April 21, 2010
Can certain foods help ward off the onset of Alzheimer's disease? A growing body of research suggests that they might.
Now, researchers in New York who studied the diets of older men and women report that certain foods may be especially effective in helping to protect against Alzheimer's. These brain-healthy foods include salad dressing, nuts, fish, tomatoes, poultry, cruciferous vegetables, fruits, and dark and green leafy vegetables.
Conversely, particular foods may be bad for brain health and be linked to an increased risk for Alzheimer's. Such foods, the researchers found, include high-fat dairy products, red meat, organ meat and butter. The findings appeared online in the Archives of Neurology, a medical journal from the American Medical Association.
“Epidemiological evidence linking diet, one of the most important modifiable environmental factors, and risk of Alzheimer’s disease is rapidly increasing,” wrote the researchers, from Columbia University Medical Center in New York. “However, current literature regarding the impact of individual nutrients or food items on Alzheimer’s disease risk is inconsistent, partly because humans eat meals with complex combinations of nutrients or food items that are likely to be synergistic.”
The researchers studied the dietary habits of 2,148 older men and women living in northern Manhattan. At the study's start, all the participants were age 65 or older and free of memory loss or other symptoms of Alzheimer's. They were given follow-up exams every one-and-a-half years for an average of four years.
Earlier research, including research done by the Columbia group, have shown that a Mediterranean-style diet rich in fish, olive oil, fruits, vegetables and red wine and low in red meat and butter may help protect against Alzheimer's. But many Americans, including the older whites, blacks and Hispanics included in this study, do not follow a Mediterranean style diet.
Instead, the researchers this time studied the diet in terms of seven main food groups and nutrients that have been tied to Alzheimer's risk. They looked at these key food groups, all of which have been linked to an increased or decreased risk of Alzheimer's.
Foods that may be linked to an increased risk of Alzheimer's include total fats, particularly:
*Saturated fatty acids: Fatty acids are the building blocks that the body uses to make fats. Eating foods high in saturated fats, like red meat, butter and dairy products, are associated with the development of degenerative diseases, including heart disease and Alzheimer's disease.
Increased intake of polyunsaturated fats and monounsaturated fats, on the other hand, may be protective against Alzheimer's:
*Monounsaturated fatty acids: These heart-healthy fats lower cholesterol and may also be good for the brain. Nuts, including walnuts, peanuts, almonds and pistachios, are high in monounsaturated fats. Avocadoes and canola and olive oils are also high in these fats.
*Omega-3 fatty acids: These polyunsaturated fats have increasingly been tied to heart and brain health and a lower risk of Alzheimer's. They include eicosapentaenoic acid (EPA) and docosahexanoic acid (DHA), both found primarily in oily cold-water fish like tuna, salmon, sardines and mackerel. A third omega-3, called alpha-linolenic acid (ALA), is found primarily in dark green leafy vegetables, flaxseed oils and certain vegetable oils.
*Omega-6 fatty acids: These unsaturated fats tend to be much more common in the American diet than their cousins, the omega-3 fatty acids. Most vegetables oils contain omega-6s, as do avocadoes, nuts, poultry, eggs and other foods. Eating them is not unhealthy. But eating omega-6's at the expense of omega-3's, in vastly higher proportions, has been linked to higher levels of inflammation that may be bad for brain health.
Additional nutrients that have been linked to better memory and thinking skills as well as a lower risk of Alzheimer's include:
*Vitamin E: This powerful antioxidant vitamin has been linked to a decreased risk of Alzheimer's in some studies. Good food sources include wheat germs, vegetable oils, nuts, leafy greens and whole grains.
*Vitamin B12: Most people get plenty of B12 in their diets, but older people may lose the ability to absorb it properly. Foods like organ meats, oysters, fish, eggs, meat and cheese, as well as fortified breakfast cereals, are high in B12. The vitamin, along with folate, helps keep levels of homocysteine, an amino acid tied to inflammation, in check.
*Folate: Foods are fortified with this B vitamin to prevent birth defects, and it is also tied to heart and brain health, including a lower risk of Alzheimer's disease. Excellent food sources of folate, or folic acid as it is also called, include green vegetables, beans, whole grains and orange juice.
In the New York study, older men and women were given extensive questionnaires asking about the specific foods they ate daily. During the study follow-up period, 253 of them developed Alzheimer’s disease.
The researchers controlled for variables like smoking and alcohol use (moderate drinking, for example, may be good for the brain, whereas excessive drinking is not). One dietary pattern was significantly associated with a reduced risk of the disease. This pattern involved high intakes of salad dressing, nuts, fish, tomatoes, poultry, fruits and cruciferous and dark and green leafy vegetables and low intakes of high-fat dairy, red meat, organ meat and butter.
The combination of nutrients in the low-risk dietary pattern reflect multiple pathways in the development of Alzheimer’s disease, the authors noted. For example, they write, "vitamin B12 and folate are homocysteine-related vitamins that may have an impact on Alzheimer’s disease via their ability of reducing circulating homocysteine levels, vitamin E might prevent Alzheimer’s disease via its strong antioxidant effect and fatty acids may be related to dementia and cognitive function through atherosclerosis, thrombosis or inflammation via an effect on brain development and membrane functioning or via accumulation of beta-amyloid.”
“Our findings provide support for further exploration of food combination–based dietary behavior for the prevention of this important public health problem,” they conclude.
Yian Gu, Ph.D.; Jeri W. Nieves, Ph.D.; Yaakov Stern, Ph.D.; et al: "Food Combination and Alzheimer’s Disease Risk: A Protective Diet." Archives of Neurology, Vol. 67(No. 6):(doi:10.1001/archneurol.2010.84), April 12, 2010.