Inositol vs Vitamin D
Both are commonly discussed for mood. Vitamin D has the stronger research base (moderate evidence), while Inositol is rated weak.
Evidence last reviewed May 2026
Evidence
🟠Weak Evidence
🟡Moderate Evidence
Research says
Research agrees
Partially supported
Expert mentions
96
1 recommend
245
3 recommend
Studies
20
referenced
20
referenced
Study dose
2000–18000mg
Doses in PCOS and gestational diabetes research typically range from 2,000–4,000 mg/day of myo-inositol, while psychiatric studies (OCD, panic disorder, bipolar) have used up to 18,000 mg/day in divided doses; the D-chiro-inositol form is studied at much lower doses and the optimal myo- to D-chiro ratio (e.g., 40:1) varies by indication.
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Best timing
MorningEveningWith food
MorningWith food
Who recommends
Caution
Generally safe
Generally safe
Inositol
Key findings
- ·Multiple meta-analyses support myo-inositol (typically 2–4 g/day) for improving metabolic and hormonal parameters in women with PCOS, representing the strongest evidence base for this supplement.
- ·Two meta-analyses of randomized controlled trials indicate that myo-inositol supplementation during pregnancy may reduce the incidence of gestational diabetes mellitus.
- ·Systematic reviews and network meta-analyses suggest inositol may provide modest benefit in Hashimoto's thyroiditis and subclinical hypothyroidism, though evidence is less definitive.
Evidence gaps
- ·Long-term safety and efficacy data are lacking across most indications — most trials are short-duration and do not establish whether benefits persist or whether adverse effects emerge with extended use.
- ·The optimal dose, form (myo-inositol vs. D-chiro-inositol vs. combined), and ratio for specific conditions have not been established through rigorous head-to-head dose-comparison trials.
Vitamin D
Key findings
- ·A strong-quality meta-analysis supports combined calcium and vitamin D supplementation for reducing osteoporosis risk in postmenopausal women.
- ·A single moderate-quality RCT (D-Health trial) found limited evidence that vitamin D supplementation significantly reduces major cardiovascular events.
- ·One moderate-quality RCT found vitamin D supplementation was associated with higher testosterone levels in men, but this has not been sufficiently replicated.
Evidence gaps
- ·No studies in this review directly tested health outcomes at the specific serum vitamin D range of 60–80 ng/mL, leaving expert claims about optimal target levels unsupported by the current evidence base.
- ·The testosterone finding comes from a single moderate-quality RCT; additional well-powered replication trials are needed before this can be considered an established benefit.