Basic Nutrition for Successful Aging: Part II
Although eating is an activity everyone should know a great deal about, many persons fail to eat a nutritionally balanced diet and do not take advantage of the many natural food sources that not only can provide necessary nutrients, but can also help maintain health and promote a more successful aging process. Many persons eat to excess or fail to consume basic requirements necessary for health. Malnutrition is not something observed only in third-world countries. In addition to a necessary amount of proteins, carbohydrates, and fats, we must ensure an adequate intake of vitamins, minerals, and trace elements.
The elderly are particularly prone to developing protein-calorie malnutrition, as well as many other vitamin and mineral deficiencies. This may result from problems that occur with increased frequency later in life, such as poor dentition, loss of taste, difficulty swallowing, malabsorption, or drug-nutrient interaction. An inability to obtain the necessary fresh foods, as may occur during the winter time or if someone is dependent on others to shop for him or her, may also predispose to nutritional inadequacies. Nonperishable foods may contain high concentrations of sodium and nitrates and may lack vitamins due to processing methods. A person eating less than 1500 calories a day may lack the simple variety of foods necessary to ensure a proper intake of vitamins; this is not uncommon during later life, and a daily vitamin can add insurance to the diet where doubt exists. What is most worrisome is the growing number of individuals who are obese. Over 30% of the U.S. population is currently considered to be overweight and at risk of developing obesity-associated problems later in life, such as heart disease, diabetes, arthritis, sleep apnea, strokes, and hypertension, among others.
A healthy diet must start early in life when patterns of eating become ingrained and tastes and preferences acquired. Childhood obesity is on the rise, and families would be wise to consider their diets in relation to all members of the family unit. Portion size has increased in recent decades, and fast food has become a more staple part of the diet, with more children growing up in homes with their only parent or both parents working. Snack foods have proliferated with high concentrations of “refined” sugar; soda and fruit drinks have frequently replaced healthier foods. While food labels are now required, it often takes considerable knowledge or even an advanced degree to understand the details provided. The number of portions listed on a label, even for foods contained in what appears to be a single-serving package, may be missed by the nonskilled reader or someone who cannot read the small print. Caloric content is often much higher than what one had thought. Number of grams of fiber listed may be based on a 100-gram portion. The casual reader may confuse the number listed with the actual amount contained in what he or she will eat in a single serving: 100 grams of puffed wheat is clearly different than 100 grams of bran buds, for example. Certain foods may have protective effects against heart disease and cancer, while others may actually promote disease. Diets high in animal fat may predispose to rectal, colon, breast, and prostate cancer. The prostate cancer death rate is five times higher in the United States and in northern Europe than it is in Hong Kong, Iran, Turkey, and Japan, where diets emphasize more vegetables, grains, beans, cereals, and fruits. These foods also have been epidemiologically associated with a lower incidence of stroke. Fat also predisposes to heart disease. Conversely, diets rich in omega oils and fiber, for example, can help prevent certain age-prevalent illnesses.
The topic of nutrition and what one needs to do to ensure a more successful aging process is quite exhaustive, and a total review is beyond the scope of this article. Data concerning dietary factors and caloric intake and their role in possibly increasing lifespan remains controversial, especially in humans, and this will remain a topic for another time. This two-part article focuses on known associations between certain key dietary components and health and disease, attention to which may promote a more successful aging process. Part I (Clinical Geriatrics 2006;14:16-24) discussed energy, protein, and fats, and Part II examines fiber, multivitamins and micronutrients, antioxidants, and calcium.
