Obesity has already been tied to a wide range of health problems, including cognitive decline. Now, a new study published recently in The Journal of the American Medical Association (JAMA) shows that people who are severely obese are at a higher risk of death.

“Estimates of the relative mortality risks associated with normal weight, overweight, and obesity may help to inform decision making in the clinical setting,” said the study’s authors.

Researchers at the National Center for Health Statistics at the Centers for Disease Control and Prevention (CDC), compiled the results of 97 studies that analyzed the affects of body mass index (BMI) on mortality. The studies included more than 2.88 million patients and more than 270,000 deaths from all over the world, but primarily from North America and Europe.

The patients were classified into four different categories based on their BMI. The overweight category included patients with a BMI of 25 to under 30, grade 1 obesity included those from 30 to under 35, and grades 2 and 3 obesity included patients with a BMI of 35 or greater.

The study found that patients who were classified as being the most obese (grades 2 and 3) had a 29% higher risk of death. Those with grade 1 obesity had a lower risk of death (5% lower), as did those classified as overweight (6% lower).

“Possible explanations have included earlier presentation of heavier patients, greater likelihood of receiving optimal medical treatment, cardioprotective metabolic effects of increased body fat, and benefits of higher metabolic reserves,” said the study’s authors.