如何使用食物来增强免疫系统

Want to fight off infectious diseases this winter? Consider boosting your immune system with nutritious food.

"What we eat is very important in terms of how our immune system responds to pathogens and how well it can defend itself against a pathogen," said Dr. Simin Meydani, senior scientist and leader of the nutritional immunology team at Tufts University's Jean Mayer USDA Human Nutrition Research Center on Aging.

Micronutrients such as vitamin C, vitamin D, vitamin B complex, zinc and selenium can help "pump up" the body's defenses against colds, flu and even Covid-19, Meydani said, but you won't boost immunity by "eating a large amount of one single nutrient or food component."

Forget focusing on "superfoods." A large variety of foods are needed to provide the micronutrients the body needs to mount a robust cellular immune response, said Stanford School of Medicine nutrition scientist Christopher Gardner.

"There isn't any one food or nutrient to rely on here, but rather it is the interplay of 'harmonious interactions' between the various micronutrients," Gardner said.

Plan your daily menus around a large variety of fresh and colorful red, yellow, orange, blue and green fruits and vegetables, along with some high-quality whole grains, a bit of lean protein and a splash of healthy oils.

Plants and grains are also the basis of the top-rated Mediterranean diet and DASH diet, which stands for "dietary approaches to stop hypertension," or high blood pressure. Both the Mediterranean and DASH diets avoid processed foods and focus on fruits, vegetables, beans, lentils, whole grains, nuts and seeds.

The Mediterranean diet can reduce the risk for high cholesterol, dementia, memory loss, depression and breast cancer, numerous studies found. Meals from the sunny Mediterranean region have also been linked to stronger bones, a healthier heart and longer life. Oh, and it helps with weight loss, too.

An overall picture

Just how much you can jump-start immunity with nutrients depends on your age, overall health and stress levels, according to Meydani.

In addition to eating well, it's important to stay at a healthy weight, reduce your stress, get quality sleep and regular exercise to keep those natural defenses in fighting shape. Without that healthy baseline, your body will have to work harder to knock out invaders -- and may even lose the match.

"The best defense against the acute threat of the coronavirus is chronically good health," said Dr. David Katz, founder and president of the True Health Initiative, a nonprofit dedicated to promoting evidence-based lifestyle medicine.

"If you encounter the virus a week from now, two weeks from now, three weeks from now, there is a chance you will do better because of what you do with your diet right now," he said.

Pump up the volume

If you want to maximize the impact of food on your immune system, you'll need to dramatically increase the amount of fruits and vegetables you eat each day, Meydani advised.

Her team investigated immune responses in animals fed two to three servings of fruits and veggies a day, and compared them to those who ate five to six servings a day or eight to nine servings a day.

"The eight to nine servings a day was where we were seeing the best effect," Meydani said. "So it's not just increasing the intake by a little bit, you've got to increase it substantially. People need to work at it in order to reach that level."

Finding ways to insert fruits and veggies into every meal and snack during the day may do more than pump up your immunity. A 2017 study found a significant reduction in the risk of heart attack, stroke, cancer and early death by eating 10 portions of fruit and vegetables each day.

Current dietary guidelines in the United States recommend at least 2 cups of fruit and 2.5 cups of vegetables a day. Yet surveys by the US Department of Agriculture found the average American eats only 0.9 cups of fruit and 1.4 cups of vegetables per day

It's not just Americans. One in 5 deaths globally -- that's about 11 million people -- occurred because of too much sodium and a lack of whole grains, fruit, nuts and seeds, a 2017 study found.

Anti-inflammatory foods

There is another reason to pack your plate with a variety of fruits and veggies -- the need to control your body's inflammatory response to bacteria and viruses.

"A certain amount of inflammatory response is needed to get rid of the pathogens and to help the the body's immune system perform its function," Meydani said. "But if you produce too many inflammatory components, it can be damaging to surrounding tissues. It can cause autoimmune diseases. It can cause chronic diseases."

