Salt has for years been cited as a cause of high blood pressure.

多年来，食盐一直被认为是导致高血压的原因。

Now new research suggests high-salt diets may harm your brain, too.

现在一项新的研究表明，高盐饮食可能也会损害你的大脑。

The latest study to show a link between a high-salt diet and memory and thinking problems was done in mice.

最近的一项研究表明，高盐饮食与记忆力和思维问题之间存在联系。

But earlier research on humans suggests a link between high-salt diets and brain health as well.

但是早期的人类研究表明高盐饮食和大脑健康之间也有联系。

In the newest study, researchers fed mice either 8 or 16 times the normal amount of salt in their diet.

在最新的研究中，研究人员给小鼠喂了8到16倍于正常量的盐。

Within 8 to 12 weeks, the mice showed signs of memory and thinking problems.

在8到12周内，老鼠表现出了记忆和思考问题的迹象。

They had trouble telling new and familiar objects apart.

他们很难区分新的和熟悉的物体。

It got harder for them to get through mazes¹.

他们更难通过迷宫。

And they couldn’t build a nest as well.

他们也不能建造一个巢穴。

These behaviors are all central to a mouse’s interaction with the world.

这些行为都是老鼠与周遭世界互动的核心行为。

“We translate that in humans to activities of daily living, and that’s what we would call severe cognitive² impairment or dementia,” says Costantino Iadecola, MD, a professor of neurology and neuroscience at Weill Cornell Medical College in New York City and the study’s lead researcher.

“我们将其转化为日常生活的活动，这就是我们所说的严重的认知障碍或痴呆症，”Costantino Iadecola说，他是纽约威尔康奈尔医学院神经学和神经科学的教授，也是该研究的首席研究员。

For humans, the impairment would be like having memory problems, disorientation, and not being able to dress, cook, pay bills, or do other everyday things.

对人类来说，损伤就像记忆问题、迷失方向、不能穿衣、做饭、付账单或做其他日常事情一样。

Iadecola says the amount of salt he and his colleagues fed the mice was extreme.

他说，他和他的同事给老鼠喂食的盐的含量是极端的。

It likely would be 5 to 6 times the salt in a typical American diet.

这可能是典型美国饮食中盐的5到6倍。

But he says “no one knows exactly how much salt Americans eat, because most of it is hidden in processed foods or restaurant foods.

但他说，“没有人确切知道美国人吃了多少盐，因为大部分盐都藏在加工食品或餐馆食品中。”

I’m sure it’s grossly underestimated.”

我敢肯定这是被严重低估了。”

Also, mice showed the same level of impairment no matter which of the two high-salt diets they ate.

而且，不管他们吃的是哪种高盐饮食，老鼠的损伤程度都是一样的。

That suggests to Iadecola that less salt could cause the same problems: “I suspect that you can get cognitive impairment from even lower levels than we used.”

这就意味着，对于盐来说，盐的减少可能会导致同样的问题：“我怀疑你的认知能力会比我们所使用的更低。”

Potential Game-changer

潜在的决定因素

The study could change the conversation about diet with her patients, says Pinky Agarwal, MD, a neurologist who specializes in movement disorders³ like Parkinson’s disease at EvergreenHealth in Kirkland, WA, and a fellow of the American Academy of Neurology.

医学博士平基阿加瓦尔说，这项研究可能会改变与患者的饮食对话。他是一名神经学家，在华盛顿州柯克兰的 EvergreenHealth 公司专门研究类似帕金森病的运动障碍症，同时也是美国神经学研究院的研究员。

When doctors think about salt and patient health, they focus mostly on high blood pressure, or hypertension, cardiovascular disease, and stroke, she says.

她说，当医生想到盐和病人的健康时，他们主要关注高血压、高血压、心血管疾病和中风。

““If a patient does not have hypertension, we don’t talk about salt at all,” says Agarwal, who was not involved in the study.

