Research on people recruited randomly from the community suggests that, after adjusting for various demographic, behavioral, and physical characteristics, there is no association between sleep apnea and hypertension.
Hypertension and obstructive sleep apnea are both highly prevalent, and share risk factors, so unsurprisingly, most people with OSA have HTN. This overlap has made it fiendishly hard to determine if OSA actually causes HTN. The widespread belief that OSA causes HTN was creeping close to dogma, egged on by cross-sectional studies that suggested an independent association (after controlling for age, BMI, etc), and therapy trials that showed a ~2 mm Hg reduction in blood pressure with treatment of OSA with continuous positive airway pressure (CPAP).
As Irene Cano-Pumarega et al point out, though, even an independent association between OSA and HTN does not prove causality. There could still be a hidden, unmeasured factor that causes both HTN and OSA. Longitudinal cohort studies are the gold standard for this type of question, and they’ve published theirs in the December AJRCCM.
They enrolled Spaniards selected randomly from the community who did not have sleep apnea by initial polysomnogram, and followed them for ~7.5 years (the Vitoria cohort). At the end, subjects underwent home polygraphy (not polysomnography). They had a cohort of 1,180 subjects left to analyze after excluding those with OSA at study onset or who were lost to followup.