Vitamin D and Sleep

Vitamin D receptors are expressed throughout the hypothalamus, midbrain, and brainstem — including sleep-regulatory nuclei. Observational studies consistently link low serum 25(OH)D to poor sleep quality and short sleep duration. The randomised evidence is cautiously supportive but not definitive.

Observational data

A 2018 meta-analysis pooling nine cohort studies (~9,400 participants) found deficient individuals were 1.5–2× more likely to report sleep disorders, poor sleep quality, or sleep durations under 5 hours. The association survived adjustment for age, sex, BMI, and physical activity — but confounding by lifestyle (indoor time, depression) is hard to eliminate.

Randomised trials

Small trials in vitamin-D–deficient adults with insomnia have shown improvements in subjective sleep quality (Pittsburgh Sleep Quality Index) and, in one Iranian trial, polysomnographic sleep latency after 8 weeks of 50,000 IU weekly cholecalciferol. Larger trials in unselected populations have not shown clear benefit. The pattern mirrors most vitamin D outcomes: correcting deficiency helps, supplementing sufficient people doesn't.

Obstructive sleep apnea (OSA)

OSA patients have consistently lower 25(OH)D than matched controls, and severity of OSA (higher AHI) correlates with lower 25(OH)D. Whether vitamin D deficiency causes OSA (through respiratory muscle weakness or upper-airway inflammation) or vice versa (via reduced daytime activity and outdoor time) is unresolved. Supplementation is unlikely to substitute for CPAP but may improve muscle function.

Should you take vitamin D at night?

A common online claim is that evening vitamin D dosing disrupts sleep because it suppresses melatonin. The evidence is anecdotal — no rigorous trial has demonstrated the effect. Time-of-day dosing doesn't measurably affect steady-state 25(OH)D. If you subjectively notice sleep changes after evening vitamin D, switch to morning. Otherwise pick whichever timing you'll keep consistent — see our timing page.

Practical guidance

• If you sleep poorly and haven't checked 25(OH)D recently, it's a reasonable test.
• Correct any deficiency (aim for 30–40 ng/mL) with 1,000–2,000 IU/day cholecalciferol.
• Don't expect dramatic sleep improvement from vitamin D alone — sleep hygiene, CBT-I, and treating any OSA remain first-line.
• If evening dosing seems to bother your sleep, try morning; there's no absorption downside.