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Smoking and Small, Dense Low-Density Lipoproteins

We thank Dr Kucuk et al for their interesting letter regarding our recent article published in Angiology, entitled ‘‘Size and subclasses of low-density lipoproteins in patients with obstructive sleep apnea.’’ Indeed, we have investigated for the first time whether patients with obstructive sleep apnea (OSA) may have alterations in plasma lipoprotein subclasses. This is of potential importance, since patients with OSA are at increased risk of atherosclerotic morbidity and mortality, with higher risk of hypertension, dyslipidemia, and the metabolic syndrome (MetS). Alterations in plasma lipids are common in OSA and include reduced highdensity lipoprotein cholesterol as well as raised triglycerides and low-density lipoprotein (LDL) cholesterol concentrations. We therefore investigated LDL subclass distribution, since not only the quality but also the quantity of LDL can influence cardiovascular risk, and it has been previously hypothesized that atherogenic lipoproteins may play a role in OSA. In our study, we found that in patients with OSA the presence of concurrent MetS is an independent predictor of LDL size and subclasses, whereas the severity of OSA does not contribute independently to alterations in lipid phenotype. As highlighted by Kucuk et al, smoking can affect the plasma lipid profile and, therefore, its association with LDL phenotype is of interest. We did not evaluate in our study the relative contribution of smoking, so it cannot be excluded that the effect of smoking may have contributed to the main finding of our study, that the presence of concurrent MetS was an independent predictor of LDL size and subclasses in patients with OSA. It is well known that smoking may enhance oxidative stress, and previous studies have reported enhanced oxidative stress in OSA. The exact relationships between smoking status and alterations in LDL subclasses are still not fully elucidated. Therefore, it would be of interest to assess in future studies whether smoking habit is associated with alterations in LDL subclasses in patients with OSA as well as in the general population. Whatever the findings will be, promoting smoking cessation should remain one of the highest priorities in the battle against cardiovascular diseases.