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Low Serum Micronutrient Concentrations Predict Frailty Among Older Women Living in the Community

¹ The Johns Hopkins Medical Institutions, Baltimore, Maryland.
² Division of Nutritional Sciences, Cornell University, Ithaca, New York.
³ Department of Medicine, University of Michigan, Ann Arbor.

Address correspondence to Richard Semba, MD, MPH, 550 N. Broadway, Suite 700, Baltimore, MD 21205. E-mail: rdsemba{at}jhmi.edu

Abstract

Background. Micronutrient deficiencies are common among older adults. We hypothesized that low serum micronutrient concentrations were predictive of frailty among older disabled women living in the community.

Methods. We studied 766 women, aged 65 and older, from the Women's Health and Aging Study I, a population-based study of moderately to severely disabled community-dwelling women in Baltimore, Maryland. Serum vitamins A, D, E, B₆, and B₁₂, carotenoids, folate, zinc, and selenium were measured at baseline. Frailty status was determined at baseline and during annual visits for 3 years of follow-up.

Results. At baseline, 250 women were frail and 516 women were not frail. Of 463 nonfrail women who had at least one follow-up visit, 205 (31.9%) became frail, with an overall incidence rate of 19.1 per 100 person-years. Compared with women in the upper three quartiles, women in the lowest quartile of serum carotenoids (hazard ratio [HR] 1.39; 95% confidence interval [CI], 1.01–1.92), -tocopherol (HR 1.39; 95% CI, 1.02–1.92), and 25-hydroxyvitamin D (HR 1.34; 95% CI, 0.94–1.90) had an increased risk of becoming frail. The number of nutritional deficiencies (HR 1.10; 95% CI, 1.01–1.20) was associated with an increased risk of becoming frail, after adjusting for age, smoking status, and chronic pulmonary disease. Adjusting for potential confounders, we found that women in the lowest quartile of serum carotenoids had a higher risk of becoming frail (HR 1.54; 95% CI, 1.11–2.13).

Conclusions. Low serum micronutrient concentrations are an independent risk factor for frailty among disabled older women, and the risk of frailty increases with the number of micronutrient deficiencies.

A major obstacle to the study of frailty has been the lack of a standardized definition. In the past, frailty has sometimes been used synonymously with disability and comorbidity, however, mounting consensus indicates that frailty is a physiologically based condition with a clinical presentation that predicts disability and may result from comorbidity as well as multisystem physiologic dysregulation with aging (1). Recently, frailty was defined as a clinical syndrome based on having at least three of five criteria: unintentional weight loss, self-reported exhaustion, weakness, slow walking speed, and low physical activity (5). This definition was based on biologic theory and supported by evaluation of criterion and construct validity in the Cardiovascular Health Study (CHS; 5).

Micronutrient deficiencies are common among older adults. Older adults may have an inadequate intake of specific nutrients such as vitamin D (6), vitamin A (7), vitamin E (8), vitamin B₆ (9), vitamin B₁₂ (10), folate (10), zinc (11), and selenium (12). The intake of carotenoids and vitamin C may decline with older age (13). A high prevalence of multiple micronutrient deficiencies occurs among frail women (14). Although micronutrient deficiencies could potentially increase the risk of frailty through multiple pathways involving oxidative stress, inflammation, muscle and bone metabolism, and immunity, the relationship between micronutrients and the risk of becoming frail has not been well characterized. We hypothesized that older women with micronutrient deficiencies were at higher risk of becoming frail and that a higher number of micronutrient deficiencies was associated with a greater risk of becoming frail. To address these hypotheses, we measured the associations between serum micronutrient concentrations and both prevalent and incident frailty in a longitudinal cohort (from the Women's Health and Aging Study I (WHAS I) of older, disabled, community-dwelling women living in Baltimore, Maryland.

METHODS

Participants
The participants were women, 65 years old, in the WHAS I, a population-based study of the causes of physical disability in older women living in the community. WHAS I participants were recruited from an age-stratified random sample of women aged 65 years selected from Medicare enrollees residing in 12 contiguous ZIP code areas in Baltimore (15). Women were screened to identify self-reported physical disability with (i) mobility, (ii) upper extremity function, (iii) higher functioning household management, and (iv) self-care. WHAS I included the one-third most disabled women aged 65 years. Of the 1409 women who were eligible, 1002 agreed to participate in the study in 1992. There were no major differences in sociodemographic or reported health characteristics between participants and nonparticipants (15). Standardized questionnaires were administered in the participant's home, and a trained registered nurse conducted an examination of each participant by using a standardized protocol. Approximately 75% of women also consented to phlebotomy. A previous analysis has shown that those women who did not participate in the blood drawing had less education and a higher prevalence of frailty compared to those who participated in the blood drawing (14). Further details on the methods and design of WHAS I are published elsewhere (15). Chronic diseases were adjudicated based on the questionnaire, physical examination, and physician contact (15). Women were followed for 36 months, and frailty status was ascertained at baseline and at 12 and 36 months.

