July/August 2016

Nutrition's Link to Brain Health
By Matthew Ruscigno, MPH, RD
Today's Geriatric Medicine
Vol. 9 No. 4 P. 18

Studies suggest a diet rich in antioxidants, phytochemicals, and the B vitamins may promote cognitive function in older adults.

Loss of cognitive function often is believed to be a natural consequence of aging, a time during which the brain no longer performs as sharply as it did in an individual's younger years. This line of thinking is analogous to the perception of heart failure in the mid-20th century. The medical community understood the heart's physiology and knew it had the potential to fail, but there was limited knowledge of heart failure's association with lifestyle and nutrition until the Framingham Heart Study, which began in 1948. However, decades of research have proven that healthful dietary and lifestyle choices starting at an early age and continuing throughout the lifespan can greatly increase the life expectancy of the heart and that of the individual.

Evidence directly linking good nutrition and lifestyle choices to cognitive health isn't as strong, but new research continues to suggest that these two components may prolong brain function. And the compounds showing the most promise in promoting brain health are antioxidants, phytochemicals, and the B vitamins found in fruits, vegetables, whole grains, legumes, and fish.1

Cognitive Function and Diet
Much of the research on vitamin and mineral intake related to cognition is observational and has limited interpretation. Despite this fact, health care professionals shouldn't dismiss these studies. For example, a June 2014 study published in BMJ Open by the Alzheimer's Disease Core Center at New York University School of Medicine concluded that vitamin B12, vitamin D, folate, beta-carotene, and omega-3 fatty acids are considered Alzheimer's disease–protective nutrients, "associated with higher intake of vegetables, fruits, whole grains, fish, and legumes, and with lower intake of high-fat dairy, processed meat, and sweets," the researchers wrote.2

The Mediterranean Eating Style
A parallel-group randomized clinical trial from Spain examining 447 adults found that those who ate a Mediterranean diet—one supplemented with olive oil and the other with nuts—scored better on cognitive tests at the four-year follow-up compared with the control group that ate an unregulated low-fat diet.3 These results aren't surprising in light of a study published in the June 2015 issue of Frontiers in Aging Neuroscience that evaluated the benefits of a Mediterranean eating style for maintaining cognitive function. The authors mentioned that a dietary pattern including fruits, vegetables, whole grains, red wine, and some fish is beneficial for brain health. The nutritional components specified were omega-3 fatty acids, antioxidant nutrients, and phytochemicals—especially resveratrol.4

Role of B Vitamins
In addition to omega-3s, antioxidants, and phytochemicals, there's significant research interest in the role B vitamins play in maintaining cognitive health.5,6 The B-complex vitamins produce neurotransmitters such as serotonin and regulate energy use in the brain, so it's plausible that inadequate intake could reduce cognition.

Folate
Folate is involved in energy production in the brain and elsewhere and aids in the production of DNA and RNA, the body's genetic material. Folate availability increases nitric oxide, which protects the arterial endothelium. Increased nitric oxide improves vasoconstriction and vasodilation, or the narrowing and widening of blood vessels that control blood flow. Protecting the endothelium from oxidative damage is a piece of the heart disease and stroke prevention puzzle, though it isn't entirely clear what role this may play in protecting cognitive function. There's some research that shows low folate consumption is associated with reduced cognition. In a cohort study of nearly 1,000 seniors, those in the highest quartile of folate consumption had the lowest rates of Alzheimer's disease.7

Folate also donates methyl groups for the production of methylcobalamin, which is involved in the methylation of homocysteine to methionine. When folate intake is adequate, this process moderates homocysteine levels. Low folate consumption leads to an increase in serum homocysteine, which researchers hypothesize is a risk factor for heart disease and is associated with decreased cognitive function in old age.8 This premise is known as the homocysteine hypothesis.

