Sleep disorders, encompassing conditions such as insomnia, obstructive sleep apnea, periodic limb movement disorder, and narcolepsy, represent a widespread chronic health issue globally (1, 2). It is estimated that approximately 10% to 30% of adults worldwide experience sleep disorders of varying severity, with the prevalence of insomnia symptoms generally increasing with age (3). Chronic sleep disturbances not only reduce quality of life but also elevate the risk of cardiovascular disease, type 2 diabetes, and serious mental illnesses such as depression and anxiety. In addition to lifestyle, sleep environment, and psychosocial factors, serum 25-hydroxyvitamin D (25(OH)D) concentrations are believed to be closely related to the occurrence and development of sleep disorders.

As a fat-soluble vitamin, vitamin D plays a crucial role in regulating calcium-phosphorus metabolism, maintaining bone health, and balancing mineral levels (4). 25(OH)D is the primary circulating form of vitamin D in the body, and its level can reflect the nutritional status of vitamin D. Epidemiological evidence suggests that vitamin D deficiency is associated not only with musculoskeletal diseases (5), but also with an increased risk of various chronic conditions, including cardiovascular disease, autoimmune diseases, and cancer (6–9). Increasing evidence links vitamin D deficiency to a higher risk of psychiatric disorders such as sleep disturbances, depression, and anxiety (10, 11). A Mendelian randomization study based on NHANES data found that low 25(OH)D concentrations in the general adult population were significantly associated with an increased risk of sleep disorders, even after controlling for confounders (12). A meta-analysis also revealed a general association between vitamin D deficiency and sleep disorders in Asian populations (13).

Current studies provide preliminary evidence of the association between vitamin D and sleep disorders, primarily focusing on the general population. Global epidemiological data indicate that, despite recent declines in the incidence and mortality of cardiovascular diseases among individuals with prediabetes and diabetes, the prevalence of mental illnesses, including sleep disorders and depression, continues to rise yearly (14). However, research on the relationship between vitamin D deficiency and sleep disorders in individuals with prediabetes and diabetes remains limited, with insufficient systematic evidence. Additionally, compared to the general population, individuals with prediabetes and diabetes are often more prone to vitamin D deficiency, with lower serum 25(OH)D concentrations (15–18). This may result from factors such as insulin resistance, impaired kidney function, and drug interactions.

This study aims to utilize data from the UK Biobank, a large prospective cohort study, to explore the association between serum 25(OH)D concentrations and the risk of sleep disorders in individuals with prediabetes and diabetes. Our research incorporates both cross-sectional and prospective cohort designs. Additionally, we examine whether there is heterogeneity in the associations across different subgroups, such as age, sex, and smoking status. Through this study, we hope to provide new insights into the mechanisms by which vitamin D influences diabetes-related sleep disorders, and to offer a scientific basis for developing targeted clinical interventions to improve sleep quality in patients.

This study, employing both cross-sectional and prospective cohort designs, systematically investigates the association between serum 25(OH)D levels and the risk of sleep disorders in individuals with prediabetes and diabetes. First, the cross-sectional study revealed a significant inverse association between serum 25(OH)D levels and the risk of sleep disorders. Building on this, our prospective study further confirmed this crucial finding. Over an average follow-up period of 12.8 years, we observed that individuals with sufficient serum 25(OH)D levels (≥75 nmol/L) had a significantly lower risk of developing sleep disorders compared to those with severe vitamin D deficiency. Specifically, the risk was reduced by 48% in the prediabetes group and by 52% in the diabetes group. These findings suggest that maintaining adequate vitamin D levels may help reduce the prevalence and future risk of sleep disorders in individuals with impaired glucose metabolism. Moreover, subgroup analyses indicated that this association was more pronounced in specific populations, including individuals aged ≤60 years, non-smokers, those with a BMI ≥30 kg/m², and females.

This study is the first to explore the association between serum 25(OH)D concentrations and the risk of sleep disorders in individuals with dysglycemia, including those with prediabetes and diabetes. Our findings are generally consistent with previous research on the relationship between vitamin D and sleep disorders. Increasing evidence suggests that vitamin D deficiency is associated with poor sleep quality (20), reduced sleep duration (21), and increased sleep disorder risk (13), with similar associations observed in various populations, such as the elderly (22), community dwellers (23), and individuals with obesity (24). An 8-week randomized controlled trial (25) found that high-dose vitamin D supplementation alleviated fatigue, reduced anxiety, and improved cognitive function. However, it is important to note that not all studies support the positive effects of vitamin D on sleep. For instance, a randomized controlled trial in overweight or obese postmenopausal women (26) found that daily supplementation with 2000 IU of vitamin D for 12 months did not improve sleep quality, depressive symptoms, or health-related quality of life. This result contrasts with our findings and those of most other studies, suggesting that the relationship between vitamin D and sleep may not be linear or unidirectional, and could be influenced by factors such as population characteristics, vitamin D supplementation dosage, and study design.

