Posted by on December 21, 2010 - 5:11pm

Study Shows Strong Link between Obesity and Mortality

The largest study of its kind has confirmed a strong association between overweight and obesity and an increased risk of death. The study also identified a range of body-mass index (BMI) at which mortality risk is lowest, confirming earlier studies indicating that people who are in the normal weight range have a significantly lower risk of dying from a host of causes compared with those who are overweight. The findings were published December 2 in the New England Journal of Medicine.

Obesity and overweight continue to be major health problems in the United States. Approximately two-thirds of the adult U.S. population are overweight or obese, meaning that they have a BMI of 25 or higher.

Researchers from NCI and other NIH institutes, as well as from other U.S. and foreign health agencies and universities, pooled data on 1.46 million people from 19 long-term prospective cohort studies. The participants in these cohort studies were white and from more industrialized countries, limiting the extent to which the findings can be extrapolated to other populations, the researchers explained. The analysis focused on participants who had never smoked and did not have cardiovascular disease or cancer at study entry, eliminating “potentially strong confounders” of mortality risk that have affected some earlier studies, explained the study’s lead author, Dr. Amy Berrington de Gonzalez of NCI’s Division of Epidemiology and Cancer Genetics.

Overall, the lowest mortality risk was seen for those with a BMI between 20 and 24.9. Above that level, every 5-unit increase in BMI increased the risk of death by 31 percent. The risk of death was substantially elevated in the severely obese, those with a BMI of 40 or higher. Women who fell into this category had a 2.5-fold higher risk of death compared with women in the lowest risk BMI range. The risk relationship was similar for men.

Across the BMI levels that correspond with overweight and obesity, the relationship between BMI and mortality was strongest for participants who were younger than 50 at study entry, Dr. Berrington de Gonzalez added.

Although the cancer-specific mortality risk was smaller than the mortality risk associated with cardiovascular disease, the study only assessed overall cancer risk, she said. “Based on previous studies, we know that the relationship between obesity and cancer varies by cancer type,” she continued. So, while obesity is strongly associated with an increased risk of postmenopausal  breast cancer and renal cancer, for example, it is not associated with some other cancers. As a result, when cancer is considered as a single disease, the overall association is weaker, Dr. Berrington de Gonzalez said.