The term fiber refers to carbohydrates that cannot be digested. Fiber is present in varying amounts in all plant-derived foods, including vegetables, grains, legumes, and fruits. Depending on whether the fiber dissolves in water, it is classified as either soluble or insoluble. It is recommended that one-third of the daily intake of fiber be in the soluble form in order to achieve its maximum benefits. Studies throughout the world have demonstrated that a diet containing 30 or more grams of fiber per day is associated with less constipation, hemorrhoids, diverticulosis, colon cancer, gallbladder disease, and lower cholesterol levels. Metabolic parameters have also been noted to be improved with intake of fiber; there is a lower risk of developing type 2 diabetes mellitus with a high intake of cereal fiber such as that found in oats.1 Insoluble fiber is particularly helpful in reducing the risk of developing diverticular disease later in life, with as much as a 40% benefit noted following long-term use of a high-fiber diet. This is of particular importance given the fact that one-third of those over the age of 45 and as many as two-thirds of those over the age of 80 are estimated to have diverticulosis, predisposing them to the development of diverticulitis.2
The average American consumes less than 15 grams of fiber daily, with few consuming more than 20 grams. In a Harvard study following over 80,000 female nurses for 16 years, the top quintile consumed, on average, 20 grams of fiber.3 It is not surprising, therefore, that this study failed to show an association with a reduced risk for either colon cancer or polyps, as individuals from studies that reported a benefit had a much higher intake of fiber. Another study examined the relationship of fiber to coronary disease in 40,000 men who were health professionals; those with the highest intake of fiber had a 40% lower risk of coronary disease as compared to those consuming the lowest amount of fiber.4 Fiber can be best obtained through diets that are rich in whole fruits and whole-grain cereals (Table I). Brown rice and whole-grain products should be consumed instead of white rice, bread, and pasta. Legumes provide fiber and can be used as a protein source instead of meat. Raw vegetables are particularly good sources of fiber.
For those who still cannot derive sufficient fiber from their diet, there are fiber supplements, both soluble and insoluble. Caution is advised at least with some of these products, as an adequate oral intake of fluids is necessary to avoid the supplemental fiber from becoming too viscous in the intestine and potentially leading to intestinal obstruction. While 30 grams of fiber should be the daily goal, this amount of dietary fiber will not be easy for most persons to achieve given the typical American diet; increasing fiber in the diet should be gradual, as any major increase is often associated with a feeling of bloating and indigestion. While a life-long diet rich in fiber should be encouraged in order to obtain maximal benefit, even much lower levels may improve common age-prevalent problems, such as constipation and hemorrhoids, and should be encouraged.
MULTIVITAMINS AND MICRONUTRIENTS
Inadequate micronutrient intake is common among older adults. Several age-related medical conditions may predispose individuals to vitamin and mineral deficiencies. Studies have reported that vitamins A, C, D, and B12, as well as calcium, iron, zinc, and other trace minerals, are commonly deficient in the elderly population, even in the absence of malabsorption or diseases such as pernicious anemia. Foods are important sources of micronutrients. Vegetable oils, nuts, and seeds are the main dietary source of vitamin E. Fruits and vegetables are the primary sources of vitamin C. Calcium in the diet is mainly derived from dairy products (milk, yogurt, and cheese), fish (sardines with bones), and some vegetables and fruits. When dietary sources are scarce or not well tolerated, supplementation with a multivitamin formulated at 100% Daily Value can help provide vitamins and improve micronutrient status.5
Those consuming less than 1500 kcal per day have difficulty with sufficient intake of foods to ensure adequate levels of vitamins and minerals, and a daily vitamin is therefore recommended. While multivitamin supplementation might be necessary to prevent vitamin deficiency, megadoses have been associated with adverse side effects. Zinc supplementation in doses higher than 50 mg per day has been linked to depressed immune response.6 Vitamin C in large amounts may lead to stomach pain, diarrhea, flatulence, and even calcium oxalate kidney stones; high levels of vitamin A can increase the risk of osteoporosis and pseudotumor cerebri.7,8 Vitamin K-containing multivitamins may reduce the blood-thinning effect of warfarin.9 Once again, caution is advised to avoid excess intake of certain nutrients during later life, such as iron, magnesium, and the fat soluble vitamins A and D. Excess iron supplements should be avoided, as high ferritin levels have been associated with cardiovascular disease, though it is unclear whether dietary iron plays a role. Iron released from tissue iron stores may accelerate lipid peroxidation by virtue of its pro-oxidant properties, and thus promote early atherogenesis.10 Hypermagnesemia may occur even with a normal intake in those with renal impairment.
