School of Biomedical Sciences and Curtin Health Innovation Research Institute, Curtin University, Perth, Australia.
Food Funct. 2018 Dec 13;9(12):6307-6314. doi: 10.1039/c8fo01019f.
Tea consumption may improve endothelial function and blood pressure via increased bioavailability and bioactivity of nitric oxide. However, questions remain as to the impact of the common practice of adding milk.
To investigate the effect of regular consumption of black tea, with and without milk, on vascular function and blood pressure in healthy volunteers.
A randomised, controlled, crossover study was performed in 17 healthy volunteers; 7 men and 10 women, mean age 22.4 ± 3.0 years. Participants received each of the following treatments in random order for 4 weeks, with no washout period in between, (i) hot water, (ii) black tea and (iii) black tea with milk. Vascular function was assessed using flow-mediated dilatation (FMD) of the brachial artery at the end of each treatment period. In addition, participants monitored their home blood pressure for the last 7 days of each treatment period. A blood and urine sample was also collected at the end of each treatment period.
Black tea increased FMD compared to the hot water control group (1.00 ± 0.18%, P < 0.0001). Black tea with milk decreased FMD compared to both the hot water control (-0.64 ± 0.19%, P = 0.001) and black tea (-1.64 ± 0.19%, P < 0.0001). Compared with hot water, black tea did not alter blood pressure, while black tea with milk increased systolic (1.1 ± 0.5 mmHg, P = 0.03) and diastolic blood pressure (2.0 ± 0.5 mmHg, P < 0.0001). Black tea (-1.8 ± 0.5 bpm, P < 0.001) and black tea with milk (-1.8 ± 0.6 bpm, P < 0.001) lowered heart rate compared to hot water. No significant difference for plasma nitrate or nitrite was observed between treatment groups.
The addition of milk to black tea alters the acute/short-term impact of regular tea consumption on vascular function and blood pressure in young healthy men and women. The exact mechanism for this affect remains unknown and longer-term trials to establish this effect in a range of populations are warranted.
茶的摄入可通过提高一氧化氮的生物利用度和生物活性来改善内皮功能和血压。然而，关于在常见的加奶习惯对其的影响方面仍存在一些疑问。
研究在健康志愿者中，经常饮用红茶，无论是否添加牛奶，对血管功能和血压的影响。
这是一项在 17 名健康志愿者中进行的随机、对照、交叉研究；7 名男性和 10 名女性，平均年龄 22.4±3.0 岁。参与者以随机顺序接受以下三种处理，每种处理持续 4 周，期间无洗脱期，（i）热水，（ii）红茶，（iii）加奶红茶。在每个处理期末，通过肱动脉血流介导的扩张（FMD）评估血管功能。此外，参与者在每个处理期末的最后 7 天监测其家庭血压。在每个处理期末还收集了血液和尿液样本。
与热水对照组相比，红茶增加了 FMD（1.00±0.18%，P＜0.0001）。与热水对照组（-0.64±0.19%，P=0.001）和红茶对照组（-1.64±0.19%，P＜0.0001）相比，加奶红茶降低了 FMD。与热水相比，红茶没有改变血压，而加奶红茶增加了收缩压（1.1±0.5mmHg，P=0.03）和舒张压（2.0±0.5mmHg，P＜0.0001）。与热水相比，红茶（-1.8±0.5bpm，P＜0.001）和加奶红茶（-1.8±0.6bpm，P＜0.001）降低了心率。各组之间的血浆硝酸盐或亚硝酸盐无显著差异。
在红茶中添加牛奶改变了年轻人和健康女性中经常喝茶对血管功能和血压的短期影响。其确切机制尚不清楚，需要进行更长期的试验来确定在各种人群中的这种影响。