“如果病人没有高血压，我们根本就不谈盐，”没有参与这项研究的阿加瓦尔说。

“This study provides a good reason for us to ask everyone about salt intake⁵.”

“这项研究提供了一个很好的理由，让我们向所有人询问盐的摄入量。”

What Salt Does

盐的作用

The effects that Iadecola found follow an indirect path.

他发现影响是间接的。

When the mice ate their doctored food, the excess salt triggered a response in their small intestine⁶.

当老鼠吃了他们的食物，多余的盐在他们的小肠里引起了反应。

It started to produce large amounts of Th17, a type of white blood cell involved with the immune system.

它开始产生大量的Th17，一种与免疫系统有关的白细胞。

This led to a rise in levels of another component⁷ of the immune system, a protein called IL-17.

这导致了免疫系统的另一个组成部分的上升，一种叫做IL-17的蛋白质。

That was a problem for the mice, and it likely would be for humans as well.

这对小鼠来说是一个问题，而且可能对人类也是如此。

When the body produces too much IL-17, it can no longer supply enough of a chemical called nitric oxide⁸, which is made by cells lining⁹ blood vessels¹⁰.

当身体产生过多的IL-17时，它就不能再提供足够的一种叫做一氧化氮的化学物质，这种化学物质是由血管中的细胞制造的。

When nitric oxide levels drop, blood vessels cannot relax, which leads to less blood flow to the brain.

当一氧化氮水平下降时，血管不能放松，从而导致血液流向大脑的血液减少。

“You need nitric oxide for the brain to work correctly,” says Iadecola.

“你需要一氧化氮来让大脑正常工作，”Iadecola说。

This discovery that salt can lead to memory and thinking problems via reactions in the gut¹¹ is exciting, says neurologist David Hafler, MD, who was not involved in the study.

医学博士大卫哈夫勒说，这种发现盐能通过肠道内的反应导致记忆和思考问题的发现令人兴奋。他没有参与这项研究。

“This shows that dietary influences may be a major influence in vascular⁴ dementia,” says Hafler, professor and chairman of neurology and professor of immunobiology at the Yale School of Medicine.

“这表明饮食影响可能是血管性痴呆的主要影响，”哈夫勒说，他是耶鲁大学医学院的神经学教授和免疫生物学教授。

High Salt = Higher Rates of Disease

高盐=更高的发病率

Hafler’s own research supports the significance of this new study.

Hafler自己的研究支持了这项新研究的意义。

In 2013, he and his colleagues published the first study demonstrating that excess salt boosts levels of Th17 and influences the development of multiple sclerosis.

2013年，他和他的同事发表了第一份研究报告，证明过量的盐能提高Th17的水平，并影响多发性硬化症的发展。

That discovery may help explain the rise in MS and other autoimmune diseases, like psoriasis, inflammatory bowel¹² disease, and rheumatoid arthritis¹³.

这一发现可能有助于解释多发性硬化和其他自体免疫疾病的增多，如银屑病、炎症性肠病和类风湿性关节炎。

“The effect of salt is just absolutely dramatic,” says Hafler.

“盐的作用绝对是戏剧性的，”Hafler说。

Iadecola says that some studies have shown higher rates of strokes and dementia in countries where people eat a lot of salt.

他说，一些研究显示，在人们吃大量盐的国家，中风和痴呆症的发病率较高。

“Nobody has figured out how and why, and it’s been very controversial,” he says.

他说：“没有人知道所以然，这是非常有争议的。”

“Some people argue that you may do harm by limiting salt intake too much, while others encourage people to curb¹⁴ it to a very small amount.”

“有些人认为，限制盐摄入量过多会造成伤害，而另一些人则鼓励人们将盐摄入量控制在很小的范围内。”

A study published in March 2017, for example, found a link between low-salt diets and worsening thinking skills among adults over 50, especially those older than 80.

