Thorne Review: Vitamin D3, Magnesium and Vitamin K2, Checked Against the Evidence

Disclosure: We have no affiliate relationship with Thorne right now. The Thorne links on this page are plain links, and we earn nothing if you buy through them. If we join Thorne’s affiliate program later, we may earn a commission at no extra cost to you, and that would not change our assessment of the brand, good or bad. Read our full disclosure.

Not medical advice. This review is for general information. Talk to your doctor, pharmacist or another clinician before starting vitamin D, magnesium or vitamin K, especially if you take warfarin (Coumadin, Jantoven) or another blood thinner, have kidney disease, have had high calcium levels or kidney stones, are pregnant or breastfeeding, or take prescription medicines. If you take warfarin, do not start or stop any vitamin K product without talking to the clinician who manages your INR.

Thorne is the brand a lot of people end up at after they’ve read a few labels and started to worry about what’s actually in the bottle. It shows up in doctors’ offices, in pro sports locker rooms and on most “cleanest supplement” lists. It’s also one of the more expensive brands on the shelf.

So is the extra money buying anything real? For this review we looked at Thorne’s vitamin D3, magnesium and vitamin K products, the three nutrients we’ve already covered in depth in our vitamin D guide, magnesium guide, vitamin K guide and vitamin D cofactors guide. We checked every certification claim against the certifier’s own database where we could, read every Supplement Facts panel, pulled every price from Thorne’s site on November 2, 2026, and searched FDA records for recalls and warning letters.

We haven’t run our own lab tests, and we didn’t receive free products. What follows is what the public record and the research show.

The short version

• Testing is Thorne’s real strength. Thorne makes its products in its own facility in Summerville, South Carolina, says every product goes through four rounds of in-house testing, and holds facility certifications from NSF and Australia’s Therapeutic Goods Administration (TGA) (Thorne, Quality).
• NSF Certified for Sport covers some products, not all. On NSF’s own database we found Vitamin D-5,000, Magnesium Bisglycinate and Vitamin D + K2 (capsules) listed as Certified for Sport. Thorne’s Magnesium Glycinate capsules, Magnesium CitraMate, its vitamin K products and its other vitamin D strengths were not on that list when we checked (NSF Certified for Sport, certified products).
• Batch Certificates of Analysis are not posted publicly. Thorne describes its testing on each product page, but we couldn’t find a public CoA library. Life Extension, by comparison, says it will send a CoA for any product on request.
• Price: Vitamin D-5,000 works out to about $0.33 a day. The Magnesium Bisglycinate powder is about $0.87 a scoop for 200 mg of magnesium, which is pricey for magnesium. Prices checked November 2, 2026.
• Record: an FDA warning letter in 2004 over disease claims, and a 2014 voluntary recall of two chelation products (Captomer) that contained a prescription drug ingredient. We found no recalls or FDA warning letters involving Thorne’s vitamin D, magnesium or vitamin K products.
• Watch-outs: Vitamin D-10,000 is two and a half times the US upper limit for adults. Magnesium Glycinate’s label allows up to four capsules a day (480 mg), which is above the 350 mg upper limit for supplemental magnesium. Every vitamin K product is off-limits on warfarin without medical supervision.
• Our view: Thorne is a good choice if you care most about manufacturing control and, for athletes, sport certification. You pay a premium for it, and on a few products the dose choices are worth a second look.

How we scored Thorne

We rate five things from 0 to 10 and weight them as explained on our How We Review page. We didn’t lab-test any product. Each mark comes from the findings in this review, and whether we earn money from the brand isn’t part of the score.

What we rate	Weight	Mark	Why
Quality and independent verification	35%	8.5	Makes products in its own NSF GMP-certified facility with a TGA “A” rating. Three of the products we reviewed are listed in NSF’s Certified for Sport database. Several others aren’t.
Label and dose sense	20%	7.0	Clean formulas and D3 throughout, but D-10,000 is two and a half times the adult upper limit, the Magnesium Glycinate label allows up to 480 mg a day, and the D + K2 Liquid has far less MK-4 than the trials used.
Value	20%	5.5	Premium pricing: about $0.33 a day for D-5,000 and about $0.87 a scoop for Magnesium Bisglycinate, checked November 2, 2026.
Transparency	15%	6.0	Describes its testing in detail, but posts no batch Certificates of Analysis and has no formal request page.
Track record	10%	8.0	A 2004 FDA warning letter and a 2014 recall of two chelation products. Nothing involving its vitamin D, magnesium or vitamin K products.
SWA Score	100%	7.2	Weighted average: 8.5 × 35% + 7.0 × 20% + 5.5 × 20% + 6.0 × 15% + 8.0 × 10%, rounded to one decimal place

Score history: first scored November 2, 2026.

