The aim of our study was to determine the prevalence of MetS in COPD patients with different nutritional states and GOLD stages. We also determined the extent of systemic inflammation and its association with the presence of MetS by measuring high-sensitivity CRP levels. Abdominal obesity, hypertension, hyperglycemia and metabolic syndrome were also more common in the overweight/obese group (BMI ≥ 25 kg/m2; p < 0.0001). Metabolic syndrome occurred simultaneously with several cardiovascular comorbidities and type 2 diabetes. Metabolic syndrome was found in 59.1% of patients with COPD, this prevalence is higher than in previous studies, which showed a value between 21% and 58%. It also depended on the severity of the disease, the geographical location of the research, and the definition used, and suggested that metabolic syndrome is more common in patients with more severe respiratory disease .
The metabolic syndrome, defined by IDF criteria, mainly depends on abdominal obesity.
Studies have shown that the quantity of abdominal - visceral - adipose tissue is increased in patients with pulmonary obstructive diseases. The exact cause and mechanism are unspecified, but presumably unhealthy diet and inactive lifestyle play a major role in its development.
Interestingly, patients with normal nutritional status and metabolic syndrome had decreased physical performance (6MWD) compared to patients without metabolic syndrome but with COPD. Metabolic syndrome is known to reduce muscle mass, which may explain the experience mentioned above, and it is confirmed by our present research as well. The correlation is also reversed, because the low physical activity observed in COPD can be the cause of the development of the metabolic syndrome .
The most recent GOLD recommendation on the diagnosis, treatment and prevention of COPD  highlighted the importance of comorbidities. In particular, cardiovascular disease, hypertension, lung cancer, depression, osteoporosis, and metabolic disorders such as type 2 diabetes, metabolic syndrome, as they significantly affect the prognosis, and some of them are the most common causes of death even in mild COPD .
Nearly half of COPD patients participating in a pulmonary rehabilitation program are overweight or obese, which negatively affects respiration and exercise tolerance, especially while walking, however, a contradiction was described that patients with higher BMIs live longer than patients with low or normal BMI. This paradox, the so called “Obesity paradox” disappears above 30 BMI and physical inactivity and comorbidities clearly negatively affect the survival of individuals with COPD .
The term metabolic syndrome, or “cardiometabolic syndrome,” is often used today to describe the interaction of cardiovascular, renal, metabolic, prothrombotic and inflammatory disorders that result in increased morbidity and mortality in patients with COPD.
Several studies have evaluated the lipid profile of COPD patients, but the results remain contradictory. Sibel et al. found that serum HDL levels were significantly lower, while TG levels were significantly higher in patients with stable COPD than in controls . Jiayu et al. described that there was no difference in serum TG, total chol, and LDL levels between COPD patients and controls . Breyer et al reported that metabolic syndrome was more common among overweight and obese COPD patients . Ummugulsum Can et al. examined disease severity and serum lipid levels and found that HDL levels were significantly lower in more severe COPD stages (GOLD III. and IV.) than in control subjects .
We detected a significantly increased TG level and a significantly decreased HDL cholesterol level among overweight patients (BMI > 25 kg/m²), patients with MetS had significantly higher BMI than patients without MetS in the lipid profile in our present study.
Systemic inflammation itself is associated with decreased serum HDL and increased TG levels in COPD , it has been shown that inflammatory cytokines disrupt lipid metabolism, there is an inverse correlation between serum HDL and IL-6 levels . Patients with COPD are physically inactive, which further increases the risk of dyslipidemia, and they often use corticosteroids, which also increases the occurance of dyslipidemia and obesity . In addition, smoking as well as oxidative stress are possible mechanisms for the development of dyslipidemia, and all together they contribute to the development of MetS .
MetS appears to be more common in female patients with higher BMI. This allegation was confirmed by our present study as well. Numerous studies have shown that GOLD stage II patients have the highest MetS prevalence compared to more severe GOLD stage patients . First, this observation may be due to the fact that the role of lifestyle in less advanced COPD disease has a greater effect on metabolism than other factors in the progression of the disease. Second, assuming that MetS has a higher cardiovascular risk in COPD, they may die earlier because of their CVD and may not reach end-stage COPD.
Drugs can directly affect the prevalence of MetS, e.g. oral glucocorticoids increase blood glucose levels, LDL levels and appetite, and can cause muscle atrophy and abdominal obesity. Other common drugs in the treatment of COPD, such as antidepressants, can cause decreased glucose tolerance, thus contributing to the development of MetS .
Recent studies have identified a so-called “co-morbidity predominant subtype” in COPD patients, characterized by a group of metabolic comorbidities, including CVD, T2DM, and obesity. Patients with CVD, hypertension and T2DM have been shown to be at increased risk for morbidity and mortality. Particular importance should be given to sitting position or stillness because the duration of sitting position shows a significant correlation with blood sugar levels and abdominal circumference. In Park and Larson's study, more than 11 hours of on-site sessions per day were recorded for people with COPD. This is also disadvantageous because studies in the healthy population suggest that prolonged sitting or sedentary work has a strong effect on the development of metabolic syndrome, regardless of moderate or intense physical activity. Even low-intensity physical activity can create a more favorable metabolic situation [29, 30].
Kupeli et al. and Abdelghaffar et al. reported that the presence of MetS in COPD patients increases the number (2.4 vs. 0.7) and duration (7.5–8.0 vs. 5.0–5.5 days) of exacerbations . In our study, we found a higher mMRC score in the presence of MetS and a significantly higher exacerbation rate, confirming the observations of a lower quality of life in COPD patients with MetS.
However, it is unclear whether early identification and treatment of metabolic syndrome in patients reduce the risk of developing cardiovascular disease and improves long-term clinical outcomes. Weight loss alone affects a number of risk factors that are very common in obesity, such as hypertension, dyslipidemia, and insulin resistance.Various studies have examined the effect of exercise in overweight and obese individuals through blood pressure, lipid profiles and glucose [32, 33]. Improvement in glycated hemoglobin (HbA1c) and insulin sensitivity has been described, and the total duration of exercise appears to be more important than the mode of exercise .
Our results show that the co-morbidity index increases in patients with metabolic syndrome, especially in patients who are overweight or obese, therefore, metabolic syndrome should be recognized early, and treated appropriately in patients with COPD. Our present study was a cross-sectional study, further longitudinal prospective studies are needed to study the long-term effects of metabolic syndrome on cardiovascular and other diseases in COPD patients.