Higher BMI May Decrease Death Risk for Patients With IPF

For patients with idiopathic pulmonary fibrosis (IPF), having a higher body mass index (BMI) may help reduce their risk of death, according to research published in the Journal of Health, Population and Nutrition.¹

These findings could lead to BMI becoming a clinical indicator for determining the prognosis of patients with IPF | Image credit: Olivier Le Moal – stock.adobe.com

In a review of 14 datasets including 2080 patients with IPF, researchers found that their risk of death decreased by 6% for every unit increase in BMI, measured in kg/m2 (HR, 0.94; 95% CI, 0.91-0.97; P < .001).

When breaking down the results by region, both Asian (HR, 0.95; 95% CI, 0.93-0.98, P = .001) and Western (HR, 0.91; 95% CI, 0.84-0.98, P = .014) groups showed similar patterns, with mean risk reductions of 5% and 9% for each unit increase in BMI, respectively.

Subgroup analyses also showed that study design did not significantly influence heterogeneity, with mean risk reductions of 5% found in retrospective cohort studies and of 11% in prospective cohort studies. Sample size also had minimal influence on heterogeneity, with smaller studies (< 100 participants) seeing risk reductions of 7% while larger studies (> 100 participants) having similar reductions of 6%.

Studies with better adjustments for confounding factors and higher quality scores demonstrated more consistent findings (HR, 0.93; 95% CI, 0.90-0.96, P < .001). Sensitivity tests confirmed the stability of the results (HR, 0.93-0.95; 95% CI, 0.90-0.96 to 0.92-0.98), and there was no significant bias in the publication data (Egger’s test, P = .159).

According to the researchers, these findings could lead to BMI becoming a clinical indicator for determining the prognosis of patients with IPF. Though, it’s important to know that increase in BMI does not necessarily mean increase in body fat, as many people associate with BMI.

“As has been suggested in patients with heart failure, higher BMI in patients with IPF may not be primarily associated with increased fat mass, but rather with increased fat-free mass (muscle mass),” the researchers explained. “This may increase oxygen consumption through increased muscle diffusion, mitochondrial respiratory capacity, and skeletal muscle strength, thereby improving exercise tolerance and cardiorespiratory fitness.”

Another theory suggests that brown adipose tissue or body fat helps reduce inflammation in the body by lowering levels of lipopolysaccharides, which trigger harmful inflammatory responses. In short, brown fat helps regulate body temperature by burning calories to generate heat, especially in cold conditions.² Unlike white fat, which mainly stores energy and insulates organs, brown fat is more metabolically active and behaves more like lean body mass, burning stored energy to maintain body warmth and regulate blood sugar. Additionally, beige fat is a mix of white and brown fat cells that can convert white fat to brown, contributing to calorie burning.

“In addition, it may also be a possibility that the interaction between BMI and clinical symptoms in patients with IPF is influenced by disease states, such as heart failure, in which a negative correlation between BMI and poor outcomes has been described,” the researchers added.¹

The study has several limitations, including the small sample sizes of the included studies, which limits the generalizability of the findings. All the studies were observational with many confounding factors, and while most performed adjustments, the inconsistency in these corrections may have overstated the link between BMI and mortality risk. Additionally, due to limited data, the meta-analysis could not evaluate associations between different BMI categories or levels of BMI change and mortality risk. Future research should focus on addressing these gaps.

References

1. Pan D, Wang Q, Yan B, Su X. Higher body mass index was associated with a lower mortality of idiopathic pulmonary fibrosis: a meta-analysis. J Health Popul Nutr. 2024;43(1):124. doi:10.1186/s41043-024-00620-5
2. Brown fat. Cleveland Clinic. Updated August 7, 2022. Accessed August 21, 2024. https://my.clevelandclinic.org/health/body/24015-brown-fat