How much vitamin D should I take?

It depends on your blood level, which is why testing first is the recommendation rather than a formality. For general maintenance in someone with an adequate level, 1,000 to 2,000 IU daily is a common and sensible range, reviewed every 12 months. For correcting a documented deficiency, higher doses are used for a defined period and then reduced — that is a decision for a clinician, and it should be followed by a repeat test rather than continuing indefinitely. Most guidance treats a level above 30 ng/mL as sufficient.

Is D3 better than D2?

Yes, for practical purposes. Cholecalciferol, D3, is the form your skin makes and it raises and sustains blood 25-hydroxyvitamin D more effectively than ergocalciferol, D2, at equivalent doses. D2 is still used in some prescription formulations and in vegan products, and if you avoid animal products a lichen-derived D3 is now widely available, which gives you the better form without the compromise.

Do I need to take vitamin K2 with vitamin D?

The rationale is that vitamin K-dependent proteins help direct calcium into bone rather than into soft tissue, so the pairing is biologically sensible. The evidence for clinical benefit from combining them is reasonable rather than conclusive. It is a defensible addition if you are taking vitamin D for bone health, and it is contraindicated if you take warfarin — vitamin K is exactly what warfarin acts against, and that is the most important interaction on this page.

Why is vitamin D deficiency so common on a GLP-1?

Mostly it was common before you started. Low levels are widespread in the general population, particularly at higher latitudes, in people with darker skin, and in those with limited sun exposure. What this drug adds is a substantial reduction in food intake, which reduces dietary contribution, and vitamin D is stored in adipose tissue, so the picture during rapid fat loss is more complicated than it looks. That is a reason to measure rather than assume in either direction.

The Research

Supplements

The Best Vitamin D Supplements

The one nutrient where guessing the dose is genuinely common and genuinely wrong in both directions. Seven ranked — and the case for testing before you buy any of them.

Elise Hall, MDMay 3, 20265 min read

This is the supplement people are most confident about and most often wrong about, in both directions — taking 10,000 IU indefinitely because a podcast said so, or taking nothing while sitting at 16 ng/mL.

It also matters more on this drug than most, because vitamin D underpins calcium absorption and therefore bone, and bone mineral density falls with substantial weight loss. That argument is made in full in the bone health rankings.

Test first. Genuinely.

The dose that is right for you depends on where you are starting, and the range in the population is enormous.

Under 20 ng/mL (50 nmol/L): deficient. Needs correction at a higher dose for a defined period, then a repeat test.
20–30 ng/mL: insufficient. Maintenance dosing usually moves this comfortably.
Above 30 ng/mL: generally considered sufficient. Re-check every 12 months.

Ask for 25-hydroxyvitamin D, which is the storage form and the one that reflects status. It belongs on the list in reading your own labs, alongside B12 and ferritin.

And it accumulates. Vitamin D is fat-soluble, stored, and cleared slowly. This is one of the few supplements where genuine harm from over-supplementation is documented — hypercalcaemia, kidney stones and renal impairment at sustained very high intakes. “More is better” is wrong here in a way it is not for, say, vitamin C.

The rubric

D3 rather than D2.
Dose options, so you can match a level rather than take what the shop had.
Independent verification — USP or equivalent.
Delivery form. Oil-based softgels and drops absorb better than dry tablets.
Absence of unnecessary additions, particularly high-dose K2 if you take warfarin.
Ease of splitting or titrating, which favours drops.
Cost per year, since this is a permanent purchase for most people.

The ranking

1. Thorne Vitamin D-5000

Best for correcting a documented deficiency.

D3 in an oil base, well made, with the testing and manufacturing standards Thorne is known for. 5,000 IU is a correction dose rather than a maintenance one, typically for 8–12 weeks, which makes this the right product for a specific job — bringing a low level up over a defined period, then re-testing.

Where it falls short. It is the wrong product for most people to take indefinitely. If your level is already sufficient, 5,000 IU daily is more than you need and it accumulates. Thorne also sells a version combined with K2, which is a reasonable pairing for bone and is contraindicated on warfarin — check which one you are buying.

2. Nature Made Vitamin D3 2000 IU

Best maintenance dose, verified, cheapest per year.

USP Verified, which is a genuine independent check and is unusual at supermarket prices. 2,000 IU is the dose most adults with a sufficient level should actually be taking, the softgel is small, and it costs very little annually.

Where it falls short. Limited dose options within the range. No frills at all, which is the point.

3. Pure Encapsulations Vitamin D3

Cleanest formulation, best dose range.

Hypoallergenic, minimal excipients, and available across a wide span of strengths — 1,000, 2,000, 5,000 IU — which makes it the easiest brand to move up and down as your blood level changes. That flexibility is worth more than it sounds when you are correcting then maintaining.

Where it falls short. Premium priced for a commodity nutrient. Sold mainly through practitioner and specialist channels.

4. NOW Foods Vitamin D-3

Best value across multiple strengths.

Inexpensive, widely available, third-party tested, and offered from 400 IU up to high strengths, so you can match a dose without switching brands.

Where it falls short. Documentation is thinner than the clinical-grade brands. Softgels are soy-oil based, which matters to a small number of people.

5. Carlson Super Daily D3 Drops

Best for anyone who struggles to swallow capsules.

Liquid drops delivering a defined dose per drop, which solves two problems at once: swallowing difficulty, which is real on a drug that slows gastric emptying, and fine dose titration. One drop, on food, no capsule.

Where it falls short. Easy to mis-count drops, and the dose per drop is high enough that a miscount matters. Bottles need reasonable care with storage. More expensive per IU than tablets.

6. Sports Research Vitamin D3 with Coconut Oil

Best absorption-oriented softgel at a fair price.

D3 suspended in coconut oil, third-party tested, non-GMO verified, and reasonably priced. The oil base is a genuine advantage for a fat-soluble vitamin, particularly if you take it with a low-fat meal.

Where it falls short. Fewer dose options. The absorption advantage over other oil-based softgels is marginal rather than dramatic.

7. Garden of Life Vitamin Code Raw D3

Whole-food framing, weakest case.

Whole-food-derived D3 with organic sourcing certifications, well tolerated, and suitable for people who prefer this format.

Where it falls short. The whole-food framing carries a premium without a demonstrated clinical advantage over well-made synthetic D3 — vitamin D is a defined molecule and your body cannot tell where it came from. Lower doses per capsule. Ranked last on value rather than on quality.

Summary

Product	Form	Typical dose	Verification	Titratable	Overall
Thorne D-5000	D3, oil	Correction	Strong	Limited	1st
Nature Made D3	D3, softgel	Maintenance	USP Verified	Limited	2nd
Pure Encapsulations	D3, capsule	Both	Strong	Excellent	3rd
NOW D-3	D3, softgel	Both	Third-party	Good	4th
Carlson Drops	D3, liquid	Both	Third-party	Excellent	5th
Sports Research	D3, softgel	Maintenance	Third-party	Limited	6th
Garden of Life	D3, whole-food	Maintenance	Certifications	Limited	7th

Taking it properly

With the meal containing the most fat. Absorption of a fat-soluble vitamin improves substantially with dietary fat, and on an intake of 800–1,000 calories your fattiest meal may not be dinner. This costs nothing and is the most commonly skipped step.

Daily rather than weekly, unless a clinician has specifically prescribed a loading regimen over 8–12 weeks.

Re-test after 3 months of a correction dose, or 8–12 weeks if the level was very low, then settle onto maintenance. Do not stay on a correction dose indefinitely because it felt like it was working.

Check the K2 question against warfarin. If you take warfarin, avoid combined D3/K2 products — this is the interaction on this page most likely to cause harm.

Do not stack. The tolerable upper intake for adults is 4,000 IU a day from all sources. A multivitamin plus a combined bone product plus a standalone D3 adds up faster than people expect, and the totals are what matter — the same arithmetic that applies in the multivitamin rankings.

Questions I get about this month

How much vitamin D should I take?: It depends on your blood level, which is why testing first is the recommendation rather than a formality. For general maintenance in someone with an adequate level, 1,000 to 2,000 IU daily is a common and sensible range, reviewed every 12 months. For correcting a documented deficiency, higher doses are used for a defined period and then reduced — that is a decision for a clinician, and it should be followed by a repeat test rather than continuing indefinitely. Most guidance treats a level above 30 ng/mL as sufficient.
Is D3 better than D2?: Yes, for practical purposes. Cholecalciferol, D3, is the form your skin makes and it raises and sustains blood 25-hydroxyvitamin D more effectively than ergocalciferol, D2, at equivalent doses. D2 is still used in some prescription formulations and in vegan products, and if you avoid animal products a lichen-derived D3 is now widely available, which gives you the better form without the compromise.
Do I need to take vitamin K2 with vitamin D?: The rationale is that vitamin K-dependent proteins help direct calcium into bone rather than into soft tissue, so the pairing is biologically sensible. The evidence for clinical benefit from combining them is reasonable rather than conclusive. It is a defensible addition if you are taking vitamin D for bone health, and it is contraindicated if you take warfarin — vitamin K is exactly what warfarin acts against, and that is the most important interaction on this page.
Why is vitamin D deficiency so common on a GLP-1?: Mostly it was common before you started. Low levels are widespread in the general population, particularly at higher latitudes, in people with darker skin, and in those with limited sun exposure. What this drug adds is a substantial reduction in food intake, which reduces dietary contribution, and vitamin D is stored in adipose tissue, so the picture during rapid fat loss is more complicated than it looks. That is a reason to measure rather than assume in either direction.

Sources

Written by

Elise Hall, MD

Board-certified internist in Los Angeles, twenty-one years in practice. She writes about GLP-1 medications and metabolic health for people who want the reasoning, not just the conclusion — and publishes her own year on one of these drugs alongside it.

More about Dr. Hall Get the Sunday letter

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