Who Thorne is

Thorne started in 1984 in Idaho and moved its manufacturing to Summerville, South Carolina. The company went public in 2021 as Thorne HealthTech and was taken private again in October 2023, when the investment firm L Catterton bought it for $10.20 a share, about $680 million in total (Thorne press release, 2023).

That ownership change matters a little for readers. Private equity owners usually want growth, and Thorne’s product line and marketing have expanded since. So far we haven’t seen anything that suggests quality has slipped, but it’s a reason to keep checking certifications rather than relying on the brand’s past reputation.

Thorne markets itself heavily through health professionals and sports teams, and its Quality page says it runs more than 100,000 quality tests a year in its own labs (Thorne, Quality). Its Amazon listings also call it the “#1 most recommended clinical brand,” based on a survey (Amazon listing, Thorne Vitamin D + K2 Liquid). Survey rankings like that tell you about popularity among the people surveyed, not about what’s in the capsule, so we gave them no weight.

Testing and certifications, checked one by one

Supplements in the US don’t need FDA approval before they’re sold. The FDA can act after a problem shows up, but nobody checks a bottle against its label before it reaches you (FDA, Dietary Supplements). That’s why independent testing matters. One study of over-the-counter vitamin D pills found that the actual dose ranged from 9% to 146% of what the label promised (LeBlanc et al., 2013).

Here’s what Thorne claims, and what we could confirm.

Facility certifications

Claim	What it means	Could we confirm it?
NSF GMP certification (NSF/ANSI 455-2) for the Summerville campus	An outside auditor checks the factory against a written good manufacturing practice standard for supplements	Thorne posts the certificate on its Quality page (Thorne, Quality)
“A” rating from Australia’s TGA	Australia regulates supplements as low-risk medicines, with stricter manufacturing rules than the US	Stated and certificate posted by Thorne (Thorne, Quality). We did not find an independent copy.
GRMA certification	An industry nonprofit’s audit of manufacturing practices	Stated by Thorne (Thorne, Quality)
Four rounds of in-house testing	Raw materials, in-process checks, finished product, and shelf-life (stability) testing	This is Thorne’s own description. In-house testing isn’t independent, though the facility audits above do check that the system exists.

A facility certification is a good sign that the factory is well run. It does not mean an outside lab tested the specific bottle you buy.

Product certification: NSF Certified for Sport

NSF Certified for Sport is the stricter, product-level seal. To carry it, a product’s contents are tested against its label and for contaminants, and then lots are screened for substances banned in sport, and the facility is audited. Certified products are listed publicly on nsfsport.com, where you can search by brand and product (NSF Certified for Sport, certified products).

Thorne says it makes more than 20 Certified for Sport products (Thorne, Quality). On November 2, 2026, NSF’s database listed these Thorne products in the categories we reviewed (NSF Certified for Sport, certified products):

• Thorne D-5,000 (Vitamin D-5,000)
• Thorne Magnesium Bisglycinate (the powder)
• Thorne Vitamin D + K2 (the 5,000 IU capsule)

We did not find Vitamin D-1,000, Vitamin D-10,000, Magnesium Glycinate capsules, Magnesium CitraMate, Magnesium Citrate powder, Vitamin K (3-K Complete), Vitamin K2 Liquid or Vitamin D + K2 Liquid on the Certified for Sport list. Thorne’s page for the D + K2 Liquid refers to the “NSF Contents Certified” mark, a separate NSF program that checks label claims and contaminants but doesn’t screen for banned substances, and the Amazon listing describes the product the same way (Thorne, Vitamin D + K2 Liquid; Amazon listing). We couldn’t confirm that certification on NSF’s public site, so treat it as the brand’s claim until you see the mark on your bottle.

Why this matters to you: if you compete in tested sport, buy only a product and lot that appears on nsfsport.com. If you don’t compete, the Certified for Sport mark is still a useful sign that an outside lab has checked the label and looked for contaminants, but it isn’t the only way a product can be good.

Certificates of Analysis

A Certificate of Analysis (CoA) is a lab report for a specific batch, showing measured potency and contaminant results. Thorne’s product pages say it tests “each ingredient… for identity, purity, and potency” and checks for heavy metals, pesticides and microbes (Thorne, Vitamin D-5,000). But Thorne doesn’t post batch CoAs on its site, and we found no formal CoA request page. Some customers have asked for public CoAs on forums for years. You can ask through Thorne’s support team (Thorne, Contact), and we’d suggest you do if lot-level results matter to you.