Definition and Classification of Frailty
Women were categorized as frail or not frail according to a recent frailty phenotype (5) that was based on the presence of five characteristics: (i) unintentional weight loss (self-reported weight loss of 10 pounds or more in the prior year), (ii) self-reported exhaustion, (iii) weakness (measured grip strength in the lowest quintile at baseline), (iv) slow walking speed (the slowest quintile on test of timed walking speed), and (v) low level of physical activity (lowest quintile of physical activity scale). Women were defined as frail by the presence of at least three, and not frail if they had up to two of the five components.

Cutoff points in each measure that met the criteria for frailty were standardized to those used for women in the CHS (5) as closely as possible. Components of the frailty phenotype were measured using standardized questions (weight loss and exhaustion) and protocols. Unintentional weight loss was self-reported. Weakness was assessed by level of maximal grip strength using a handheld dynamometer (15), and the same cutoffs were used in both CHS and WHAS I (grip strength adjusted by body mass index [BMI]: 17 kg for BMI 23 kg/m², 17.3 kg for BMI >23 and 26 kg/m², 18 kg for BMI >26 and 29 kg/m², and 21 kg for BMI >29 kg/m²). Walking speed was measured over 15 ft in CHS and over 4 m in WHAS I by using a standardized protocol for timed walking (15). In WHAS I, the lowest quintile of walking speed, adjusted by height, was 0.65 m/s for height 159 cm and 0.76 m/s for height >159 cm. Physical activity level was determined using a subset of the Minnesota Leisure Time Activities Questionnaire (15). A weighted score of kilocalories expended per week was calculated from questions on frequency and duration of physical activities, and lowest quintile of physical activity in WHAS I was <90 kcal of physical expenditure on the activity scale for six activities.

Laboratory Analysis
Nonfasting blood samples were obtained by venipuncture between 9:00 AM and 2:00 PM with sample processing conducted following a standardized protocol. Blood samples were delivered to Quest Diagnostics Laboratories (Teterboro, NJ) on the day of blood drawing. Serum samples were stored continuously at –70°C until the time of analyses for carotenoids, retinol, -tocopherol, zinc, and selenium, which are stable at these long-term storage conditions at –70°C (16). Serum carotenoids, retinol, and -tocopherol levels were determined by high performance liquid chromatography (16).

Serum selenium and zinc levels were measured by graphite furnace atomic absorption spectrometry using a PerkinElmer AAnalyst 600 (Norwalk, CT) with Zeeman background correction. For selenium, samples were diluted 1:4 with a Triton-X (Sigma Chemical, St. Louis, MO) and nitric acid solution (Fisher Scientific, Pittsburgh, PA), and the matrix modifier was a palladium and magnesium nitrate solution (both PerkinElmer). The instrument was calibrated daily using SeroNorm Trace Elements Serum Level 1 (Accurate Chemical and Scientific Corp., Westbury, NY). For zinc, samples were diluted 1:200 with di-water, and the matrix modifier was magnesium nitrate (PerkinElmer).

Total carotenoids were calculated (in µmol/L) as the sum of -carotene, ß-carotene, ß-cryptoxanthin, lutein/zeaxanthin, and lycopene. Serum 25-hydroxyvitamin D [25(OH)D] was measured using a radioreceptor assay (17). Pyridoxal 5-phosphate was measured using high performance liquid chromatography (14). Serum vitamin B₁₂ and folate were measured by radio immunoassay (RIA; 18). Within-run and between-run coefficients of variation, respectively, were: 10.7% and 23.9% for -carotene, 7.0% and 19.1% for ß-carotene, 4.7% and 8.5% for ß-cryptoxanthin, 4.1% and 4.6% for lutein/zeaxanthin, 10.0% and 14.0% for lycopene, 4.1% and 9.7% for -tocopherol, 7.5% and 9.6% for 25-hydroxyvitamin D, 5.8% and 4.8% for selenium, and 2.8% and 3.9% for zinc.