Folate deficiency inhibits DNA repair and increases neuron susceptibility to oxidative damage, which could potentially contribute to cognitive decline. Excellent sources of folate include spinach and other dark leafy greens, asparagus, black-eyed peas, lentils, and pinto, garbanzo, and black beans. The folate recommendation for adults is 400 mcg per day though there's some evidence that levels above this may be beneficial. As part of the Folic Acid and Carotid Intima-media Thickness trial, researchers in the Netherlands gave 800 participants either 800 mcg of folic acid or a placebo for three years. At follow-up, the supplementation group scored higher on memory and cognition tests. At baseline, 100% of participants had low folate intake and elevated homocysteine, giving credence to the hypothesis that high homocysteine levels impair cognition.9 While this study used supplements, it's possible to exceed the Recommended Dietary Allowance (RDA) for folate by eating folate-rich foods. Folic acid supplementation should occur under the guidance of a physician, as excess folate intake could mask vitamin B12 deficiency.

Vitamin B12 and the Homocysteine Hypothesis
Just as folate plays a role in helping to maintain cognition, so does vitamin B12. In fact, the methylation of homocysteine requires adequate serum B12; therefore, low levels of B12 lead to an increase in homocysteine. One cohort study of 1,779 people, primarily Mexican-American women, in Sacramento, California, found that the dementia rate was highest in the tertile with the lowest plasma vitamin B12 and that elevated homocysteine was associated with greater risk of dementia and cognitive impairment without dementia.10

Low vitamin B12, and therefore high homocysteine, is a concern for those eating a vegan diet because B12 is found only in animal products or fortified foods. Organ meats and sardines are concentrated sources of B12, though all animal foods, fortified nondairy milks, and many meat alternatives are additional sources. Absorption, which is often reduced in older adults, influences plasma levels.

The B Vitamin Complex
There are eight B vitamins and all of them have roles related to cognitive function. However, some researchers believe that the evidence for the homocysteine hypothesis is insufficient to recommend patients take individual B vitamins. A 2016 review in the journal Nutrients argues that there are limited clinical trials on folate and B12, so there's little reason to ignore the other B vitamins.11 A research group in Oxford conducted a double-blind intervention study to examine the effect of a folate, B12, and B6 supplement on mild cognitive impairment. The researchers found that subjects in the supplement group who had high homocysteine levels at baseline had a statistically significant reduction in cognitive decline. However, the supplement group showed cognitive improvements independent of homocysteine levels when tested for executive and planning function. These results may indicate another role B vitamins have or the effect of B6, but there isn't enough research to draw this conclusion.12 However, the B vitamins do have overlapping functions, and it's plausible that they have both individual and collective influence on cognition. Niacin, for example, may be helpful in Parkinson's disease treatment, but more research in this area is needed.13

Lifestyle Factors in Maintaining Cognitive Function
In addition to the beneficial dietary components, evidence shows that lifestyle factors contribute to better cognitive function in older adults. Maintaining a healthy body weight, engaging in regular physical activity as recommended for older adults in the 2015–2020 Dietary Guidelines for Americans, and mental stimulation, such as reading, playing games, and interacting socially, all are associated with maintaining brain health.14 Some researchers propose categorizing cognition-related disorders as an additional type of diabetes, a so-called type 3 diabetes because of the increased risk of Alzheimer's disease facing those with type 2 diabetes. This hypothesis is based on a connection between insulin resistance and decreased cognitive function.15,16

Improving Older Adults' Diets
Educating older adults effectively about the role diet, nutrition, and lifestyle behaviors play in maintaining cognitive health is paramount, but it's important to keep in mind that it's difficult for older adults to develop new behaviors after establishing certain habits that have spanned many decades. Nonetheless, health professionals can introduce concepts and foods to prolong cognition.

When counseling older adults, prioritize food over supplements, with the exception of vitamin B12, because of the possible beneficial synergistic effects among nutrients, phytochemicals, and other compounds found in whole foods. Beans are an excellent source of many B vitamins; they're readily available and easy to incorporate into meals. Whole grains are nutrient dense and contain more fiber and protein than their refined counterparts, but the taste and texture may be difficult for some older adults because whole grains are denser and have increased texture and a more pronounced mouth feel. Refined wheat and rice products in the United States are enriched with the B vitamins thiamin, riboflavin, niacin, and folic acid. While not nutritionally ideal, refined wheat and rice products can aid in meeting B vitamin requirements.

Not all older adults have cooking skills or have access to kitchens or cooking utensils, but caregivers or those who work with them can help prepare the following types of meals rich in B vitamins.

