How much vitamin D should I take per day?

The RDA is 600 IU/day for adults under 70 and 800 IU/day over 70 (IOM 2011), set to maintain bone health in most people. Common maintenance supplementation runs 1000-2000 IU/day, which is what VITAL used (Manson 2019). The tolerable upper intake level (UL) for adults is 4000 IU/day. Doses above the UL should be tied to a measured deficiency and clinician oversight, not taken open-ended.

Is D3 better than D2?

Yes, on the metric that matters. Tripkovic 2012's meta-analysis found D3 (cholecalciferol) raises and sustains serum 25(OH)D more effectively than D2 (ergocalciferol) at equivalent doses. D2 is mainly relevant as a prescription high-dose or vegan option. For raising and holding status, choose D3.

Should I take K2 or magnesium with vitamin D?

The cofactor case is mechanistic, not proven on hard outcomes. Vitamin K2 directs calcium toward bone via carboxylation, and magnesium is a cofactor in vitamin D metabolism. RCTs showing that adding K2 or magnesium to D3 improves clinical endpoints are limited. If your diet is low in K2-rich foods or you are magnesium-insufficient, a combo product is reasonable; it is not a requirement for D3 to work.

Do I need a blood test before supplementing?

It is the only way to dose precisely. The relevant marker is serum 25-hydroxyvitamin D (25-OH-D); a common sufficiency target is 30-50 ng/mL (75-125 nmol/L). Below 20 ng/mL is deficient. A maintenance dose of 1000-2000 IU/day is low-risk without testing, but anyone using higher doses or correcting a suspected deficiency should test, then retest in 8-12 weeks.

Can you take too much vitamin D?

Yes. Toxicity is from supplements, not sun, and presents as hypercalcemia. It generally requires sustained intake well above the 4000 IU/day UL, often 10000 IU/day or more for months, pushing 25-OH-D above ~100 ng/mL (NIH ODS). Symptoms include nausea, kidney stones, and in severe cases renal damage. Staying at or below the UL without a measured deficiency keeps the risk near zero.

Does an oil-based softgel absorb better than a dry capsule or tablet?

Vitamin D is fat-soluble, so an oil-based softgel has a theoretical absorption edge, and most softgels here use olive, coconut, or fish oil. In practice, the difference is small when a dry tablet is taken with a meal containing fat. The practical rule: take whatever form you own alongside food. Form matters less than consistency.

Comparison · ranked· Supplements

Best vitamin D, ranked by cost per 1000 IU

Evidence reviewed·05 sources cited·Dr. Soraya Khan, RDN

Tier B evidence

Vitamin D3 supplements ranked by $/1000 IU of cholecalciferol, with D3-vs-D2, K2/magnesium cofactor notes, and third-party testing status.

Vol. 1Issue 042026-06-22larderlab.com

Educational use only. Larderlab content is educational. Pantry, macro, and supplement guidance is not a substitute for medical advice. Consult a registered dietitian or your physician before making material changes to your diet or supplementation.

DisclosureLarderlab tests and recommends products independently. We sometimes earn a commission when you buy through our links, rankings are decided before the affiliate relationship is checked, not after.

§ 1 · Editor's pick, Best verified-formula $/1000 IU

Confidence: High

Pure Encapsulations Vitamin D3

D3 (cholecalciferol) in a single-ingredient softgel with a short, hypoallergenic excipient list and per-lot third-party testing. The 5000 IU SKU lands near $0.005 per 1000 IU, which is a defensible mid-tier price for a verified, additive-free formula. The honest caveat: the cholecalciferol itself is chemically identical to what is in a $0.002 generic tablet. The premium buys documented purity and a well-sourced carrier oil, not a better molecule or higher absorption. If excipient sensitivity is not a concern, NOW Foods delivers the same active for less.

Check price · Pure EncapsulationsAffiliate link · funds the dose testing

§ 2 · Systems table

Every product, ranked.

9 rows · click to sort

Systems tableDefault sort: rank (editorial). Click any column header to re-sort.

9 rows · click a ▲ header to sort

#				Notes	Confidence
01	NOW Foods Vitamin D-3	Best $/1000 IU	01	D3 (cholecalciferol) in an olive-oil softgel, available 1000-10000 IU. UL-tested and GMP-audited in NOW's own labs. Roughly $0.002 per 1000 IU at the 5000 IU strength. The commodity pick: oil-based delivery, no K2, lowest credible unit cost.	High
02	Kirkland Signature Vitamin D3	Best warehouse value	02	D3 softgels, typically 2000 IU, in a large Costco count. Around $0.002-0.003 per 1000 IU. USP-verified on most lots. Source documentation is thinner than NOW; buy when the USP mark is on the bottle.	High
03	Nature Made Vitamin D3	Best mainstream USP	03	D3 (cholecalciferol) softgel, 1000-5000 IU, USP Verified. Oil-based. About $0.004 per 1000 IU. The shelf-presence pick: pharmacy availability plus the USP stamp at near-budget pricing.	High
04	Doctor's Best Vitamin D3	Budget oil-based	04	D3 in extra-virgin olive oil softgels, 1000-5000 IU. Around $0.003 per 1000 IU. Single ingredient, no K2. Comparable to NOW on price and delivery; choose on whichever is cheaper at purchase.	Medium
05	NatureWise Vitamin D3	Mid-tier oil-based	05	D3 in organic olive oil, 1000-5000 IU, third-party tested. Roughly $0.006 per 1000 IU. Functionally identical to NOW with heavier marketing; the price gap buys branding, not absorption.	Medium
06	Pure Encapsulations Vitamin D3	Best verified-formula	06	D3 softgel, 1000-5000 IU, hypoallergenic excipients, per-lot third-party testing. About $0.005 per 1000 IU. The pick for documented purity and excipient sensitivity, not for raw cost.	Medium
07	Sports Research Vitamin D3 + K2	Best D3/K2 combo	07	5000 IU D3 plus 100 mcg K2 (MK-7) in coconut oil, Informed-tested. Around $0.008 per 1000 IU before allocating cost to the K2. Reasonable if you want both cofactors in one softgel; redundant if you already eat K2-rich foods or take it separately.	Medium
08	Thorne Vitamin D + K2 (liquid)	Adjustable-dose clinical	08	Liquid D3 (1000 IU/drop) with K2 (MK-4), NSF Certified for Sport. Roughly $0.015 per 1000 IU. Pay the premium for drop-level dose titration and anti-doping certification, not for a better molecule.	Medium
09	Carlson Vitamin D3	Premium oil-based	09	D3 in softgels, 1000-5000 IU, third-party tested. About $0.01 per 1000 IU. Quality is solid; the unit cost runs several times NOW for the same cholecalciferol.	Medium

