THORNE Vitamin D-1,000, Vitamin D3 Supplement, 1,000 IU, 90 Capsules

Thorne's Vitamin D-1,000 is a simple product: one capsule, 1,000 IU of vitamin D3 (as cholecalciferol). A 90-capsule bottle costs about $17 on Amazon and has a 4.8-star average from around 3,700 reviews.

What you get

The capsule contains vitamin D3, which Thorne's listing describes as better absorbed and more effective at raising vitamin D levels than D2. That matches the general research consensus. The listing says the product is third-party tested and certified to confirm that what's in the bottle matches the label and that it contains no unsafe levels of contaminants. Thorne also markets it as gluten and dairy free.

Supplements aren't FDA-approved before they're sold, so that kind of independent testing is the main reassurance you get about quality.

Why choose 1,000 IU

The NIH Office of Dietary Supplements recommends 600 IU a day for adults up to 70 and 800 IU over 70, with an upper limit of 4,000 IU a day from all sources. A 1,000 IU capsule sits just above the recommended intake. That leaves plenty of room if you also get vitamin D from fortified milk, cereal or a multivitamin, and it's an easy dose to adjust with your doctor's input.

At about 19 cents a capsule, it costs roughly three times as much per day as Nature Made's 2,000 IU softgels. You're paying for the brand and its testing program.

Who it's for

• People who want a modest daily D3 dose rather than a higher one
• Anyone who already gets some vitamin D from food or a multivitamin
• Shoppers who prefer brands with third-party certification

Who should skip it

If your doctor has found you're deficient and prescribed a higher dose, follow that plan instead. People with kidney disease, sarcoidosis or high blood calcium should ask a doctor before taking vitamin D. And vitamin D won't help tiredness that has another cause. Our why am I always tired guide covers the others.

Alternatives

The Nature Made Vitamin D3 2000 IU softgels are USP Verified and much cheaper per day, at a higher dose. For how vitamin D stacks up against iron and B12 as a cause of fatigue, see iron, B12, or vitamin D, and for our full list, the best vitamins for energy and tiredness.