How Much Vitamin D Should I Take Daily?

There are two influential bodies producing different vitamin D dosing recommendations, which is the source of most online confusion:

The Institute of Medicine (IOM, now NASEM) sets the RDA at 600 IU/day for adults under 70 and 800 IU/day for adults over 70 (Ross et al. 2011). The RDA is designed to prevent overt deficiency disease (rickets, osteomalacia) in 97.5% of healthy individuals, NOT to optimize for the many other vitamin D-modulated outcomes that have emerged since the 1990s.

The Endocrine Society Clinical Practice Guideline (Holick et al. 2011) recommends 1,500-2,000 IU/day for adults to reach "sufficiency" defined as serum 25(OH)D ≥30 ng/mL. This higher target is grounded in the broader vitamin D research base — fracture prevention, immune modulation, cardiovascular markers — which suggests optimal levels lie above the rickets-prevention threshold.

The pragmatic resolution: test your serum level, dose to the Endocrine Society target, and retest.

The standard mistake in vitamin D supplementation is using a generic dose without knowing your baseline. The same 2,000 IU/day could push one person from sufficient to suboptimal-high (40 → 70 ng/mL) and another from deficient to barely-sufficient (12 → 25 ng/mL). The correct dose is whatever brings YOUR serum level into the 30-50 ng/mL target zone.

The variables that drive individual variation: skin pigmentation (melanin reduces UV-driven synthesis), latitude (UVB intensity drops outside ±40°), season (winter months produce minimal endogenous D at high latitudes), BMI (vitamin D is fat-soluble and sequesters in adipose tissue), age (skin synthesis efficiency drops 50%+ by age 70), and absorption efficiency.

The test to order: 25-hydroxyvitamin D (25-OH-D), NOT 1,25-dihydroxyvitamin D. The former is the storage form and the correct marker for sufficiency; the latter is the active hormone form and is tightly homeostatically controlled — it tells you little about your baseline status.

The Endocrine Society Clinical Practice Guideline lays out the repletion + maintenance protocol clearly. Deficient adults respond to 5,000 IU/day over 8-12 weeks (or 50,000 IU weekly under physician supervision); this is the standard repletion course. After serum levels reach 30+ ng/mL, the dose drops to maintenance levels.

The K2 pairing is a research-supported but underappreciated detail. Vitamin D upregulates calcium absorption from the gut, but without adequate K2 (specifically MK-7 menaquinone), the absorbed calcium can deposit in arterial walls and soft tissues rather than bone. Geleijnse et al. in Journal of Nutrition (2004) demonstrated that higher K2 intake associated with reduced coronary calcification. The pragmatic pairing: K2 MK-7 at 90-180 mcg/day when your vitamin D dose exceeds 2,000 IU/day.

See our best time to take vitamin D guide for the timing + fat-absorption protocol that maximizes the bioavailability of whatever dose you settle on.

Vitamin D toxicity is rare but real. The mechanism is hypercalcemia — vitamin D drives calcium absorption, and at sustained very-high serum levels (typically >150 ng/mL), calcium can spill into urine (causing kidney stones), soft tissues, and arteries. The IOM UL of 4,000 IU/day is conservatively set because longer-term safety data thins above that level, not because immediate harm is expected at 5,000-6,000 IU/day.

The 50,000 IU weekly repletion protocol is safe because the dose averages to ~7,000 IU/day — under the acute-toxicity threshold — and is time-limited to 8-12 weeks for actual deficiency correction. It's NOT a maintenance dose.

The single best toxicity safeguard is the same as the optimization safeguard: test your 25(OH)D. If you're between 30-80 ng/mL, you're in the wide safety+efficacy zone. If you cross 100 ng/mL, reduce dose.

The D3-over-D2 finding is unusually clear in the supplement literature. Heaney's 2011 head-to-head trial established that D3 is the more efficient form per IU, and subsequent meta-analyses have replicated this. The mechanism involves differences in binding to vitamin D-binding protein and slower degradation of D3 in circulation.

For vegan users: lichen-derived D3 supplements are now widely available and match the efficacy of standard (lanolin-derived) D3. Look for "vegan D3" or "D3 from lichen" on the label.