Type 2 diabetes status required for BMI mortality studies

Future studies on the association between body mass index (BMI) and mortality should take into account the impact of type 2 diabetes status in the population, according to researchers in the US.
Chandra Jackson of the Harvard School of Public Health and colleagues conducted a study which found that the relationship between BMI and mortality may be stronger in adults without type 2 diabetes than those diagnosed with diabetes.
The results of their six-year analysis showed that death rates were substantially higher among the study participants who were diagnosed with type 2 diabetes, compared to those who were diabetes free.
Mortality rates, however, fell considerably for diabetics with a high BMI, compared to individuals with normal BMI, but rose sharply in people who did not suffer from the metabolic disease.
Due to these differences, Jackson and her colleagues believe that type 2 diabetes status should be taken into account in future BMI-mortality studies, as is done with heart disease, cancer and smoking to ensure valid population estimates. Each of these conditions can influence body weight and may distort the relationship between BMI and mortality.
She said: “This finding was surprising, but it may be due to a commonly observed phenomenon in chronic disease epidemiology called ‘reverse causation’ where a person’s weight at the time of the survey can be affected by their disease if it leads to weight loss and muscle wasting during advanced stages.
“This apparent obesity paradox that has been observed in the past among individuals with diabetes may actually be due to methodological limitations that can bias these types of studies.
“From clinical and public health points of view, achieving and maintaining a healthy weight should continue to be recommended for both those with and without diabetes.”