LC-MS/MS Links Vitamin D Levels to Sleep Timing

A recent small-scale study conducted by researchers at Nagasaki University, Hokuriku University, and the National Institute for Environmental Studies (all in Japan) looked at how getting vitamin D, whether from food or from sun exposure, relates to actual vitamin D levels in the blood, which is the standard way doctors check whether someone has enough of this vitamin. The study also explored whether those vitamin D levels were connected to how well people slept and whether they experienced symptoms of depression. To measure vitamin D levels precisely, researchers used liquid chromatography-tandem mass spectrometry (LC-MS/MS). A paper based on this research was published in the Journal of Physiological Anthropology.¹

How Common is Vitamin D Deficiency, and Why Does It Matter?

Vitamin D deficiency is a significant concern in modern society. A comprehensive meta-analysis that reviewed 308 epidemiological studies involving 7.95 million participants from 81 countries and published between 2000 and 2022 found that the prevalence of vitamin D deficiency was 47.9% (95% confidence interval [CI], 44.9–50.9%). In areas located between latitudes 20° and 40° north, such as Japan, the prevalence was notably higher at 60.2% (55.5–64.9%), with this trend consistent across various age groups.² A report focusing on health checkup participants in Japan for the 2019 fiscal year (n = 5,481) indicated an even higher prevalence of 79%.³ Our research involvingpregnant women (n = 203) and female university students (n = 224) revealed deficiency rates of 79.8% and 80.8%, respectively.^4,5 “The widespread nature of vitamin D deficiency,” write the authors of the paper,¹ “is being rigorously examined as a public health issue that impacts individuals of all ages.”

How Was the Study Designed?

Twenty-nine young women took part in the study, which was done twice (once in spring and once in summer). To figure out how much vitamin D people were getting from food, participants filled out a questionnaire about their diet. To estimate how much vitamin D their skin was producing from sunlight, researchers tracked their sun exposure over a two-week period. Sleep patterns were tracked using a two-week sleep diary, and symptoms of depression and trouble sleeping were measured using standard questionnaires.¹

What Did the Researchers Find?

On average, blood vitamin D levels were noticeably higher in summer than in spring, which makes sense, since people get more sun exposure in the warmer months. Interestingly, while how much vitamin D people got from food did not really change much between the two seasons, the amount their bodies made from sunlight nearly doubled from spring to summer, which was a meaningful difference. The study also found that women who had lower blood vitamin D levels or ate less vitamin D in summer tended to fall asleep and wake up later than others. However, when it came to changes in vitamin D levels overall, there was no clear link between those changes and shifts in depression or insomnia symptoms.¹

The researchers admitted that their study did have a few limitations worth noting. First, sun exposure was estimated rather than directly measured, and in real life, people are not in direct sunlight the whole time they're outside; they often duck into shade. Therefore, using a wearable device that tracks actual ultraviolet (UV) exposure would give more accurate results in future research. Second, the dietary information relied on self-reporting, which tends to lead to people under-reporting what they eat. To account for this, the researchers had to adjust based on estimated calorie burn, but a more precise approach would involve having participants photograph or log their meals in detail. Third, to really understand whether correcting a vitamin D deficiency helps with things like depression or sleep problems, future studies should focus specifically on people who are both vitamin D-deficient and dealing with those conditions, and researchers would need to figure out exactly how much of a boost in vitamin D levels is actually needed to make a difference. Finally, sleep was measured using a diary, which relies on self-reporting and may not perfectly match reality. Using wearable sleep-tracking devices alongside diaries, together with better UV tracking tools, would help future studies get more precise and reliable results.¹

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References

1. Yoshizu, R.; Sasaki, T.; Nakajima, H. et al. An Exploratory Study on the Association Between Vitamin D Intake or Synthesis and Sleep Health in Young Adult Women: An Observational Study. J Physiol Anthropol. 2026. DOI: 10.1186/s40101-026-00436-8
2. Cui, A.; Zhang, T.; Xiao, P. et al. Global and Regional Prevalence of Vitamin D Deficiency in Population-Based Studies from 2000 to 2022: A Pooled Analysis of 7.9 Million Participants. Front Nutr. 2023, 10, 1070808. DOI: https://doi.org/10.3389/fnut.2023.1070808
3. Miyamoto, H.; Kawakami, D.; Hanafusa, N. et al. Determination of a Serum 25-Hydroxyvitamin D Reference Ranges in Japanese Adults Using Fully Automated Liquid Chromatography-Tandem Mass Spectrometry. J Nutr. 2023, 153 (4), 1253–1264. DOI: https://doi.org/10.1016/j.tjnut.2023.01.036
4. Miyazaki, A.; Takahashi, M.; Shuo, T. et al. Determination of Optimal 25-Hydroxyvitamin D Cutoff Values for the Evaluation of Restless Legs Syndrome Among Pregnant Women. JCSM 2023, 19 (1), 73–83. DOI: https://doi.org/10.5664/jcsm.10270
5. Yamashita, N.; Ishii, S.; Kotoku, Y. et al. Loneliness, Insomnia Symptoms, Social Jetlag, and Vitamin D Deficiency in Relation to Mental Health Problems in Japanese Female University Students: A Cross-Sectional Study. J Physiol Anthropol. 2025, 44 (1), 19. DOI: https://doi.org/10.1186/s40101-025-00403-9