Higher doses of a green tea-based supplement increase post-exercise blood flow following an acute resistance exercise bout in recreationally resistance-trained college-aged men

Abstract

Background: There are animal data suggesting green tea can enhance blood flow. However, human data are lacking. Thus, the purpose of this study was to examine the acute effects of low and high doses of a green teabased supplement (GBS) on brachial artery blood flow before and following a resistance exercise bout. Methods: In this, double-blinded placebo-controlled trial, college-aged males (n = 18) who self-reported recreationally resistance training for the previous 6 ± 3 years were assigned to one of two studies including a low (300 mg serving) (n = 9) or high dose (600 mg serving) (n = 8; 1 drop) GBS study. During testing sessions, participants reported to the laboratory following an overnight fast and rested in a supine position for 15 min. Thereafter, baseline measurements for resting heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), brachial artery diameter (BAD) and blood flow (BBF) were obtained (PRE). Participants then consumed either their respective GBS dose or a similar placebo dose (microcrystalline cellulose) in a supine resting state. HR, SBP, DBP, BAD and BBF were measured 45 min after placebo or GBS ingestion (PRE2). Participants were then placed in a recumbent position and performed 4 sets of 10 arm curl repetitions using an 11 kg dumbbell. Participants returned to a supine position and HR, SBP, DBP, BAD and BBF were obtained within the first 3 min following exercise (POST), 15 min after exercise (15POST), and 45 min after exercise (45POST). Participants returned to the laboratory 24-48 h later to repeat the same protocol with either GBS or the placebo depending on randomization. Two-way (supplement x time) repeated measures ANOVAs were used to compare dependent variables between testing sessions for Study 1 (300 mg of GBS and placebo) and Study 2 (600 mg of GBS and placebo), and statistical significance was set at p < 0.05. No statistical comparisons were made between studies.

Green and white teas as health-promoting foods

“…Quercetin reduces also oxidative stress and acts on the renin-angiotensin-aldosterone system by improving vascular function. 45 Despite evidence of possible beneficial effects, these only show slight associations in epidemiological studies and therefore more studies are needed. 22,42,43…”

“…25 There are several studies that highlight the effects of green and white teas and their bioactive compounds both in in vitro and in animal studies. 22,25,[45][46][47] The research carried out by Xia et al showed a significant reduction in blood glucose and an improvement in glucose intolerance in mice after drinking white tea. In addition, a protective activity of the β-cells in the Langerhans islets against oxidative and inflammatory damage was observed.…”

“…47 This confirms a previous study with pre-diabetic rats which drank white tea for two months, finding increased sensitivity to insulin. 45 Therefore, white tea has a clear potential for blood glucose control and to protect against diabetes. 45,47 Green tea effects on blood glucose levels are attributed to altered insulin tolerance in peripheral tissues such as skeletal muscles and adipocytes.…”

“…45 Therefore, white tea has a clear potential for blood glucose control and to protect against diabetes. 45,47 Green tea effects on blood glucose levels are attributed to altered insulin tolerance in peripheral tissues such as skeletal muscles and adipocytes. 25 Diabetic mice treated with green tea polyphenols for 15 days showed a 44% reduction in serum glucose.…”

“…46 EGCG supplementation has also showed to improve glucose tolerance and to prevent the destruction of the Langerhans islets, modulate gene expression of relevant enzymes 25 and reducing serum glucose levels. 45 Tea flavonoids, on the other hand, can suppress the intestinal absorption of glucose by inhibiting the activity of -glucosidase and stimulating the glucose transporter 4 (GLUT4) by mediating glucose absorption and increasing insulin sensitivity. 46 In addition, green tea quercetin and genistein inhibited the activity of the insulin receptor tyrosine kinase IRS-1, IRS-2.…”