The “No List” and leucine

Thorne keeps a “No List” of fillers and additives it won’t use, including magnesium stearate, which it says “can inhibit absorption” (Thorne, Quality). Instead, many Thorne capsules use leucine, an amino acid, to help powder flow through the machines. You’ll see it in the vitamin D capsules. That’s a sensible choice for people who want short ingredient lists. The claim about magnesium stearate is weaker than Thorne’s marketing suggests; we cover it in the “Beyond the mainstream” section below.

Thorne’s vitamin D3 products

All prices below are one-time purchase prices from thorne.com, checked on November 2, 2026. Thorne often discounts subscriptions, and prices change, so check before you buy.

Product	Vitamin D3 per serving	Other actives	Size	Price	Per serving	NSF Certified for Sport
Vitamin D-1,000	1,000 IU (25 mcg)	None	90 capsules	$17	$0.19	Not listed
Vitamin D-1,000, 180 servings	1,000 IU (25 mcg)	None	180 capsules	$33	$0.18	Not listed
Vitamin D-5,000	5,000 IU (125 mcg)	None	60 capsules	$20	$0.33	Yes
Vitamin D-5,000, 120 servings	5,000 IU (125 mcg)	None	120 capsules	$39	$0.33	Yes
Vitamin D-10,000	10,000 IU (250 mcg)	None	60 capsules	$26	$0.43	Not listed
Vitamin D + K2 (capsule)	5,000 IU (125 mcg)	180 mcg vitamin K2 as MK-7	60 capsules	$30	$0.50	Yes
Vitamin D + K2 Liquid	1,000 IU (25 mcg) per 2 drops	200 mcg vitamin K2 as MK-4 per 2 drops	600 servings	$34	$0.06	Not listed

What’s in the capsules

The capsules use vitamin D3 (cholecalciferol) with leucine, microcrystalline cellulose, silicon dioxide and a vitamin E antioxidant in a plant-cellulose (hypromellose) shell (Thorne, Vitamin D-5,000). They’re dry capsules, not oil-filled softgels. That’s fine, but vitamin D is fat-soluble, and taking any vitamin D with a meal that contains fat improves absorption. In one trial, peak blood levels were 32% higher when people took vitamin D3 with a fat-containing meal compared with a fat-free one (Dawson-Hughes et al., 2015).

The D3 is generally better at raising blood levels than D2 (Tripkovic et al., 2012), and every Thorne D product uses D3. Thorne doesn’t say on these pages whether its D3 comes from lanolin (sheep’s wool), which is the usual source. If you’re vegan, ask before buying.

Our take on the vitamin D doses

The US Recommended Dietary Allowance is 600 IU a day for adults up to age 70 and 800 IU after that. The Tolerable Upper Intake Level, the most adults should take daily without medical supervision, is 4,000 IU (NIH ODS, Vitamin D).

• D-1,000 is the dose we’d point most people toward if they don’t have a blood test showing low levels. It’s simple and hard to overdo.
• D-5,000 is above the upper limit. Plenty of clinicians do prescribe 5,000 IU for people with a documented deficiency, often for a set period and with follow-up testing. It’s a reasonable tool in that setting. As an every-day, no-test default, it’s more than most people need.
• D-10,000 is two and a half times the upper limit. Thorne’s own page tells people with high calcium to check with a clinician first (Thorne, Vitamin D-10,000). In a three-year Canadian trial, adults taking 10,000 IU a day lost slightly more bone density at the wrist than those taking 400 IU, the opposite of what most people buying it want (Burt et al., 2019). We would only use this strength under a clinician’s care.

Big trials like VITAL found that 2,000 IU a day didn’t lower cancer or heart disease rates in generally healthy adults who weren’t deficient (Manson et al., 2019). Vitamin D matters a lot if you’re low. If you’re not, more doesn’t appear to add much. Our vitamin D guide goes through who’s most likely to be low and how testing works.

