A majority of patients with daytime sleepiness and musculoskeletal pain also have low levels of vitamin D.
MINNEAPOLIS—Patients with daytime sleepiness and musculoskeletal pain are likely to have vitamin D insufficiency or deficiency, according to research presented at the 25th Anniversary Meeting of the Associated Professional Sleep Societies.
“Clinicians should be alerted to the fact that patients with [sleep disturbance and] pain may have a potentially reversible mechanism for musculoskeletal discomfort,” reported David E. McCarty, MD, a Sleep Medicine Specialist at the Louisiana State University Health Sciences Center at Shreveport, and colleagues. “Testing for vitamin D deficiency should be considered, even in areas with high amounts of natural sunlight exposure.”
An Unexpected Resolution
Dr. McCarty pointed out that some patients who have vitamin D deficiency may experience diffuse musculoskeletal pain—termed osteomalacic myopathy—which can often interfere with sleep quality but responds to supplemental vitamin D treatment.
With these factors in mind, he began to check the vitamin D levels of patients who had complained of chronic musculoskeletal pain as part of the workup that was conducted for other sleep disturbances.
“It just made sense to me that if a person is hurting, the quality of his or her sleep will suffer, and his or her waking day will be more difficult,” Dr. McCarty told Neurology Reviews. “If there was an easily reversible component to this, I wanted to identify it and treat it, if possible.” He found that a high number of patients had low levels of vitamin D and that one patient—who had a syndrome compatible with idiopathic CNS hypersomnia—experienced complete resolution of her daytime sleepiness symptoms after treatment for vitamin D deficiency.
“It was completely unexpected,” Dr. McCarty said. “Nothing else changed—only the vitamin D level. She went from being dramatically functionally impaired by sleepiness to having no impairment at all.”
The mechanism for this patient’s improved symptoms was not immediately clear, but it did not appear to be related to objective measures of sleep quality or sleep quantity. This observation raised the possibility that vitamin D deficiency plays an as-yet unidentified role in sleepiness itself, said Dr. McCarty.
Reviewing Vitamin D Levels
To test this hypothesis, Dr. McCarty and colleagues performed a retrospective chart review of 153 patients at a sleep clinic. All the patients complained of musculoskeletal pain, received venous blood sampling for 25-OH vitamin D (25-OH D), and took the Epworth Sleepiness Scale (ESS) test.
The researchers defined 25-OH D values less than 20 ng/mL as deficient, values between 20 and 29.9 ng/mL as insufficient, and values of 30 ng/mL as sufficient. They defined patients with ESS scores of 10 or more as sleepy and the remaining patients as nonsleepy. Patients’ demographic information and BMI, along with the months in which their assays were drawn, also were considered.
Eighty-four percent of patients had either vitamin D insufficiency (30%) or deficiency (54%). Nonobese patients sampled during summer months were the most likely to have normal levels of vitamin D, while obese patients and African Americans were the most likely to have vitamin D deficiency.
Among the 81 participants whose ESS scores were determined within two weeks of their 25-OH D assay, there was a trend observed toward an inverse correlation between 25-OH D values and ESS scores. Sleepy subjects had significantly lower 25-OH D scores than did nonsleepy subjects.
A Causal Relationship?
The trend toward an inverse correlation between low vitamin D levels and sleepiness does not imply causality, emphasized Dr. McCarty and colleagues. “Indeed, it is possible that sleepier patients tend to have less natural sunlight exposure and thus have lower vitamin D levels,” they wrote. “Nonetheless, it is biologically plausible that low vitamin D could contribute to sleepiness, via its effects on systemic inflammation. More research is needed to define whether vitamin D deficiency mechanistically contributes to excessive daytime sleepiness and to determine if supplementation offers a novel method for alleviating it.”
—Jack Baney