Statistical Analysis
Descriptive statistics were used to characterize the study population and to describe nutrient concentrations. Nutrients had a skewed distribution and were analyzed using logarithmic transformation and presented as geometric means and 95% confidence intervals (CI). The participants were categorized into quartiles based on nutrient concentration. Quartiles were used because conventional cutoffs for deficiencies have usually been extrapolated from middle-aged populations to those persons 65 years old, and these cutoffs may not necessarily be meaningful for older adults (19). Thus, poor nutritional status for each nutrient was defined as the lowest quartile of the distribution of each nutrient. The distribution of nutrients showed that quartile cutoffs were optimal for these analyses. The lowest quartile cutoffs for each nutrient at baseline were: total carotenoids, 1.038 µmol/L; retinol, 1.97 µmol/L; -tocopherol, 15.87 µmol/L; 25-hydroxyvitamin D, 35.4 nmol/L; vitamin B₆, 17.8 nmol/L; vitamin B₁₂, 300 pg/mL; folate, 13.4 nmol/L; selenium, 105 µg/L; and zinc, 0.73 µg/mL. BMI was categorized as underweight (<18.5 kg/m²), normal range (18.5–24.9 kg/m²), overweight (25–29.9 kg/m²), or obese (30 kg/m²) according to World Health Organization criteria (20).

Grouped-time Cox proportional hazard models (21) were used to examine the risk of becoming frail, because frailty was determined every 12 months. Women who did not have at least one follow-up visit after enrollment because of death, refusal, or loss to follow-up were excluded from the longitudinal analyses. Women who died, refused further participation, or were lost to follow-up after a second or third follow-up visit were censored according to their frailty status at their last visit in the study. The hazards ratio (HR) for becoming frail was calculated for the lowest quartile of each nutrient's distribution, using all other quartiles combined as the reference. The analysis of the number of nutrient deficiencies and the incidence of frailty was limited to nine nutrients (retinol, -tocopherol, 25-hydroxyvitamin D, vitamin B₆, vitamin B₁₂, folate, selenium, zinc, and total carotenoids). The number of nutrient deficiencies was modeled as a linear term. Categorized versions of the deficiency variable (1–2 deficiencies, 3 deficiencies) showed a stepwise increase and supported the use of the linear term for maximal power.

Total carotenoids were used instead of individual carotenoids because most carotenoids are contained in the same food group of fruits and vegetables. Women were included in the analyses if they had at least four nutritional measures. BMI was not included in the final model because one of the components of frailty is the unintentional loss of 10 pounds or more (5). The statistical program used was SAS (SAS Institute, Cary, NC) (22).

RESULTS

Serum micronutrients were measured in 766 women, of whom 250 were frail and 516 were not frail at baseline. The demographic and health characteristics of frail and nonfrail women at baseline are shown in Table 1. Frail women were older (p <.0001), less educated (p =.002), had a higher prevalence of cardiovascular disease (p <.0001), and a higher proportion of frail women than nonfrail women had a BMI <18.5 kg/m² (p <.0001). There were no significant differences in the proportion of women who were current smokers, used multivitamins, or had diabetes mellitus, osteoarthritis, or chronic pulmonary disease by frailty status at baseline. A larger proportion of frail women reported fair or poor appetite compared with women who were not frail (p <.0001).

The relationship between the number of nutrient deficiencies (retinol, -tocopherol, 25-hydroxyvitamin D, vitamin B₆, vitamin B₁₂, folate, selenium, zinc, and total carotenoids) and incidence rates of frailty for 451 women are shown in Figure 1. Women with no nutrient deficiencies had the lowest incidence rate of frailty, and the incidence of frailty increased with higher number of deficiencies. In a final multivariate grouped-time Cox proportional hazards model (Table 5), the number of nutrient deficiencies was associated with the incidence of frailty (HR 1.10; 95% CI, 1.01–1.20, p =.029) after adjusting for age, smoking, and chronic pulmonary disease.

View larger version (5K): [in this window] [in a new window]   Figure 1. Number of nutrient deficiencies and incidence rates of frailty among 451 women in the Women's Health and Aging Study I

DISCUSSION

This study shows that older women who had one or more indicators of poor micronutrient status had significantly higher risk of becoming frail compared to women without any indicator of poor micronutrient status. The strengths of this study are that it was a population-based longitudinal study of older women living in the community and that frailty was measured using a recently validated, standardized definition (5). The serum micronutrients measured in this study are widely used and valid indicators of nutrient status (23,24). To our knowledge, this is the first study to show that low serum micronutrient concentrations increase the risk of becoming frail in a population-based study of older women living in the community.