The two D + K2 products are not the same

These two get mixed up a lot, and they’re quite different:

• Vitamin D + K2 capsules pair 5,000 IU of D3 with 180 mcg of MK-7, the long-acting form of K2 used in the Dutch bone and artery trials (Knapen et al., 2013; Knapen et al., 2015). It’s NSF Certified for Sport. At 5,000 IU of D, it carries the same dose caveats as D-5,000.
• Vitamin D + K2 Liquid gives 1,000 IU of D3 and 200 mcg of MK-4 in two drops. The label lets you take two drops up to three times a day (Thorne, Vitamin D + K2 Liquid). The low price per serving is real, and drops make it easy to adjust a dose. The catch is the K2 form. MK-4 leaves the blood quickly. In a Japanese study, a single 420 mcg dose of MK-4 couldn’t be detected in the blood at all, while the same dose of MK-7 was well absorbed and lasted up to 48 hours (Sato et al., 2012). The positive MK-4 trials used 45 mg a day, more than 200 times this dose (Shiraki et al., 2000). So the liquid’s K2 is in an awkward middle zone, with too little MK-4 to match the trials. It’s still a fine vitamin D product.

Why pair D with K2 at all? Vitamin D raises calcium absorption, and vitamin K activates proteins that help put calcium into bone and keep it out of artery walls. The biology is sound, but the large combined trials haven’t shown clear benefits yet. We cover that evidence in our cofactors guide.

Thorne’s magnesium products

Product	Magnesium form	Elemental magnesium per serving	Size	Price	Per serving	Per 100 mg magnesium	NSF Certified for Sport
Magnesium Bisglycinate (powder)	Bisglycinate	200 mg per scoop	60 scoops	$52	$0.87	$0.43	Yes
Magnesium Bisglycinate travel packs	Bisglycinate	200 mg per packet	30 packets	$47	$1.57	$0.78	Yes (same formula)
Magnesium Glycinate (capsules)	Glycinate	120 mg per capsule	90 capsules	$26	$0.29	$0.24	Not listed
Magnesium Glycinate, 180 servings	Glycinate	120 mg per capsule	180 capsules	$46	$0.26	$0.21	Not listed
Magnesium CitraMate	Malate (80 mg) and citrate (55 mg)	135 mg per capsule	90 capsules	$22	$0.24	$0.18	Not listed
Magnesium Citrate (powder)	Citrate	250 mg per scoop	60 scoops	$39	$0.65	$0.26	Not listed

Prices are one-time purchase prices from thorne.com, checked November 2, 2026. The travel pack listing on NSF is not separate; we’ve assumed it shares the powder’s certification because it’s the same formula. Confirm on nsfsport.com if it matters for competition.

Magnesium Bisglycinate powder

This is Thorne’s best-known magnesium and the one with the sport certification. One scoop gives 200 mg of magnesium as bisglycinate, sweetened with monk fruit and flavored with citric acid. You mix it into at least 8 ounces of water (Thorne, Magnesium Bisglycinate).

The good: 200 mg is a sensible dose, under the 350 mg upper limit for supplemental magnesium (NIH ODS, Magnesium). Bisglycinate is usually gentle on the gut. And a powder is easier for people who struggle with pills.

The not-so-good: at about 43 cents per 100 mg of magnesium, it costs roughly twice as much as Thorne’s own glycinate capsules for the same mineral. You’re paying for the powder format and the sport certification. Some people also don’t like the taste, which is tart.

What does the research say about magnesium bisglycinate for sleep, the reason most people buy it? A 2025 trial from Germany gave 155 adults with poor sleep either 250 mg of magnesium as bisglycinate or a placebo. Insomnia scores improved a bit more with magnesium than with placebo after four weeks, but the effect was small (the authors called it “modest”), and people who ate less magnesium to begin with seemed to benefit most (Schuster et al., 2025). An earlier review of trials in older adults found only low-quality evidence for magnesium and insomnia (Mah & Pitre, 2021). Our magnesium guide covers this in much more detail.

Fair expectation: if your diet is low in magnesium and your sleep is poor, it may help a little. It isn’t a sleeping pill.

Magnesium Glycinate capsules

Each capsule has 120 mg of magnesium from magnesium glycinate. The capsule shell is plant cellulose, and the only other ingredients are silicon dioxide and medium-chain triglyceride oil (Thorne, Magnesium Glycinate). It’s the best value of Thorne’s glycinate options.

One thing we’d flag: the label says to take “1 capsule one to four times daily.” Four capsules is 480 mg of magnesium, above the 350 mg upper limit for supplemental magnesium set by the National Academies (NIH ODS, Magnesium). The upper limit exists mainly because of diarrhea and stomach upset, and clinicians sometimes go higher on purpose. But if you’re self-dosing, we’d stop at two capsules (240 mg) unless your clinician says otherwise.

