Diet and Health Outcomes in Vulnerable Populations
Address for correspondence: Joseph R. Sharkey, Ph.D., M.P.H., RD, Associate Professor and Director, School of Rural Public Health, MS 1266, College Station, TX 77843-1266. Voice: +1-979-458-4268; fax: +1-979-458-4264.
Good nutritional health is essential to physical and cognitive function, prevention or management of chronic health conditions, and prevention of disability. Poor nutritional health describes dietary intakes of inadequate amounts of energy, protein, and individual or multiple micronutrients. Homebound older adults are considered the most vulnerable for poor nutritional health; many are poor and experience persistent food insufficiency. This chapter discusses the importance of dietary intakes, especially for homebound older adults, and presents resource-related factors that influence food choice and food acquisition. These factors include limited household income, food insufficiency, and utilization of community nutrition assistance programs. Of importance is that low dietary intakes influence balance, gait speed, leg strength, and overall lower extremity physical performance (LEP). This is crucial since decreased LEP is associated with increased disability over time. It is time to review policies and programs that influence dietary intake of homebound older adults.
Community-based services face the challenge of assisting an increasing number of older adults to remain independent in the community. Many are living longer, nutritionally at-risk, and chronically impaired.1–5 Poor nutritional status is believed to be a risk factor for functional impairment,2,6,7 and functional impairment/limitation is an antecedent to functional disability.8–10 As an important public health concern, disability status is a strong predictor of further declines in function, increased number of acute illnesses, and other adverse health outcomes, such as increased risk of nursing home placement and increased risk of death.11–14 Among community-dwelling older adults, the increasing number of individuals eligible for home-delivered nutrition are the subgroup considered the most vulnerable for poor dietary intake, poor nutritional status, and physical disability. 1,9,15–17
Magnitude of the Problem
Nationwide persons ages 60 and older constitute 21.5% of the population, and their number is rapidly increasing, with an expected peak reaching 28% by the year 2030. By 2030, there will be about 70 million older persons, more than twice their number in 1996. Subsumed within this increase are expansions in the older minority population (from 13% of older adults in 1990 to 25% in 2030), in the ratio of women to men, in the number living alone, and in the number of poor (especially among minority elders).18 The elderly population itself is growing older, with the fastest growing segment of the population being those persons ages 85 years and older.19 With projections based on lowest mortality expectations, the 85 and older group could reach 23.5 million by 2040, nearly eight times the 1990 level.18 There are concomitant increases in the number of older persons residing in the community who are nutritionally at-risk and chronically impaired.1–5,20 Many are in need of food and nutrition assistance programs and home-based and community-based services in order to live independently.21
Although older adults at risk for high service utilization and adverse health outcomes may represent only 5–10% of the total Medicare population, they account for up to 60% of the population's total healthcare utilization.22 In 1995 among noninstitutionalized persons 70 years of age and older, 32% reported difficulty performing and 25% reported inability to perform at least one of nine physical activities; 20% had difficulty performing at least one basic Activity of Daily Living (ADL) and 10% had difficulty performing at least one Instrumental Activity of Daily Living (IADL).23 Basic ADL activities include bathing, dressing, eating, personal grooming, transferring, and walking across a small room.24 The higher functioning IADLs include use of the telephone (look up numbers, dial, answer), travel via car or public transportation, food or clothes shopping (regardless of transportation), meal preparation, housework, prepare and take the correct dose of medication, and management of money (write checks, pay bills).25 Another report estimated 23% of older people living in the community have difficulties with ADLs and 28% with IADLs.26 Ultimately, physical functioning may underpin an older person's ability to remain independent.
There is also a high proportion of independent older adults who are not disabled but who are at risk for functional loss and disability. Among a national sample of functionally independent persons 70–74 years of age, in a 2-year period, 19% of men and 32% of women became disabled.26 Additionally, approximately 10% of nondisabled community-dwelling adults aged 75 years and older lose independence in basic ADLs each year.27 In a study of 331 older adults who regularly received home-delivered meals, 19% (n = 63) of persons who completed the baseline in-home assessment were institutionalized or deceased 1 year later.9 Almost 56% of individuals institutionalized or deceased reported at least one disability (range of one to seven disabilities) at base line, compared with 39% of those who remained in the community. Of the 268 persons who completed both the baseline and 1-year in-home assessment, 32% declined in function during that year and 36% remained disabled at both assessments. It is believed that the absolute number of older persons with disability will dramatically increase over the next decade, with a doubling of the number of persons with ADL dependencies by 2020 or 2030.
