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Head-to-head evidence comparison — which supplement is right for you?
Iodine vs Vitamin D3: Vitamin D3 has the stronger overall evidence (7.5 vs 8.5/10); they're alternatives for testosterone & cortisol balance — the best pick depends on your goals. Take the 60-second quiz for a pick tailored to your goals.
Vitamin D3 wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Mixed evidence
4 of 11 studies with measurable effects showed benefit.
Top outcomes
Verdict
Probably helps
18 of 30 studies with measurable effects showed benefit.
Top outcomes
Shared outcomes (1)
Outcomes where both Iodine and Vitamin D3 have evidence — compare verdict strength side-by-side.
150-300mcg for maintenance; higher only if deficient under supervision
Any time with food
Potassium iodide (most common and studied)
2000-4000 IU daily
Morning with breakfast
D3 (cholecalciferol) softgel or liquid
4-12 weeks
4-8 weeks
4-8 weeks
4-8 weeks
2-4 weeks
4-8 weeks
Maternal Iodine Status and Birth Outcomes: A Systematic Literature Review and Meta-Analysis
Nutrients (2023) · Meta analysis · n=42269
Birth weight was similar between UIC ≥ 150 μg/L and <150 μg/L (difference = 30 g, 95% CI −22 to 83, p = 0.3, n = 13, I2 = 89%) with no evidence of linear trend (4 g per 50 μg/L, −3 to 10, p = 0.2, n = 12, I2 = 80%).
Iodine fortification of foods and condiments, other than salt, for preventing iodine deficiency disorders
The Cochrane database of systematic reviews (2019) · Meta analysis · n=4317
This is equivalent to an increase of 38.32 µg/L (95% CI 24.03 to 52.61 µg/L).
Systematic review and meta-analysis of iodine nutrition in modern vegan and vegetarian diets
The British journal of nutrition (2023) · Meta analysis · n=4421
Vegan diets had the poorest iodine intake (17·3 µg/d) and were strongly associated with lower iodine intake (P = < 0·001) compared with omnivorous diets.
Vitamin D supplementation vs. placebo and incident type 2 diabetes in an ancillary study of the randomized Vitamin D and Omega-3 Trial
Nature communications (2025) · Meta analysis · n=5205
Mean body mass index (BMI) was 27.5 kg/m2 (SD = 5.3), with 51% female and 17% Black race/ethnicity.
Vitamin D Supplementation for Patients with Dysmenorrhoea: A Meta-Analysis with Trial Sequential Analysis of Randomised Controlled Trials
Nutrients (2024) · Meta analysis · n=687
TSA revealed that the current RCTs provide sufficient information.
Vitamin D and respiratory tract infections
BMJ (2017) · Meta analysis · n=11321
12% reduction in respiratory infections overall
Based on meta-analyses showing urinary iodine concentration increases with supplementation. Effects only meaningful in iodine-deficient populations. Excessive intake (>300mcg) may increase thyroid cancer risk. Most studies used potassium iodide; kelp-derived forms have variable bioavailability.
Meta-analysis showed 12% overall reduction in respiratory infections, with greater benefits in severely deficient individuals. Daily dosing more effective than bolus. Conservative estimate assumes most users not severely deficient.
AI-estimated from published studies. Interpret as directional guidance.
Vitamin D3 has a higher evidence score (7.5/10 vs 8.5/10) and wins in 2 of 3 categories.
For testosterone & cortisol balance, Iodine has a higher relevance score (85 vs 55).
No known interactions between Iodine and Vitamin D3 have been documented in our database. However, always consult a healthcare provider before combining supplements.
Selenium helps; iodine can WORSEN Hashimoto’s. The honest take on "thyroid support".
What’s safe while nursing, the truth about milk-supply herbs, and what to avoid (it passes into milk).
Commonly recommended vs ask-your-clinician vs avoid — a general, safety-first overview.
The honest tier list — proven staples vs situational vs mostly marketing. The hub the other guides feed into.
The right pick depends on your goals. Answer a few quick questions for a personalised recommendation — or dig into the full evidence on each.