Diabetes mellitus is a leading cause of mortality and increased disability-adjusted life years worldwide. In Korea, the prevalence of diabetes increased from 8.6% to 11.0% in 2001 to 2013 and the prevalence of adult obesity, which is the most important risk factor of diabetes, increased from 29.2% to 31.8% during the same period. There has been a dramatic increase in the number of obese Koreans with diabetes in recent decades and the prevalence of diabetes in people aged 40 years and older also increased in 2001 to 2013. Nevertheless, the mean age at the first diagnosis of diabetes was very similar for men in 2005 and 2013, while the mean age for women decreased slightly. There is an inverse linear relationship between body mass index and age at the diagnosis of diabetes among those who are newly diagnosed. Accordingly, the prevalence of diabetes is increasingly shifting to younger individuals and those who are obese. Therefore, public efforts should focus on healthy lifestyle changes, primary prevention measures, screening for the early detection of diabetes, and long-term management.
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Branched-chain amino acids (BCAAs) are essential amino acids that are not synthesized in our body; thus, they need to be obtained from food. They have shown to provide many physiological and metabolic benefits such as stimulation of pancreatic insulin secretion, milk production, adipogenesis, and enhanced immune function, among others, mainly mediated by mammalian target of rapamycin (mTOR) signaling pathway. After identified as a reliable marker of obesity and type 2 diabetes in recent years, an increasing number of studies have surfaced implicating BCAAs in the pathophysiology of other diseases such as cancers, cardiovascular diseases, and even neurodegenerative disorders like Alzheimer's disease. Here we discuss the most recent progress and review studies highlighting both correlational and potentially causative role of BCAAs in the development of these disorders. Although we are just beginning to understand the intricate relationships between BCAAs and some of the most prevalent chronic diseases, current findings raise a possibility that they are linked by a similar putative mechanism.
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Iodine is a micronutrient essential for the production of thyroid hormones. Iodine deficiency is the most common cause of preventable mental impairment worldwide. Universal salt iodization (USI) has been introduced in many countries as a cost-effective and sustainable way to eliminate iodine deficiency disorders for more than 25 years. Currently, the relationship between USI and iodine excess has attracted more attention. Iodine excess can lead to hypothyroidism and autoimmune thyroiditis, especially for susceptible populations with recurring thyroid disease, the elderly, fetuses, and neonates. Nationwide USI was introduced in China in 1996. This review focused on the effects of iodine excess worldwide and particularly in China.
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Adipocyte differentiation, termed adipogenesis, is a complicated process in which pluripotent mesenchymal stem cells differentiate into mature adipocytes. The process of adipocyte differentiation is tightly regulated by a number of transcription factors, hormones and signaling pathway molecules. Recent studies have demonstrated that microRNAs, which belong to small noncoding RNA species, are also involved in adipocyte differentiation.
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Nonalcoholic fatty liver disease (NAFLD) is strongly associated with insulin resistance, obesity, and dyslipidemia. NAFLD encompasses a wide range of states from the simple accumulation of triglycerides in the hepatocytes to serious states accompanied by inflammation and fibrosis in the liver.
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Subclinical thyroid disease is defined biochemically by an abnormal thyrotropin (TSH) level and normal serum-free thyroxine level. The prevalence of this condition varies according to the reference range for TSH and geographic or demographic factors. Recently, several studies, including our community-based cohort studies, have reported on the incidence of subclinical thyroid disease in Korea. Using these studies, we reviewed the prevalence and risk factors of subclinical thyroid disease, focusing on subclinical hypothyroidism.
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Abdominal obesity is associated closely with insulin resistance, diabetes, and cardiovascular disease. Waist circumference (WC) is a useful surrogate marker commonly used for abdominal adiposity. The determination of WC cutoff levels is important in the prevention and treatment of obesity, type 2 diabetes, and related cardiovascular diseases. Recent epidemiological evidence suggested that appropriate optimal cutoffs for Koreans ranged over 80 to 89.8 cm in males and 76.1 to 86.5 cm in females. We analyzed the data from two large cohorts using receiver operating characteristic curve analysis with the incidences of diabetes, hypertension, dyslipidemia, cerebrovascular disease, myocardial infarct, angina, coronary artery disease, and multiple metabolic risk factors as outcome variables. Optimal WC cutoff points for Koreans were 85 cm in males and 80 cm in females. However, considering the prevalence of abdominal obesity and the health costs for its prevention and management, 90 cm in males and 85 cm in females are probably more appropriate thresholds for abdominal obesity. These values may be modified once better research is performed through prospective studies using representative populations, common health outcomes, and proper analytical approaches.
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A Novel Indicator of Children’s Lipid Accumulation Product Associated with Impaired Fasting Glucose in Chinese Children and Adolescents
Differences in the Association Among the Vitamin D Concentration, Dietary Macronutrient Consumption, and Metabolic Syndrome Depending on Pre- and Postmenopausal Status in Korean Women: A Cross-Sectional Study
Skeletal muscle is the largest organ of the body in non-obese individuals and is now considered to be an endocrine organ. Hormones (myokines) secreted by skeletal muscle mediate communications between muscle and liver, adipose tissue, brain, and other organs. Myokines affect muscle mass and myofiber switching, and have profound effects on glucose and lipid metabolism and inflammation, thus contributing to energy homeostasis and the pathogenesis of obesity, diabetes, and other diseases. In this review, we summarize recent findings on the biology of myokines and provide an assessment of their potential as therapeutic targets.
