Long-Term Beetroot Extract Supplementation Improves Morphological Muscle Quality and Rate of Force Development in Postmenopausal Women: A Randomized Clinical Trial

<b>Background:</b> Low estrogen levels during menopause reduce nitric oxide (NO) production, contributing to decline in skeletal muscle quality and function. Although acute and short-term dietary nitrate supplementation has demonstrated promising effects, long-term benefits, particularly on muscle quality in postmenopausal women, are not well established. <b>Objectives:</b> The objective was to investigate the effects of long-term (12-week) nitrate-rich beetroot extract supplementation on morphological and functional muscle quality, rate of force development (RFD), maximal strength, and circulating nitrate/nitrite concentrations in postmenopausal women. <b>Methods:</b> In a randomized, double-blind, placebo-controlled design, 20 postmenopausal women (21 years ± 7 since menopause) consumed 20 g/day of a nitrate-rich beetroot extract (BET; 548 mg nitrate/day) or a nitrate-depleted beetroot extract (PLA; 43 mg nitrate/day) for 12 weeks. Outcome measures, including muscle quality (functional via muscle strength/thickness ratio; morphological via ultrasound echo intensity), RFD, maximal voluntary isometric contraction (MVIC), and serum nitrate/nitrite levels, were evaluated at baseline, 8 weeks, and 12 weeks. <b>Results:</b> BET significantly increased serum nitrate (0.005) and nitrite (0.022) levels compared to PLA at both week 8 and week 12. Morphological muscle quality also improved significantly in the BET group (interaction effect, <i>p</i> = 0.014). Early-phase rate of force development (RFD) increased between 30 and 100 ms, whereas late-phase RFD increased between 100 and 200 ms. RFD_peak also improved by week 8, and these gains were maintained through week 12 (interaction effect, <i>p</i> < 0.05). Although there was no significant difference between groups for functional muscle quality, MVIC increased at week 12 in the BET group, but no significant Time × Group interaction was observed. <b>Conclusions:</b> Twelve weeks of nitrate-rich beetroot extract supplementation improved morphological muscle quality and RFD, suggesting potential clinical relevance for preventing structural and neuromuscular function decline in postmenopausal women. This study was registered with ReBEC (RBR-87qh649) and approved on 8 October 2024.