Possible Difference Between Older Men And Women In Dietary Nitrate’s Effects On Muscle Contractility

Aging is associated with declines in muscle contractile function; specifically, reductions in muscle force, speed, and power, which majorly contribute to the increased prevalence of disability and risk of falls/fractures in this population. We have repeatedly demonstrated that acute ingestion of nitrate (NO3-) rich beetroot juice, a source of nitric oxide (NO) via the NO3- → NO2- → NO pathway, can improve muscle contractility in older individuals. It is not clear, however, whether older men and women benefit equally from such NO3- supplementation. PURPOSE: We sought to determine whether there is a possible sex-related difference in the effects of dietary NO3- on muscle contractile function in older individuals. METHODS: Pooled data from our previous studies were used to compare the effects of acute NO3- intake on muscle contractile function in 11 men and 19 women 65-79 y of age. Maximal knee extensor velocity (Vmax) and power (Pmax) were assessed using an isokinetic dynamometer. RESULTS: Two-way analysis of variance (ANOVA) demonstrated a significant effect of treatment (P = 0.0215) but not of sex (p = 0.2153) on Vmax. The interaction effect was also not significant (p = 0.4148). Pmax also exhibited a significant difference due to treatment (p = 0.0372) as well as sex (p = 0.0071), but no interaction effect (p = 0.3964). However, based on Holm-Šidák tests Pmax (W/kg) significantly increased in women following acute NO3- ingestion (3.55 ± 0.92 vs. 3.83 ± 1.08, +9%, p = 0.0353), whereas there was no increase in men (4.78 ± 1.06 vs. 4.90 ± 1.31, +2%, p = 0.4116). This may be because the women received a higher mass-specific dose of NO3- (μmol/kg) (233 ± 42 vs. 147 ± 29, +58%, p < 0.0001). Correspondingly, plasma NO3- and NO2- concentrations (μmol/L) were higher in the women (715 ± 198 vs. 409 ± 103, +75%, p < 0.0001 and 1.082 ± 0.889 vs. 0.640 ± 0.442, +69%, p < 0.0001, respectively). CONCLUSIONS: The beneficial effects of acute dietary NO3- ingestion on muscle speed and power may be greater in older women more than in older men, but additional research will be required to elucidate whether this apparent sex-related difference remains when the dose of NO3- is equal relative to body mass. Supported by: NCATS UL1 TR002529, NIAMS P30 AR072581, NIA R21 AG053606