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Glucose variability has been identified as a potential risk factor for diabetic complications; oxidative stress is widely regarded as the mechanism by which glycemic variability induces diabetic complications. However, there remains no generally accepted gold standard for assessing glucose variability. Representative indices for measuring intraday variability include calculation of the standard deviation along with the mean amplitude of glycemic excursions (MAGE). MAGE is used to measure major intraday excursions and is easily measured using continuous glucose monitoring systems. Despite a lack of randomized controlled trials, recent clinical data suggest that long-term glycemic variability, as determined by variability in hemoglobin A1c, may contribute to the development of microvascular complications. Intraday glycemic variability is also suggested to accelerate coronary artery disease in high-risk patients.
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Circulating calcium is a risk factor for vascular disease, a conclusion arising from prospective studies involving hundreds of thousands of participants and extending over periods of up to 30 years. These associations may be partially mediated by other cardiovascular risk factors such as circulating lipid levels, blood pressure, and body mass index, but there appears to be a residual independent effect of serum calcium. Polymorphisms of the calcium-sensing receptor associated with small elevations of serum calcium are also associated with cardiovascular disease, suggesting that calcium plays a causative role. Trials of calcium supplements in patients on dialysis and those with less severe renal failure demonstrate increased mortality and/or acceleration of vascular disease, and meta-analyses of trials in those without overt renal disease suggest a similar adverse effect. Interpretation of the latter trials is complicated by a significant interaction between baseline use of calcium supplements and the effect of randomisation to calcium in the largest trial. Restriction of analysis to those who are calcium-naive demonstrates a consistent adverse effect. Observational studies of dietary calcium do not demonstrate a consistent adverse effect on cardiovascular health, though very high or very low intakes may be deleterious. Thus, obtaining calcium from the diet rather than supplements is to be encouraged.
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The aging process is associated with progressive loss of muscle mass and strength, as well as decline in physical functioning. Although consensus diagnosis has not been reached, sarcopenia is increasingly defined by both loss of muscle mass and loss of muscle function or strength. The cause of sarcopenia is suggested as multifactorial, including hormonal changes, inflammatory pathway activation, fatty infiltration, poor nutrition, and decreased physical activity. Sarcopenia is often associated with visceral obesity. Sarcopenic obesity in the elderly impacts metabolic complications and represents a major public health challenge in a rapidly aging society. Further research about sarcopenia and sarcopenic obesity may be needed to confront the influence of aging society in Korea.
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Skeletal muscle is regarded as an endocrine and paracrine organ. Muscle-derived secretory proteins, referred to as myokines, mediate interactions between skeletal muscle mass and other organs such as the liver, adipose tissue, pancreas, bone, and the cardiovascular system. As individuals age, reduced levels of physical activity and sarcopenia (loss of skeletal muscle mass and strength) are associated with physical frailty and disability. Recently, several studies have suggested that the loss of skeletal muscle mass may contribute to metabolic disease. Therefore, herein, we focus on the relationships between skeletal muscle mass and metabolic diseases, including metabolic syndrome and non-alcoholic fatty liver disease.
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Prevalence of Metabolic Syndrome and Association with Grip Strength in Older Adults: Findings from the HOPE Study
The proper development and coordination of the hypothalamic-pituitary-gonadal (HPG) axis are essential for normal reproductive competence. The key factor that regulates the function of the HPG axis is gonadotrophin-releasing hormone (GnRH). Timely release of GnRH is critical for the onset of puberty and subsequent sexual maturation. Misregulation in this system can result in delayed or absent puberty and infertility. Congenital hypogonadotropic hypogonadism (CHH) and Kallmann syndrome (KS) are genetic disorders that are rooted in a GnRH deficiency but often accompanied by a variety of non-reproductive phenotypes such as the loss of the sense of smell and defects of the skeleton, eye, ear, kidney, and heart. Recent progress in DNA sequencing technology has produced a wealth of information regarding the genetic makeup of CHH and KS patients and revealed the resilient yet complex nature of the human reproductive neuroendocrine system. Further research on the molecular basis of the disease and the diverse signal pathways involved will aid in improving the diagnosis, treatment, and management of CHH and KS patients as well as in developing more precise genetic screening and counseling regime.
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Nonalcoholic fatty liver disease (NAFLD) is thought to stem from the body's inability to store excess energy in adipocytes; as such, it is commonly viewed as the hepatic manifestation of metabolic syndrome. The pathogenesis of NAFLD involves ectopic fat accumulation, which also takes place in the liver, muscle and visceral fat. NAFLD is rapidly becoming more widespread in Korea, with an estimated prevalence of 30% in adults. Type 2 diabetes mellitus (T2DM) and NAFLD share insulin resistance as a common pathophysiological mechanism, and each of these two diseases affects the development of the other. Recent studies have suggested that NAFLD is often present as a comorbidity in T2DM patients. The mutual interrelationship between these conditions is shown by findings suggesting that T2DM can exacerbate NAFLD by promoting progression to nonalcoholic hepatosteatosis or fibrosis, while NAFLD causes the natural course of diabetic complications to worsen in T2DM patients. It remains unknown whether one disease is the cause of the other or vice versa. In this review, I would like to discuss current epidemiological data on the associations between NAFLD and T2DM, and how each disease affects the course of the other.
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Elevated TPOAb is a Strong Predictor of Autoimmune Development in Patients of Type 2 Diabetes Mellitus and Non-Alcoholic Fatty Liver Disease: A Case–Control Study