A person’s fat-free mass index, a measure that is similar to body mass index (BMI) but takes into account overall muscle mass, is a significant predictor both of preserved lung function and survival in idiopathic pulmonary fibrosis (IPF) patients, a study published in the journal Respirology reports.
In the study, “Fat-free mass index predicts survival in patients with idiopathic pulmonary fibrosis,” researchers led by Dr. Yuji Tohda of the Department of Respiratory Medicine and Allergology, Faculty of Medicine at Kindai University in Osaka, Japan, enrolled 44 patients with IPF. They assessed patients’ body composition, and examined the relationship between body composition and lung function, as measured by forced vital capacity (FVC), and survival.
A significant positive correlation was found between fat-free mass index (FFMI) and FVC, meaning that patients with greater muscle mass for their height also tended to have better lung function. Similarly, patients with a high FFMI had better carbon monoxide diffusion capacity in their lungs and could walk a longer distance in six minutes, a test used to measure exercise tolerance.
The researchers also found a negative correlation between FFMI and age. In other words, overall muscle mass decreased with age.
To estimate how muscle mass might affect survival, the researchers observed patients for an average of 2.3 years (at maximum, for 3.4 years). They found that several variables — including a higher FFMI — were significantly associated with survival, although BMI [a measure of weight against height, that does not distinguish between sources of body weight, like fat or muscle] was not.
“Taking account of not only lung function but also fat-free mass was revealed to be important in IPF practice. Methods for increasing or preserving muscle mass in IPF patients should be further investigated,” Osamu Nishiyama, the study’s first author, said in a press release.
IPF is characterized by progressive worsening of lung function. FVC is a significant predictor of survival and is recognized as the most important marker of the disease. The predictive potential of FFMI is only beginning to be examined in-depth in IPF patients.