VOA慢速英语2019 科学家证实压力会导致头发变白（在线收听）

A new study provides scientific evidence to support the idea that stress can cause a person's hair to turn gray.

一项新的研究提供科学证据证实了压力可能会导致头发变白的观点。

A team from America's Harvard University said the new study is the first to show a clear link between stress and graying hair. The findings were recently published in the journal Nature.

美国哈佛大学的一个团队表示，这项新研究首次证实了压力和头发变白两者之间的明确联系。该研究结果最近发表在《自然》期刊上。

Researchers say they discovered a chemical process that can change hair color during times of stress. The process is linked to the body's "fight-or-flight" reaction that can happen during dangerous situations.

研究人员表示，他们发现了一种在压力时期可以改变头发颜色的化学过程。该过程与人体在危险情况下可能发生的“战斗或逃避”的反应有关。

Ya-Chieh Hsu is a professor of Stem Cell and Regenerative Biology at Harvard. She said in a statement that the research team was in search of the first scientific confirmation of the commonly held belief that stress can cause gray hair. "Everyone has an anecdote to share about how stress affects their body, particularly in their skin and hair - the only tissues we can see from the outside," Hsu said.

许雅捷是哈佛大学的干细胞和再生生物学教授。她在一份声明中表示，该研究团队是在寻找压力会导致白头这种普遍观点的科学证据。许教授表示：“每个人都发生过一些压力如何影响他们身体的轶事，尤其是对皮肤和头发的影响，这也是我们唯一能从外面观察到的组织。”

The team used experiments with mice to look at how stress affects stem cells in hair follicles. Most people have about 100,000 hair follicles on their head. The follicles are responsible for making melanocytes, the cells that give hair its color. As people age, melanocyte production is reduced. This causes a person's hair to begin turning gray naturally.

该团队通过小鼠实验来研究压力如何影响毛囊中的干细胞。大多数人头上有大约10万个毛囊。毛囊负责生成黑素细胞，也就是赋予头发颜色的细胞。随着年龄增长，黑素细胞的生成就会减少。这会导致人们的头发开始自然地变白。

At first, the researchers suspected that an immune attack caused by a stressful event might be targeting the melanocyte stem cells. That theory, however, turned out to be false. The mice lacking immune cells still showed signs of graying hair.

起初，研究人员怀疑是压力事件导致的免疫攻击可能会以黑素干细胞为目标。但是这种理论被证实是错误的。缺乏免疫细胞的小鼠仍然显示出了毛发变白的迹象。

The team also thought the hormone cortisol, which always increases in the body during times of stress, might be a likely cause. However, when researchers removed the gland that produces the cortisol hormones, the hair of mice still turned gray.

该团队还认为荷尔蒙皮质醇可能是元凶，这种皮质醇通常在面临压力时期会在体内增加。但是，当研究人员去除产生皮质醇激素的腺体时，小鼠的毛发仍然会变白。

The scientists then centered their experiments on the body's sympathetic nervous system. This is the body system that controls "fight-or-flight" reactions in dangerous situations.

然后科学家将他们的实验聚焦在人体的交感神经系统上。这是在面临危险情况下控制“战斗或逃避”的身体系统。

The sympathetic nervous system is made up of a collection of nerves that extend through the body, including the skin. When the mice were subjected to short-term pain or placed in stressful laboratory conditions, these nerves released a chemical called norepinephrine. The chemical then flowed through the stem cells up into the hair follicles -- where melanocytes are kept.

交感神经系统由遍布整个身体（包括皮肤）的神经组成。当小鼠遭受短期疼痛或处于有压力的实验室条件下，这些神经会释放一种被称为去甲肾上腺素的化学物质。然后这种化学物质通过干细胞向上流入保存黑素细胞的毛囊。

The researchers found that when the norepinephrine was released, all the melanocyte stem cells were highly activated and changed into pigment-producing cells. This overproduction process resulted in the early loss of color-producing cells.

研究人员发现，当去甲肾上腺素释放出来时，所有黑素细胞干细胞均被高度激活并转为产生色素的细胞。这种过度生产的过程导致了颜色生成细胞的早期损失。

Ya-Chieh Hsu said the experiments confirmed the team's belief that stress is bad for the body. She added that the results demonstrated the harmful effects are more major than what the researchers had imagined. "After just a few days, all of the pigment-regenerating stem cells were lost. Once they're gone, you can't regenerate pigments anymore. The damage is permanent," Hsu said.

许雅捷表示，实验证实了该团队的观点，即压力对身体有害。她还表示，结果证实这类有害影响比研究人员想象的更为严重。许雅捷表示：“仅仅在几天之后，所有色素再生干细胞都耗光了。一旦耗光就无法再次生成色素。这种损害是永久性的。”

The scientists said their research could lead to new treatments for stress-related graying in the future. Graying hair is just one example of how stress affects the body. New experiments could also be carried out in other areas, as well, the team said. These could include studies to see whether stress can also cause changes in body tissues.

科学家们表示，他们的研究可能会在将来得出与压力有关的头发变白的新疗法。头发变白只是压力影响身体的案例之一。该团队表示，新实验也可以在其它领域进行。其中可能包含检查压力是否还会导致人体组织变化的实验。

Hsu said she would also like to study whether stress has a large effect on the overall aging process. "We don't know if that is true yet. We are interested in finding out the link," she said.

许雅捷表示，她还想研究压力是否对整个衰老过程产生重大影响。她说：“我们不知道这是不是真的。我们有兴趣找出其中的关联。”