Vitamin D
25-hydroxyvitamin D — a steroid hormone essential for bone health, immune regulation, and mood.
Optimal Range
40-60 ng/mL (optimal) · 30-100 ng/mL (sufficient)
Risk-Stratified Targets
| Population / Context | Target |
|---|---|
| Optimal (longevity) | 40–60 ng/mL |
| Sufficient | 30–40 ng/mL |
| Insufficient | 20–29 ng/mL |
| DeficientAssociated with increased fracture, infection, and mortality risk | < 20 ng/mL |
| Potentially toxicRisk of hypercalcemia | > 100 ng/mL |
Why It Matters
Vitamin D deficiency affects an estimated 40-50% of adults worldwide and is linked to immune dysfunction, osteoporosis, depression, and increased all-cause mortality. Supplementation is one of the most cost-effective longevity interventions.
Understanding Vitamin D
Despite its name, vitamin D is not technically a vitamin — it is a steroid hormone synthesized in the skin upon exposure to UVB radiation and then activated through two hydroxylation steps in the liver and kidneys. The form measured in blood tests (25-hydroxyvitamin D, or 25(OH)D) reflects your body's total vitamin D stores and is the standard marker for assessing status.
Vitamin D's biological roles extend far beyond calcium absorption and bone health. It modulates over 1,000 genes involved in immune regulation, cell differentiation, inflammation, and apoptosis. Deficiency has been epidemiologically linked to increased risk of autoimmune diseases (multiple sclerosis, type 1 diabetes, rheumatoid arthritis), respiratory infections, cardiovascular disease, depression, and several cancers — though the causal nature of many of these associations is still debated.
An estimated 40–50% of the global population is vitamin D deficient or insufficient. Risk factors include living at high latitudes, dark skin pigmentation (melanin blocks UVB), obesity (vitamin D is sequestered in fat tissue), aging (reduced skin synthesis capacity), and indoor lifestyles. Most adults require 2,000–5,000 IU of vitamin D3 daily to maintain optimal levels, though individual needs vary. Testing every 3–6 months when supplementing allows for dose titration to the 40–60 ng/mL target.
Key Research
Vitamin D Deficiency
Holick MF · N Engl J Med (2007)
Key finding: Comprehensive review establishing vitamin D deficiency as a global pandemic affecting an estimated 1 billion people, with implications for bone health, cancer, autoimmune disease, and cardiovascular disease.