The leading causes of disability among older persons are health conditions, especially arthritis, heart disease, stroke, respiratory diseases, and diabetes. In 1995, among noninstitutionalized persons 70 years of age and over, 79% had at least one of seven chronic conditions common among the elderly; a majority had arthritis; approximately one-third had hypertension; 25% heart disease; and 11% currently diabetes.23 Among a national sample of participants in the Title III Home-Delivered Meal Program, 64% reported having arthritis, 55% hypertension, 44% heart disease, 30% lung and breathing problems, 25% diabetes, 20% high blood cholesterol, 20% had suffered a stroke, and 59% had at least three chronic conditions.1
Theoretical Framework for Diet and the Development of Health-related Disability
Current modeling of the development of health-related disability describes a progressive, multi-stage process that begins with the development of a disease or medical condition, which is followed by functional limitation (restrictions in basic upper body, lower body, and cognitive actions) and may lead to disability in performing social roles.8,10 There are a number of predisposing risk factors (including demographic, social, lifestyle, behavioral, psychological, environmental, and biologic) and introduced risk factors (extra-individual and intra-individual) that speed up or slow down the pathway. These risk factors can affect the presence and severity of impairment, functional limitation, and disability.
Poor nutritional status, in the form of inadequate dietary intake of protein and energy and/or micronutrient deficiencies, may trigger or accelerate functional decline through weight loss and loss of muscle mass, decreased strength and power, decreased walking speed and impaired balance, and decline in activity.3,6 It is this change in muscle strength that may produce a change in lower or upper body function, and subsequent physical disability. Chronic undernutrition is exacerbated by decreased chemosensory activity (taste and smell), poor dentition, dementia, depression, illness, and hospitalization. The risk factors that predict an inadequate dietary intake among older persons include poverty, inadequate financial resources, race/ethnicity, living situation, chronic disease, mental status, dentition, geographic locale, household and individual food security, and medications.17
Disease/Medical Conditions/Impairments, Physical Limitations, and Disability
Several nutrition-related diseases/conditions can affect the transition to disability; these include heart disease, congestive heart failure, high blood pressure, cancer, stroke, diabetes, and osteoporosis. From the Established Populations for Epidemiologic Studies of the Elderly (EPESE) study of 6070 older persons, the diagnoses related to progressive disability were stroke, hip fracture (higher in women), congestive heart failure (higher in men), pneumonia, diabetes, and dehydration.28
Among all community-dwelling adults ages 70 years and over, 11% report having diabetes,23 and among participants in the Home-Delivered Meal Program, approximately 25% report having diabetes.1 In particular, Sharkey and colleagues found that homebound older adults with diabetes were at increased risk for worse overall lower extremity physical performance than persons without diabetes, after controlling for other influences.7 The effect of diabetes on functional disability may operate through deficits in vision and distal sensory function. Vision impairment is reported to limit mobility, limit social contacts, and be a risk factor for hip fracture, disability in functional status (e.g., walking, getting outside, transferring in and out of bed, grocery shopping, and paying bills), and mortality.29–31
Physical Limitations and Disability
Functional limitations (upper-extremity, lower-extremity, and balance) are a strong driving force in the disablement process.9 Performance measures of physical limitations are powerful predictors of disability.9,32,33 Scores for walking, chair stand, and balance are all related to lower extremity strength and predictive of 1-year incident disability9,27,34 and 4-year disability.35 Furthermore, the burden of multiple limitations may be greater than the sum of single limitations.36
Lower extremity strength is a fundamental component of the sensorimotor function, which supports mobility and mobility-related activities.37 Age-related loss in skeletal muscle mass is a direct cause of age-related decrease in muscle strength, and decreased muscle strength is a cause of increased prevalence of disability.37 The effect of muscle weakness on impaired mobility is independent of the effects of chronic disease, dementia, depression, and other characteristics of old age.38 Specific mobility functions like transferring, walking, balancing, or carrying objects are related to changes in muscle strength and fiber type distribution.39
A substantial body of literature suggests an association between risk for poor nutritional status and malnutrition,1,40–44 and between poor nutritional status and decreased immune response,45–47 early hospital readmission,48–50 mortality,50,51 increased length of stay and hospital costs,5,50,52,53 premature institutionalization,26,40,50 and functional impairment.2,6,7
A poor nutritional status includes deficiency, dehydration, undernutrition, nutritional imbalances, and obesity, with an emphasis of deterioration over time.54 Since nutrient needs or intake are affected by changes in energy, protein and micronutrient requirements, and dietary intake,55 there is increased interest in the conditions or factors that increase the risk for restricted dietary intake and poor nutritional status.
