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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

1. Morris MC, Evans EA, Bienias JL, et al. Dietary fats and the risk of incident Alzheimer’s disease. Arch Neurol. 2003;60:194-200.
2. Luchsinger JA, Tang MX, Shea S, Mayeux R. Caloric intake and the risk of Alzheimer’s disease. Arch Neurol. 2002;59:1258-1263.
3. Laitinen MH, Ngandu T, Rovio S, et al. Fat intake at midlife and risk of dementia and Alzheimer’s disease: a population-based study. Dement Geriatr Cogn Disord. 2006;22:99-107.
4. Engelhart MJ, Geerlings MI, Ruitenberg A. Diet and risk of dementia: Does fat matter? The Rotterdam Study. Neurology. 2002a;59:1915-1921.
5. Hanson AJ, Bayer-Carter JL, Green PS, et al. Effect of apolipoprotein E genotype and diet on apolipoprotein E lipidation and amyloid peptides. JAMA Neurol. Published ahead of print June 17, 2013.
6. Puglielli L, Tanzi RE, Kovacs DM. Alzheimer’s disease: The cholesterol connection. Nature Neurosci. 2003;6:345-351.
7. Ohara T, Doi Y, Ninomiya T, et al. Glucose tolerance status and risk of dementia in the community: The Hisayama Study. Neurology. 2011;77:1126-1134.
8. Solomon A, Kivipelto M, Wolozin B, Zhou J, Whitmer RA. Midlife serum cholesterol and increased risk of Alzheimer’s and vascular dementia three decades later. Dement Geriatr Cogn Disord. 2009;28:75-80.
9. Anoop S, Anoop M, Meena K, Luthra K. Apolipoprotein E polymorphism in cerebrovascular & coronary heart diseases. Indian J Med Res. 2010;132:363-378.
10. Tonstad S, Butler T, Yan R, Fraser GE. Type of vegetarian diet, body weight and prevalence of type 2 diabetes. Diabetes Care. 2009;32:791-796.
11. Georgios Tsivgoulis, M.D., University of Alabama at Birmingham, and University of Athens, Greece; Sam Gandy, M.D., associate director, Mount Sinai Alzheimer's Disease Research Center, New York City; April 30, 2013, Neurology.
12. The 9th International Conference on Alzheimer’s Disease and Related Disorders in Philadelphia, July 17-22, 2004. Jae Kang P2-283. Fruit and Vegetable Consumption and Cognitive Decline in Women (Mon., 7/19, 12:30 p.m.)
13. Morris MC, Evans DA, Tangney CC, Bienias JL, Wilson RS. Associations of vegetable and fruit consumption with age-related cognitive change. Neurology. 2006b;67:1370-1376.
14. Devore EE, Goldstein F, van Rooij FJ, et al. Dietary antioxidants and long-term risk of dementia. Arch Neurol. 2010;67:819-825.
15. Morris MC, Evans DA, Tangney CC, et al. Relation of the tocopherol forms to incident Alzheimer disease and cognitive change. Am J Clin Nutr. 2005;81:508-514.
16. de Jager CA, Oulhaj A, Jacoby R, Refsum H, Smith AD. Cognitive and clinical outcomes of lowering homocysteine-lowering B-vitamin treatment in mild cognitive impairment: A randomized controlled trial. Int J Geriatr Psychiatry. 2012;27:592-600.
17. Douaud G, Refsum H, de Jager CA, et al. Preventing Alzheimer's disease-related gray matter atrophy by B-vitamin treatment. PNAS. 2013;110:9523-9528.
18. Brewer GJ. The risks of copper toxicity contributing to cognitive decline in the aging population and Alzheimer’s disease. J Am Coll Nutr. 2009;28:238-242.
19. Stankiewicz JM, Brass SD. Role of iron in neurotoxicity: a cause for concern in the elderly? Curr Opin Clin Nutr Metab Care. 2009;12:22-29.
20. Kawahara M, Kato-Negishi M. Link between aluminum and the pathogenesis of Alzheimer’s disease: The integration of aluminum and amyloid cascade hypotheses. Int. J Alzheimer’s Dis. 2011;276393.
21. Crapper DR, Kishnan SS, Dalton AJ. Brain aluminum distribution in Alzheimer’s disease and experimental neurofibrillary degeneration. Science. 1973;180:511-513.
22. Crapper DR, Krishnan SS, Quittkat S. Aluminum, neurofibrillary degeneration and Alzheimer’s disease. Brain. 1976;99:67-80.
23. Martyn CN, Osmond C, Edwardson JA, Barker DJP, Harris EC, Lacey RF. Geographical relation between Alzheimer’s disease and aluminum in drinking water. Lancet. 1989;333:61-62.
24. Rondeau V, Jacqmin-Gadda H, Commenges D, Helmer C, Dartigues J-F. Aluminum and silica in drinking water and the risk of Alzheimer’s disease or cognitive decline: Findings from 15-year follow up of the PAQUID cohort. Am J Epidemiol. 2009;169:489-496.
25. Colcombe SJ, Kramer AF, Erickson KI, et al. Cardiovascular fitness, cortical plasticity, and aging. Proc Natl Acad Sci USA. 2004;101:3316-3321.
26. DeFina LF, Willis BL, Radford NB, et al. The Association Between Midlife Cardiorespiratory Fitness Levels and Later-Life Dementia: A Cohort Study. Ann Intern Med. 2013;158:213-214.
27. Scarmeas N, Luchsinger JA, Schupf N, et al. Physical activity, diet, and risk of Alzheimer’s disease. JAMA. 2009;302:627-637.



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