Eight weeks of nitrate-rich beetroot extract supplementation on fasting nitrate and nitrite levels and skeletal muscle contractile properties in postmenopausal women: Results of a randomized, placebo-controlled, and parallel trial.

BACKGROUND

Menopause is linked to reduced estrogen and nitric oxide (NO) production, which may contribute to declines in muscle function and quality of life. Acute dietary nitrate intake from beetroot has been shown to improve NO bioavailability and muscle function in older. However, the effects of prolonged dietary nitrate supplementation (i.e., longer than two weeks) remain unexplored. This study investigated the effects of four and eight weeks of dietary nitrate supplementation on muscle contractile properties and nitrate tolerance in postmenopausal women.

METHODS

This was a randomized, double-blind, placebo-controlled, and parallel study. Participants received daily 20 g of nitrate-rich beetroot extract (BET, containing ∼548 mg/8.8 mmol nitrate) or nitrate-depleted beetroot extract (PLA, containing ∼43 mg/0.7 mmol nitrate) for eight weeks. Outcomes, including circulating nitrate and nitrite levels and muscle contractile properties, were assessed at baseline, week 4, and week 8.

RESULTS

Twenty-two participants completed the study. Fasting nitrate and nitrite levels were significantly higher in the BET group than in the PLA group-nitrate at week 4 and both nitrate and nitrite at week 8. At week 8, maximal knee extensor torque (F) was significantly greater in the BET group compared to PLA (p = 0.004), while no changes were seen for maximal power (P) or velocity (V). Peak torque and power improved at week 8, especially at angular velocities of 60°·s and 90°·s for torque, and at 90°·s, 180°·s, and 270°·s for power.

CONCLUSIONS

This study demonstrated that eight weeks of nitrate-rich beetroot extract increases fasting nitrate and nitrite levels, enhancing muscle strength and power in postmenopausal women.