Effect of curcumin supplementation on muscle oxygen saturation parameters during handgrip exercise in elderly individuals at risk of cardiovascular disease

Introduction: Curcumin is a polyphenol derived from the curcuma longa plant, used as a food spice. It has been shown that curcumin presents an anti-inflammatory and antioxidant effect, which has been mentioned as a protector of the cardiovascular system. In elderly at risk for cardiovascular disease, the impairment of the microvascular response is also impaired, so it is believed that muscle oxygenation to physical demand may also be deficient. Thus, considering that aging may impair vascular responsiveness and curcumin supplementation has been shown to be cardioprotective, we hypothesized that curcumin supplementation might improve muscle oxygenation in the elderly. The aim of the present study was to evaluate the effect of a single dose of curcumin on muscle oxygenation during handgrip exercise assessed by near-infrared spectroscopy (NIRS) in elderly.
Materials and Methods: The study was conducted in a randomized, double-blind, crossover and placebo-controlled manner. Fourteen older adults at risk for cardiovascular disease (CVD) ingested 10 g of curcumin (CUR) or 1 g of maltodextrin as placebo (PLA), without effect on vascular response. Two hours after supplementation, NIRS was used to evaluate forearm muscle oxygen saturation (SmO2) during 3 sets of handgrip exercise and exercise recovery. Handgrip exercise was performed at 30% maximal voluntary isometric contraction. The following NIRS variables were assessed: SmO2minimum which corresponds to the lowest SmO2 during the exercise; SmO2maximum which corresponds to the highest SmO2 during the exercise recovery; the O2 resaturation rate was calculated over 3s (SmO2 upslope_3s) and 5s (SmO2 upslope_5s) immediately following exercise in order to assess the microvascular reactivity.
The project was approved by the Research Ethics Committee of the Federal University of Rio de Janeiro and Clinical Trials (CAAE 97055018.1.0000.5699).
ANOVA two-way repeated measure statistical analysis was performed in order to detect significant differences between interventions over the sets of exercise. Cohen’s d was calculated to better interpretation of the data as the magnitude of the supplementation effect. Thus, cohen’s d, with values < 0.2 considered trivial, 0.2-< 0.5 small effect, 0.5-< 0.8 moderate effect, and ≥ 0.8 large effect.
Results and Conclusion: There was no significant difference in NIRS variables (P > 0.05). However, it is important to note that a medium to large effect size after CUR supplementation at set 1 (d = 0.4), set 2 (d = 0.6), and set 3 (d = 0.5) was observed, indicating that a beneficial effect of CUR on microvascular reactivity after exercise should not be completely neglected. Indeed, our data are preliminary and one limitation is the sample size (14 participants). Thus, the present study analyzed the effect size to better understand our results, since this measurement can be discerned as the meaningful of the intervention. Previous studies have shown that microvascular reactivity is impaired in older adults during exercise recovery. These findings are associated with endothelial dysfunction in that population. Considering that CUR may present antioxidant effect, leading to improvement on endothelial function, our findings suggest that muscle oxygen saturation enhanced after single dose of 10 g of CUR supplementation. Thus, future studies evaluating the effect of chronic curcumin ingestion on microvascular function is warranted to better delineate this effect.