Vitamin D blood levels: how much is good, how much is too little

Vitamin D status is measured as serum 25-hydroxy-D3 (25(OH)D). About 70–80% of people in Estonia are deficient in winter. But the "normal range" the lab prints doesn't equal "optimal".

Reference range vs optimal

• < 25 nmol/L (10 ng/mL) — severe deficiency
• 25–50 nmol/L (10–20 ng/mL) — deficiency
• 50–75 nmol/L (20–30 ng/mL) — borderline — labs say "normal", it is NOT optimal
• 75–125 nmol/L (30–50 ng/mL) — optimal (Endocrine Society, Holick 2007)
• > 250 nmol/L (100 ng/mL) — toxicity possible

Why deficiency is the norm in Estonia

Skin only makes vitamin D under UVB (290–315 nm). In Estonia (~59° N) UVB is only sufficient from May to September at midday. October to March, skin produces essentially none.

How much D3 to take

• 25(OH)D < 30 nmol/L — 5000 IU/day for 8–12 weeks, then 2000 IU
• 30–50 nmol/L — 3000 IU/day, retest at 12 weeks
• 50–75 nmol/L — 2000 IU/day
• > 75 nmol/L — 1000–2000 IU/day in winter

D3 + K2 together: why

D increases calcium absorption; K2 (menaquinone) directs calcium from blood into bones and teeth, not arteries. With D doses over 2000 IU, add 100–200 μg K2 (MK-7 form).