• Soups and stews. Soups and stews offer excellent ways to incorporate beans and vegetables into the diet. They tend to be nutrient dense, and patients who have trouble chewing or swallowing find them easier to eat. Because many vegetables often are hidden in stews, patients who have a taste aversion to a particular vegetable likely won't notice it in stew. Soups and stews also are good ways to use vegetables that are nearing the end of their shelf life. Lentils are ideal because they don't require soaking and can be cooked until they're soft.

• Blended vegetables for sauces. Many vegetables can be lightly sautéed, blended, and added to sauces, such as marinara. This slightly changes the consistency and taste of the sauce, but it could be much more palatable for individuals who have trouble eating whole vegetables. Many of the nutrients and much of the fiber are retained in this cooking style.

• Beans and vegetables added to common dishes. Older clients can incorporate beans into salads, pastas, and rice dishes without significantly altering the taste or texture. A common technique used to encourage behavior change is to attach new habits to old ones, and the same can be done with food and nutrition. Recommend patients incorporate vegetables they like into easy-to-prepare dishes. For example, instead of eating spinach only as a side dish, suggest its addition to main entrées.

• International cuisine. The United Nations declared 2016 the International Year of Pulses to celebrate the significant impact beans have around the world as a sustainable and affordable source of nutrients for billions of people. Adding international foods to a food service rotation is an easy way to incorporate more beans into a menu. Mexican and Central American cuisines emphasize pinto and black beans, and lentils are integral to many foods from southern Asia. Hummus, a Middle Eastern specialty made with olive oil, tahini, garlic, lemon, and chickpeas, is soft, nutrient dense, and easy for an older adult or food service kitchen to prepare.

• Include berries. Popular and readily available, berries such as strawberries, blueberries, and raspberries are nutrient dense and rich in antioxidants and flavonoids, which could be beneficial for brain health.17,18 Berries are soft and easy for older patients to eat and therefore, should be an important part of their diet. Most often people are encouraged to buy fresh berries, but frozen berries are easier to store for longer periods of time and have the same nutrient profiles as the fresh varieties. Patients can eat berries as a dessert or add them to oatmeal or smoothie recipes if they have difficulty chewing or swallowing.

• Sip tea. Other than water, tea is the most consumed beverage in the world, and it may be beneficial for preventing cognitive decline.19 In March 2016, the Netherlands Nutrition Centre released its food pyramid and dietary guidelines that recommend the Dutch drink three cups of tea per day. The research isn't extensive, but the antioxidants and L-theanine found in tea may help maintain brain function.20 The caffeine found in tea may be beneficial for cognition,21 but it could be problematic for those who have difficulty sleeping. Recommending tea for older adults otherwise has little risk with potential benefits.

Increasing Access to Healthful Food
Despite the many healthful foods available to help maintain and promote cognitive health, many older adults with limited mobility and resources may not have access to them. Health professionals can work with elder programs, nonprofits, charities, and kitchen staffs in creative ways to increase access to vital foods. For example, Debra King, MS, RD, LD, FAND, director of Nutrition Services for Meals and Wheels in Waco, Texas, accessed a community grant through Meals and Wheels to set up a farmers' market food truck in areas with limited access to fresh produce. Through the grant, discounts are offered to people who use SNAP (Supplemental Nutrition Assistance Program) benefits and to adults aged 60 and older.

While there are no established recommendations for B vitamins or other nutrients to protect against cognitive decline specifically outside of meeting the RDA for each nutrient, there's enough evidence suggesting there are problems associated with deficiency or less than adequate intake related to brain health. The B vitamins are common in many foods; therefore, it should be possible for most older adults to meet their needs with food alone.

A study published in the March 2016 issue of Nutrients on preventive approaches for dementia concluded there isn't enough evidence yet to recommend specific foods, but that healthful dietary patterns, mainly a diet high in flavonoids and unsaturated fatty acids that meets nutritional needs, are associated with improved cognition.22 As the baby boomer generation ages, more and more older adults will be at risk of cognitive decline, and geriatricians can educate them and the facilities serving them on the importance of nutrition in keeping their brains functioning at their best.

— Matthew Ruscigno, MPH, RD, is the past chair of the Vegetarian Nutrition Dietetic Practice Group of the Academy of Nutrition and Dietetics. He's the coauthor of No Meat Athlete and Appetite for Reduction and has a private practice in Los Angeles.

References
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