§ 3 · What we'd skip

Named, with the reason.

Nordic Naturals Vitamin D3 (in cod liver oil)

Skip for D3 alone

D3 carried in fish oil, 1000 IU per softgel. Around $0.04 per 1000 IU, the priciest in this set per IU. Reasonable only if you want the omega-3s too; a dedicated fish-oil plus a cheap D3 is more cost-efficient.

Methodology

§ 4 / spec

How this was specified

01Inputs measured: Retail price (dated) · label claim · Certificate of Analysis · third-party test (Informed Sport / NSF / ConsumerLab / Clean Label) · leucine per serving from COA, not marketing.
02Protocols tested: Per-kg target from four literature ranges (IOM RDA, Phillips 2017, Morton 2018, ISSN). Brands scored against Moore 2015 leucine-per-dose threshold (~0.4 g/kg).
03Cost-basis verified: $/gram of protein and $/gram of leucine at warehouse pricing (Costco), mail-order (Amazon), and DTC retail. Re-checked quarterly, flagged when drift exceeds 15%.
04Confidence level: High on ranked order. Medium on absolute $/g (prices drift). Low on serving-size claims where COA is older than 18 months, flagged [VERIFY].

§ 5 · Questions

What people ask us most.

How much vitamin D should I take per day?: The RDA is 600 IU/day for adults under 70 and 800 IU/day over 70 (IOM 2011), set to maintain bone health in most people. Common maintenance supplementation runs 1000-2000 IU/day, which is what VITAL used (Manson 2019). The tolerable upper intake level (UL) for adults is 4000 IU/day. Doses above the UL should be tied to a measured deficiency and clinician oversight, not taken open-ended.
Is D3 better than D2?: Yes, on the metric that matters. Tripkovic 2012's meta-analysis found D3 (cholecalciferol) raises and sustains serum 25(OH)D more effectively than D2 (ergocalciferol) at equivalent doses. D2 is mainly relevant as a prescription high-dose or vegan option. For raising and holding status, choose D3.
Should I take K2 or magnesium with vitamin D?: The cofactor case is mechanistic, not proven on hard outcomes. Vitamin K2 directs calcium toward bone via carboxylation, and magnesium is a cofactor in vitamin D metabolism. RCTs showing that adding K2 or magnesium to D3 improves clinical endpoints are limited. If your diet is low in K2-rich foods or you are magnesium-insufficient, a combo product is reasonable; it is not a requirement for D3 to work.
Do I need a blood test before supplementing?: It is the only way to dose precisely. The relevant marker is serum 25-hydroxyvitamin D (25-OH-D); a common sufficiency target is 30-50 ng/mL (75-125 nmol/L). Below 20 ng/mL is deficient. A maintenance dose of 1000-2000 IU/day is low-risk without testing, but anyone using higher doses or correcting a suspected deficiency should test, then retest in 8-12 weeks.
Can you take too much vitamin D?: Yes. Toxicity is from supplements, not sun, and presents as hypercalcemia. It generally requires sustained intake well above the 4000 IU/day UL, often 10000 IU/day or more for months, pushing 25-OH-D above ~100 ng/mL (NIH ODS). Symptoms include nausea, kidney stones, and in severe cases renal damage. Staying at or below the UL without a measured deficiency keeps the risk near zero.
Does an oil-based softgel absorb better than a dry capsule or tablet?: Vitamin D is fat-soluble, so an oil-based softgel has a theoretical absorption edge, and most softgels here use olive, coconut, or fish oil. In practice, the difference is small when a dry tablet is taken with a meal containing fat. The practical rule: take whatever form you own alongside food. Form matters less than consistency.

What would change our mind

A published Certificate of Analysis from a ranked brand that contradicts the label claim we scored against. An independent lab result (Clean Label, ConsumerLab) finding heavy-metal or amino-spiking failures on a current top pick. A peer-reviewed meta-analysis that shifts the leucine-per-dose threshold. Any of those triggers a dated revision within a week.

Sources

Every claim, cited.

05 refs

The Larderlab Team · byline

The Larderlab Team builds evidence-led frameworks for eating, lifting, and stocking a kitchen. We cite every claim. We publish the spreadsheet when possible. We buy what we review at retail price. When new data lands, we revise with a dated note.

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