Chronic inflammation has been linked in studies to cancer, heart disease, diabetes, arthritis, depression, Alzheimer's and many other diseases. In cases of Covid-19, extreme inflammatory reactions to the virus, called "cytokine storms," have been linked to more severe cases and death.

"In relation to Covid-19, the recommendation to increase fruits and vegetable consumption is even more important," Meydani said, "because of all the anti-inflammatory compounds such as flavonoids in them that can reduce the cytokine storm."

Unfortunately, today's Western diet is full of overly processed, fat-laden foods, sugary drinks and red and processed meats that can cause persistently high levels inflammation in the body.

Eating a lot of unhealthy, "ultraprocessed" foods like ice cream, cookies and pre-made consumer foods may shorten your life -- just a 10% increase in such foods was significantly associated with a 14% higher risk of death from all causes, studies have shown.

Instead, choose leafy greens, tomatoes, fruits, nuts, fatty fish and olive oil -- foods that can support a healthy inflammatory response without sending it into overdrive.

Studies are also finding that fermented foods such as kimchi, sauerkraut or kombucha may also help battle some types of inflammation by improving the microbiome in the digestive system,

"We observed a lowering of (approximately) 19 inflammatory markers in the study participants who consumed fermented foods for 10 weeks," said Stanford's Gardner, who co-authored a recent study.

Are supplements needed?

Just like any mammal, the human body is built to absorb nutrients from whole fruits, vegetables, nuts, grains and proteins more efficiently than processed foods or supplements.

But people with limited access to healthy food choices or who have certain medical conditions or anyone over the age of 65 may need to focus on adding specific micronutritents to their diet.

"I'm not talking about the frail elderly that are homebound," Meydani said. "I'm talking about older people who are healthy, active, but above the age of 65. For them, I think certain nutrient supplementation might be very helpful."

The role of zinc

Most people in the United States get enough zinc from the foods they eat. But a study by Meydani's team older adults with low serum zinc levels had twice as much pneumonia and a longer duration of pneumonia and antibiotic use than people with adequate levels.

Using zinc lozenges in the early stages of cold or flu, such as in the first 24 hours, may give the immune system a boost and reduce the duration of sickness by about a day, according to a review of 13 studies

The daily recommended dose is 8 milligrams for women and 11 milligrams for men for no longer than five days. Zinc can also interfere with the effectiveness of antibiotics or negatively interact with some blood pressure and rheumatoid arthritis medications, so check with your doctor before adding it to your diet.

The mineral selenium

A natural mineral found in the soil and absorbed by plants, selenium plays an important role in inflammation and immunity. We need the mineral to activate immune cells. It also appears to be able to reduce inflammatory response.

Most Americans get plenty of selenium from their diet -- it can be found in seafood, meat, poultry, eggs, dairy products, breads, cereals, and nuts, especially Brazil nuts, which can contain up to 91 micrograms.

It would only take five Brazil nuts to reach the daily upper limit of selenium for adults -- 400 micrograms a day. Taking too much can cause nausea, diarrhea, skin rashes, loss of hair or nails, discolored teeth, irritability and nervous system problems, according to the NIH's Office of Dietary Supplements.

Some benefits from vitamin C

Hundreds of studies over the years have looked at the benefits of vitamin C for the immune system -- and clinical trials are currently underway investigating the impact of vitamin C transfusions on the severity of Covid-19.

Most people believe that vitamin C boosts the immune system and protects against colds. However, reviews of studies to date find only a mild beneficial effect compared to a placebo, leaving some experts loathe to sing its praises.

Dual properties of vitamin E

Vitamin E can play a dual role in boosting the body's immune response. It acts as an antioxidant in the body, helping to protect cells from the damage caused by free radicals.

"Vitamin E can have an anti-inflammatory effect, but it can also boost your cell-mediated immunity in certain populations," Meydani said.

Some of the best sources for vitamin E are vegetable oils like sunflower and safflower; peanuts, hazelnuts and almonds; seeds; and wheat germ. Many people turn to supplements to boost their intake -- but be careful, high doses of vitamin E might increase the risk of bleeding.

