BGU’s BMI Study in New England Journal of Medicine
April 7, 2011
The Jerusalem Post — Seventeen-year-olds whose body mass index (BMI) is today considered at a somewhat-elevated- but-normal level are at a substantial risk of obesity-related disorders – including heart disease – in young adulthood, according to a new Ben-Gurion University Faculty of Health Sciences/Sheba Medical Center study that followed up 37,000 youngsters the year before being conscripted into the IDF.
The important research, which with more evidence could lead nutritionists, endocrinologists, pediatricians and other specialists to rethink their assessments of risk factors, was published on Thursday in the prestigious New England Journal of Medicine.
BMI, calculated easily (free BMI calculator sites are on the Internet) as weight in kilograms divided by the square of height in meters, is a well-accepted indicator of normal weight, overweight and obesity. A BMI between 18.5 and 25 is considered normal, while between 25 and 30 is overweight and minor obesity; between 30 and 35 is unhealthy obesity; and over that extremely unhealthy, morbid obesity.
The study was conducted by a joint research team led by endocrinology researcher Prof.
Assaf Rudich and nutritionist and epidemiology Prof. Iris Shai of BGU and Dr. Amir Tirosh, an endocrinologist at Sheba’s Talpiot program and Brigham and Women’s Hospital-Harvard Medical School.
They found that baseline BMI at adolescence can help predict the early occurrence not only of heart disease in young adulthood but also of type 2 diabetes, which is usually predicted mainly by recent BMI rises and weight gain in adulthood and not examining the adolescent BMI.
For heart disease, both elevated BMI in adolescence and recent BMI levels as a young adult are independent risk factors.
Rudich told The Jerusalem Post they found elevated BMI has a “distinctive relationship” with obesity-related coronary heart disease and diabetes in adults between the age of 30 and 40.
The large cohort study was made possible by following 37,000 male pre-IDF conscriptees through young adulthood.
“I can’t say that BMI norms have to be reassessed now. It is very complex, and one observational study can’t do it. More work, including interventional studies [in which there are lifestyle and behavior changes] has to be done, but these are important findings that raise many questions.”
He noted that the NEJM published a Norwegian study in 2007 on BMI in childhood but it could not compare with the new Israeli research, which followed up people through their 30s and 40s.
“It is well established,” he said, “that an obese teenager is likely to become an obese adult, and an obese adult has an elevated risk of developing type 2 diabetes and/or heart disease from start of his 50s.”
What has been unknown is whether BMI at adolescence is a risk factor for the two diseases even if the teenager is not in the obese range and if this is associated with BMI at adolescence independent of BMI at adulthood.
Coronary heart risk in young adulthood has rarely been studied and certainly for not such long periods of follow-up, but the fact that the IDF monitors the health of professional IDF officers made this possible.
When professional soldiers were tested by the IDF every few years, their BMI was found to rise at a rate 0.2 to 0.3 BMI units annually, reaching an average weight gain of about 15 kilos between the ages of 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.
They found that every one-unit rise of BMI was associated with a 10 percent increased risk for type 2 diabetes in early adulthood and a 12 percent increase in the risk for heart disease. During the 17-year study period, 1,173 new cases of diabetes and 327 new cases of heart disease were diagnosed.
Women in the professional army were not monitored for this study from age 17 because there are not enough who remain so long as career army personnel, Rudich said. However, it is worrisome also for women, as female conscriptees are known to gain more weight than men during military service.
“Our results suggest that the obesity problem in children and teens is likely just the tip of the iceberg for increased risk for the occurrence of type 2 diabetes and heart disease in one’s 30s and 40s,” Tirosh said.