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Vitamin D (test-gated)

D3

ModerateReal, but too small for your device to notice

Moderate

Some good studies, not many repeats

Why this rating

Moderate: strong in deficient groups, null in replete ones; latest ARI meta-analysis (2024) non-significant.

2
studies
40
experiments
61,589
people (largest study)
1
kinds of study
In short

It fixes tiredness and weakness only in people who are actually low on it. A 2024 review found it does not protect against colds and flu in general.

The bottom line

Vitamin D fixes fatigue and muscle weakness when you're deficient and does essentially nothing when you're not. The much-cited protection against respiratory infections has shrunk with every update — the 2024 meta-analysis found no significant overall effect. Test your level, then decide.

How it works

Hormone-like regulation of muscle protein synthesis and innate immunity; effects saturate once 25(OH)D is adequate.

Who it helps, and who it doesn't

Deficient individuals (25(OH)D < 20 ng/mL), little sun exposure, darker skin at high latitude. Retest in 3 months.

What to buy

What to look for
  • ✓Vitamin D3 (cholecalciferol) 1,000–2,000 IU
  • ✓Softgel in oil for absorption; D3+K2 is fine
What to avoid
  • ✕Mega-doses (≥10,000 IU) without a blood level
Safety notes
  • ⚑ 25(OH)D
  • · Hypercalcemia at chronic high doses; thiazide interaction.

As an Amazon Associate, Umbral earns from qualifying purchases. Product data is provided by Amazon and may change; ratings and prices shown are Amazon’s, not Umbral’s. Recommendations are based on the evidence grade and the form used in trials, never on commission.

Nature Made Vitamin D3 2000 IU, 250 softgels
Nature Made Vitamin D3 2000 IU, 250 softgels
4.8(25,272)
$12.49

Maintenance dose; retest 25(OH)D in 3 months.

Buy on Amazon
Amazon price on Sep 18, 2026.
Everlywell At-Home Vitamin D Test Collection Kit
Everlywell At-Home Vitamin D Test Collection Kit
4.0(129)
$99.00

You collect the sample and mail it to a CLIA-certified lab, which is why this one is worth buying and the instant strip tests are not. Test before you supplement and retest in three months.

Buy on Amazon
Amazon price on Sep 18, 2026.
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Prefer to compare yourself? This opens Amazon’s full selection for this supplement, filtered to the form we recommend.

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What the studies measured

Every result, next to the line that means no effect

Each diamond is a study's best estimate. The thin line shows how sure the study was: the shorter the line, the more certain the result.

  • Acute respiratory infection odds (2024 update)
    % odds · Jolliffe 2024
    −6.00
    −12 … 0
−10−50NO EFFECT

Each unit gets its own scale, so numbers are never mixed on one line. When a study gave no range, we leave it blank instead of inventing one.

Studies over time

2 studies over 1 years

2023 — 2024
20232024
Review combining many studiesControlled experimentEarly or observational studyHover a dot for details
Dose
1,000–2,000 IU/day (UL 4,000)
Timing
With food; retest in 3 months
Where to buy

The studies

  1. 1.
    Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of stratified aggregate data
    The Lancet Diabetes & Endocrinology · 2024 · meta-analysis · 40 experiments · n = 61,589

    No statistically significant overall protection (OR 0.94, 95% CI 0.88–1.00).

  2. 2.
    Effect of vitamin D supplementation on muscle strength in athletes: a meta-analysis
    Frontiers in Nutrition · 2023 · meta-analysis

    Strength gains concentrated in athletes with low baseline 25(OH)D.

Umbral is a wellness product, not a medical device. It does not diagnose, treat, cure or prevent any disease. Supplement information is educational; talk to a clinician before starting anything, especially if you are pregnant, under 18, managing a condition or taking medication.

These statements have not been evaluated by the Food and Drug Administration.