例如，一项于2017年3月发表的研究发现，在50岁以上的成年人中，低盐饮食与不断恶化的思维能力之间存在联系，尤其是那些80岁以上的人。

Two previous studies, however, reached different conclusions.

然而，之前的两项研究得出了不同的结论。

Canadian researchers reported in 2011 that older adults who got little exercise were more likely to have memory and thinking problems if they ate a high-salt diet.

加拿大研究人员在2011年的报告中指出，那些很少运动的老年人如果吃高盐饮食，他们的记忆力和思考问题就会更大。

In 2013, a Turkish study showed that lower levels of salt were linked to better brain ability in adults with high blood pressure.

2013年，一项土耳其的研究表明，低水平的盐与高血压的成年人的大脑能力有关。

More Than Just Hypertension

不仅仅是高血压

Agarwal says there’s probably a need for tests and questionnaires that will let doctors find out how much salt their patients eat.

阿格沃尔说，可能需要进行测试和问卷调查，让医生们了解他们的病人吃了多少盐。

Most dietary salt, after all, does not come from the saltshaker on your kitchen table.

毕竟，大多数的饮食盐并不是来自你餐桌上的盐瓶。

It’s in processed foods and restaurant meals, and that makes it hard to calculate.

这是在加工食品和餐馆的食物中，这使得盐的摄入量计算变得复杂。

Another complication: Different people will have different salt requirements, just like mice.

另一个难题是：不同的人会有不同的盐摄入标准，就像老鼠一样。

In Iadecola’s study, older mice showed signs of impairment earlier than the younger mice.

在一项研究中，年龄较大的老鼠比年轻的老鼠表现出更早的损伤迹象。

Other things, such as genetics, also will play a part in how much salt is too much.

其他的东西，比如基因，也会在盐的摄入量过多的问题上发挥作用。

“It’s becoming very clear that it very much depends on the genetic¹⁵ variation within the individual as to what salt will do,” says Hafler.

Hafler说：“很明显，这在很大程度上取决于个人体内的基因变异，以及盐的作用。”

He says that evolution shaped humans to need about 500 milligrams of salt per day.

他说，进化使人类每天需要大约500毫克盐。

Many Americans eat more than 6 times that amount every day, the American Heart Association says.

美国心脏协会说，许多美国人每天的食量是这一数字的6倍多。

“We’re consuming much more salt than nature intended,” Hafler says.

“我们摄入的盐比天然的盐分要多得多，”Hafler说。

Effects May Be Reversible

过量食盐的后果可能是可逆的

If you love salty food, there could be some good news.

如果你喜欢吃咸的食物，可能会有一些好消息。

Once the mice returned to their normal diet, their brain function returned to normal as well.

一旦老鼠恢复正常饮食，它们的大脑功能也恢复正常。

That suggests that problems caused by eating too much salt may be reversed once you cut back.

这表明，吃太多盐所引起的问题可能会在你减少的时候被逆转。

And, of course, these problems may be prevented by avoiding a high-salt diet in the first place, says Agarwal: “It’s something that can be controlled.”

当然，这些问题可以通过避免高盐饮食来避免，阿加瓦尔说：“这是可以控制的。”

The mice in the study remained on their high-salt diet for only 3 months.

研究中的老鼠只在高盐饮食中坚持了3个月。

Is there a point at which the brain will begin to suffer permanent damage?

是否有这样一个点，大脑会开始遭受永久性损伤?

“We don’t know what will happen if you do this for 10 years,” says Iadecola.

“我们不知道如果你这样做了10年，会发生什么，”Iadecola说。

“My suggestion is that because the blood flow is reduced in the brain and because then the blood vessels in the brain don’t work correctly, something major is going to happen if you keep this up.

“我的建议是，因为大脑中的血液流动减少了，因为大脑中的血管不能正常工作，如果你坚持下去，就会发生一些重大的事情。”

Watching salt intake may be an important step to preventing dementia.”

观察盐摄入量可能是预防痴呆的重要一步。”