Research
Hormonal
Vitamin D3 supplementation at 100 mcg (4000 IU)/day significantly improves subjective wellbeing compared to the Adequate Intake (AI) of 15 mcg (600 IU)/day in patients with baseline insufficiency.
If you have low vitamin D levels, taking 4000 IU daily during winter may improve your mood and energy more than the standard 600 IU. This is particularly relevant if you feel low energy or mood dips in winter.
ModerateSupportsMEDIUM confidence
Between December and February, wellbeing score improved more for the 100-mcg/day group than for the lower-dosed group (1-tail Mann-Whitney p = 0.036).
Why this rating
Randomized controlled trial but lacks a placebo group and relies on subjective questionnaires with a one-tailed hypothesis.
Source
Randomized comparison of the effects of the vitamin D3adequate intake versus 100 mcg (4000 IU) per day on biochemical responses and the wellbeing of patients
Reinhold Vieth et al. · Nutrition Journal · 2004
DOI 10.1186/1475-2891-3-8
rct · n=130Cited 219×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
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