Dietary intakes of micronutrients are integral to daily living. Vitamin D may have a direct effect on muscle and muscle weakness 55–57 and bone health.58 Since vitamin B12 is needed for the nervous system and to protect against cognitive decline, deficiency is associated with peripheral neuropathy, subacute system degeneration, muscle weakness, mental changes, cardiovascular and cerebrovascular disease, and vibration sensitivity.55,58–60 Calcium serves many roles, which include structural functions, regulatory functions, blood clotting, and muscle contraction.61 Vitamin A is important in the vision cycle, immune response, taste, hearing, appetite, and growth.62 As one of the antioxidants in the defense system, vitamin E is also important for normal immune function.63 Also important are vitamins C and K, zinc, B6, folate, thiamin, riboflavin, niacin, magnesium, and iron.55,58,64–70
In addition to the importance of the various micronutrients, there are increased requirements for older persons. The reasons for an age-related increase in micronutrient requirements include: (1) decline in immune function associated with vitamin E, zinc, vitamin B6, and other antioxidants; (2) intestinal absorption of calcium declines; (3) skin synthesis of vitamin D diminishes; (4) renal hydroxylation to the active metabolite 1,25-dihydroxyvitamin D decreases; (5) metabolic utilization of vitamin B6 is less efficient; (6) diminished or absent capacity to secrete stomach acid secondary to atrophic gastritis impairs the absorption of vitamin B12, calcium, iron, folic acid, and possibly zinc; (7) loss of estrogen increases the needs for calcium and vitamin D; (9) decrease in gut motility and impaired thirst sensation predispose to constipation, which may respond to increased insoluble fiber in the diet; and (10) use of common drugs that cause nutritional depletion and deficiency.55,58,71–74
Inadequate intakes of key nutrients have been reported by many researchers. Using the Estimated Average Requirement (EAR) which is the basis for determination of the Recommended Dietary Allowance (RDA) in the new Dietary Reference Intakes, Sharkey and colleagues found, in a sample of 345 homebound older adults who were receiving home-delivered meals, large percentages of men and women reporting dietary intakes below the EAR for vitamins E, A, C, B12, folate, magnesium, B6, and zinc.17 A national sample (n= 818) of home-delivered meal participants reported percentages with a dietary intake less than 2/3 of the RDA for energy (44%), protein (14%), vitamin A (32%), vitamin C (31%), vitamin D (29%), vitamin E (54%), thiamin (11%), riboflavin (9%), niacin (12%), vitamin B6 (36%), folate (21%), vitamin B12 (13%), calcium (34%), iron (16%), magnesium (40%), and zinc (56%).1 Using <75% of the RDA as the definition of nutrient inadequacy for 1156 New England elders, Posner and colleagues reported nutrient inadequacies for vitamins A and C, protein, thiamin, and calcium.75 Additionally, Sharkey and colleagues examined the dietary intake of musculoskeletal-related nutrients, that is, calcium, vitamin D, magnesium, and phosphorus.7 Using three random 24-hour dietary recalls and the newly released dietary reference intakes, that identify age- and sex-specific nutrient intake recommendations for older adults, data were collected from 321 homebound older men and women on random days.76 In terms of relative intake, 75% of the participants consumed <69% of the recommended Adequate Intake (AI) for calcium, <44% of the AI for vitamin D, and <75% of the RDA for magnesium.7
The putative risk factors for poor dietary intake include diseases/medical conditions (especially those that interfere with appetite or eating), medications (especially the interference with appetite and/or nutrient metabolism), oral status (which includes problems with eating, chewing, and swallowing), social isolation, depressive symptoms, mental status, economic difficulties, and excessive alcohol use.4,16,17,22,40,41,44,54,55,77–84 Each of these affects an individual's ability to acquire, prepare, and/or consume food.4
Poverty and Dietary Intake
Indicators of poor income—lowest levels of income, food stamp use, and food insufficiency—are associated with lower dietary intakes among homebound older adults.9,15,17,43,85,86 In a series of studies of homebound older adults, Sharkey and colleagues found that the lowest level of income was associated with decreasing dietary intake in individual nutrients.9,15,17,43,85,86 Almost one of four women in the study reported an income of less than $500 per month, with another 46% with an income of $500 to $750 per month. Both low levels of income were associated with the decreasing intakes of overall calories (energy), protein, calcium, and magnesium.17 In this same sample of 345 homebound older adults, food stamp users were more likely to have lower nutrient intakes, as were individuals who did not regularly consume a breakfast meal.17
Low income (<$750/month) places homebound older adults at increased risk for food insufficiency.85 More than 81% of food insufficient older adults had an income <$750/month, as did 73% of individuals identified as being at risk for food insufficiency. In this study of 279 homebound older adults, Sharkey found that being food insufficient was associated with lowest quartile of dietary intakes in energy, protein, calcium, magnesium, phosphorus, vitamin B6, folate, zinc, and vitamin A.85 In fact, the risk for lowest intake for multiple nutrients was much greater for food insufficient individuals. More than 55% of food insufficient persons and 35% of those at risk for food insufficiency consumed diets with the lowest quartile in at least two of four musculoskeletal nutrients (vitamin D, calcium, magnesium, and phosphorus) and at least five of 15 nutrients.85 In addition, homebound older adults with low income were more likely to remain food insufficient 1 year later or decline in food sufficiency.15,86 Many older adults with lowest incomes reported that they did not have enough food to eat or enough money for food.15 As a result, many adopted such practices as seeking free food, eating cheaper meals, or eating smaller meals.15
Association between Nutritional Status and Function
Though a considerable body of work describes poor nutritional status, there are limited characterizations of an association between nutritional status and functional disability.40,80–82,87–91
A variety of measures have been used to describe nutritional status in these studies, such as DETERMINE Checklist, body mass index (BMI), weight change, and dietary intake.