Sleep is a complex physiological process finely regulated by various factors, including neurotransmitters (27), hormones (28), inflammatory status (29), and circadian rhythms (30). Individuals with dysglycemia are at a higher risk for sleep disorders (31). In addition to hyperglycemia caused by insulin resistance, which may affect neurotransmitter levels in the brain related to sleep regulation (32, 33), the common vitamin D deficiency in these individuals may also play a significant role (34). Some studies suggest (35, 36) that low vitamin D levels may indirectly impact sleep quality and duration by contributing to conditions such as chronic pain, myopathy, cardiovascular diseases, and mood disorders. Vitamin D, a multifunctional hormone, has receptors widely distributed in various tissues (37), including the brain. Research indicates that vitamin D may influence sleep health through several mechanisms, with the inflammatory pathway being widely recognized (38, 39). A meta-analysis demonstrated (40) elevated pro-inflammatory cytokines (such as TNF-α, IL-8, and IL-1β) in OSA patients compared to controls. Additionally, a study in the United States highlighted the essential role of IL-6 in sleep regulation (29). Although these studies suggest that vitamin D may influence sleep quality through its modulation of inflammatory responses (36), the precise mechanisms by which vitamin D affects sleep still require further investigation.

The strength of this study lies in its combination of cross-sectional and prospective designs, which provides a comprehensive analysis of the relationship between serum 25(OH)D concentrations and the risk of sleep disorders. The cross-sectional study allowed us to assess participants’ vitamin D levels and sleep disorder status at a specific point in time, enabling the identification of potential associations. The prospective study, with long-term follow-up, allowed us to observe the impact of serum 25(OH)D concentrations on the incidence of sleep disorders over time. This combined approach not only enhances the reliability of the results but also provides stronger support for causal inference (41).

Another strength of this study is the large sample size and focus on individuals with dysglycemia, which further increases the reliability and novelty of the findings. Our study found that the effect of vitamin D supplementation on reducing sleep disorder risk was most pronounced in individuals aged ≤60 years and in females. These findings suggest that age and sex may be important factors influencing the development of sleep disorders, and may also be related to variations in vitamin D concentrations among different subgroups. For example, studies have indicated that the prevalence of obstructive sleep apnea (OSA) is higher among women, particularly postmenopausal women (42). This may be due to hormonal changes that make women more susceptible to sleep problems, such as reduced sleep quality, sleep deprivation, and increased risks of OSA, restless legs syndrome, and insomnia during menopause (43–45). Recent clinical research has further elucidated the nuanced relationship between vitamin D and sex (46). Specifically, the inverse correlation between serum vitamin D and insulin resistance was statistically significant only in women with vitamin D deficiency, and not in men or women with sufficient vitamin D levels. This suggests a potential threshold effect and underscores the importance of considering sex as a critical biological factor in vitamin D’s impact on metabolic health, potentially extending to sleep regulation. In addition to age and sex, our subgroup analysis also found that BMI and smoking status may modulate the effects of vitamin D on sleep disorder risk. These results underscore the importance of considering individual characteristics when designing personalized interventions for sleep disorders.

However, this study has several limitations that should be acknowledged. First, although our findings suggest an association between higher vitamin D concentrations and reduced sleep disorder risk, as an observational study, we cannot fully exclude the influence of residual confounding factors, and causality cannot be determined. Depression is a potential confounding factor that affects a significant proportion of individuals with diabetes (47). Depression often leads to poor social interactions, dietary habits, and obesity, all of which can impact vitamin D levels (48). Furthermore, the impact of hormones on vitamin D metabolism, particularly in women (49), including menopausal status and the use of vitamin D supplements, requires further exploration.

Second, the reliance on large biobank and electronic medical records introduces potential limitations. Specifically, we used ICD codes for sleep disorders, which encompass a wide range of conditions such as insomnia, hypersomnia, narcolepsy, circadian rhythm disorders, and restless legs syndrome. The lack of more specific diagnoses, such as obstructive sleep apnea (OSA), which is particularly common in individuals with diabetes, may limit the accuracy of our findings. Future studies with more detailed sleep disorder classifications would enhance the validity of these associations. In addition, vitamin D levels were measured only at baseline, limiting our ability to capture changes over time or assess the impact of lifestyle modifications. Moreover, due to the limitations of the database, we did not include fasting blood glucose measurements, which would have provided better insight into the relationship between blood sugar control and sleep disorders. Finally, the storage and viability of serum vitamin D samples over time were not specified, which may impact the accuracy of the measurements.

This study contributes new insights into the preventive potential of vitamin D supplementation for sleep disorders in individuals with abnormal glucose metabolism. Future research, particularly randomized controlled trials, should investigate the therapeutic efficacy of vitamin D in improving sleep quality and reducing sleep disorder incidence. Additionally, understanding the biological mechanisms linking vitamin D to sleep regulation and examining potential interactions with other risk factors may facilitate the development of targeted, personalized interventions to optimize sleep health and quality of life for at-risk populations.