Vitamin D, an inexpensive supplement the body turns into a hormone governing calcium balance, is taken for long-term health. Its clearest benefits are milder eczema, less menstrual pain, and fewer repeat bouts of head-movement dizziness in those affected. Large trials in people with adequate levels did not show longer life; benefit appears concentrated with low starting levels and steady daily use. The main risk is higher blood and urine calcium. (Full Review)

Protocol

Trial-tested doses

2,000 or 4,000 IU/day

2,000 IU/day in VITAL; 4,000 IU/day or 20,000 IU/week in prediabetes trials

Single versus split dosing

One daily dose

Weekly equivalents also used; monthly or annual boluses performed worse

Form

Vitamin D3

Raises 25(OH)D more than vitamin D2, especially with intermittent dosing

Time to effect

Fewer advanced cancers

About 5 years

Emerged in VITAL with continuous use

Blood level plateau

About 3 months

Given the 15-day half-life of 25(OH)D, on a stable dose

Benefits

High: Reduced atopic dermatitis severity, less menstrual pain in primary dysmenorrhea, fewer recurrences of benign paroxysmal positional vertigo

Medium: Slower progression from prediabetes to type 2 diabetes, lower cancer mortality with daily dosing, reduced depressive symptoms, better sleep quality, improved glycemic control in type 2 diabetes, lower LDL cholesterol, fewer migraine attacks, higher pregnancy and ovulation rates in polycystic ovary syndrome, lower premenstrual syndrome severity, less chronic musculoskeletal pain, lower blood pressure

Low: Lower all-cause mortality, fewer acute respiratory infections, less severe COVID-19 illness, faster sputum clearance in pulmonary tuberculosis, fewer asthma exacerbations, fewer autoimmune diseases, less disease activity in multiple sclerosis and lupus, fewer myocardial infarctions, fewer fractures when combined with calcium, fewer falls in deficiency or with calcium, greater muscle strength, treatment of deficiency and mineral disorders affecting bone, slower cognitive decline and dementia, less irritable bowel syndrome severity, fewer relapses in inflammatory bowel disease, lower pre-eclampsia risk in pregnancy, less chronic urticaria severity

Speculative: Slower biological aging markers, lower systemic inflammation markers, lower liver enzymes in fatty liver disease

Contraindications

Hypercalcemia or hypervitaminosis D (serum calcium above the laboratory upper limit)

Abnormal sensitivity to vitamin D, including CYP24A1 loss-of-function variants

Malabsorption syndromes, for oral ergocalciferol

Granulomatous diseases (sarcoidosis, tuberculosis) and some lymphomas

Pregnancy, at doses above 400 IU/day

Key Interactions

Thiazide diuretics (hydrochlorothiazide)

Mineral oil

Orlistat (Xenical)

Atorvastatin

CYP3A4 inducers (rifampin)

Glucocorticoids (prednisone)

Magnesium supplements

Bile acid sequestrants (cholestyramine)

Active vitamin D analogues (calcitriol)

Digoxin and other digitalis drugs

Bazedoxifene

Theoretical (inferred from mechanism)

Sunlight and UVB tanning lamps

Calcium supplements and calcium carbonate antacids (Tums)

Vitamin K2 (menaquinone-7)

Risk & Side Effects

High: Hypercalcemia and hypercalciuria

Low: Falls and fractures at high or intermittent doses, bone density loss at high daily doses, kidney stones with calcium co-supplementation, vitamin D toxicity from overdosing

Speculative: Vascular and soft-tissue calcification at high doses

Monitoring

Marker	Target	Why
Serum 25(OH)D	40–60 ng/mL (Holick)	Confirms dose response, guards against excess
Serum calcium	8.5–10.2 mg/dL	Safety check; above range pauses dosing
24-hour urine calcium	100–300 mg per 24 hours	Safety check; rising value prompts dose reduction
Serum creatinine	0.6–1.3 mg/dL	Safety check; reduced kidney function changes dose or form
Parathyroid hormone (PTH)	15–65 pg/mL	Falls as deficiency is corrected

Cadence: Baseline 25(OH)D, calcium and creatinine before doses above 2,000 IU/day; repeat at 3 months, then every 6–12 months above 4,000 IU/day and after any dose change; annual at 600–2,000 IU/day is common practice, although the 2024 Endocrine Society guideline suggests against routine testing

Qualitative Assessment

Energy and muscle strength, including new aches or weakness
Mood and sleep quality
Frequency of respiratory infections
Falls or near-falls, especially after any large dose
Thirst, frequent urination, nausea, or constipation, possible signs of hypercalcemia

Vitamin D for Health & Longevity

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment