NOW Foods Vitamin D3 & K2 Review (2026): Worth It After 40?

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Vitamin D3 + K2 is one of the most recommended supplement pairings for adults over 40 — and one of the most oversold. NOW Foods’ version is the best-selling D3 & K2 product on iHerb, costs about eight cents a day, and has more than 80,000 ratings. So is it actually the right pick, or just the cheap one? Here’s the honest version: what’s in the capsule, what the research really says about vitamin D, K2, and metabolism after 40, and the one formulation detail most reviews skip over.

At a Glance: NOW Foods Vitamin D3 & K2

What’s Actually In It

Each capsule delivers 1,000 IU of vitamin D3 (cholecalciferol) sourced from lanolin — the standard, well-absorbed form used in most clinical trials — plus 45 mcg of vitamin K2. There’s no filler stack, no proprietary blend, and no “metabolism support” extras, which is a good sign. NOW is a large, GMP-certified manufacturer with decades of third-party testing history, so label accuracy isn’t a real concern here.

The detail that matters: the K2 is the MK-4 form, not MK-7. Both are real vitamin K2, but MK-7 stays in the blood for days while MK-4 is cleared within hours. Most of the supplement research on K2 and bone or arterial health in Western adults has used MK-7 at 90–180 mcg, or MK-4 at pharmacological doses of 45 mg (a thousand times what’s in this capsule). At 45 mcg of MK-4, think of the K2 here as a modest bonus, not a therapeutic dose.

What the Research Actually Says About Vitamin D, K2, and Metabolism After 40

Low vitamin D is common after 40, and correcting a deficiency matters

Vitamin D status tends to fall with age: skin makes less of it from sunlight, more time is spent indoors, and higher body fat “stores” vitamin D away from circulation. Large surveys consistently find that a substantial share of middle-aged adults are insufficient, especially in winter and at northern latitudes. In people who are genuinely deficient, supplementation reliably improves bone health markers and muscle function, and reduces fall risk in older adults. That’s the well-established case for taking it.

Vitamin D and weight loss: the observational link doesn’t survive the trials

Low vitamin D is strongly associated with obesity and insulin resistance in observational studies. But when researchers give vitamin D to overweight adults in randomized trials, the effect on weight and body fat is small to nonexistent. A 2018 meta-analysis in the European Journal of Clinical Nutrition made the gap explicit: across observational studies, higher blood vitamin D tracked with lower body fat, but in randomized trials vitamin D3 supplementation had no significant effect on body-fat percentage (Golzarand et al., 2018). Correcting a deficiency may modestly improve insulin sensitivity in some groups, but vitamin D is not a fat-loss supplement, and anyone selling it as a “metabolism booster” is stretching the evidence. If you’re working on insulin resistance, the levers that actually move it are covered in our guide to insulin resistance and metabolism.

K2 helps direct calcium — but the strongest evidence uses bigger doses

Vitamin K2 activates proteins (osteocalcin and matrix Gla protein) that help keep calcium in bone and out of arterial walls. The Rotterdam Study (Geleijnse et al., 2004, Journal of Nutrition) followed 4,807 older adults for about seven years and found that those with the highest dietary K2 intake had a 57% lower risk of dying from coronary heart disease and about half the odds of severe aortic calcification — while K1 intake showed no such link. That is an observational association, not proof of cause, and Japanese trials using 45 mg of MK-4 daily improved bone outcomes in postmenopausal women. Those are real findings, but they involve dietary intake over decades or doses far above what’s in a general supplement. A 45 mcg MK-4 add-on is reasonable insurance for people with low K2 intake (most Western diets), not a treatment.

The “D3 needs K2” claim is plausible, not proven

The popular argument is that vitamin D increases calcium absorption, so you need K2 to steer that calcium correctly. The mechanism is sound, but there is no strong trial evidence that pairing K2 with moderate-dose D3 changes outcomes in healthy adults. It’s a sensible combination, not a mandatory one.

The Honest Caveats

1,000 IU may be too little. For someone with a normal baseline, 1,000 IU is a reasonable maintenance dose. For someone with a confirmed deficiency — common after 40, especially with higher body weight — doctors typically use 2,000–4,000 IU daily, or short higher-dose courses. Two capsules a day is an option, but at that point a dedicated higher-dose D3 may be simpler. The right move is a 25-hydroxyvitamin D blood test first.

