Nutritional Risk in Older Adults with Rheumatoid Arthritis: Sex-Specific Patterns and Clinical Implications of the Prognostic Nutritional Index

Background/Objectives: Nutritional risk is increasingly recognized as a relevant but under-assessed dimension of rheumatoid arthritis (RA), particularly in older adults managed in outpatient settings. Simple nutritional indices such as the Prognostic Nutritional Index (PNI) may help identify individuals at increased nutritional risk beyond conventional disease activity measures. This study aimed to characterize nutritional risk in older adults with RA using the Prognostic Nutritional Index, explore sex-specific patterns, and identify clinical associations of PNI variability, with complementary analyses focusing on high nutritional risk. Methods: We conducted an observational cross-sectional study including 275 consecutive adults aged ≥50 years with RA attending routine follow-up at a tertiary rheumatology clinic. Nutritional risk was assessed using the PNI, calculated from serum albumin and total lymphocyte count, and analyzed primarily as a continuous variable and secondarily using established cut-off values. Clinical characteristics, inflammatory markers, body mass index, laboratory parameters, and patient-reported outcomes were recorded. Analyses were stratified by sex. Multivariable linear regression models were used to identify factors associated with PNI variability, and complementary logistic regression analyses were performed to explore factors independently associated with high nutritional risk (PNI < 40). Results: More than half of the cohort (53.3%) exhibited PNI values compatible with nutritional risk. Men showed lower PNI values than women, with a markedly greater prevalence of high nutritional risk (18.0% vs. 5.0%, p < 0.001). In multivariable linear regression analyses, higher C-reactive protein levels and increasing age were independently associated with lower PNI values, whereas sex was not an independent determinant of PNI. In multivariable logistic regression analyses, increasing age and male sex were independently associated with high nutritional risk. In multivariable linear regression models restricted to men, hemoglobin emerged as the principal independent correlate of PNI. In complementary logistic regression analyses focusing on high nutritional risk (PNI < 40), hemoglobin remained the sole independent predictor (OR = 0.94, 95% CI 0.91–0.98; p < 0.01), supporting a robust association with clinically relevant nutritional risk. Conclusions: Nutritional risk assessed by the PNI is common among older adults with RA. Although sex does not independently determine PNI as a continuous measure, male sex is associated with severe nutritional risk. The PNI captures a clinically relevant dimension of disease burden that extends beyond joint inflammation and traditional activity indices, supporting its use as a pragmatic nutritional screening tool in routine rheumatology practice.