Do you need a vitamin D supplement?

What we can tell you today: how thoroughly this has been studied.

Well studied

15 studies, including 2 that bring together the results of several trials in people.

5 Repeated evidence 2 studies

4 Large controlled trial 8 studies

3 Small study in people 5 studies

This says how thoroughly something has been studied — not whether it works for you. What each study actually found is in the study itself, and in the plain-language write-ups we are adding.

Appears under: Hair and nails · Sleep, energy and the brain · Menopause and hormones

The studies

5 Repeated evidence Genotypic Spectrum and its Correlation with Alopecia and Clinical Response in Hereditary Vitamin D Resistant Rickets: Our Experience and Systematic Review.
2023 · Calcified tissue international
5 Repeated evidence Serum 25 hydroxyvitamin D in non-scarring alopecia: A systematic review and meta-analysis.
2024 · Journal of cosmetic dermatology
4 Large controlled trial Synergistic effects of exercise, cognitive training and vitamin D on gait performance and falls in mild cognitive impairment-secondary outcomes from the SYNERGIC trial.
2025 · Age and ageing · 161 participants
4 Large controlled trial Impact of Vitamin D Supplementation on Cognition in Adults With Mild to Moderate Vitamin D Deficiency: Outcomes From the VitaMIND Randomized Controlled Trial.
2025 · Journal of the American Medical Directors Association · 620 participants · manufacturer helped fund this
4 Large controlled trial The Effects of Vitamin D-Enriched Mushrooms and Vitamin D3 on Cognitive Performance and Mood in Healthy Elderly Adults: A Randomised, Double-Blinded, Placebo-Controlled Trial.
2021 · Nutrients · 436 participants
4 Large controlled trial Cognition and Vitamin D in Older African-American Women- Physical performance and Osteoporosis prevention with vitamin D in older African Americans Trial and Dementia.
2019 · Journal of the American Geriatrics Society · 260 participants
4 Large controlled trial The severity of vasomotor symptoms and number of menopausal symptoms in postmenopausal women and select clinical health outcomes in the Women's Health Initiative Calcium and Vitamin D randomized clinical trial.
2021 · Menopause (New York, N.Y.) · 20,050 participants
4 Large controlled trial Effect of omega-3 and vitamin D co-supplementation on psychological distress in reproductive-aged women with pre-diabetes and hypovitaminosis D: A randomized controlled trial.
2021 · Brain and behavior · 168 participants
4 Large controlled trial Calcium and vitamin D supplementation do not influence menopause-related symptoms: Results of the Women's Health Initiative Trial.
2016 · Maturitas · 17,101 participants
4 Large controlled trial Effect of monthly vitamin D3 supplementation in healthy adults on adverse effects of earthquakes: randomised controlled trial.
2015 · BMJ (Clinical research ed.) · 308 participants
3 Small study in people Vitamin D and probiotic co-supplementation affects mental health, hormonal, inflammatory and oxidative stress parameters in women with polycystic ovary syndrome.
2019 · Journal of ovarian research · 60 participants
3 Small study in people Combined microneedling with topical vitamin D3 or bimatoprost versus microneedling alone in the treatment of alopecia areata: A comparative randomized trial.
2023 · Journal of cosmetic dermatology · 25 participants
3 Small study in people Correlations between serum 25-hydroxyvitamin D levels and nailfold microvascular changes in psoriatic arthritis patients with distal interphalangeal arthritis treated with TNF inhibitors.
2026 · Frontiers in immunology · 75 participants
3 Small study in people A unique insertion/duplication in the VDR gene that truncates the VDR causing hereditary 1,25-dihydroxyvitamin D-resistant rickets without alopecia.
2007 · Archives of biochemistry and biophysics
3 Small study in people 'Atrophic telogen effluvium' from cytotoxic drugs and a randomized controlled trial to investigate the possible protective effect of pretreatment with a topical vitamin D analogue in humans.
2005 · The British journal of dermatology