The Impact of Cigarette Smoking on Metabolic Syndrome

Abstract

Metabolic syndrome (MetS) is a constellation of interconnected cardiometabolic disorders, including obesity, hyperglycemia, dyslipidemia, and elevated blood pressure. MetS is a precursor to type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD); it increases the risk of T2DM by 3-4 times and the risk of CVD by 1.4-fold, and is more prevalent in obese individuals. As the obesity rates increase, the prevalence of MetS in the population is increased. In 2006, the global prevalence of MetS in adults was estimated to be 20%-25%, and in China, in 2007-2008, using the criteria of the Chinese Joint Committee for Developing Chinese Guidelines on Prevention and Treatment of Dyslipidemia in Adults (JCDCG), it reached 21.9% among the adult population aged ≥20 years old. Smoking is a significantand modifiablerisk factor for many of the common chronic diseases, such as cancer, lung disease, and CVD, and is a potential MetS risk factor. Many people are active or passive smokers; globally, 1.1 billion people are smokers, which is approximately one third of the adult population. In 2002, the Chinese National Survey described 350 million active smokers, and 540 million passive smokers, aged between 15 and 69 years of age. Consequently, the impact of smoking on MetSand other diseasesis of great interest. The association between active smoking and MetS risk, or the risk of one of its associated disorders, is not fully understood. Among more than 1 000 components, nicotine is the best-known of the major harmful components released from cigarette smoke. Nicotinic acetylcholine receptors (nAChRs) are widely expressed in the central and peripheral nervous system. As ligand-gated ion channels, nicotine mediates a fast synaptic transmission of the neurotransmitter at the neuromuscular junction and ganglia through binding to nAChRs. This directly or indirectly augments the release of several important neurotransmitters and hormone, mainly including arginine vasopressin (AVP), corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), growth hormone (GH), dopamine (DA), serotonin, glutamate, and γ-aminobutyric acid in the central nervous system, acetylcholine (ACh) in the central and peripheral nervous system, epinephrine and norepinephrine by the adrenal medulla, cortisol by the adrenal cortex. Note that the hypothalamic-pituitary-adrenal axis (HPA) and the renin-angiotensin-aldosterone system (RAAS) have been implicated in those processes. So it is obvious that there are associations between smoking and some metabolic disorders. Here, we review the associations between smoking and MetS, and smoking and its associated disorders, and present the available evidence of the risk of MetS associated with smoking.