降低AD风险的7条饮食原则:美国《饮食预防阿尔茨海默病指南》发布 (zt)

       2013年7月，《饮食预防阿尔茨海默病指南》由美国医师医药责任协会（Physicians Committee for Responsible Medicine，PCRM）开发完成并在营养和大脑国际会议（华盛顿，PCRM和乔治华盛顿大学医学院联合举办）上发布。

PCRM是一个非营利组织，它的宗旨是“提倡预防医学（特别是良好的营养），进行临床研究，倡导更高的科研伦理标准”。PCRM主席和指南的主要作者Neal Barnard教授说:“当前临床医生正处于一个争夺食物（a battle over food）的时期，特别是改善阿尔茨海默病的食物，例如，减少饱和脂肪酸和反式脂肪酸摄入。我们有能力防治AD(到2050年将影响1亿人)。还要等什么呢？”

与防止心脏疾病的饮食习惯非常相似，指南推荐避免食用饱和脂肪酸和反式脂肪酸，多食用植物性食物，增加维生素E和B的摄入。“将饮食与体育锻炼相结合，并避免含有铁、铜的复合维生素，可以最大限度的保护大脑，”Barnard说。

参加会议的547名卫生保健提供者推荐了他们的食谱，例如烤西兰花沙拉、五香鹰嘴豆咖喱、小白菜和蓝梅冰沙。

媒体邀请多位AD专家对指南进行了评论，他们的观点一致：这些建议是对健康饮食和运动的，建议是好的，但是遵循这些建议会确切地降低AD风险还缺乏高水平的证据。

降低AD风险的7条饮食原则

1. 减少饱和脂肪酸和反式脂肪酸摄入。

2. 蔬菜、豆类（黄豆、豌豆、扁豆）、水果和全麦应该作为主要食物。

3. 每天食用一盎司坚果或种仁（一小把）可提供充足的维生素E。

4. 每天的食谱应包括一种提供维生素B12的可靠食物，例如，增富食品或能够提供至少2.4μg/日（成人）维生素B12的替代食品。

5.选择不含铁元素和铜元素的复合维生素，只有在医生指导时再补充铁元素。

6.避免使用含铝的炊具、抗酸药、发酵粉或其他产品。

7. 每周有氧运动3次，每次运动量相当于40分钟快步行走。

指南证据
Barnard教授列举了支持这项指南的多项研究。例如，在芝加哥健康和衰老项目中，摄入饱和脂肪酸最多的人（约每天25g）患阿尔茨海默病的几率是摄入一半量饱和脂肪酸人的2-3倍。同时，他也承认，并不是所有的研究结果都一致。例如，荷兰一项研究发现，避免摄入饱和脂肪酸没有保护作用，尽管参与者的年龄低于芝加哥研究。他认为，高脂饮食和/或引起胆固醇升高的饮食促进大脑中β淀粉样蛋白斑的产生。高脂饮食还会增加肥胖和2型糖尿病的风险，二者是阿尔茨海默病的危险因素。

一项对凯萨医疗机构患者的大型研究显示，与胆固醇水平低于200 mg/dL的人相比，胆固醇高于250 mg/dL的人30年后阿尔茨海默病风险增加50%，Barnard报告。他指出，ε4 APOE等位基因，与阿尔茨海默病风险显著相关，它产生一种蛋白对胆固醇转运发挥关键作用。

指南推荐的蔬菜、豆类、水果和全麦类食品富含维生素，例如叶酸和维生素B6，对大脑健康有保护作用。对地中海饮食和富含蔬菜饮食的研究，例如芝加哥研究，表明与其他饮食模式相比，二者可以降低认知问题的风险。

Barnard引用牛津大学一项研究，有高同型半胱氨酸和记忆问题的老年人补充维生素B能够改善记忆，减少脑萎缩。他指出，在潜在有害的金属中，过量的铁和铜与认知问题有关。但是铝对AD的影响仍然有争议，已经证实AD患者的脑中含有铝，英国和法国的研究已经发现阿尔茨海默病患病率高的地区自来水中含铝的浓度更高。

Barnard补充，已经有多项研究发现运动和阿尔茨海默病风险降低有关。

专家视点
阿尔茨海默病协会的Heather Snyder教授评论，已有证据支持运动降低AD风险，健康饮食和保持活力总是好的建议。因此，我们认可这些观点。但是指南的其它方面还没有充分的证据支持，还没达到给出处方的高度。她补充说，有些关于特定的饮食/维生素的积极证据，但也有一些研究出现了相反的结果。因此，在个别食物上很难达成共识。她指出，有些食物是有益的，比如深绿色蔬菜（菠菜饱和脂肪酸含量低且具有抗氧化作用），但不是决定性的。

