In the relationship between obstructive sleep apnea (OSA) and hypertension, the presence of moderate-to-severe OSA is significantly associated with the presence of hypertension, as well as the development of hypertension. Continuous positive airway pressure (CPAP) therapy has shown a significant antihypertensive effect, especially when CPAP is used for ≥4 h per day. In the relationship between OSA and diabetes, the presence of moderate-to-severe OSA is significantly associated with the presence of diabetes, as well as the development of diabetes. The effect of CPAP therapy on the improvement of insulin resistance in OSA patients has been indicated in meta-analyses, although the result of each study is not consistent. In the relationship between OSA and dyslipidemia, some cross-sectional studies have shown a significant association, and the effects of CPAP therapy on dyslipidemia are inconclusive. There is a certain association between lifestyle diseases and OSA, but evidence for the improvement of these conditions with CPAP therapy is not robust.