix Gla protein and osteocalcin carboxylation are mechanistically compelling but lack large outcome RCTs [22][27][28].
• Trial-emulation analyses (UK Biobank) suggesting vitamin D mortality benefit is concentrated in the deficient subgroup, implying prior mega-trials were underpowered by enrolling largely replete participants [15].

Controversial:

• Universal population-wide vitamin D screening versus targeted, risk-based testing/empirical supplementation — current major guidance (2024 Endocrine Society) has moved away from universal screening, but implementation and threshold definitions (20 vs. 30 ng/mL) remain unsettled. evidence_strength: limited, consensus: moderate [16][46].
• Calcium supplementation and cardiovascular risk: some interventional-study reviews report a possible increase in coronary events/myocardial infarction with calcium supplements, while others report no significant cardiovascular signal; consensus is unresolved. evidence_strength on this comparison: moderate, consensus: mixed across reviews [23][9].

Unsupported / overstated:

• That vitamin D, vitamin E, or calcium supplementation in nutritionally replete adults meaningfully reduces cancer, cardiovascular events, or all-cause mortality — VITAL, HOPE-type vitamin E trials, and multiple calcium/vitamin D CVD reviews have not supported this claim despite strong observational associations [13][18][23].

6. Practical Clinical Applications

Vitamin A. Do not supplement empirically in well-nourished patients; reserve for documented deficiency (malabsorption, cirrhosis, bariatric surgery, cystic fibrosis) with ophthalmologic screening if symptomatic [4]. Avoid preformed vitamin A doses near or above the UL (~3,000 µg RAE/day) in reproductive-age women given teratogenicity [6]; prefer β-carotene–rich foods, which are not associated with toxicity due to regulated conversion.

Vitamin D. Favor targeted screening (osteoporosis, malabsorption, CKD, liver disease, corticosteroid use, pregnancy, age >75) over universal testing in healthy adults [16][46]. Empirical supplementation (600–2,000 IU/day depending on risk group) is reasonable without testing in many at-risk populations. Do not promise fracture, cancer, or cardiovascular risk reduction from supplementation in replete adults — set expectations using VITAL/D-Health data [13][7]. Toxicity (25(OH)D >80 ng/mL) requires very high, sustained intake and is almost always iatrogenic [34].

Vitamin E. No role for high-dose supplementation in cardiovascular or cancer prevention; counsel patients against it, and specifically flag bleeding risk with concurrent anticoagulants/antiplatelets [18].

Vitamin K. In patients on warfarin, counsel on consistency rather than avoidance of vitamin K–rich foods; sudden increases or decreases in leafy-green intake, or initiation/discontinuation of high-vitamin-K nutritional supplements, are the actual danger [10]. Hold or adjust vitamin K–antagonist dosing, not dietary vitamin K, when INR drifts from a stable diet.

Calcium. Prioritize dietary calcium; reserve supplements for documented low intake or fracture-risk populations already receiving vitamin D, and pair with a bleeding/cardiovascular-risk conversation given the unresolved CVD signal [23][9]. Target 1,000–1,200 mg/day combined diet plus supplement; avoid supplementation in patients with hypercalciuria or nephrolithiasis history without specialist input.

Magnesium. Consider repletion in hypertension, T2DM, or documented hypomagnesemia (diuretic use, malabsorption, alcohol use disorder); avoid supplementation in CKD without monitoring due to impaired excretion and hypermagnesemia risk [33][36].

Phosphorus. Restrict to 800–1,000 mg/day in CKD stage 3–5 with elevated phosphate/PTH, prioritizing avoidance of inorganic food-additive phosphate over whole-food (organic) phosphate reduction, and balance restriction against adequate protein intake [37][38].

7. Clinical Pearls

• Fat-soluble vitamin toxicity is a storage phenomenon — chronic megadosing, not a single high meal, is the usual mechanism, and the liver (vitamin A) and serum calcium (vitamin D) are the organs to monitor.
• "Vitamin K makes clots" is an oversimplification patients on warfarin often internalize incorrectly — the goal is dietary consistency, not avoidance.
• A hazard ratio for low vitamin D and disease X does not mean supplementing vitamin D prevents disease X; VITAL is the canonical teaching example.
• Calcium supplements without vitamin D are largely ineffective for fracture prevention; the pairing matters more than either component alone.
• In CKD, phosphate from additives in processed food is nearly 100% absorbed, versus far less from whole foods — the source of phosphorus matters as much as the quantity.

