Abstract
Postprandial macro- and microvascular blood flow and metabolic dysfunction manifest with advancing age, so vascular transmuting interventions are desirable. In this randomised, single-blind, placebo-controlled, crossover trial, we investigated the impact of the acute administration of green tea extract (GTE; containing ~500 mg epigallocatechin-3-gallate) versus placebo (CON), alongside an oral nutritional supplement (ONS), on muscle macro- and microvascular, cerebral macrovascular (via ultrasound) and leg glucose/insulin metabolic responses (via arterialised/venous blood samples) in twelve healthy older adults (42% male, 74 ± 1 y). GTE increased m. vastus lateralis microvascular blood volume (MBV) at 180 and 240 min after ONS (baseline: 1.0 vs. 180 min: 1.11 ± 0.02 vs. 240 min: 1.08 ± 0.04, both p < 0.005), with MBV significantly higher than CON at 180 min (p < 0.05). Neither the ONS nor the GTE impacted m. tibialis anterior perfusion (p > 0.05). Leg blood flow and vascular conductance increased, and vascular resistance decreased similarly in both conditions (p < 0.05). Small non-significant increases in brachial artery flow-mediated dilation were observed in the GTE only and middle cerebral artery blood flow did not change in response to GTE or CON (p > 0.05). Glucose uptake increased with the GTE only (0 min: 0.03 ± 0.01 vs. 35 min: 0.11 ± 0.02 mmol/min/leg, p = 0.007); however, glucose area under the curve and insulin kinetics were similar between conditions (p > 0.05). Acute GTE supplementation enhances MBV beyond the effects of an oral mixed meal, but this improved perfusion does not translate to increased leg muscle glucose uptake in healthy older adults.
Highlights
Increased vascular resistance [1] and endothelial dysfunction [2] are both hallmarks of advancing age and are each central risk factors for cardiometabolic disease [3]
leg vascular conductance (LVC) increased at 55 min in the green tea extract (GTE) condition (0 min: 2.51 ± 0.23 vs. 55 min: 3.76 ± 0.19 mL/min, p = 0.023) and at 85 min in the CON condition
leg vascular resistance (LVR) decreased in both conditions, with the onset occurring at 55 min in the GTE
Summary
Increased vascular resistance [1] and endothelial dysfunction [2] are both hallmarks of advancing age and are each central risk factors for cardiometabolic disease [3]. Blunted muscle microvascular blood flow responses are observed in older adults following anabolic stimuli (e.g., feeding) [10,11], and nutrient-induced increases in whole-limb perfusion are attenuated with advancing age [5]. These diminished vascular responses are hypothesised to contribute to age-related “anabolic resistance” to nutrition, via the attenuated delivery and/or utility of nutrients (e.g., amino acids) and hormones (e.g., insulin) to muscle [12], it does not fully explain anabolic resistance, since enhancing microvascular blood flow does not improve muscle anabolism [13]. Determining nutraceutical strategies for maintaining/potentiating vascular and metabolic responses in older adults may have significant ramifications for reducing cardiovascular disease risk and could play a role in the maintenance of muscle health
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