Mealtime irregularity is associated with higher serum growth differentiation factor-15 levels in older adults: the explanatory role of dietary quality

PURPOSE: This study examined the association between mealtime irregularity and Growth Differentiation Factor-15 (GDF-15)-a potential biomarker of biological aging-and evaluated whether this association could be explained by poor dietary quality among community-dwelling older adults. METHODS: This cross-sectional study analyzed data from 378 disability-free adults aged ≥ 65 years from the Higashiura Study. Eating habits (regular vs. irregular) were assessed during the interviews. Dietary quality was evaluated using nutrient density scores from the Nutrient-Rich Food Index, calculated from 3-day dietary records. The association among mealtime irregularity, dietary quality, and serum GDF-15 levels was examined using mediation analysis after adjusting for age, sex, comorbidities, sleep duration, physical activity, smoking status, employment status, and total energy intake. RESULTS: Participants with irregular mealtimes were significantly younger than those with regular mealtimes (mean ± standard deviation: 73.3 ± 4.6 vs. 75.1 ± 5.6 years, p = 0.014) and had higher serum GDF-15 levels (least-squares means, 95% confidence interval [CI]: 1161.4, 1063.4-1270.2 vs. 1028.0, 988.4-1068.9 pg/mL, p = 0.009). In the mediation analysis, lower nutrient density partially explained the association between mealtime irregularity and higher GDF-15 levels (β, 95% CI: total effect: 0.053, 0.0078-0.0977; direct effect: 0.046, 0.0004-0.0898; indirect effect: 0.008, 0.0001-0.0205; mediation proportion: 14.5%). CONCLUSION: Although participants with irregular mealtimes were significantly younger than those with regular mealtimes, they showed higher levels of biological aging markers. Dietary quality partially accounted for this association. These findings suggest that dietary quality may be an important consideration for older adults with irregular mealtimes.