降低AD風險的7條飲食原則:美國《飲食預防阿爾茨海默病指南》發布 (zt)

       2013年7月，《飲食預防阿爾茨海默病指南》由美國醫師醫藥責任協會（Physicians Committee for Responsible Medicine，PCRM）開發完成並在營養和大腦國際會議（華盛頓，PCRM和喬治華盛頓大學醫學院聯合舉辦）上發布。

PCRM是一個非營利組織，它的宗旨是“提倡預防醫學（特別是良好的營養），進行臨床研究，倡導更高的科研倫理標準”。PCRM主席和指南的主要作者Neal Barnard教授說:“當前臨床醫生正處於一個爭奪食物（a battle over food）的時期，特別是改善阿爾茨海默病的食物，例如，減少飽和脂肪酸和反式脂肪酸攝入。我們有能力防治AD(到2050年將影響1億人)。還要等什麽呢？”

與防止心髒疾病的飲食習慣非常相似，指南推薦避免食用飽和脂肪酸和反式脂肪酸，多食用植物性食物，增加維生素E和B的攝入。“將飲食與體育鍛煉相結合，並避免含有鐵、銅的複合維生素，可以最大限度的保護大腦，”Barnard說。

參加會議的547名衛生保健提供者推薦了他們的食譜，例如烤西蘭花沙拉、五香鷹嘴豆咖喱、小白菜和藍梅冰沙。

媒體邀請多位AD專家對指南進行了評論，他們的觀點一致：這些建議是對健康飲食和運動的，建議是好的，但是遵循這些建議會確切地降低AD風險還缺乏高水平的證據。

降低AD風險的7條飲食原則

1. 減少飽和脂肪酸和反式脂肪酸攝入。

2. 蔬菜、豆類（黃豆、豌豆、扁豆）、水果和全麥應該作為主要食物。

3. 每天食用一盎司堅果或種仁（一小把）可提供充足的維生素E。

4. 每天的食譜應包括一種提供維生素B12的可靠食物，例如，增富食品或能夠提供至少2.4μg/日（成人）維生素B12的替代食品。

5.選擇不含鐵元素和銅元素的複合維生素，隻有在醫生指導時再補充鐵元素。

6.避免使用含鋁的炊具、抗酸藥、發酵粉或其他產品。

7. 每周有氧運動3次，每次運動量相當於40分鍾快步行走。

指南證據
Barnard教授列舉了支持這項指南的多項研究。例如，在芝加哥健康和衰老項目中，攝入飽和脂肪酸最多的人（約每天25g）患阿爾茨海默病的幾率是攝入一半量飽和脂肪酸人的2-3倍。同時，他也承認，並不是所有的研究結果都一致。例如，荷蘭一項研究發現，避免攝入飽和脂肪酸沒有保護作用，盡管參與者的年齡低於芝加哥研究。他認為，高脂飲食和/或引起膽固醇升高的飲食促進大腦中β澱粉樣蛋白斑的產生。高脂飲食還會增加肥胖和2型糖尿病的風險，二者是阿爾茨海默病的危險因素。

一項對凱薩醫療機構患者的大型研究顯示，與膽固醇水平低於200 mg/dL的人相比，膽固醇高於250 mg/dL的人30年後阿爾茨海默病風險增加50%，Barnard報告。他指出，ε4 APOE等位基因，與阿爾茨海默病風險顯著相關，它產生一種蛋白對膽固醇轉運發揮關鍵作用。

指南推薦的蔬菜、豆類、水果和全麥類食品富含維生素，例如葉酸和維生素B6，對大腦健康有保護作用。對地中海飲食和富含蔬菜飲食的研究，例如芝加哥研究，表明與其他飲食模式相比，二者可以降低認知問題的風險。

Barnard引用牛津大學一項研究，有高同型半胱氨酸和記憶問題的老年人補充維生素B能夠改善記憶，減少腦萎縮。他指出，在潛在有害的金屬中，過量的鐵和銅與認知問題有關。但是鋁對AD的影響仍然有爭議，已經證實AD患者的腦中含有鋁，英國和法國的研究已經發現阿爾茨海默病患病率高的地區自來水中含鋁的濃度更高。

Barnard補充，已經有多項研究發現運動和阿爾茨海默病風險降低有關。

專家視點
阿爾茨海默病協會的Heather Snyder教授評論，已有證據支持運動降低AD風險，健康飲食和保持活力總是好的建議。因此，我們認可這些觀點。但是指南的其它方麵還沒有充分的證據支持，還沒達到給出處方的高度。她補充說，有些關於特定的飲食/維生素的積極證據，但也有一些研究出現了相反的結果。因此，在個別食物上很難達成共識。她指出，有些食物是有益的，比如深綠色蔬菜（菠菜飽和脂肪酸含量低且具有抗氧化作用），但不是決定性的。

印第安納大學老齡化研究中心Malaz Boustani教授觀點與之類似，“不幸的是，沒有高水平的證據支持這項指南；但是指南上的飲食副作用非常小”。他認為，這是一個非常健康的飲食，這些建議對人體不會有傷害。但是否對降低AD風險有價值還不清楚。“是的，有些觀察性研究表明部分建議可能是有益的，但沒有來自隨機對照研究的確切證據。”

Boustani指出，最近，美國國家老年研究所對文獻進行了回顧，沒有發現任何有力的證據來支持這些指南中的建議。一項隨機對照試驗表明，維生素E沒有延緩AD和潛在病理的作用。“我想說的是，人們是否能負擔的起指南推薦的這些食物。如果負擔得起，嚐試是無害的。攝入飽和脂肪酸和反式脂肪酸含量低的食物和每日運動總是好的。無論如何我們都應該做到。”

紐約西奈山認知健康中心Samuel Gandy博士說，這項指南很有意義，但在說“能夠降低AD風險”之前，必須有至少一項隨機臨床試驗支持才行。紐約愛因斯坦醫學院Joe Verghese補充，“新的膳食指南主要基於觀察性研究，看似合理，但是缺乏設計良好的臨床試驗證據——沒有營養障礙的老年人補充營養可以預防AD。”

編譯自：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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