The Impact of Undernutrition on Post-Tuberculosis Lung-Function: A Prospective Cohort Study
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Published on: October 5, 2015
Pranay Sinha1, Meagan Karoly1, Sanjay Gaikwad2
1Boston Medical Center, Boston, MA, USA.
Background:
Undernutrition is the leading driver of tuberculosis worldwide, yet its effect on the lungs of people who complete treatment is not well defined.
Research Question:
Among adults treated for drug-sensitive pulmonary tuberculosis, is undernutrition associated with worse post-treatment lung function, radiographic severity, exercise capacity and respiratory quality of life, and does systemic inflammation mediate that association?
Study Design And Methods:
Adults (≥18 years) with drug-sensitive pulmonary tuberculosis were enrolled at treatment initiation in India. We measured associations of baseline body mass index (BMI), mid-upper arm circumference (MUAC), and premorbid BMI with spirometry, chest radiograph score, six-minute walk distance and St George's Respiratory Questionnaire score. Plasma IFN-γ, TNF-α and IL-6 were measured at baseline and month 2; counterfactual mediation analysis partitioned the effect of undernutrition on lung function into direct and inflammation-mediated components.
Results:
Of 156 participants analyzed, 76 (48.7%) had a ventilatory defect; 52 (33.3%) had airflow obstruction and 31 (19.9%) had restrictive spirometry. Each 1 kg/m2 higher baseline BMI was associated with lower odds of any ventilatory defect (adjusted odds ratio [aOR], 0.78; 95% CI, 0.67-0.90), and BMI below 16 kg/m2 carried five-fold higher odds than BMI ≥18.5 kg/m2 (aOR, 5.08; 95% CI, 1.76-16.02). MUAC and premorbid BMI showed similar associations. Lower BMI was associated with restrictive spirometry (aOR, 0.74 per kg/m2; 95% CI, 0.59-0.89) but not airflow obstruction (aOR, 0.91; 95% CI, 0.80-1.03). Undernourished participants had higher baseline IL-6, which mediated 32% (FEV1) and 49% (FVC) of the association with impaired lung function.
Interpretation:
Undernutrition before and at treatment initiation is a potentially modifiable determinant of post-treatment lung impairment, with systemic inflammation mediating part of the effect. Nutritional assessment belongs in routine tuberculosis care, and nutritional support should be tested to prevent lung-function impairment in tuberculosis survivors.
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