"The optimal level from our studies was 200 international units per day," Meydani said. "This is very important, because people think that if something is good for your immune system, then the higher you go, the better it will be. And that's not the case."

The sunshine vitamin

Just like vitamin C, evidence on D's immune-boosting properties is mixed, Meydani said.

"We can't say that giving higher levels of vitamin D is going to improve your immune response and fight respiratory infections," she said. "Some studies have shown some benefit, but others have not confirmed them."

Your body makes vitamin D from the sun, so people with darker skin or who live in areas with little sunshine might be deficient, as are the elderly and exclusively breastfed babies, who require a daily supplement. Many foods in the Western diet are supplemented with vitamin D, and taking too much can be toxic.

"Vitamin D toxicity almost always occurs from overuse of supplements," according to the NIH's Office of Dietary Supplements. "Signs of toxicity include nausea, vomiting, poor appetite, constipation, weakness and weight loss."

It's still early days, but scientists are studying the connection between vitamin D and Covid-19. Most promising is the anti-inflammatory properties of vitamin D -- the hope is that supplementation will tamp down any hyperactive immune response to the virus.

"Cytokine storms," where the immune system goes haywire and overwhelms the body, are one of the leading causes of death from Covid-19.

A few studies have found low levels of zinc and vitamin D are associated with more severe Covid-19 symptoms, but more controlled research is needed "before we reach a conclusion," Meydani believes.

"So, I would say, people should make sure they do not have low levels of zinc, D or C, particulary those at risk of low consumption of these nutrients such as elderly," she said. "But at this point we don't know if giving higher level of these nutrients in those whose baseline levels are sufficient is going to provide additional protection."

如何使用食物来增强免疫系统

这个冬天想与传染病作斗争吗？考虑用有营养的食物来增强你的免疫系统。

“就我们的免疫系统如何对病原体做出反应以及它如何抵御病原体而言，我们吃的东西非常重要，”塔夫茨大学让迈耶美国农业部高级科学家兼营养免疫学团队负责人 Simin Meydani 博士说人类衰老营养研究中心。

Meydani 说，维生素 C、维生素 D、维生素 B 复合物、锌和硒等微量营养素可以帮助“增强”身体对感冒、流感甚至 Covid-19 的防御能力，但“吃大量”并不能提高免疫力。一种单一营养素或食物成分的量。”

忘记关注“超级食品”吧。斯坦福大学医学院营养科学家克里斯托弗加德纳说，需要各种各样的食物来提供身体所需的微量营养素，以产生强大的细胞免疫反应。

“这里没有任何一种食物或营养素可以依赖，而是各种微量营养素之间'和谐相互作用'的相互作用，”加德纳说。

围绕各种新鲜多彩的红色、黄色、橙色、蓝色和绿色水果和蔬菜，以及一些优质全谷物、一点瘦肉蛋白和少量健康油来计划您的日常菜单。

植物和谷物也是最受好评的地中海饮食和 DASH 饮食的基础，它代表“阻止高血压的饮食方法”或高血压。地中海饮食和 DASH 饮食都避免加工食品，并专注于水果、蔬菜、豆类、扁豆、全谷物、坚果和种子。

许多研究发现，地中海饮食可以降低患高胆固醇、痴呆、记忆力减退、抑郁和乳腺癌的风险。来自阳光明媚的地中海地区的膳食也与更强壮的骨骼、更健康的心脏和更长的寿命有关。哦，它也有助于减肥。

整体图

根据迈达尼的说法，你可以用多少营养物质来启动免疫力取决于你的年龄、整体健康状况和压力水平。

除了吃得好之外，保持健康体重、减轻压力、获得优质睡眠和定期锻炼也很重要，以保持这些自然防御系统处于战斗状态。如果没有健康的基线，您的身体将不得不更加努力地击倒入侵者——甚至可能输掉比赛。