印第安纳大学老龄化研究中心Malaz Boustani教授观点与之类似，“不幸的是，没有高水平的证据支持这项指南；但是指南上的饮食副作用非常小”。他认为，这是一个非常健康的饮食，这些建议对人体不会有伤害。但是否对降低AD风险有价值还不清楚。“是的，有些观察性研究表明部分建议可能是有益的，但没有来自随机对照研究的确切证据。”

Boustani指出，最近，美国国家老年研究所对文献进行了回顾，没有发现任何有力的证据来支持这些指南中的建议。一项随机对照试验表明，维生素E没有延缓AD和潜在病理的作用。“我想说的是，人们是否能负担的起指南推荐的这些食物。如果负担得起，尝试是无害的。摄入饱和脂肪酸和反式脂肪酸含量低的食物和每日运动总是好的。无论如何我们都应该做到。”

纽约西奈山认知健康中心Samuel Gandy博士说，这项指南很有意义，但在说“能够降低AD风险”之前，必须有至少一项随机临床试验支持才行。纽约爱因斯坦医学院Joe Verghese补充，“新的膳食指南主要基于观察性研究，看似合理，但是缺乏设计良好的临床试验证据——没有营养障碍的老年人补充营养可以预防AD。”

编译自：Dietary Guidelines Aim to Reduce Alzheimer's Risk .Medscape .Jul 25,2013.

[回家路]

Dietary Guidelines for Alzheimer’s Prevention


A special report from the Physicians Committee for Responsible Medicine


Alzheimer’s disease affects nearly half of North Americans by age 85. The American Academy of Neurology forecasts that, unless preventive measures are developed, Alzheimer’s rates will nearly triple over the next four decades. Worldwide, Alzheimer’s rates will affect 100 million people by 2050.

While treatments for the disease remain unsatisfactory, scientific studies suggest that preventive strategies are now feasible. Evidence suggests that specific diet and exercise habits can reduce the risk by half or more. Although significant gaps in scientific knowledge remain, studies suggest that the same foods that are beneficial for the heart are also healthful for the brain and may reduce the risk of Alzheimer’s disease.

Dietary Guidelines

The seven dietary principles to reduce the risk of Alzheimer’s disease were prepared for presentation at the International Conference on Nutrition and the Brain in Washington on July 19 and 20, 2013.

The guidelines are as follows:

1. Minimize your intake of saturated fats and trans fats. Saturated fat is found primarily in dairy products, meats, and certain oils (coconut and palm oils). Trans fats are found in many snack pastries and fried foods and are listed on labels as “partially hydrogenated oils.”

2. Vegetables, legumes (beans, peas, and lentils), fruits, and whole grains should be the primary staples of the diet.

3. One ounce of nuts or seeds (one small handful) daily provides a healthful source of vitamin E.

4. A reliable source of vitamin B12, such as fortified foods or a supplement providing at least the recommended daily allowance (2.4 mcg per day for adults) should be part of your daily diet.

5. When selecting multiple vitamins, choose those without iron and copper, and consume iron supplements only when directed by your physician.

6. While aluminum’s role in Alzheimer’s disease remains a matter of investigation, it is prudent to avoid the use of cookware, antacids, baking powder, or other products that contribute dietary aluminum.

7. Include aerobic exercise in your routine, equivalent to 40 minutes of brisk walking three times per week.

Discussion

As Alzheimer’s rates and medical costs continue to climb, simple changes to diet and lifestyle may help in preventing cognitive problems.

Saturated and Trans Fats

In addition to reducing the risk of heart problems and overweight, avoiding foods high in saturated and trans fats may also reduce the risk of Alzheimer’s disease. Saturated fat is found in dairy products and meats; trans fats are found in many snack foods.

Researchers with the Chicago Health and Aging Project followed study participants over a four-year period. Those who consumed the most saturated fat (around 25 grams each day) were two to three times more likely to develop Alzheimer’s disease, compared with participants who consumed only half that amount.1

Similar studies in New York and in Finland found similar results. Individuals consuming more “bad” fats were more likely to develop Alzheimer’s disease, compared with those who consumed less of these products.2,3 Not all studies are in agreement. A study in the Netherlands found no protective effect of avoiding “bad” fats,4 although the study population was somewhat younger than those in the Chicago and New York studies.

