A study of almost 800 patients with Rheumatoid Arthritis has come to the paradoxical conclusion that a higher body mass index (BMI) is associated with a lower death rate, researchers report in the Archives of Internal Medicine.

The findings indicate that patients “who have a low body weight are at increased risk of dying,” said lead investigator Dr. Augustin Escalante. “Patients who would be considered obese actually lived longer. This is an unexpected result. In most otherwise healthy people, being obese is associated with a reduction in lifespan.”

Escalante and colleagues at the University of Texas Health Science Center, San Antonio estimated the effect of body mass index on survival in 779 Rheumatoid Arthritis patients who were followed for up to seven years.

Overall there were 123 deaths, which amounted to 3.6 deaths per 100 people per year. Body mass index was inversely associated with death rates; patients with a body mass index of 30 or higher, indicating obesity, had a death rate of 1.7 per 100 people per year and the death rate increased as body mass index fell.

In those with a body mass index of less than 20, indicating low-normal weight, the rate reached 15.0 deaths per 100 people per year. The high body mass index advantage was still seen after factors such as age at Rheumatoid Arthritis onset, disease duration and gender.

However, “when we accounted for the severity of the arthritis, and for the number and severity of other diseases, the difference in (death rate) between patients with low and high body weight was attenuated,” Escalante said. Therefore people with low body weight probably die early because they have worse disease and more frequently have other illnesses.

Because the study was based on observations, rather than a controlled study with a placebo group, he added, no conclusions about whether arthritis patients should try to gain or lose weight can be made based on the findings.

Nevertheless, “doctors should be aware of the higher death rates associated with low body weight in Rheumatoid Arthritis patients, he said. “These patients should be evaluated carefully, and their doctors should implement appropriate diagnostic and therapeutic interventions to identify and treat potentially reversible conditions.”

SOURCE: Archives of Internal Medicine, July 25, 2005.