食鹽過量不但導致高血壓也會損害大腦

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

多年來，食鹽一直被認為是導致高血壓的原因。

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

現在一項新的研究表明，高鹽飲食可能也會損害你的大腦。

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

最近的一項研究表明，高鹽飲食與記憶力和思維問題之間存在聯繫。

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

但是早期的人類研究表明高鹽飲食和大腦健康之間也有聯繫。

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，研究人員給小鼠餵了8到16倍於正常量的鹽。

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

在8到12周內，老鼠表現出了記憶和思考問題的跡象。

They had trouble telling new and familiar objects apart.

他們很難區分新的和熟悉的物體。

It got harder for them to get through mazes.

他們更難通過迷宮。

And they couldn’t build a nest as well.

他們也不能建造一個巢穴。

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

這些行為都是老鼠與周遭世界互動的核心行為。

“We translate that in humans to activities of daily living, and that’s what we would call severe cognitive 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.

“我們將其轉化為日常生活的活動，這就是我們所説的嚴重的認知障礙或痴呆症，”Costantino Iadecola説，他是紐約威爾康奈爾醫學院神經學和神經科學的教授，也是該研究的首席研究員。

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.

對人類來説，損傷就像記憶問題、迷失方向、不能穿衣、做飯、付賬單或做其他日常事情一樣。

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

他説，他和他的同事給老鼠餵食的鹽的含量是極端的。

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

這可能是典型美國飲食中鹽的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.

但他説，“沒有人確切知道美國人吃了多少鹽，因為大部分鹽都藏在加工食品或餐館食品中。”

I’m sure it’s grossly underestimated.”

我敢肯定這是被嚴重低估了。”

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

而且，不管他們吃的是哪種高鹽飲食，老鼠的損傷程度都是一樣的。

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.”

這就意味着，對於鹽來説，鹽的減少可能會導致同樣的問題：“我懷疑你的.認知能力會比我們所使用的更低。”

Potential Game-changer

潛在的決定因素

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

醫學博士平基阿加瓦爾説，這項研究可能會改變與患者的飲食對話。他是一名神經學家，在華盛頓州柯克蘭的 EvergreenHealth 公司專門研究類似帕金森病的運動障礙症，同時也是美國神經學研究院的研究員。

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

她説，當醫生想到鹽和病人的健康時，他們主要關注高血壓、高血壓、心血管疾病和中風。

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

“如果病人沒有高血壓，我們根本就不談鹽，”沒有參與這項研究的阿加瓦爾説。

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

“這項研究提供了一個很好的理由，讓我們向所有人詢問鹽的攝入量。”

What Salt Does

鹽的作用

The effects that Iadecola found follow an indirect path.

他發現影響是間接的。

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

當老鼠吃了他們的食物，多餘的鹽在他們的小腸裏引起了反應。

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

它開始產生大量的Th17，一種與免疫系統有關的白細胞。

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

這導致了免疫系統的另一個組成部分的上升，一種叫做IL-17的蛋白質。

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

這對小鼠來説是一個問題，而且可能對人類也是如此。

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

當身體產生過多的IL-17時，它就不能再提供足夠的一種叫做一氧化氮的化學物質，這種化學物質是由血管中的細胞製造的。

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

當一氧化氮水平下降時，血管不能放鬆，從而導致血液流向大腦的血液減少。

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

“你需要一氧化氮來讓大腦正常工作，”Iadecola説。

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

醫學博士大衞哈夫勒説，這種發現鹽能通過腸道內的反應導致記憶和思考問題的發現令人興奮。他沒有參與這項研究。

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

“這表明飲食影響可能是血管性痴呆的主要影響，”哈夫勒説，他是耶魯大學醫學院的神經學教授和免疫生物學教授。

High Salt = Higher Rates of Disease

高鹽=更高的發病率

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

Hafler自己的研究支持了這項新研究的意義。

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，他和他的同事發表了第一份研究報告，證明過量的鹽能提高Th17的水平，並影響多發性硬化症的發展。

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

這一發現可能有助於解釋多發性硬化和其他自體免疫疾病的增多，如銀屑病、炎症性腸病和類風濕性關節炎。

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

“鹽的作用絕對是戲劇性的，”Hafler説。

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

他説，一些研究顯示，在人們吃大量鹽的國家，中風和痴呆症的發病率較高。

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

他説：“沒有人知道所以然，這是非常有爭議的。”

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

“有些人認為，限制鹽攝入量過多會造成傷害，而另一些人則鼓勵人們將鹽攝入量控制在很小的範圍內。”

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，一項於2017年3月發表的研究發現，在50歲以上的成年人中，低鹽飲食與不斷惡化的思維能力之間存在聯繫，尤其是那些80歲以上的人。

Two previous studies, however, reached different conclusions.

然而，之前的兩項研究得出了不同的結論。

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.

加拿大研究人員在2011年的報告中指出，那些很少運動的老年人如果吃高鹽飲食，他們的記憶力和思考問題就會更大。

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，一項土耳其的研究表明，低水平的鹽與高血壓的成年人的大腦能力有關。

More Than Just Hypertension

不僅僅是高血壓

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

阿格沃爾説，可能需要進行測試和問卷調查，讓醫生們瞭解他們的病人吃了多少鹽。

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

畢竟，大多數的飲食鹽並不是來自你餐桌上的鹽瓶。

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

這是在加工食品和餐館的食物中，這使得鹽的攝入量計算變得複雜。

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

另一個難題是：不同的人會有不同的鹽攝入標準，就像老鼠一樣。

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

在一項研究中，年齡較大的老鼠比年輕的老鼠表現出更早的損傷跡象。

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

其他的東西，比如基因，也會在鹽的攝入量過多的問題上發揮作用。

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

Hafler説：“很明顯，這在很大程度上取決於個人體內的基因變異，以及鹽的作用。”

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

他説，進化使人類每天需要大約500毫克鹽。

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

美國心臟協會説，許多美國人每天的食量是這一數字的6倍多。

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

“我們攝入的鹽比天然的鹽分要多得多，”Hafler説。

Effects May Be Reversible

過量食鹽的後果可能是可逆的

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

如果你喜歡吃鹹的食物，可能會有一些好消息。

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

一旦老鼠恢復正常飲食，它們的大腦功能也恢復正常。

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

這表明，吃太多鹽所引起的問題可能會在你減少的時候被逆轉。

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.”

當然，這些問題可以通過避免高鹽飲食來避免，阿加瓦爾説：“這是可以控制的。”

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

研究中的老鼠只在高鹽飲食中堅持了3個月。

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

是否有這樣一個點，大腦會開始遭受永久性損傷?

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

“我們不知道如果你這樣做了10年，會發生什麼，”Iadecola説。

“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.

“我的建議是，因為大腦中的血液流動減少了，因為大腦中的血管不能正常工作，如果你堅持下去，就會發生一些重大的事情。”

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

觀察鹽攝入量可能是預防痴呆的重要一步。”