The mechanisms by which certain fats may influence the brain remains a matter of investigation. Studies suggest that high-fat foods and/or the increases in blood cholesterol concentrations they may cause can contribute to the production beta-amyloid plaques in the brain, a hallmark of Alzheimer’s disease. These same foods increase the risk of obesity and type 2 diabetes, common risk factors for Alzheimer’s disease.5-7

Cholesterol and APOEe4

High cholesterol levels have been linked to risk of Alzheimer’s disease. A large study of Kaiser Permanente patients showed that participants with total cholesterol levels above 250 mg/dl in midlife had a 50 percent higher risk of Alzheimer’s disease three decades later, compared with participants with cholesterol levels below 200 mg/dl.8 The APOEe4 allele, which is strongly linked to Alzheimer’s risk, produces a protein that plays a key role in cholesterol transport. Individuals with the APOEe4 allele may absorb cholesterol more easily from their digestive tracts compared with people without this allele.9

Nutrient-Rich Foods

Vegetables, legumes (beans, peas, and lentils), fruits, and whole grains have little or no saturated fat or trans fats and are rich in vitamins, such as folate and vitamin B6, that play protective roles for brain health. Dietary patterns that emphasize these foods are associated with low risk for developing weight problems and type 2 diabetes.10 They also appear to reduce risk for cognitive problems. Studies of Mediterranean-style diets11 and vegetable-rich diets have shown that reduced risk of cognitive problems, compared to other dietary patterns.12 The Chicago Health and Aging Project tracked study participants ages 65 and older, finding that a high intake of fruits and vegetables was associated with a reduced their risk of cognitive decline.13

Vitamin E

Vitamin E is an antioxidant found in many foods, particularly nuts and seeds, and is associated with reduced Alzheimer’s risk.14,15 A small handful of typical nuts or seeds contains about 5 mg of vitamin E. Other healthful food sources include mangoes, papayas, avocadoes, tomatoes red bell peppers spinach, and fortified breakfast cereals.

The Role of B-Vitamins in Reducing Homocysteine

Three B-vitamins—folate, B6, and B12—are essential for cognitive function. These vitamins work together to reduce levels of homocysteine, an amino acid linked to cognitive impairment. In an Oxford University study of older people with elevated homocysteine levels and memory problems, supplementation with these three vitamins improved memory and reduced brain atrophy.16,17

Healthful sources of folate include leafy greens, such as broccoli, kale, and spinach. Other sources include beans, peas, citrus fruits, and cantaloupe. The recommended dietary allowance (RDA) for folic acid in adults is 400 micrograms per day, or the equivalent of a bowl of fortified breakfast cereal or a large leafy green salad topped with beans, asparagus, avocadoes, sliced oranges, and sprinkled with peanuts.

Vitamin B6 is found in green vegetables in addition to beans, whole grains, bananas, nuts, and sweet potatoes. The RDA for adults up to 50 is 1.3 milligrams per day. For adults over 50, the RDA is 1.5 milligrams for women and 1.7 milligrams for men. A half cup of brown rice meets the recommended amount.

Vitamin B12 can be taken in supplement form or consumed from fortified foods, including plant milks or cereals. Adults need 2.4 mcg per day. Although vitamin B12 is also found meats and dairy products, absorption from these sources can be limited in older individuals, those with reduced stomach acid, and those taking certain medications (e.g., metformin and acid-blockers). For this reason, the U.S. government recommends that B12 supplements be consumed by all individuals over age 50. Individuals on plant-based diets or with absorption problems should take vitamin B12 supplements regardless of age.

Hidden Metals

Iron and copper are both necessary for health, but studies have linked excessive iron and copper intake to cognitive problems.18,19 Most individuals meet the recommended intake of these minerals from everyday foods and do not require supplementation. When choosing a multiple vitamin, it is prudent to favor products that deliver vitamins only. Iron supplements should not be used unless specifically directed by one’s personal physician.

The RDA for iron for women older than 50 and for men at any age is 8 milligrams. For women ages 19 to 50 the RDA is 18 milligrams. The RDA for copper for men and women is 0.9 milligrams.

Aluminum

Aluminum’s role in Alzheimer’s disease remains controversial. Some researchers have called for caution, citing aluminum’s known neurotoxic potential when entering the body in more than modest amounts20 and the fact that aluminum has been demonstrated in the brains of individuals with Alzheimer’s disease.21, 22 Studies in the United Kingdom and France found increased Alzheimer’s prevalence in areas where tap water contained higher aluminum concentrations.23,24

Some experts hold that evidence is insufficient to indict aluminum as a contributor to Alzheimer’s disease risk. While this controversy remains unsettled, it is prudent to avoid aluminum to the extent possible. Aluminum is found in some brands of baking powder, antacids, certain food products, and antiperspirants.

Physical Exercise and the Brain

In addition to following a healthful diet and avoiding excess amounts of toxic metals, it is advisable to get at least 120 minutes of aerobic exercise each week. Studies have shown that aerobic exercise—such as running, brisk walking, or step-aerobics—reduces brain atrophy and improves memory and other cognitive functions.25

A recent study published in Annals of Internal Medicine found that adults who exercised in midlife, around age 40, were less likely to develop dementia after age 65 compared with their sedentary peers.26 A similar study in New York found that adults who exercised and followed a healthy diet reduced their risk for Alzheimer’s by as much as 60 percent.27

Conclusion

Satisfactory treatments for Alzheimer’s disease are not yet available. However, evidence suggests that, with a healthful diet and regular exercise, many cases could be prevented.

References

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