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Taking a probiotic supplement might reduce cognitive decline and could help when you're stressed
Scientists already know that probiotic supplements show promise in helping treat gut health conditions like IBS and gastrointestinal upset after taking antibiotics.
Now, scientists think that they might also slow down cognitive decline as we age, according to Jessica Eastwood, a nutritional psychology researcher in the department of psychology and clinical language sciences at the University of Reading in England.
In younger people, Eastwood told Insider, probiotics might even help people perform better when they're stressed.
"The microbes in your gut can affect your health in so many different ways," Eastwood said.
Here's some of what we know about probiotics and brain health.
Your gut and brain are intimately connected
Your gut and brain are closely connected, a partnership that's known as the "gut-brain axis."
What affects the brain can affect the gut too, and vice-versa. That's why you might have butterflies in your stomach when you're nervous, Eastwood said.
The connection is so strong that flares of GI conditions like IBS or Crohn's disease can set off mental health issues like depression or anxiety, according to Harvard Health.
Scientists aren't exactly sure yet how these two systems work together. "Understanding exactly how these bugs in your gut are affecting your brain is still a little bit unknown," Eastwood said.
Probiotics can prevent natural cognitive decline
As we age, our cognitive functioning, which includes memory and executive functioning, naturally declines.
Eastwood and her team published a 2021 review which found that taking a daily probiotic might reduce cognitive decline in otherwise healthy older adults.
"Taking a probiotic supplement might be particularly helpful in just helping to mitigate that natural decline and maintaining cognitive function for longer," Eastwood said. Eastwood said that this might be especially beneficial as people continue to live longer.
The review also found that a daily probiotic might help improve cognitive performance in older adults who have a mild cognitive impairment or have Alzheimer's disease.
While these findings are exciting, Eastwood said that bigger and better research trials are needed.
More recently, a study presented at the American Society for Nutrition meeting in July of this year that found that older adults who took a probiotic had cognitive improvement compared to those that took a placebo.
Probiotics might also help reduce stress
Probiotics won't usually boost cognitive functioning in younger people since "they're already performing at ceiling," Eastwood said. But "where you do see an effect in younger adults is if they are stressed."
Sometimes, Eastwood said, if you're stressed, your cognitive performance goes down. But in the same 2021 review, "we find that if you take probiotics, you get this sort of buffering effect — so it reduces that decline."
In other words, taking a probiotic may help maintain normal cognitive functioning despite stress.
"In young adults that are doing exams or going through a particularly stressful period, that's maybe where there could be some use," Eastwood said.
Most studies on probiotics have had people take them daily for four weeks to six months, Eastwood said. In a 2019 study, women ages 18 to 40 who took probiotics daily for 28 days performed better on a stressful task than those who took a placebo.
We don't know which strains are the best yet
Since probiotic research is still in its early stages, we don't yet know which strains of probiotics might be the most helpful for cognitive function.
If you're interested in trying a probiotic, Eastwood recommends a multi-strain probiotic that contains a combination of the most researched strains including lactobacillus, bifidobacterium, and lactococcus species.
And as with any new supplement, you should check with your doctor first to make sure it's safe for you to take.
注释：
probiotic: n
表示" 益生菌"，如：Forecast in China in the next few years, the probiotic market will have a rapid development and prospects. 预测在未来几年内，中国的益生菌市场将会有一个较快的发展，前景十分广阔。
Gastrointestinal: adj
表示"胃肠的"，means "of or relating to the stomach and intestines"，如：The infection route may have been the gastrointestinal tract. 感染源可能是来自肠胃道。
buffer: v
表示" 缓冲；减轻"，means "act as a buffer to"，如：Support from family and friends acts as a buffer against stress. 家庭和朋友的支持有助于减缓压力。
placebo: n
表示" 安慰剂"，如：Does endowment insurance really matter to everyone? Or is it just a placebo? 养老保险对我们真的重要吗？还是只是一种心理安慰？
lactobacillus
表示"乳酸杆菌"，means "a Gram-positive rod-shaped bacterium that produces lactic acid (especially in milk)"，如：
bifidobacterium: n
表示"双歧杆菌属"，如：Bifidobacterium Longum to enhance our immunity . 双歧乳杆菌能够提高人体免疫力。
lactococcus: n
表示" 乳球菌属"，如：We have launched a new product line, NICE? Expression System for Lactococcus lactis. 我们现在开发了一条新的产品线----乳酸乳球菌表达系统
中文简要说明：
肠道有人体第二个大脑的称号，拥有自主运作神经系统、种类复杂的微生物群，与免疫、代谢与疾病发生有关，也与大脑健康有紧密关联。众所周知，益生菌有助平衡肠道菌相、促进肠道健康，英国研究人员表示，益生菌可能也能减退认知能力下降，从而降低失智症发生机率。
综合美国《财经内幕》（Business Insider）、英国《每日邮报》（Daily Mail）15日报导，英格兰的瑞丁大学（University of Reading）营养心理学研究人员伊斯伍德（Jessica Eastwood）表示，学界已知益生菌能改善肠躁症、抗生素导致的肠胃不适等问题，如今科学家认为，益生菌可能也有助于减缓长者认知能力衰退，帮助年轻人在压力之下有更好的表现。
益生菌（probiotics）是消化系统的「好菌」，有助于抵挡可能致病的有害细菌，可缓解腹泻便秘等消化问题、增强免疫、调节食欲、改善忧郁症、降低发炎症状。优格、奶酪、脱脂乳、大豆、泡菜、味噌等许多食物含有益生菌，市面也贩卖多种益生菌补充剂。
大脑与肠道之间存在肠脑轴线（gut-brain axis），两者彼此影响，例如精神紧张时有的人会觉得胃肠不舒服，肠躁症等肠胃疾病发作时也可能引发忧虑、焦虑等问题，至于确切相互作用如何进行，学界仍未完全掌握。
伊斯伍德与研究团队2021年发表的文献综述，研究了30篇论文，受试参与者从27周大的胎儿到82岁老人都有，以不同任务测量认知能力。这份综述指出，每天服用益生菌可能有助健康的老年人降低认知能力退化的风险。她说，服用益生菌补充剂可能尤其有助于减缓自然衰退，让认知能力维持更长久。对于轻度认知障碍或患有阿兹海默症（最常见的失智症种类）的长者，每天服用益生菌也有助于改善认知能力。不过这些都需要更大规模的研究试验以进一步证明。
今年7月在美国营养学会会议发表的研究结果指出，与服用安慰剂的老人相较，服用益生菌的长者认知能力有进步。
伊斯伍德说，压力有时会让认知能力下降，研究团队发现，益生菌能提供缓冲作用，减少认知力下降，这对于准备应考或处于庞大压力之下的年轻人而言有好处。2019年一项研究显示，18岁至40岁女性连续28天服用益生菌，在压力任务之中的表现优于服用安慰剂的女性。
益生菌研究仍处于早期阶段，学界还无法确切指出哪种菌株对于认知能力最有帮助。伊斯伍德建议服用多菌株益生菌，通常包含最多人研究的菌株组合，例如乳酸杆菌（lactobacillus）、比菲德氏菌（bifidobacterium）、乳酸球菌属（lactococcus）等等，最好先找医师咨询再行服用，以确保安全。
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