“抵御冠状病毒急性威胁的最佳防御措施是长期保持健康，”真正健康倡议的创始人兼总裁大卫卡茨博士说，该倡议是一家致力于促进循证生活方式医学的非营利组织。

“如果你在一周后、两周后、三周后遇到这种病毒，你有可能会因为你现在的饮食而做得更好，”他说。

提高音量

Meydani 建议，如果你想最大限度地提高食物对免疫系统的影响，你需要大幅增加每天吃的水果和蔬菜的数量。

她的团队研究了每天吃两到三份水果和蔬菜的动物的免疫反应，并将它们与每天吃五到六份或八到九份的动物进行比较。

“每天八到九份是我们看到最好效果的地方，”梅达尼说。 “所以这不仅仅是一点点增加摄入量，你必须大幅增加它。人们需要努力才能达到那个水平。”

想办法在白天的每顿饭和零食中加入水果和蔬菜，不仅可以提高您的免疫力。 2017 年的一项研究发现，每天吃 10 份水果和蔬菜可以显着降低心脏病发作、中风、癌症和早逝的风险。

美国当前的饮食指南建议每天至少吃 2 杯水果和 2.5 杯蔬菜。然而美国农业部的调查发现，美国人平均每天只吃 0.9 杯水果和 1.4 杯蔬菜

不仅仅是美国人。 2017 年的一项研究发现，全球五分之一的死亡人数——即约 1100 万人——是由于钠含量过高以及缺乏全谷物、水果、坚果和种子造成的。

消炎食物

将各种水果和蔬菜放在盘子里还有另一个原因——需要控制身体对细菌和病毒的炎症反应。

“需要一定程度的炎症反应来清除病原体并帮助身体的免疫系统发挥其功能，”Meydani 说。 “但如果你产生过多的炎症成分，就会损害周围的组织。它会导致自身免疫性疾病。它会导致慢性疾病。”

在研究中，慢性炎症与癌症、心脏病、糖尿病、关节炎、抑郁症、阿尔茨海默氏症和许多其他疾病有关。在 Covid-19 的情况下，对病毒的极端炎症反应（称为“细胞因子风暴”）与更严重的病例和死亡有关。

“对于 Covid-19，增加水果和蔬菜消费的建议更为重要，”Meydani 说，“因为其中的所有抗炎化合物，如类黄酮，都可以减少细胞因子风暴。”

不幸的是，今天的西方饮食充满了过度加工、富含脂肪的食物、含糖饮料以及红色和加工肉类，这些会导致体内持续高水平的炎症。

吃大量不健康的“超加工”食品，如冰淇淋、饼干和预制消费食品可能会缩短您的寿命——此类食品仅增加 10% 就与 14% 的全因死亡风险显着相关，研究表明。

相反，选择绿叶蔬菜、西红柿、水果、坚果、富含脂肪的鱼和橄榄油——这些食物可以支持健康的炎症反应，而不会导致炎症反应过度。

研究还发现，泡菜、酸菜或康普茶等发酵食品也可能通过改善消化系统中的微生物群来帮助对抗某些类型的炎症，

“我们观察到，食用发酵食品 10 周的研究参与者（大约）19 种炎症标志物降低，”斯坦福大学的 Gardner 说，他是最近一项研究的合著者。

需要补充吗？

就像任何哺乳动物一样，人体可以比加工食品或补充剂更有效地从整个水果、蔬菜、坚果、谷物和蛋白质中吸收营养。

但是，无法获得健康食品选择的人、患有某些疾病的人或任何 65 岁以上的人可能需要专注于在饮食中添加特定的微量营养素。

“我不是在谈论那些呆在家里的虚弱老人，”梅达尼说。 “我指的是 65 岁以上的健康、活跃的老年人。对他们来说，我认为某些营养补充剂可能非常有帮助。”

锌的作用

大多数美国人从他们吃的食物中获得足够的锌。但是，Meydani 团队的一项研究表明，血清锌水平低的老年人患肺炎的几率是水平足够的人的两倍，而且肺炎和抗生素使用的持续时间更长。