Several researchers, using the DETERMINE Checklist or versions of the Level I and Level II screens of Nutrition Screening Initiative,54 reported cross-sectional5,7 and prospective9,52 associations between risk for poor nutritional status and physical disabilities (ADL and IADL). Boult and colleagues reported functional disability and depressive symptoms 1 year after screening older adults, who were at high risk for hospitalization, for nutritional risk.52 Additionally, Sharkey and colleagues43,92,93 reported that home-delivered meals participants at high risk for poor nutritional status were several times more likely to have both ADL and IADL disabilities as other participants. In a cross-sectional analysis of baseline data, Jensen and colleagues reported independent associations with self-reported functional limitations for weight loss, weight gain, depression, taking three or more medications, age ≥75, poor appetite, special diet, eating problems (such as difficulty chewing or pain in mouth and teeth), income below poverty level, eating alone, and spending less than $25–30/wk on food. In the multivariate logistic model, they found that age, poor appetite, poverty, medications, eating problems, depression, and eating alone were all significantly associated with functional limitation.5
Several studies associated poor nutritional status, as indicated by a low or high BMI, with functional impairment.2,7,9,94,95 Marshall and colleagues reported that BMI >30 and BMI <21 were associated with functional impairments.83 Using the data from 4000 participants in the Duke EPESE, Landerman and colleagues found the effect of BMI (using the 15th and 85th percentiles from NHANES II) is mediated by chronic health problems, hip fracture, poor health, and hospitalization.96 Ensrud and colleagues found similar results from a study of 9704 nonblack women, with impaired function strongly associated with increased obesity.94 When Gill and colleagues defined good nutrition as neither a low BMI (<20.7 for men and <19.1 for women) nor a weight loss greater than 10 lb in the previous year, they found good nutritional status associated with ADL disability recovery.97
Jensen and colleagues reported an independent association with the presence of any ADL/IADL limitation for weight loss or weight gain of 10 lb in the past 6 months.5 Covinsky and colleagues reported that the presence of a 10% weight loss the previous 6 months was predictive of at least one ADL disability 3 months and 1 year after hospital discharge.50 Gray-Donald and colleagues reported that a change in weight was strongly correlated with a change in handgrip strength among 145 homebound older adults.98 With 475 participants in the Nun Study, Tully and Snowdon found that a 3% annual weight loss was associated with increased ADL dependence.99
The reports on micronutrients and functional disability are thin. Guralnik and colleagues describe an association between B12 deficiency and physical limitations, including grip strength, knee extension strength, functional reach, and vibration sensitivity.59 They posit that B12 deficiency has an impact on all steps of the pathway from disease to disability. Inadequate intake of a number of nutrients has been associated with decreased body strength, lower resistance to infection, and poorer indicators of quality of life.100 Using three 24-hour dietary recalls and performance-based measures of lower extremity physical performance (static and dynamic balance, gait speed, and leg strength), Sharkey and colleagues found that lowest intakes in musculoskeletal-related nutrients were associated with worst performance in individual and multiple measures of lower extremity physical performance.7 It was through lower extremity physical performance that dietary intake was associated with basic ADL disability and with decline in ADL over 1 year.9
Homebound older adults are considered the most vulnerable subgroup of older adults for poor dietary intake, poor nutritional health, nutrition-related health conditions, functional decline, and disability. The maintenance of function relies to a large extent on the nutrients derived from dietary intake. The convergence of limited financial resources and risk or presence of food insufficiency constrains older persons from acquiring the foods necessary for optimal nutrient intake. It is time to review policies and programs that influence dietary intake of homebound older adults.
Conflicts of Interest
The author declares no conflicts of interest.