8. Common Misconceptions

• "Fat-soluble vitamins can't be toxic like drugs." They clearly can — hypervitaminosis A and D are well-described, dose-dependent, and can be severe or fatal.
• "More vitamin D is always better for bone and heart health." Mega-trial data show a threshold effect for bone and no benefit for cardiovascular outcomes in replete adults, with some evidence of harm (falls, fractures) at high intermittent doses [7][16].
• "Natural K2 supplements are risk-free for anyone." High-dose menaquinone can still interfere with anticoagulation and its cardiovascular outcome evidence remains preliminary [10][27].
• "Calcium supplements are purely protective." The unresolved cardiovascular signal means they are not a "why not just take it" decision, particularly in patients without documented low intake [9][23].
• "Vitamin E is a proven heart-healthy antioxidant." Landmark RCTs refuted this; the mechanistic antioxidant story did not translate to clinical benefit and some analyses show harm [18][21].

9. Summary

Vitamin A, D, E, and K and the major minerals calcium, magnesium, and phosphorus share storage-dependent pharmacokinetics that make both deficiency and toxicity clinically real, and — with the exception of clear deficiency states like xerophthalmia, rickets, and vitamin K deficiency bleeding — this nutrient class exemplifies the recurring failure of large supplementation RCTs to replicate the benefits suggested by observational cohorts. Vitamin A and vitamin D act as nuclear-receptor–binding hormones governing vision, immunity, and mineral metabolism; vitamin E is a membrane antioxidant whose supplementation trials disappointed; vitamin K couples coagulation to bone and vascular calcium handling and interacts critically with warfarin; and calcium, magnesium, and phosphorus are interlocked through the PTH–calcitriol–FGF23 axis, with disruption most severe in chronic kidney disease. The clinical discipline this module builds is to treat documented deficiency confidently, to counsel against unsupported high-dose supplementation, and to communicate honestly that "low-normal" levels of vitamin D, calcium, or vitamin E in an otherwise healthy patient are not, on current mega-trial evidence, a mandate for aggressive repletion.

10. References

Ordered by evidence strength / relevance. Evidence level and AllNutrition trust score (0–1) as returned by the tool.