根据对 13 项研究的回顾，在感冒或流感的早期阶段使用锌锭剂，例如在最初的 24 小时内，可能会增强免疫系统并将疾病持续时间缩短约一天

每日推荐剂量为女性 8 毫克，男性 11 毫克，不超过五天。锌还会干扰抗生素的有效性或与某些血压和类风湿性关节炎药物产生负面影响，因此在将其添加到您的饮食之前请咨询您的医生。

矿物质硒

硒是一种在土壤中发现并被植物吸收的天然矿物质，在炎症和免疫中起着重要作用。我们需要矿物质来激活免疫细胞。它还似乎能够减少炎症反应。

大多数美国人从他们的饮食中获得了大量的硒——它可以在海鲜、肉类、家禽、鸡蛋、乳制品、面包、谷物和坚果中找到，尤其是巴西坚果，其含量高达 91 微克。

只需要 5 个巴西坚果就可以达到成人每日硒的上限——每天 400 微克。根据美国国立卫生研究院膳食补充剂办公室的说法，摄入过多会导致恶心、腹泻、皮疹、脱发或指甲、牙齿变色、易怒和神经系统问题。

维生素 C 的一些好处

多年来，数百项研究着眼于维生素 C 对免疫系统的益处——目前正在进行临床试验，调查维生素 C 输血对 Covid-19 严重程度的影响。

大多数人认为维生素 C 可以增强免疫系统并预防感冒。然而，迄今为止的研究评论发现，与安慰剂相比，只有轻微的有益效果，让一些专家不愿意赞美它。

维生素E的双重特性

维生素 E 在增强身体的免疫反应方面可以发挥双重作用。它在体内充当抗氧化剂，有助于保护细胞免受自由基造成的损害。

“维生素 E 可以具有抗炎作用，但它也可以增强某些人群的细胞介导的免疫力，”Meydani 说。

维生素 E 的一些最佳来源是植物油，如向日葵和红花；花生、榛子和杏仁；种子；和小麦胚芽。许多人求助于补充剂来增加摄入量——但要小心，高剂量的维生素 E 可能会增加出血的风险。

“我们研究的最佳水平是每天 200 国际单位，”梅达尼说。 “这非常重要，因为人们认为，如果某些东西对您的免疫系统有益，那么您的免疫系统越高，效果就会越好。但事实并非如此。”

阳光维生素

Meydani 说，就像维生素 C 一样，关于 D 增强免疫特性的证据是混合的。

“我们不能说提供更高水平的维生素 D 会改善您的免疫反应并对抗呼吸道感染，”她说。 “一些研究显示出一些益处，但其他研究尚未证实。”

您的身体会从阳光中制造维生素 D，因此皮肤较黑或生活在阳光不足地区的人可能缺乏维生素 D，老年人和纯母乳喂养的婴儿也可能缺乏维生素 D，他们需要每天补充。西方饮食中的许多食物都补充了维生素 D，摄入过多会中毒。

“维生素 D 毒性几乎总是由过度使用补充剂引起，”美国国立卫生研究院膳食补充剂办公室表示。 “中毒迹象包括恶心、呕吐、食欲不振、便秘、虚弱和体重减轻。”

现在还为时尚早，但科学家们正在研究维生素 D 和 Covid-19 之间的联系。最有希望的是维生素 D 的抗炎特性——希望补充剂能抑制对病毒的任何过度活跃的免疫反应。

“细胞因子风暴”，即免疫系统失控并淹没身体，是 Covid-19 导致死亡的主要原因之一。

一些研究发现，低水平的锌和维生素 D 与更严重的 Covid-19 症状有关，但“在我们得出结论之前”还需要更多的对照研究，Meydani 认为。

“所以，我想说的是，人们应该确保他们的锌、D 或 C 含量不低，尤其是那些有可能摄入这些营养素不足的人，例如老年人，”她说。 “但在这一点上，我们不知道为那些基线水平足够的人提供更高水平的这些营养素是否会提供额外的保护。”