The K2 form and dose are the weak link. If K2 is your main reason for buying, a product built around MK-7 at 90–180 mcg is more in line with the research. NOW’s product is best understood as “vitamin D3 with a little K2.”

Warfarin interaction. Vitamin K in any form interferes with warfarin (Coumadin) and similar anticoagulants. If you take a blood thinner, do not add this without talking to your prescriber.

Not vegan. The D3 comes from lanolin (sheep’s wool). It’s vegetarian-friendly but not vegan.

Pros and Cons

Pros: very low cost per serving; clean two-ingredient formula from a GMP manufacturer with a long track record; small, easy-to-swallow capsule; sensible 1,000 IU dose for daily maintenance; Kosher and Halal certified; 4.8-star average across a very large review base.

Cons: MK-4 form of K2 at a small dose; 1,000 IU is on the low side for correcting a deficiency; no vitamin D3 from a vegan source; no third-party sport certification (irrelevant for most readers, relevant for tested athletes).

Who It’s Actually For

This is a good fit if you’re over 40, get limited sun for part of the year, want a low-cost daily vitamin D habit, and like the idea of a little K2 alongside it. It’s also a sensible companion to a magnesium supplement, since magnesium is required to activate vitamin D — see our Doctor’s Best Magnesium Glycinate review and our explainer on magnesium, metabolism, and sleep. If you’re navigating perimenopause, when bone density starts to matter more, the D3 side of this product is worth taking seriously.

It’s a poor fit if a blood test has already shown you’re deficient (you’ll likely need more D3), if you take warfarin, or if you specifically want a research-dose MK-7 product.

Price and Value

At $9.17 for 120 capsules, NOW’s D3 & K2 works out to roughly eight cents a day — about as cheap as vitamin D supplementation gets from a reputable brand. The 240-count bottle ($17.14) drops it a little further. For value, it’s hard to argue with; you’re paying pennies for a clean, accurately dosed maintenance product. Just be clear about what you’re buying: excellent-value D3 with a token amount of K2.

How It Compares to an MK-7 Product

The main alternative on iHerb is a D3 + K2 formula using MK-7, such as California Gold Nutrition’s Vitamin D3 + K2 as MK-7 (4.8★, 37,000+ ratings, from $9.22 for 60 capsules). Per capsule it costs more, but the MK-7 form lines up better with the K2 research. The honest trade-off: NOW is the better buy if vitamin D is your priority and K2 is a bonus; an MK-7 product is the better buy if K2 for bone and arterial support is the reason you’re shopping. Either way, the vitamin D dose — not the brand — is what should be matched to your blood level.

Frequently Asked Questions

Does NOW Foods Vitamin D3 & K2 help with weight loss?

No. Vitamin D deficiency is linked with obesity in observational studies, but randomized trials giving vitamin D to overweight adults show little or no effect on weight. Correcting a deficiency supports bone, muscle, and possibly insulin sensitivity — it doesn’t burn fat.

Is 1,000 IU of vitamin D3 enough after 40?

For maintenance in someone with normal levels, 1,000 IU is reasonable. For a confirmed deficiency, most clinicians use 2,000–4,000 IU or more. A 25-hydroxyvitamin D blood test is the only way to know which group you’re in.

What’s the difference between MK-4 and MK-7?

Both are forms of vitamin K2. MK-7 has a long half-life (days) and is effective at 90–180 mcg. MK-4 clears in hours and has mainly been studied at very high doses (45 mg). NOW’s product uses 45 mcg of MK-4, which is a small supportive amount rather than a research dose.

Can I take it with magnesium?

Yes, and it’s a sensible pairing — magnesium is a cofactor for the enzymes that activate vitamin D. Many people take both with a meal containing some fat, which helps absorption of these fat-soluble vitamins.

Who should not take vitamin K2?

Anyone on warfarin or similar vitamin K antagonist blood thinners, unless their prescriber approves. People with kidney disease or on high-dose calcium should also check with a doctor before adding D3 and K2.