1. Immunometabolic control of cytokine production by micronutrients in health, aging, and inflammation. Frontiers in Immunology (2026). Review — trust 0.748.
2. Diet Components, Immune Function and IgE-Mediated Food Allergy. Nutrients (2025). Review — trust 0.727.
3. The vitamin rheostat: A unified model of epigenetic feedback in vitamin homeostasis. BBA - Gene Regulatory Mechanisms (2026). Review — trust 0.625.
4. Rethinking Vitamin A Deficiency: Its Causes, Ophthalmologic Presentation, and Management Gaps at a New England Tertiary Hospital. Nutrients (2026). Observational — trust 0.688. (with supporting data from High rate of marginal vitamin A deficiency in children aged 0–6 years in Quanzhou, China, Frontiers in Public Health 2026, observational, trust 0.767)
5. Impact of vitamin D supplementation on all-cause mortality: Randomized trials revisited. Clinical Nutrition (2026). RCT — trust 0.817.
6. Hypervitaminosis: The deleterious effects of vitamins on the skin. Clinics in Dermatology (2026). Review — trust 0.70.
7. Revisiting the Role of Vitamin D in Fracture Prevention in the Era of Mega-Trials. Endocrinology and Metabolism (2026). Review — trust 0.733.
8. Research on Vitamin D Metabolic Regulation in the Pathogenesis of Related Diseases. Frontiers in Endocrinology (2026). Review — trust 0.73.
9. Calcium, vitamin D, or combined supplementation to prevent fractures and falls: systematic review and meta-analysis. The BMJ (2026). Systematic review — trust 0.892.
10. Pharmacological Management of Thrombosis: Current State and Future Strategies (warfarin/VKORC1 mechanism), International Journal of Molecular Sciences (2026), review, trust 0.695; with case reports An Unlikely Culprit of Hospital-Acquired Warfarin Resistance (IMCRJ 2026, observational, trust 0.635) and Possible Interaction Between Hibiscus and Warfarin (Cureus, observational, trust 0.562).
11. Hypervitaminosis: The deleterious effects of vitamins on the skin (chronic vitamin A toxicity, hepatotoxicity, bone). Clinics in Dermatology (2026). Review — trust 0.70.
12. Vitamin D as a cellular endocrine system: Tissue-specific microcircuits, immune reprogramming, and metabolic resistance. iScience (2026). Review — trust 0.777.
13. Vitamin D receptor in tumors: A review of biological mechanisms, therapeutic potentials, and prognostic values (VITAL cancer findings). Critical Reviews in Oncology/Hematology (2026). Review — trust 0.715.
14. Vitamin D Supplementation And Incident Type 2 Diabetes In The Vitamin D And Omega-3 Trial. Journal of the Endocrine Society (2024). Systematic review — trust 0.817.
15. Impact of vitamin D supplementation on all-cause mortality: Randomized trials revisited. Clinical Nutrition (2026). RCT — trust 0.817.
16. The 2024 Endocrine Society Guideline on Vitamin D: Comprehensive Summary and Critical Appraisal. Nutrients (2026). Review — trust 0.695. (with Classical homeostatic physiology sheds light on vitamin D controversies, Trends Endocrinol Metab 2026, review, trust 0.72)
17. The triad of collagen, vitamin C, and vitamin E in aging. Frontiers in Nutrition (2026). Review — trust 0.745.
18. Targeted Supplementation and Nutritional Strategies for Healthy Aging. Current Nutrition Reports (2026). Review — trust 0.833.
19. VITamin D and OmegA-3 TriaL (VITAL): Effects of Vitamin D Supplements on Risk of Falls in the US Population. Journal of Clinical Endocrinology & Metabolism (2020). RCT — trust 0.765.
20. Reaction rate calculations indicate that α-tocopherol primarily acts as a membrane protein antioxidant in vivo. Free Radical Biology and Medicine (2026). Observational — trust 0.688.
21. The role of nutrition in prostate cancer risk, progression, and mortality: A comprehensive review. Clinical Nutrition ESPEN (2026). Review — trust 0.733.
22. Dietary vitamin K intakes, chronic obstructive pulmonary disease, adult asthma, and lung function: a prospective cohort study in the UK Biobank. American Journal of Clinical Nutrition (2026). Observational — trust 0.762.
23. Effects of calcium and vitamin D supplementation on cardiovascular disease outcomes: A review of interventional studies. Trends in Cardiovascular Medicine (2025). Review — trust 0.69. (with Editorial commentary: Calcium/Vitamin D supplements and the heart, Trends Cardiovasc Med 2025, review, trust 0.705)
24. 40 years later: Why do immune cells have vitamin D receptors? Journal of Steroid Biochemistry and Molecular Biology (2026). Review — trust 0.73.
25. Vitamin D–AMP axis in host defense against fungal infections. Frontiers in Nutrition (2026). Review — trust 0.812.
26. Vitamin D in Gut and Systemic Immune Tolerance and in Infections' Risk: An International Evidence-Based Consensus Statement. Reviews in Endocrine and Metabolic Disorders (2026). Review — trust 0.757.
