Sometimes poor sleep isn't about your bedtime routine at all. A few nutrient shortfalls are linked to restless nights, and a simple blood test can help rule them out.
Iron and restless legs
Restless legs syndrome (RLS) causes an uncomfortable urge to move your legs, usually in the evening or at night, which can make it hard to fall asleep. Low iron is closely tied to it.
The American Academy of Sleep Medicine's latest guideline recommends that everyone with RLS has their iron levels checked, including ferritin, a measure of the body's iron stores.¹
RLS is more common in women, and it often appears in the last months of pregnancy, usually easing after birth.² Women are also more likely to run low on iron, especially during pregnancy or with heavy periods.³
Don't start iron pills on a hunch, though. High doses can cause nausea and constipation, and a common inherited condition makes some people store too much iron.³ If you think your iron might be low, talk to your doctor before taking any supplements. A simple blood test can tell you where you stand.
Vitamin D and sleep
Vitamin D, often called the sunshine vitamin, helps your body absorb calcium and supports your muscles and immune system. Your skin makes it from sunlight, but few foods contain it naturally.⁴
People who are low in vitamin D are more likely to have sleep problems, including poorer-quality and shorter sleep.⁵ You're more likely to run low if you spend little time outdoors, have darker skin, are older, or live with obesity.⁴
Good food sources include oily fish like salmon and trout, fortified milk and cereals, egg yolks, and mushrooms grown under UV light.⁴ Supplements may help some people sleep better, but research is still early.⁶ Too much vitamin D can be harmful, so it's worth getting your levels checked first.⁴
Magnesium is another one to watch. Early research suggests it may help some people fall asleep a little faster.⁷
What to do next
- Notice your patterns. Restless legs, waking unrefreshed, or daytime tiredness are worth jotting down. Your Sleepwave history can help you spot trends to share with your doctor.
- Ask about a blood test. If symptoms last, ask your doctor to check your iron (including ferritin) and vitamin D.¹ ⁴
- Skip high-dose supplements without advice. More isn't always better, and some supplements interact negatively with medicines.³ ⁴
Getting checked takes the guesswork out, and it might be the missing piece in your sleep puzzle.
References
- Winkelman JW, Berkowski JA, DelRosso LM, et al. Treatment of restless legs syndrome and periodic limb movement disorder: an American Academy of Sleep Medicine clinical practice guideline. Journal of Clinical Sleep Medicine. 2025;21(1). doi:10.5664/jcsm.11390. https://doi.org/10.5664/jcsm.11390
- National Institute of Neurological Disorders and Stroke. Restless legs syndrome. Last reviewed March 13, 2026. https://www.ninds.nih.gov/health-information/disorders/restless-legs-syndrome
- NIH Office of Dietary Supplements. Iron: fact sheet for health professionals. Updated September 4, 2025. https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/
- NIH Office of Dietary Supplements. Vitamin D: fact sheet for health professionals. Accessed October 13, 2026. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
- Gao Q, Kou T, Zhuang B, Ren Y, Dong X, Wang Q. The association between vitamin D deficiency and sleep disorders: a systematic review and meta-analysis. Nutrients. 2018;10(10):1395. doi:10.3390/nu10101395. https://doi.org/10.3390/nu10101395
- Abboud M. Vitamin D supplementation and sleep: a systematic review and meta-analysis of intervention studies. Nutrients. 2022;14(5):1076. doi:10.3390/nu14051076. https://doi.org/10.3390/nu14051076
- Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review & meta-analysis. BMC Complementary Medicine and Therapies. 2021;21(1):125. doi:10.1186/s12906-021-03297-z. https://doi.org/10.1186/s12906-021-03297-z
