ABSTRACT
Both D-aspartic acid (DAA) and nitrate have received considerable attention in recent years. Vitamin D3 is also considered important for overall physical health and has been associated with elevated blood testosterone. The present study evaluated the impact of a DAA-nitrate-vitamin D3 containing dietary supplement on anaerobic exercise performance, blood testosterone and nitrate/nitrite in men. Methods: 24 resistance-trained men (mean age: 23 years) were assigned to ingest a DAA-nitrate-vitamin D3 supplement or a placebo for 28 days. Exercise performance (upper body muscle power, force, and endurance; Wingate cycle sprints), in addition to blood total and free testosterone and nitrate/nitrite was measured before and after 14 and 28 days of supplementation. Results: No increase in total or free testosterone was noted at either measurement time (p>0.05), with values remaining stable or decreasing slightly following intake of the supplement. Nitrate/nitrite was increased significantly following intake of the supplement (p<0.05), from 19.1±2.1 µmol∙L-1 (pre) to 70.0±12.4 µmol∙L-1 at 14 days and 68.6±7.7 µmol∙L-1 at 28 days. Despite this increase in nitrate/nitrite, no performance variable was impacted in a statistically significant manner by supplementation (p>0.05). However, the cumulative number of repetitions performed during a five-set bench press challenge was 11.3% higher after 28 days of supplementation, as compared to 3.6% higher for placebo. Conclusion: Twenty-eight days of treatment with a DAA-nitrate-vitamin D3 supplement increases blood nitrate/nitrite and can moderately improve repetitive bench press performance. However, this supplement does not result in an increase in total or free testosterone or any other performance measure.