27. Nutritional Support of Chronic Obstructive Pulmonary Disease (vitamin K1/K2, matrix Gla protein). Nutrients (2025). Review — trust 0.812.
28. CRITICAL IMPLICATIONS OF FEMALE BONE METABOLISM IN ORTHOPEDICS: STATE OF THE ART (osteocalcin, magnesium, phosphorus). Journal of ISAKOS (2026). Review — trust 0.73.
29. Hypomagnesemia: A Clinical and Nutritional Update. Current Nutrition Reports (2026). Review — trust 0.73.
30. Surgery for kidney-related hyperparathyroidism: A review (PTH/calcitriol/calcitonin physiology). American Journal of Surgery (2026). Review — trust 0.748. (with Research on Vitamin D Metabolic Regulation in the Pathogenesis of Related Diseases, Front Endocrinol 2026, review, trust 0.73, for hyper-/hypocalcemia etiologies)
31. Serum Magnesium Concentrations in the United States—An Updated Population Reference Interval in Children and Adults. The Journal of Nutrition (2026). Observational — trust 0.802.
32. Association between plasma magnesium levels and glycolipid metabolism in a southern Chinese population. Frontiers in Endocrinology (2026). Observational — trust 0.74.
33. Potential synergistic influence of magnesium and vitamin D supplementation on blood pressure reduction: a narrative review. Nutrition Research (2026). Review — trust 0.675.
34. Vitamin D and skeletal health: Practical approaches for bone health across the lifespan. Current Problems in Pediatric and Adolescent Health Care (2026). Review — trust 0.70.
35. The Effects Of Elevated Phosphate On The Kidney: Damaging The Gatekeeper. Pflügers Archiv - European Journal of Physiology (2026). Review — trust 0.765.
36. Association between low magnesium status and new-onset dementia in the general population: a propensity score-matched cohort study. Frontiers in Nutrition (2026). Observational — trust 0.887.
37. Nutritional Status Evaluation and Intervention in Chronic Kidney Disease Patients: Practical Approach. Nutrients (2025). Review — trust 0.742.
38. Executive Summary of Evidence-Based Guidelines for the Diagnosis and Treatment of Pediatric CKD-Mineral and Bone Disorder (Version 2024). Kidney International Reports (2026). Guideline — trust 0.912.
39. Effects of vitamin and multiple micronutrient supplementation for pregnant and/or lactating women on maternal and infant nutritional status in low- and middle-income countries: a systematic review and meta-analysis. Advances in Nutrition (2025). Systematic review — trust 0.892.
40. Childhood malnutrition, rickets, and anemia: a systematic review and meta-analysis on global prevalence, determinants, and public health implications. Frontiers in Public Health (2026). Systematic review — trust 0.857.
41. Clinical efficacy of different supplemental doses of vitamins A and D in preventing bronchopulmonary dysplasia in preterm infants: A network meta-analysis based on randomized controlled trials. Medicine (2026). Systematic review — trust 0.86.
42. Beyond a Universal Threshold: Reconsidering the Clinical Meaning of Vitamin D Insufficiency. Endocrinology and Metabolism (2026). Review — trust 0.695.
43. Updated perspectives on vitamin D deficiency, screening, supplementation and clinical guidance. Cardiovascular Diabetology – Endocrinology Reports (2026). Review — trust 0.762.
44. Impact of Vitamin D and Calcium on Falls and Fractures in Older Adults. Endocrine Practice (2025). Review — trust 0.742.
45. Vitamin D and calcium supplementation in women undergoing pharmacological management for postmenopausal osteoporosis: a level I of evidence systematic review. European Journal of Medical Research (2025). Systematic review — trust 0.817.
46. Rethinking Vitamin D Deficiency: Controversies and Practical Guidance for Clinical Management. Nutrients (2025). Review — trust 0.73.

Supporting sources also surfaced: Impact of Dietary Patterns on Skeletal Health (Nutrients 2025, systematic review, trust 0.807); Nutrition and Osteoporosis Prevention (Curr Osteoporosis Rep 2024, review, trust 0.705); Endocrine-related osteoporosis: the state of the art (Front Endocrinol 2026, review, trust 0.73); Phosphate-Mediated Regulation of Intracellular Calcium Dynamics (Cells 2026, review, trust 0.695); Calcium, vitamin D, vitamin K2, and magnesium supplementation and skeletal health (Maturitas 2020, review, trust 0.627); Association of vitamin K intake with physical function, handgrip strength, and mortality among U.S. adults (Nutr Res Pract 2026, observational, trust 0.70); Vitamin D as a multisystem regulatory hormone (JSBMB 2026, review, trust 0.748); International Society of Sports Nutrition position stand on dietary antioxidants (JISSN 2026, guideline, trust 0.907).