Magnesium CitraMate

Each capsule combines 80 mg of magnesium as dimagnesium malate with 55 mg as magnesium citrate, 135 mg in total (Thorne, Magnesium CitraMate). It’s the cheapest Thorne magnesium per milligram. Citrate is well absorbed. In a small comparison trial, magnesium citrate raised blood and urine levels more than magnesium oxide did (Walker et al., 2003). Citrate also pulls water into the gut, so some people find it slightly laxative.

Magnesium Citrate powder

At 250 mg per scoop, this is a bigger dose than the others, and Thorne describes it as powdered magnesium for bowel regularity that “helps to relieve occasional constipation” (Thorne, Magnesium Citrate). If you’re buying magnesium for sleep or general intake rather than regularity, the bisglycinate or glycinate options will probably sit better.

Which Thorne magnesium to pick

• Sleep or calm, and you swallow pills easily: Magnesium Glycinate capsules, one or two a day.
• You compete in tested sport, or you prefer a drink: Magnesium Bisglycinate powder.
• Budget, or you also want a mild help with regularity: Magnesium CitraMate.
• Constipation is the main issue: Magnesium Citrate powder, after checking with your clinician if you have kidney problems.

Thorne’s vitamin K products

Product	K1	MK-4	MK-7	Size	Price	Per serving	NSF Certified for Sport
Vitamin K (3-K Complete)	1,000 mcg	5 mg (5,000 mcg)	90 mcg	60 capsules	$31	$0.52	Not listed
Vitamin K2 Liquid	None	15 mg per 15 drops	None	80 servings	$75	$0.94	Not listed
Vitamin D + K2 (capsule)	None	None	180 mcg	60 capsules	$30	$0.50	Yes
Vitamin D + K2 Liquid	None	200 mcg per 2 drops	None	600 servings	$34	$0.06	Not listed

Prices checked on thorne.com, November 2, 2026.

Vitamin K (3-K Complete)

This capsule combines all three forms: 1,000 mcg of K1, 5 mg of MK-4 and 90 mcg of MK-7 (Thorne, Vitamin K). The label allows one or two capsules a day.

The thinking behind combining forms is that each acts a little differently. K1 goes mostly to the liver, MK-7 stays in the blood longest, and MK-4 is the form your own tissues make (NIH ODS, Vitamin K). That’s reasonable on paper, but no trial has tested this particular mix. The MK-7 dose (90 mcg) is half of the 180 mcg used in the Dutch trials, and the MK-4 dose (5 mg) is about a ninth of the 45 mg Japanese osteoporosis dose. So it’s well-dosed for general intake but doesn’t match any studied regimen.

Vitamin K2 Liquid

This is a high-dose MK-4 product: 15 mg per 15 drops, up to three times a day, which reaches the 45 mg used in Japanese osteoporosis trials (Thorne, Vitamin K2 Liquid; Shiraki et al., 2000). In Japan, 45 mg of MK-4 is a prescription osteoporosis treatment. In our view, this is not something to start on your own. If a clinician has recommended high-dose MK-4 for your bones, this is a clean way to take it, but it’s expensive at nearly a dollar for each 15 mg dose.

Warfarin, and why it matters for every product here

All four K-containing products carry Thorne’s warning that vitamin K interferes with drugs like Coumadin and that they shouldn’t be taken together (Thorne, Vitamin K). That warning is right. MK-7 is especially potent. In volunteers on a warfarin-type drug, as little as 10 to 45 mcg of MK-7 a day was enough to shift clotting tests (Theuwissen et al., 2013). Even the D + K2 capsule’s 180 mcg is far above that.

Newer blood thinners such as apixaban (Eliquis) and rivaroxaban (Xarelto) don’t work through vitamin K, so this specific interaction doesn’t apply to them. Still, tell your prescriber about any supplement you take.

Recalls, warning letters and controversies

We searched the FDA’s warning letter records, openFDA’s recall (enforcement) database for food and drug recalls, and news archives on November 2, 2026. Here is everything we found.

