C.S.C, D.C.H, M.B.B.S
Obesity in adulthood is associated with a striking reduction in life expectancy for both men and women. Among 3457 subjects in the Framingham Study, done in the United States, those who were obese (Body Mass Index or BMI ≥30 kg/m2 at age 40 years lived 6 to 7 years less than those who were not (BMI ≤24.9 kg/m2). Those who were overweight (BMI 25 to 29.9 km/m2) at age 40 years lived about 3 years less, and those who were both obese and smoked lived 13 to 14 years less than normal–weight nonsmokers. The steady rise in life expectancy during the past two centuries may come to an end because of the increasing prevalence of obesity. Being overweight during adolescence also increase the risk of premature death as an adult. The analysis of Nurses’ Health Study has shown the risk of premature death increases with higher BMIs at age 18 years. For a BMI at age 18 of 18.5 to 21.9, 22 to 24.9, 25 to 29.9, and ≥30 kg/m2, the hazard ratio for premature death were 0.98, 1.18, 1.66, and 2.79, respectively.
A prospective study from the United States, at National Cancer Institute, National Institutes of Health, Bethesda, valuated the relationship between BMI and risk of death over a maximum follow–up period of 10 years among over 500,000 men and women aged 50 to 71 years. Among the subset of individuals 50 years of age (when prevalence of chronic disease is low) who had never smoked, an increased risk of death was associated with being either overweight (20 to 50 percent increase in those between 26.5 to 29.9 kg/m2) or obese (two– to over threefold increase in those ≥30 kg/m2).
Overweight and obesity, when analyzed together, is associated with increased mortality from diabetes and kidney disease. Obesity, when analyzed alone, is associated with increased cardiac mortality and cancers considered to be obesity–related (colon, breast, esophageal, uterine, ovarian, kidney, and pancreatic cancer), but not with mortality from other cancers or non–cardiac mortality.
There are some recent studies which showed that obese people live longer. Overweight was shown to be associated with reduced mortality from non cancer, non–cardiovascular causes, but not with cancer or cardiovascular mortality. In them being underweight was associated with increased mortality from non cancer and non–cardiac causes, but not cancer and cardiac CVD causes. Obesity and increased central fat are associated with increased morbidity in addition to mortality. Overweight and obese individuals have a higher relative risk of hypertension, hypercholesterolemia, and diabetes mellitus compared with normal weight individuals. The risk of hypertension and diabetes increases with increasing BMI.
In the Nurses’ Health and the Health Professionals studies, the risk of developing a chronic disease (gallstones, hypertension, heart disease, colon cancer and stroke (in men only)) increased with increasing BMI, even in those in the upper half of the healthy weight range (BMI 22.0 to 24.9 kg/m2). Obesity is measured by using a measurement called BMI, which is calculated by dividing a person’s weight in kilograms by the square of their height in meters.
A BMI of 18.5 to 23 is considered normal (Asians). One below 18.5 is considered underweight and 25 or above is considered obese.