BEETter AGING: Short-Term Dietary Nitrate Supplementation Enhances Muscle Contractile Properties in Older But Not in Young Adults

TL;DR

In a randomized, double-blind crossover trial, 7-day nitrate-rich beetroot juice supplementation increased plasma nitrate/nitrite more than 7-fold in both young and older men but improved plantar-flexor submaximal electrically evoked force, shortened Db100 half-relaxation time/area under the curve, and prolonged time to exhaustion only in older adults. No maximal voluntary or twitch/doublet peak-force benefits were seen in either group.

Key findings

• Plasma nitrate and nitrite increased more than 7-fold after beetroot juice versus placebo in both older and young adults (all P≤0.02).
• No changes were observed in maximal voluntary isometric contraction, potentiated single twitch, or 100 Hz doublet peak force after beetroot juice in either group. In older adults only, Db100 area under the curve was reduced by −7±6 N·s and Db100 half-relaxation time by −0.05±0.06 s versus placebo, while time to exhaustion was longer by +32±43 s (all P<0.02).
• In older adults, beetroot juice significantly increased submaximal force produced by trains of electrical pulses (P<0.001), about +11%, with higher relative forces at 20–50 Hz. In the fatiguing test, young adults reached task failure at ~1 min after both treatments, whereas older adults exercised for ~2 min and significantly longer after beetroot juice than placebo (P=0.010).

Methods

• Randomized, double-blind, crossover design with a 15-day washout; 22 healthy males participated: 11 older (69±4 y) and 11 young (26±2 y) adults. Exclusion criteria included cardiovascular, metabolic, or neuromuscular disease; NO-affecting drugs/supplements; and antimicrobial mouthwash or antibiotics in the prior 30 days.
• Participants consumed either nitrate-rich beetroot juice (2 × 70 ml daily, ~12.4 mmol NO3−) or nitrate-depleted placebo for 7 days. Plasma nitrate/nitrite were measured by chemiluminescence; dominant-leg plantar flexors were assessed for maximal voluntary isometric contraction, potentiated single twitch, 100 Hz doublet, and an isometric fatiguing test at 70% maximal voluntary isometric contraction until exhaustion; non-dominant leg force-frequency relationship was assessed at 1–100 Hz.
• Analysis used two-way and three-way ANOVA with Bonferroni post hoc tests, α=0.05, with effect sizes reported as eta squared.

Limitations

• Stated by the authors: the study did not directly investigate mechanisms; plasma nitrate/nitrite may only partially reflect NO availability; results might differ during dynamic exercise; and further studies are needed.
• Evident from the text: the sample was small (11 per group), included only healthy males, used short-term 7-day supplementation, and tested isometric plantar-flexor tasks, so findings may not generalize to females, clinical populations, longer supplementation, or dynamic exercise settings.