Previous studies among adults have shown that high blood glucose and insulin resistance in youth strongly predict the risk of type 2 diabetes mellitus in people in their mid-fifties. However, no study in the world has examined the earliest signs and consequences of high blood glucose and insulin resistance on the heart.
The study tracked 1,595 adolescents aged 17 to 24 years old from the University of Bristol’s Children of the 90s cohort.
To assess the prevalence of prediabetes — a condition marked by elevated fasting blood glucose levels, which indicates how well the body regulates blood sugar in the absence of recent food intake — two different thresholds were used: a stricter cut-off of ≥5.6 mmol/L as recommended by the American Diabetes Association and a higher threshold of ≥6.1 mmol/L, which is the present recommendation in many countries. Diabetes UK defines prediabetes as 6-6.4% mmol/L.
The study found that 6.2% of 17-year olds had fasting blood sugars ≥5.6 mmol/L, which increased nearly fivefold to 26.9% by age 24 years. Only 1.1% of adolescents had levels ≥6.1 mmol/L, but the prevalence increased fivefold to 5.6% by 24 years of age.
The prevalence of excessive heart enlargement (left ventricular hypertrophy) increased threefold from 2.4% at 17 years of age to 7.1% at 24 years of age . Heart enlargement can cause the heart to pump less efficiently and may lead to future complications.
Excess fat mass explained over two-thirds of the association between high blood sugar and increased insulin resistance with cardiac damage in youth, highlighting the important relationship between obesity and heart health.
Persistent fasting blood sugar levels ≥5.6 mmol/L between 17 and 24 years of age was associated with a 46% increased risk of left ventricular hypertrophy. The risk was threefold if fasting blood sugar was persistently ≥6.1 mmol/L. High blood glucose was also associated with decreased heart muscle relaxation, altered normal heart function, and increased the pressure of blood flow return to the heart. These results have been adjusted for possible confounding factors, such as fat mass.
Professor Andrew Agbaje, Associate Professor of Clinical Epidemiology and Child Health at the University of Eastern Finland and the study’s senior author, said: “Previous results from the same Children of the 90s cohort indicate that late adolescence is a critical period in the development of cardiometabolic diseases.
“Our current findings confirm that even healthy-looking teens and young adults, who are mostly normal weight, may be at risk of cardiovascular diseases, if they have high blood sugar and insulin resistance. Surprisingly, we observed that high blood sugar may impact females' hearts faster than males.”
The participants' fasting blood glucose and insulin were measured at ages 17 and 24 years, along with echocardiography measurements of the heart.
Blood pressure, heart rate, socio-economic status, family history of cardiovascular disease, smoking status, accelerometer measure of sedentary behaviour and physical activity, as well as fat and lean mass, were accounted for in the analyses.
Professor Agbaje added: “The five-fold increase in the prevalence of prediabetes within 7 years of growth from late adolescence to young adulthood highlights the critical importance of lifestyle. A healthy balanced diet, regular exercise, and managing conditions like obesity are key to reducing the risk of prediabetes.”
The study was conducted by the Baylor College of Medicine in the US; University of Bern in Switzerland; Murdoch Children’s Research Institute in Australia, Universities of Bristol and Exeter in the UK, and the University of Eastern Finland.