THE ROLE OF ANTIOXIDANTS IN HEALTH AND DISEASE
Many amino acids are susceptible to oxidation by various reactive oxygen species (ROS). Elderly persons are at higher risk for antioxidant deficiencies, and when antioxidant defenses are inadequate, oxidized proteins with modified functions tend to accumulate during aging and may result in or influence a number of age-related diseases. Oxidative stress can come from both endogenous and exogenous sources. Potential sources of oxidative stress include the mitochondria, ionizing radiation exposures, metabolism of exogenous compounds, and pathologic metabolic processes.11 In 1956, Denham Harman first proposed the free-radical theory of aging and disease.12 Harman hypothesized that the aging process may be in part due to free-radical processes involving oxygen and continuous ongoing reactions throughout the cells and tissues.12,13
Metabolic processes in the body result in the production of reactive substances known as oxidants. Oxidants are molecules that have an extra unpaired electron. The extra electron makes the free-radical molecule highly reactive and could potentially damage cellular structures, particularly the cell membrane. The ROS include the free radicals: superoxide anions (O2.-), hydroxyl free radicals (.OH) alkoxyl (LO.), peroxyl (LOO.), and nitric oxide (NO.); and the nonradicals: hydrogen peroxide (H2O2), lipid hydroperoxide (LOOH), and hypochlorous acid (HOCl). The body possesses enzymes that convert oxidants into nontoxic molecules to protect cells from the deleterious effects of oxidative stress. These include superoxide dismutase (SOD), catalase, glutathione (GSH), glutathione peroxidase (GPx), and glutathione reductase (GR). Free radicals are generated in the brain by ongoing oxygen metabolism and biological events associated with aging.14
The brain derives its energy almost exclusively from oxidative metabolism of the mitochondrial respiratory chain, and the leakage of high-energy electrons along the mitochondrial transport chain causes formation of O2.- and H2O2.15 Oxidative stress has been shown to occur early in the progression of Alzheimer’s disease before the development of hallmark pathologies, such as neurofibrillary tangles and senile plaques.16 The role of antioxidants in disease prevention has been extensively studied over the years. Recently, Mette M. Berger17 reviewed the literature on the role of antioxidants in the prevention of cardiovascular diseases, age-related ocular diseases, and cancer. Based largely on European studies, Berger suggested that selenium supplementation may reduce the incidence of, and mortality from, carcinomas of several sites, including lung, colorectal, and prostate cancers.17 The author proposed supplementation of vitamins A, C, and E with selenium and zinc.
On the other hand, after reviewing the available data from randomized trials, the U.S. Preventive Services Task Force (USPSTF) concluded that the evidence was insufficient to recommend for or against the use of supplements of vitamins A, C, or E, multivitamins with folic acid, or antioxidant combinations for the prevention of cancer or cardiovascular disease. In addition, the USPSTF recommended against the use of beta-carotene supplements, either alone or in combination, for the prevention of cancer or cardiovascular disease. The role of antioxidants in the human diet remains controversial.
While no one would argue against a diet or supplemental vitamin to ensure intake of the Recommended Dietary Allowances (RDAs) of the above listed antioxidants, the exact benefits of additional antioxidants remain unknown in humans. In various animal models, these appear to have beneficial effects on disease as well as longevity. In 1982, Harman18 showed that dietary manipulations expected to lower the rate of production of free-radical reactions increased the lifespan of mice, rats, and fruit flies, and further inhibited the development of some forms of cancer and enhanced humoral and cell-mediated immune responses. Hagen and colleagues19 argued that mitochondrial oxidative dysfunction may be a principal underlying event in aging. By feeding older rats normal mitochondrial metabolites such as acetyl-l-carnitine (ALC) and alpha-lipoic acid (ALA), these authors showed significant progress in reversing some of this age-associated decay.19 Clearly, additional research is needed before any definite conclusions can be reached.
