Is high cholesterol associated with risk of type 2, cardiovascular diseases and high mortality rates?
Dyslipidemia is a comorbidity in diabetes. Independent association between elevated triglycerides (TG), cardiovascular (CV) and mortality is largely debatable. Elevated TG is connected to high density lipoprotein (HDL), low density lipoprotein (LDL) and other lipoproteins. Hypertriglyceridemia is associated with considerably increased long term mortality and cardiovascular risk. Correlations between lower HDL cholesterol led to studies recommending that HDL values could be cited as more likely contributors to risk than the TG themselves. Classification of elevated TG as a major CV risk factor is therefore very important since it regulates whether high TG should be a goal for treatment. Type 2 diabetes is categorized by both insulin resistance and hyperinsulinemia. In hyperlipidemia patients, free fatty acids act as precursors to glycogenesis in the liver, thereby increasing apoptosis in beta cells of the pancreas and increasing insulin resistance in muscles. This therefore results in decreased insulin secretion and persistent hyperglycemia.
The purpose of this study was to discover the occurrence of and the risk factors for type 2 diabetes. Using a stratified, multistage cluster sampling, the study took place in 2 rural districts and 4 urban districts. Only people 16 years of age and above were recruited. Subjects with any serious disease, type 1 diabetes or pregnancy were not allowed in the study. The levels of serum (TG), total cholesterol (TC), and high density lipoprotein cholesterol (HDL-C) were measured and subjects were given a 2-h 75-g oral glucose tolerance test (OGTT). Statistical analysis used included SPSS for windows, chi-square and students’ t-tests, which were used to assess univariate differences. Logistic regression was also used for assessment of odds ratio (ORs) and 95% confidence interval (CI) for type 2 diabetes.
Of the 17,526 subjects, 82.2% (14,401) finished the study with an overall response. Of the 14,385 participants, 5,084 were from rural areas and 9,301 were from urban areas. The subjects were 16-88 years. 10.1% (1,456) of the subjects had type 2 diabetes with 699 (11.4%) of them being men and 757 (9.2%) women. Occurrence of isolated impaired fasting glucose (IGF), isolated impaired glucose tolerance (IGT), and combined IFG and IGT was 10.8%, 4.1% and 2.4% respectively. Type 2 diabetes frequency was 7.0%, with men showing a drastically higher incidence of diabetes than women (X2=18.28, P<0.01). Prevalence of type 2 diabetes also increased with age from 0.9% to 22.5%, as did impaired glucose regulation. The frequency of isolated IFG, type 2 diabetes, and combined IFG and IGT in urban areas was significantly greater than in rural areas P<0.01 whilst that of isolated IGT in rural areas was higher than in urban areas P<0.01. The prevalence of type 2 diabetes was higher in those with hyperlipidemia than in those without hyperlipidemia (16.9% vs 7%, P <0.01). Univariate analysis showed that sex, age, BMI, waist circumference, fasting plasma glucose (FPG), 2h- postprandial plasma glucose (2h PG), triglycerides, TC/HDL-C and non HDL-C were connected to diabetes. Multivariable logistics, however, revealed they were independently related to type 2 diabetes. Those with hyperlipidemia had increased levels of FBG and 2hPG compared to those without hyperlipidemia. The occurrence of type 2 diabetes increased significantly with increasing BMI for both hyperlipidemia and those without hyperlipidemia.
Patients with hyperlipidemia have a greater chance of developing type 2 diabetes and irregular glucose metabolism as well as increased morbidity and mortality from type 2 diabetes and cardiovascular disease. Serum lipid profiles are worse in people with diabetic than in those without. Hypertriglyceridemia was the most common phenotype of hyperlipidemia with risk of isolated hypercholesterolemia and isolated hypertriglyceridemia being almost alike. Mixed hyperlipidemia were more than 3 times higher at developing type 2 diabetes than those with normal lipid level. However, isolated low HDL-C showed no effect on the prevalence of type 2 diabetes. Isolated low HDL-C revealed no effect on type 2 diabetes occurrence. Normally type 2 diabetes and hyperlipidemia are detected in the same individuals because of shared risk factors. Aggressive interference in dyslipidemia reduces cardiovascular events in type 2 diabetes. The weaknesses of this study include:
- Patients self-reporting their diagnosis of diabetes using just a questionnaire but not using a blood test, which probably led to a bias;
- The study did not tell us how long the patients have had diabetes;
- They also failed to evaluate the family history of diabetes in the development of type 2 diabetes.
In conclusion, it is highly recommended to screen patients with hypertension or hyperlipidemia for type 2 diabetes.
- The prevalence of type 2 diabetes was higher in subjects with hyperlipidemia than in those without hyperlipidemia
- Patients with hyperlipidemia have a bigger risk of developing type 2 diabetes and unusual glucose metabolism as well as increased morbidity and mortality from type 2 diabetes and cardiovascular disease.
- There is not sufficient evidence for regularly screening asymptomatic patients for T2DM, but it is suggested to screen patients with hypertension or hyperlipidemia.
Chen, Guang-Yu et al. “Prevalence of and Risk Factors for Type 2 Diabetes Mellitus in Hyperlipidemia in China.” Medical Science Monitor : International Medical Journal of Experimental and Clinical Research 21 (2015): 2476–2484. PMC. Web. June 9 2016.
Cui HB, et al. “Modified classic risk factors for coronary artery disease in Chinese Han population” Chin Med Sci J, 216-23 22?(4) 2007
Tenenbaum, Alexander, Robert Klempfner, and Enrique Z Fisman. “Hypertriglyceridemia: A Too Long Unfairly Neglected Major Cardiovascular Risk Factor.” Cardiovascular Diabetology 13 (2014): 159. PMC. Web. June 9 2016.
Zhang L et al. “Blood lipid levels in relation to glucose status in seven populations of Asian origin without a prior history of diabetes: the DECDA study”. Diabetes Metab Res 549-57 25(6) 2009
Jia wp, et al. “Epidemiological characteristics of diabetes mellitus and impaired glucose in Chinese adult population: the Shanghai Diabetes Studies”. Diabetologia 286-92 50(2) 2007