Older women may be at higher risk of micronutrient malnutrition because of difficulty with shopping and meal preparation and because of the anorexia of aging (7,25). Micronutrient deficiencies may be one major pathway by which women are at higher risk of becoming frail. In turn, frailty increases the risk for adverse outcomes, including hospitalizations and mortality (1). The current definition of frailty includes unintentional weight loss as one criterion (5), and weight loss could be associated with micronutrient deficiencies. When unintentional weight loss was excluded as a criterion for frailty in these longitudinal analyses, micronutrient deficiencies were still predictive of incident frailty. Among older adults, indicators of micronutrient malnutrition may be more sensitive in assessment of nutritional status than indicators of macronutrient status (such as weight loss or low BMI) may be. Increased use of micronutrients may potentially contribute to nutrient deficiencies, and further studies are needed to address this issue in older adults.

Micronutrient malnutrition may play a role in the pathogenesis of frailty through different biological pathways. In the present study, low serum carotenoid concentrations were predictive of frailty. Serum carotenoid concentrations are considered the most valid biochemical indicator of fruit and vegetable intake (23); thus, in general, low serum carotenoids also represent a low intake of fruits and vegetables. Fruits and vegetables are rich sources of antioxidants, including the carotenoids, vitamin C, flavonoids, and other polyphenols. Recent data from different large cohort studies suggest that a high fruit and vegetable intake is protective against inflammation, cardiovascular disease, and mortality (26–29). Low intake of fruits and vegetables may increase the risk of frailty through increased oxidative stress, inflammation, and sarcopenia (26,30). Other studies support this idea, as in older adults low serum carotenoid and vitamin E concentrations were associated with sarcopenia (16), and low antioxidant intake was associated with impaired muscle strength and physical performance (31). Low fruit and vegetable intake was recently shown to be predictive of functional limitation and disability in the Atherosclerosis Risk in Communities Study (32).

Vitamin D deficiency may increase the risk of osteoporosis and hip fracture (33), myopathy, disability (17), and falls (34). Vitamin B₆, B₁₂, and folate deficiencies are associated with higher homocysteine concentrations and an increased risk of cardiovascular disease (35), bone fractures (36), and decreased cognitive function (37). Selenium plays a role in oxidant defense enzymes and may protect against inflammation and some types of cancer (38), and zinc is important for normal immune function, wound healing, taste, and smell in older adults (39). The present study suggests that for each additional nutrient deficiency, the risk of a woman becoming frail increased by almost 10%. The cumulative effect of micronutrient deficiencies may be the potential disruption of normal homeostatic mechanisms that maintain the musculoskeletal system, reduce oxidative stress and inflammation, and allow normal immune function.

About one quarter of the women did not participate in the blood drawing at baseline, which could have possibly biased the sample. However, nonparticipants were older and more likely to be frail; thus, most of the nonparticipants would have been excluded from the longitudinal analysis because they were already frail at baseline. Another limitation is that serum vitamin C concentrations were not measured. The present study involved a population that represented the one-third most disabled group of women living in the community; further studies are needed to determine whether low serum micronutrients predict frailty among healthier older men and women living in the community.

The prevention of frailty remains a major challenge in medicine and public health, and interventions are needed that will prevent or delay frailty. The prevention of micronutrient deficiencies may potentially reduce the risk of frailty; however, such a hypothesis would need to be tested through controlled clinical trials with appropriate treatment and design. The type of nutritional interventions, such as micronutrient supplementation or increasing intake of fruits and vegetables, would need careful consideration in future intervention studies (40). The recent data on fruit and vegetable intake from different longitudinal cohort studies (26–29,32), and the findings of the present study that link low carotenoid levels with increased risk of frailty, suggest that modification of dietary intake may be an appropriate intervention that should be examined for the prevention of frailty.

Acknowledgments

This work was supported by the National Institute on Aging (grants R01 AG11703-01A1 and R01 AG027012-01), the National Institutes of Health-National Center for Research Resources, Outpatient Department General Clinical Research Center (OPD-GCRC) (grants RR00722 and R01 AI41956), and National Institute on Aging (contract N01-AG12112).

We thank Amanda Ray, Dana Totin-Moncrief, and Barbara Dancheck for laboratory analyses of vitamins A, E, carotenoids, zinc, and selenium, and Qian-Li Xue for his advice regarding data analyses.

Footnotes

Decision Editor: Luigi Ferrucci, MD, PhD

Received March 9, 2005

Accepted July 27, 2005

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