• 2004 FDA warning letter. FDA reviewed Thorne’s website and said it promoted several products, including Perfusia-SR, lycopene, coleus, bacopa and MSM, for treating or preventing diseases, which made them unapproved drugs in the legal sense (FDA warning letter, 2004, archived by Quackwatch). None of those products are the vitamin D, magnesium or K products in this review. Warning letters over marketing claims were common for supplement companies at that time.
• 2014 Captomer recall. FDA warned consumers not to use Thorne’s Captomer and Captomer-250, sold as supplements for heavy metal chelation. They contained DMSA, the active ingredient in a prescription drug for lead poisoning in children. Thorne had received several adverse event reports and agreed to a voluntary recall (FDA, 2014). openFDA records these as Class II recalls D-1383-2014 and D-1384-2014 (openFDA drug enforcement). This was a real lapse. Selling a prescription-strength chelator as a supplement shouldn’t have happened, whatever the intent.
• 2014 California Proposition 65 settlement. A nonprofit alleged that several Thorne products, mostly protein powders, meal-replacement products and multivitamins, exposed consumers to lead or cadmium above California’s warning threshold. The case ended in a consent judgment (California Attorney General, Prop 65 settlement). Prop 65 limits are very strict, much lower than federal limits, and these cases are common across the supplement industry. None of the products named were vitamin D, magnesium or K products.
• Since 2014: we found no recalls in openFDA’s database and no FDA warning letters addressed to Thorne. An unconfirmed report of a 2025 cyber incident circulates on review sites. We couldn’t verify it with Thorne or any regulator, so we haven’t counted it.

That’s a fairly clean record for a company of Thorne’s age and size, with one serious episode that’s now 12 years old.

Who Thorne suits, and who should skip it or check first

Thorne is a good fit if you

• compete in a drug-tested sport and need NSF Certified for Sport products (choose D-5,000, Vitamin D + K2 capsules or Magnesium Bisglycinate, and check the lot on nsfsport.com)
• want products made start to finish in the brand’s own audited facility
• prefer short ingredient lists without magnesium stearate or artificial colors
• want a liquid vitamin D you can dose by the drop (the D + K2 Liquid)

Thorne may not be the best fit if you

• are on a tight budget. Life Extension’s vitamin D3 softgels cost a fraction of the price per day. If cost matters most, Deal Supplement sells low-cost D3, K2 and magnesium on Amazon; it says it lab-tests its raw materials, but it doesn’t list a USP or NSF seal on finished products.
• want to see batch lab reports before you buy
• are vegan and need confirmed non-animal vitamin D3

Check with a clinician before using these products if you

• take warfarin or another vitamin K antagonist. Don’t use any K-containing product without your anticoagulation clinic’s input.
• have kidney disease. Your kidneys clear magnesium, and kidney disease also changes how your body handles vitamin D. Both can build up (NIH ODS, Magnesium).
• have had high blood calcium, kidney stones, sarcoidosis or another granulomatous disease, or hyperparathyroidism. These raise the risk from vitamin D.
• are pregnant or breastfeeding. Thorne’s own labels tell pregnant users to check with a practitioner first (Thorne, Magnesium Glycinate).
• take antibiotics (tetracyclines or quinolones), bisphosphonates for bone loss, or thyroid hormone. Magnesium can block their absorption, so they usually need to be spaced a few hours apart (NIH ODS, Magnesium).
• take thiazide diuretics. These raise calcium levels, which matters if you also take high-dose vitamin D (NIH ODS, Vitamin D).
• are buying for a child. The D + K2 Liquid isn’t intended for children under 12 months (Thorne, Vitamin D + K2 Liquid), and children need lower vitamin D limits than adults.

Pros and cons

Pros

• Made in Thorne’s own NSF- and TGA-audited facility, with in-house testing at four stages
• Three products in this review are NSF Certified for Sport, with each lot listed publicly
• Simple formulas with few additives and no magnesium stearate
• A wide range of doses and formats, including drops and a powder
• No recalls or warning letters involving these product types, and no FDA actions of any kind against Thorne since 2014

Cons

• More expensive than most competitors, especially the Magnesium Bisglycinate powder
• No public Certificates of Analysis
• Most of the products in this review are not NSF Certified for Sport, even though the brand is known for it
• Some label directions go past official upper limits (Magnesium Glycinate up to 480 mg; D-10,000 by design)
• The D + K2 Liquid uses a low dose of MK-4, the K2 form with the weakest evidence at low doses
• Vitamin D3 source not stated on product pages

Beyond the mainstream: what lesser-known research suggests

Supplement brands, practitioners and readers often go further than mainstream guidelines. Some of those ideas have decent support, some are early, and some have little behind them. We label each one so you can judge for yourself:

• Early: lab or animal research, mechanism reviews or uncontrolled case series
• Observational: studies that follow people over time. They can show links but can’t prove cause.
• Small trial(s): one or a few controlled trials, usually with fewer than a few hundred people
• Weak: mostly theory or marketing, with little direct testing

None of this means any product treats or prevents a disease, and none of it replaces care from your doctor.

