A recent meta-analysis published in the journal Respiratory Research found a link between low serum levels of vitamin D and a higher risk of incidence of obstructive sleep apnea (OSA). The authors of the analysis found 29 eligible studies which met their inclusion criteria, comprising a total of 6,717 subjects.
 
OSA, which affects 2-5% of the world population, refers to a sleep-related disorder characterized by a repetitive incomplete or total obstruction of the upper respiratory tract during sleep, causing decreased blood oxygen levels, and is associated with sleepiness, fatigue, inattention, memory loss, and headaches during the day, raising significant quality of life issues and even shortening life expectancy. This is due to the many risks OSA poses on cardiovascular, cognitive, and pulmonary health issues.
 
Based on several prior studies, the authors of the meta-analysis posited that blood concentrations of vitamin D could be positively associated with reductions in the risk of developing OSA, though the pathogenesis of the disorder is not very well-understood.  One clear correlation, though, is high BMI. What the researchers found was that BMI and OSA interact to influence the vitamin D level, meaning that vitamin D levels were lowest on average among participants who had both overweight or obesity and OSA.
 
The mechanism underlying the relationship between blood concentrations of vitamin D and OSA are still a mystery, the authors of the study said.
 
“According to the source, metabolism, and various influencing factors of vitamin D, we have summarized several seemingly reasonable biological explanations,” the authors wrote. “Previous studies have proven that there is a significant correlation between the vitamin D level and obesity, and most OSA patients are obese. Most OSA patients in our study had a BMI greater than 30 […] vitamin D, as a fat soluble vitamin, is stored by adipose tissue. In obese patients, who have greater amounts of adipose tissue, the storage distribution volume of vitamin D is also markedly increased,” which the authors said reduces the amount of circulating vitamin D and its bioavailability.
 
The authors of the study went on to describe the relationship between obesity and OSA as a “vicious circle,” as disordered sleep results in significant reductions in daytime activity, aggravating obesity. However, vitamin D deficiency may be part byproduct and part cause of OSA, the researchers said, highlighting that vitamin D3 could improve several physiological, biochemical, and subjective health conditions related to inflammation, oxidative stress, energy metabolism, and more, meaning that it may have some benefit in OSA patients. More research, however, is needed.