Klean Athlete Klean-D 1000 Review 2026: Vegetarian athletes who want a certified, moderate-dose D3 tablet
Firsthand does not earn a commission from this product. We include it because rankings limited to affiliate partners can't be trusted.
Our verdict
Klean Athlete Klean-D 1000 scores 7.7/10. Each tablet supplies 25 mcg (1,000 IU) of vitamin D3, a conservative dose that stays well under the 4,000 IU adult upper limit listed by MedlinePlus, and the product is on NSF's Certified for Sport database. It is vegetarian and gluten-free, and $14.00 for 100 tablets works out to about 14 cents a day. It ranks below dotFIT mainly on cost and support: the brand's own store asks you to log in before adding to cart, and the product page lists no return terms. The product copy suggests vitamin D may help training and recovery, but large trials such as VITAL found that 2,000 IU a day did not reduce fractures in healthy adults who were not deficient, so treat it as a way to cover a shortfall, not a performance aid. Check your level with a clinician first.
Score breakdown
- Safety (30%)9.0/10
- Evidence (30%)6.5/10
- Cost & Value (20%)8.5/10
- Transparency (10%)8.5/10
- Support (10%)5.0/10
Scored per our review methodology.
Who it's for
Best for: Vegetarian athletes who want a certified, moderate-dose D3 tablet.
Pricing
$14.00 / 100 tablets (~$0.14/day) (as of 2026-10-02)
| Plan | Price | Notes |
|---|---|---|
| Official site (100 tablets) | $14.00 | Account login required to add to cart (as of 2026-10-02) |
| Other authorized retailers | Varies | Confirm the price on the official site or the retailer |
What the evidence says
- Klean-D 25 mcg (1,000 IU) appears on NSF's Certified for Sport product listing. NSF says the mark means the contents match the label, no unsafe levels of contaminants were found, the product is free of 290 substances banned by major athletic organizations, and the factory is GMP certified and audited by NSF. (NSF Certified for Sport official listing)
- MedlinePlus (NIH) lists an adult RDA of 600 IU (15 mcg) a day for ages 19 to 70 and 800 IU for adults over 70, and a safe upper limit of 4,000 IU (100 mcg) a day for adults. It says vitamin D toxicity almost always comes from too many supplements and can raise blood calcium. (MedlinePlus (NIH National Library of Medicine): Vitamin D)
- A VITAL ancillary analysis found 2,000 IU of vitamin D3 a day did not significantly lower total, nonvertebral or hip fractures versus placebo in generally healthy midlife and older adults who were not selected for deficiency or osteoporosis. (LeBoff et al., N Engl J Med 2022 (PubMed))
Pros & cons
Pros
- NSF Certified for Sport, confirmed on NSF's certified product database
- 1,000 IU (25 mcg) of vitamin D3 per tablet, a conservative dose under the 4,000 IU upper limit
- Vegetarian, gluten-free tablet with a short list of other ingredients
- 100 tablets per bottle keeps the daily cost near 14 cents
Cons & red flags
- The official site shows a 'log in to add to cart' button, so buying direct requires an account
- No return or guarantee terms appear on the product page
- Marketing copy links vitamin D to training quality and recovery, which goes further than the large trials in general adults support
- Tablet form without added fat; take it with a meal as the label directs
How it compares
Klean Athlete Klean-D 1000 scores 7.7/10 in our nutrition & supplements evaluation. See where it lands in the full ranking: Best Vitamin D Supplements of 2026.
- dotFIT Vitamin D-3 1,000 IU review — 8.0/10, adults who want a low-cost, low-dose, third-party certified vitamin d3
- Momentous Vitamin D3 2000 IU review — 7.6/10, vegans who want a certified d3 at the dose used in the largest trial
Frequently asked questions
Is Klean-D NSF Certified for Sport?
Yes. Klean-D 25 mcg (1,000 IU) appears on NSF's Certified for Sport listing, which covers label accuracy, contaminant limits and 290 banned substances.
Will Klean-D improve my athletic performance?
There is no good evidence that it will if your vitamin D level is already adequate. Its value is in correcting a low intake. Ask a clinician whether a blood test makes sense for you.
Is Klean-D vegetarian?
Yes. The product page labels it vegetarian, gluten-free and GMO-free. Other ingredients are microcrystalline cellulose, stearic acid, vegetable stearate and silica.
Get evidence-based health picks in your inbox — no hype.
Join The Firsthand Brief for a weekly, research-first read.
We never sell your email. Unsubscribe anytime. See our privacy policy.