Vitamin D for energy: only worth it if you're actually low
Evidence is mixed or early — not worth paying for yet. · Small or few RCTs, or mixed results.
If your level is low — common in winter, indoors, or with darker skin at high latitudes — topping up can lift fatigue. If it's normal, adding more does nothing measurable. Check the number before buying the bottle.
The world's evidence
- Effect, in daily-life terms
- In people with low vitamin D and fatigue, a single high dose reduced self-rated fatigue in a 4-week RCT; in the general population large trials show no benefit on major health outcomes and no consistent energy effect.
- Who was studied
- One RCT (n=120, vitamin D-deficient adults with fatigue) on fatigue; the VITAL trial (n≈25,000, 5 years) for general-population outcomes.
- Cheaper option with better evidence
- Morning daylight (10–30 min outside)
Worth knowing
Safe at typical supplement doses (1,000–2,000 IU/day); very high doses over months can raise blood calcium. The useful first step is knowing your level — a blood test, or in Japan the annual health check if it is included.
Your evidence
Research says what happens on average. Log it for 14 days and Feelments shows what changed in your sleep, energy or mood — a pattern in your own logs, not a claim.
Sources
- Randomized trial (2016) — Nowak et al., Medicine (Baltimore) — double-blind RCT (n=120, deficient adults with fatigue), single 100,000 IU dose; fatigue scores improved vs placebo at 4 weeks.
- Randomized trial (2019) — Manson et al., NEJM (VITAL) — 2,000 IU/day for ~5 years in ~25,000 adults did not lower cancer or cardiovascular events.
Last reviewed 2026-09-03. Verdicts are editorial assessments of published research, at the population level.
Feelments is for personal tracking and general wellness education. It does not provide medical advice, diagnosis, or treatment.