People with a larger waist circumference and higher glucose levels — but not those with abnormal plasma triglyceride, high-density lipoprotein cholesterol (HDL, the good cholesterol), or blood pressure levels — have an increased risk of developing type 2 diabetes, according to researchers at the Herlev and Gentofte Hospital in Denmark.
The findings were recently published in The Journal of Clinical Endocrinology and Metabolism, in the study “Components of the metabolic syndrome and risk of type 2 diabetes.”
Metabolic syndrome is a group of risk factors that increase the risk of heart disease or other diseases, such as diabetes. A large waistline, high triglyceride levels, low HDL cholesterol, high blood pressure, and high levels of blood sugar, are all risk factors for diabetes, stroke, and heart disease, and when someone exhibits at least three of these factors, they are given a diagnosis of metabolic syndrome.
However, there is a need to understand how each individual risk factor affects the development of metabolic syndrome, which in turn might be helpful in preventing diabetes. Although observational association studies have reported an association between individual risk factors and type 2 diabetes, these studies often have confounding variables that are not taken into account, and therefore it is not known whether they indeed induce diabetes or instead exist because of the disease.
Researchers focused on genetic variants known to be associated with a particular risk factor. The authors reasoned that if genetic variants associated with each of the five risk factors were also associated with higher diabetes risk, the particular risk factor would likely cause type 2 diabetes development.
The team, led by Marrianne Benn, MD, PhD, DMSc, chief physician and clinical associate professor in the department of clinical biochemistry at Herlev and Gentofte Hospital, examined data from 95,756 participants in the Copenhagen General Population Study, initiated in 2003.
Analyzing patient’s data up to 10.9 years of follow-up, researchers found that 823 women and 1,000 men developed type 2 diabetes. They had lower HDL levels, older age, higher triglyceride levels, waist circumference, blood pressure, glucose level, alcohol consumption, and pack-years in smokers, compared to those who did not develop diabetes.
Consistently, the risk for type 2 diabetes increased with increased levels of triglycerides, waist circumference, blood pressure, and glucose, and decreased levels of HDL.
However, a causal association was only found for higher waist circumference and blood sugar levels, and not for the remaining risk factors. Particularly, a 1-cm larger waist circumference was linked to a 5 percent higher observational risk and 5 percent higher causal genetic risk for diabetes development. On the other hand, a 1 mmol/L increase in glucose levels increased the observational risk of developing type 2 diabetes by 32 percent, and the genetic risk in 82 percent.
The research team was expecting to find a causal association between glucose level and diabetes, since the diagnosis of type 2 diabetes is defined by high glucose levels. However, waist circumference being causally related to the development of diabetes was a novel observation. Researchers believe that it may be because waist circumference directly correlates with the amount of visceral fat, and increases in visceral fat results in proinflammatory states that can lead to insulin resistance and diabetes development.