Magnesium stearate “blocks absorption” — Evidence: Weak

Thorne’s Quality page says it avoids magnesium stearate because it “can inhibit absorption” (Thorne, Quality). The idea is popular with clean-label shoppers. Toxicology testing found no sign that magnesium stearate damages DNA, and it’s one of the most widely used food and tablet additives (Hobbs et al., 2017). Avoiding it is fine if you prefer to.

Where it falls short: we found no human study showing that the small amounts used in capsules meaningfully lower absorption of vitamin D or magnesium. It’s not a reason on its own to pay more.

Magnesium bisglycinate for sleep — Evidence: Small trial(s)

The 2025 trial of 155 adults with poor sleep is the best direct test of the form Thorne sells as a powder. Insomnia scores improved slightly more on 250 mg of magnesium as bisglycinate than on placebo after four weeks, and people who ate less magnesium seemed to gain the most (Schuster et al., 2025).

Where it falls short: the effect was small (Cohen’s d of 0.2), sleep was measured by questionnaire rather than by sleep studies, and the finding about low-magnesium eaters came from an exploratory analysis. One trial isn’t enough to call it a reliable sleep aid.

Taking vitamin D, K2 and magnesium together — Evidence: Small trial(s)

Magnesium is needed for the enzymes that turn vitamin D into its active forms. In a US trial, magnesium supplements nudged vitamin D levels up in people who started low and down in people who started high, which suggests magnesium helps regulate vitamin D rather than simply boosting it (Dai et al., 2018; Uwitonze & Razzaque, 2018). Pairing vitamin D with K2 has a strong biological rationale and some encouraging small trials (van Ballegooijen et al., 2017). Thorne sells this pairing in one capsule.

Where it falls short: the magnesium trial measured blood levels, not health outcomes, and the D-plus-K2 evidence comes mostly from small trials and reviews. Neither combination has been shown to prevent fractures or heart disease. Our cofactors guide lays out every study we found.

Vitamin K2 for night leg cramps — Evidence: Small trial(s)

In a 2024 trial in China, 199 adults aged 65 and older with frequent night leg cramps took 180 mcg of MK-7 or placebo for eight weeks. Cramps fell to about one a week with MK-7 and rose on placebo (Tan et al., 2024). Thorne’s Vitamin D + K2 capsule has the same MK-7 dose, though it also contains 5,000 IU of vitamin D.

Where it falls short: it’s one short trial in one country, and the placebo group got worse, which widens the gap. It needs repeating before anyone relies on it.

High-dose MK-4 for bones — Evidence: Small trial(s), with integrity concerns

Japanese trials of 45 mg of MK-4 a day reported fewer fractures. In one open-label trial of 241 people with osteoporosis, fractures were less common and spine bone density held steady with MK-4 (Shiraki et al., 2000). An early meta-analysis found large benefits (Cockayne et al., 2006). Thorne’s Vitamin K2 Liquid is one of the few US products that reaches this dose.

Where it falls short: the largest Japanese trial, with 4,378 women, found no overall reduction in spine fractures (Inoue et al., 2009). A 2019 review noted that the integrity of some earlier evidence had been questioned, and the fracture benefit was no longer significant when only low-risk-of-bias trials were counted (Mott et al., 2019). Our vitamin K guide explains this in detail.

Very high vitamin D doses (the Coimbra protocol) — Evidence: Observational (uncontrolled case series)

Some practitioners, especially those following the Brazilian “Coimbra protocol,” use very high vitamin D doses for autoimmune conditions, along with a strict low-calcium diet, at least 2.5 liters of fluid a day and frequent lab checks. A German clinic reported on 319 patients taking an average of about 35,000 IU a day for up to three and a half years and found average calcium and kidney values stayed in the normal range (Amon et al., 2022).

Where it falls short: it’s a report from a clinic that uses the protocol, with no comparison group, and it describes patients under close medical supervision. It tells us nothing about whether the protocol helps the disease. Vitamin D toxicity is real and can cause dangerously high calcium and kidney damage (Marcinowska-Suchowierska et al., 2018). Please don’t try to reproduce high-dose protocols with D-10,000 capsules at home.

Vitamin D toxicity as vitamin K depletion — Evidence: Early (hypothesis)

The researcher Chris Masterjohn proposed that some of vitamin D’s toxic effects come from using up vitamin K, which would help explain why many people taking high-dose D add K2 (Masterjohn, 2007).

Where it falls short: it’s a hypothesis built on animal data and hasn’t been tested in human trials. K2 should not be treated as a way to make high vitamin D doses safe.

