A large cohort study following 37,000 teenagers for 17 years found that an elevated, yet normal range Body Mass Index (BMI) constitutes a substantial risk factor for obesity-related disorders in young adults (age 30-40).
The study showed that elevated BMI in adolescence has distinctive relationships with type 2 diabetes and coronary heart disease in young adulthood.
Researchers showed that diabetes is influenced mainly by recent BMI and weight gain. However, for coronary heart disease, both elevated BMI in adolescence and recent BMI are independent risk factors. The natural progression of coronary heart disease is probably the consequence of gradually increasing atherosclerosis during adolescence and early adulthood. It is important to note that these results were derived with BMI from well within the range defined as normal.
The study, published in the New England Journal of Medicine, assessed the occurrence of both diseases in young adulthood, an age group that has been rarely studied, but has experienced an increase in the incidence of these diseases in recent decades. It may help redefine what constitutes a "normal" or "healthy" BMI in adolescence and to highlight the role of elevated BMI at different ages in the diagnosis of different diseases.
The joint research team was led by Dr. Amir Tirosh (Sheba Tel-Hashomer Hospital's Talpiot program and Brigham and Women's Hospital and Harvard Medical School) and Profs. Iris Shai and Assaf Rudich from Ben-Gurion University of the Negev. Additional researchers from the Israel Defense Forces (IDF) Medical Corps and Tel Hashomer Hospital were also involved. The team followed IDF career personnel beginning at age 17.
The IDF recorded BMI of personnel (BMI, the weight in kilograms divided by the squared height in meters) at baseline and again every few years. During a mean follow-up period of 17 years, the average BMI of the participants rose at a rate of 0.2 to 0.3 units per year, reaching an average weight gain of approximately 15 Kg. (~30 lbs) between ages 17 and 30. The researchers were able to control for multiple risk factors for both diseases, including age, fasting blood glucose, blood lipids, blood pressure, smoking, exercise habits and family history.
The researchers found that it was possible to predict the increased risk for developing both diabetes and coronary heart disease even if the BMI was within the normal range (<25 Kg/m2) . A BMI of 25 or more is considered overweight while 30 BMI or higher is considered obese.
According to the study, every rise in one unit of BMI was associated with ~10 percent increased risk for type 2 diabetes in early adulthood, and a 12 percent increase in the risk for heart disease. Remarkably, this elevated risk was significant at a BMI at age 17 of 23.4 Kg/m2 or higher for diabetes and 20.9 Kg/m2 or higher for heart disease.
For diabetes, BMI at age 17 predicted the risk mainly since it associated with BMI later in life. However, for heart disease, both BMI at adolescence, as well as BMI at adulthood independently of each other predicted the risk of the disease. During the 17 year study period, 1,173 new cases of diabetes and 327 new cases of heart disease were diagnosed.
According to Dr. Tirosh, "Our results suggest that the obesity problem in children and teens is likely just the tip of an iceberg for increased risk for the occurrence of type 2 diabetes and heart disease in your 30s and 40s. While this is an observational study, it does suggest that an adolescent with a relatively high BMI, who grows up to become a lean adult, practically eliminated the added risk of developing diabetes attributed to his BMI at adolescence.
"Conversely, the risk of that person for heart disease will remain elevated compared to the lean teen who became a lean adult, though still will be lower than that of the heavier teen who became an obese adult. Therefore, for effective prevention of early occurrence of heart disease in adulthood, very early intervention to promote healthy lifestyle habits seems essential, even during childhood."
According to Prof. Iris Shai of BGU's Department of Epidemiology, Faculty of Health Sciences (FOHS), "Heart disease appears to have a longer 'memory' for BMI than diabetes, so the history of a person's BMI should be part of medical risk assessment. We have options, not necessarily pharmacological, to offer patients to decrease their risk for heart disease."
BGU recently published a series of intervention studies that showed that nutritional habits modification cannot only halt, but even reverse the progression of atherosclerosis, the underlying process of heart disease.
"Previous studies did not unequivocally confirm the association between pre-adulthood BMI and diseases in early adulthood, although extreme obese children are indeed more likely to become obese adults who are at elevated risk of diabetes and heart disease," explains Prof. Assaf Rudich, a researcher in the BGU FOHS and the National Institute for Biotechnology in the Negev.
"This study is significant because it demonstrates that the association exists well within the currently considered normal values for BMI, having distinct effect on two diseases occurring specifically in early adulthood - an age group that is frequently neglected," says Rudich.
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