Calcium is an essential nutrient. While 99% of calcium is present in the skeleton, 1% is found in extracellular and intracellular components of the body. The extraskeletal calcium has a vital role in nerve conduction, membrane permeability, muscle contraction, and blood clotting. In adults, 30-40% of calcium is absorbed, and 200-250 mg per day of calcium is lost through skin, hair, nails, sweat, renal excretion, and feces.20 The processes of absorption and excretion of calcium differs with age. With age, there is a decline in intestinal mucosal mass as well as dermal synthesis of vitamin D, both of which are essential for optimal calcium absorption. Furthermore, 1 alpha-hydroxylation of 25(OH) vitamin D by the kidneys in response to parathyroid hormone (PTH) secretion also decreases with age.
Estrogen, which also enhances renal calcium retention and intestinal absorption, declines in older men and is absent in postmenopausal women.21 To make matters worse, calcium intake typically decreases in the elderly. As calcium plays a vital role in many body functions, the decrease in circulating calcium in elderly individuals is compensated at the expense of bone mineral density, the body’s largest reservoir of calcium. As a consequence of this balance, PTH levels may increase in order to increase calcium retention in the kidneys, promote intestinal absorption, and also to extract calcium from the bones. Osteoporosis may be the result of such a chronic process. Evidence has shown that intake of adequate calcium during youth has the greatest effect in decreasing the risk of osteoporosis later in life, maximizing peak bone mass.22
In an older individual with signs of osteopenia and osteoporosis, calcium has a modest but important impact on bone loss. In combination with other bone-protective medications, adequate calcium intake plays a crucial role in restoring lost bone. The Food and Nutrition Board recommends 1200 mg per day of calcium in combination with 400 IU of vitamin D in osteoporosis-free individuals ages 51-70 years, and 600 IU of vitamin D in individuals over the age of 70 years. In patients with known osteoporosis, the recommended calcium intake is 1300-1700 mg per day in combination with 600 IU of vitamin D. A calcium supplement is required in persons with inadequate amounts of dietary calcium, as well as those women who are pregnant or breastfeeding.
In an effort to optimize calcium absorption, calcium supplements should be taken in multiple doses during the day (eg, 500 mg 3 times daily), as large loads of calcium decrease its absorption. Calcium is best absorbed in an acidic environment, so its absorption can be maximized if taken during meals. Several factors interfere with calcium absorption: caffeine, vitamin D deficiency, iron, oxalates, and a high phosphorus-to-calcium ratio.23 Evidence suggests that higher intakes of protein and sodium increase calcium excretion.20 Some of the most important dietary sources of calcium include dairy products (milk, yogurt, cheese, ice cream), dark green vegetables, fish with bones, and nuts (Table II). If taken in excess (more than 2500 mg per day) calcium may have some adverse effects. Excess calcium causes constipation, gas, and distension, increases the risk of urinary stone formation, and may impair absorption of other essential minerals. Very large amounts of calcium can also lead to hypercalcemia, hypercalciuria, and may even result in renal impairment. Therefore, calcium intakes higher than 2500 mg per day should be avoided.
Careful attention to diet throughout life is essential if we are to have a more successful aging process and minimize disease. How successful we age is largely determined by our genetic makeup. Nevertheless, we all have within our control the ability to lead healthier lives, and proper diet can play a key role. Physicians should incorporate questions relating to diet into medical history, and should identify and address any findings associated with either over- or undernutrition. Attention should be given to proper intake of calories, protein, and such necessary nutrients as fiber, calcium, and vitamins and minerals.
The authors report no relevant financial relationships.