Leucine in capsules — Evidence: Weak (no expected effect)

Leucine is an amino acid that matters for muscle building, and some readers ask whether the leucine in Thorne’s D capsules adds a benefit.

Where it falls short: the amount used as a flow agent is far too small to matter nutritionally. It’s there for manufacturing, not as an active ingredient.

How we’d use Thorne, in practice

1. Get a vitamin D blood test if you can. It tells you whether you need 1,000 IU or a higher dose for a while. The 25(OH)D test is the one to ask for (NIH ODS, Vitamin D).
2. Start low. For most people without a test, Vitamin D-1,000 with a meal that has some fat in it is a reasonable daily choice.
3. Add K2 thoughtfully. If you want D with K2, the Vitamin D + K2 capsule (5,000 IU with 180 mcg MK-7) matches trial doses for K2 but gives more vitamin D than most people need. Pairing D-1,000 with a separate MK-7 product is a lower-dose alternative.
4. For magnesium, start with one Magnesium Glycinate capsule in the evening, and go to two if you tolerate it and want more. Count magnesium in other products too, such as multivitamins and antacids.
5. Look up the lot on nsfsport.com if you compete.
6. Tell every clinician you see what you take, especially before surgery or a new prescription.

Check current price at Thorne

Prices, strengths and formulas change. Check the current label and price on Thorne’s site before you buy. Prices in this review were checked on November 2, 2026.

Frequently asked questions

Is Thorne third-party tested?

Partly. Thorne’s facility is audited by NSF and Australia’s TGA, and some products, including Vitamin D-5,000, Magnesium Bisglycinate and Vitamin D + K2 capsules, are NSF Certified for Sport, which includes batch testing by an outside lab. Most other products rely on Thorne’s in-house testing within that audited system.

Is Thorne worth the price?

For athletes in tested sport, yes, because certified products reduce a real risk. For everyone else, it depends on how much you value manufacturing control. You can get well-made vitamin D for less. Thorne’s magnesium capsules are reasonably priced, and the powder is the expensive part of the range.

Is Thorne’s Magnesium Bisglycinate the same as magnesium glycinate?

Thorne says the two terms are generally used for the same compound, magnesium bound to two glycine molecules (Thorne, Magnesium Bisglycinate). The products differ in format (powder versus capsules), dose and certification, not really in the magnesium form.

Which Thorne vitamin D should I take?

Without a blood test, D-1,000 is the safest daily choice for most adults. D-5,000 is common for people with a confirmed low level, often for a set period and with retesting. D-10,000 is for use under medical supervision only.

Can I take Thorne vitamin D and magnesium at the same time?

Yes. Many people take them together with an evening meal. Magnesium is needed to activate vitamin D, so the pairing makes sense.

Has Thorne ever had a recall?

Yes, once that we could find: in 2014, Thorne voluntarily recalled two chelation products, Captomer and Captomer-250, after FDA warned that they contained a prescription drug ingredient. We found no recalls of Thorne vitamin D, magnesium or vitamin K products.

The bottom line

Thorne earns its reputation on manufacturing. It makes its own products, its facility is audited by serious outside bodies, and a handful of its products carry the strictest consumer certification available, with every batch checked. Its regulatory record since 2014 is clean.

It’s not perfect. It’s expensive, it doesn’t share batch lab reports publicly, and the Certified for Sport mark covers fewer of its vitamin D, magnesium and K products than the brand’s image suggests. A few label directions also run past official upper limits, which matters if you take the label at its word.

If you want the most control over quality and you’re willing to pay for it, Thorne’s Vitamin D-5,000 (if you need that dose), Vitamin D + K2 capsules and Magnesium Glycinate or Bisglycinate are solid choices. If price matters more, read our Life Extension review next.

Sources

1. Thorne. Quality. Accessed November 2, 2026. https://www.thorne.com/quality
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3. Thorne. Vitamin D-5,000, 60 servings (product page and Supplement Facts). Accessed November 2, 2026. https://www.thorne.com/products/dp/d-5-000-vitamin-d-capsule
4. Thorne. Vitamin D-5,000, 120 servings. Accessed November 2, 2026. https://www.thorne.com/products/dp/d-5-000-120
5. Thorne. Vitamin D-1,000, 90 servings. Accessed November 2, 2026. https://www.thorne.com/products/dp/d-1000-vitamin-d-capsule
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Written by Mbatia Tony Muitungu. Read how we research and update articles in our Editorial Policy.