A large new study has found that high blood sugar and insulin resistance in teenagers can lead to serious heart damage by the time they become young adults.
Even teens who look healthy and are not overweight could be at risk if their blood sugar remains high over time.
This research is the largest and longest of its kind and was recently published in the medical journal Diabetes Care.
The study followed 1,595 teenagers from the age of 17 to 24. These young people were part of a well-known health study in the UK called the Children of the 90s, run by the University of Bristol.
Scientists from several countries—including the United States, Australia, Finland, Switzerland, and the UK—worked together on this research.
The researchers measured the teens’ fasting blood sugar levels at the beginning and end of the study, along with insulin levels, heart function, and heart structure using ultrasound scans.
Fasting blood sugar means how much sugar is in the blood after not eating for a while. Insulin resistance happens when the body doesn’t respond well to insulin, a hormone that helps control blood sugar.
Two different cut-off points were used to define high blood sugar (also called prediabetes). One was 5.6 mmol/L, which is the level used by the American Diabetes Association. The other, 6.1 mmol/L, is used in many countries.
At age 17, only about 6% of teens had blood sugar at or above 5.6. But by age 24, that number jumped to almost 27%. For the higher threshold of 6.1, the number increased from just 1% to more than 5% in those seven years.
At the same time, signs of heart damage increased sharply. An unhealthy increase in heart size, known as left ventricular hypertrophy, grew from 2.4% at age 17 to 7.1% at age 24. Heart dysfunction—meaning the heart wasn’t working as well as it should—rose from 9.2% to nearly 16%.
The study found that teens who had fasting blood sugar levels of 5.6 or higher throughout the 7 years had a 46% higher risk of heart enlargement. If their levels were even higher—6.1 or more—their risk tripled.
High blood sugar also made the heart’s muscles stiffer and caused the heart to pump less effectively. In addition, it increased the pressure of blood returning to the heart, which is a sign of worsening heart function.
Insulin resistance alone also caused problems. Teens with insulin resistance had a 10% greater risk of heart damage as they became young adults.
And interestingly, most of the damage linked to insulin resistance was related to an increase in body fat. Girls were hit especially hard. High blood sugar appeared to increase the size of the heart in females five times more than in males during this period.
The study’s lead author, Dr. Andrew Agbaje from the University of Eastern Finland, explained that even teenagers who look normal and are not overweight may be heading toward heart disease if their blood sugar and insulin levels are too high. He added that late adolescence is a crucial time in a person’s life when many long-term health problems begin to develop.
One major concern is that teens today are becoming more independent from their families and may eat more processed or sugary foods, move less, and gain more fat without realizing the harm it could cause in just a few years. The study showed that insulin resistance and extra body fat feed into each other and create a harmful cycle, making both worse over time.
This is the first major study to track how high blood sugar and insulin resistance in teenagers affect heart structure and function using repeated heart scans. It provides strong new evidence that these blood sugar problems don’t just predict future diabetes—they also directly damage the heart at a young age.
The findings also highlight the importance of prevention, especially for girls who seem more vulnerable to the effects of high blood sugar on the heart.
In conclusion, this research makes it clear that parents, doctors, and schools need to take high blood sugar and insulin resistance seriously—even in teens who seem healthy. Encouraging regular exercise, balanced eating habits, and early screening for blood sugar issues could go a long way in protecting young hearts and preventing future health problems.
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The study is published in Diabetes Care.
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