Nutritional Factors Influencing Physical Capacity Outcomes in Healthy Young Adults: A Cross-Sectional Study

<ns3:p> Abstract* Background Cardiorespiratory fitness in young adults is an early marker of cardiometabolic risk, yet the contribution of diet and vitamin status to physical capacity in this group remains insufficiently defined. Methods In a cross-sectional study, 22 healthy adults (median age 28 years) were classified into normal (VO <ns3:sub>2</ns3:sub> max ≥84% predicted; n=9) and reduced endurance (VO <ns3:sub>2</ns3:sub> max &lt;84% predicted; n=13) groups based on cardiopulmonary exercise testing on a cycle ergometer. All participants underwent anthropometry and bioimpedance analysis of body composition. Cardiopulmonary exercise testing (CPET) was used to assess rest HR, peak HR, VO <ns3:sub>2</ns3:sub> max, and VO <ns3:sub>2</ns3:sub> max (% predicted). 72-hour food diaries were analyzed with specialized software, and serum concentrations of vitamins B₁, B <ns3:sub>2</ns3:sub> , B₆, B₁ <ns3:sub>2</ns3:sub> , C, A, E, and D were measured using immunoassay and related techniques. Results The reduced endurance group reported higher total daily energy intake (2635.0 kcal/day vs. 1750.5 kcal/day; p=0.047) and carbohydrate intake (229.2 g/day vs. 163.9 g/day; p=0.007), whereas the normal endurance group consumed more vegetables (219.1 g/day vs. 110.0 g/day; p=0.025) and had higher serum vitamin D concentrations (34.6 ng/mL vs. 16.1 ng/mL; p=0.009). Physical capacity showed a positive correlation with serum vitamin D (r=0.606; p=0.003) and vegetable intake (r=0.576; p=0.008), while other measured vitamins and major food groups were not significantly associated with aerobic performance. Conclusions Among healthy young adults, better physical capacity was linked to higher vitamin D serum levels and vegetable consumption, independent of anthropometric differences. These findings suggest that optimizing vitamin D and plant-rich dietary patterns may support cardiorespiratory endurance in this population, although larger longitudinal studies are needed to confirm causality. </ns3:p>