Elucidation of Vitamin D Levels and Heart Rate Variability Influence on Endothelial Function Via Renin Angiotensin Aldosterone System Augmentation in Obstructive Sleep Apnea

Obstructive sleep apnea (OSA), which is closely related to obesity, is a chronic, serious and potentially life-threatening sleep-related breathing disorder, characterized by periodic narrowing and obstruction of the pharyngeal airway during sleep, occurring in 25% to 58% of men and 10% to 37% of women.

Untreated OSA leads to lost productivity and workplace accidents resulting in injury and fatality. Patients with OSA are involved in automobile accidents more frequently than other licensed drivers. OSA is also associated with long-term health complications, including metabolic disorders and cardiovascular diseases, which is the leading cause of death worldwide.

For decades, we have believed that the activation of RAAS, mainly in response to intravascular volume contraction, regulated the biosynthesis of aldosterone. There is growing evidence that suggests aldosterone secretion to be beyond RAAS regulation. There is new evidence that both plasma and urinary aldosterone concentrations are increased in people with obesity. This relationship, on the other hand, is less studied for patients with OSA, with equivocal data. Aldosterone levels contributed to severity of OSA in patients with primary aldosteronism and resistant hypertension. In a limited number of studies, primary aldosteronism was found to be more frequent in patients with OSA whereas patients with OSA had higher aldosterone levels and prevalence of PA.

Vitamin D plays an important role in calcium homeostasis and metabolism. It is involved in maintenance of calcium and phosphorus levels in the blood, and bone content. Vitamin D is also implicated in several non-skeletal conditions, such as cardiovascular disease, cancer, autoimmune disorders and diabetes mellitus. Vitamin D deficiency has been associated with worse cardiovascular outcomes. Vitamin D deficiency augments the RAAS leading to elevated aldosterone and lowered renin. This is supported by a reduction in aldosterone and an increase in plasma renin in patients with heart failure, arterial hypertension and primary aldosteronism when repleted with vitamin D.

Sympathetic and parasympathetic nervous system interactively regulate visceral functions to maintain the body homeostatic milieu, and to enable reaction and adaptation to external and internal stressor stimuli. Patients with OSA exhibit high levels of sympathetic activity during sleep as well as when awake. Aldosterone is found to augment sympathetic activity in patients with resistant hypertension.