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Am J Epidemiol. 2009 April 15; 169(8): 927–936.
Published online 2009 March 6. doi:  10.1093/aje/kwp007
PMCID: PMC2727232

Overweight and Obesity Over the Adult Life Course and Incident Mobility Limitation in Older Adults

The Health, Aging and Body Composition Study

Abstract

Obesity in middle and old age predicts mobility limitation; however, the cumulative effect of overweight and/or obesity over the adult life course is unknown. The association between overweight and/or obesity in young, middle, and late adulthood and its cumulative effect on incident mobility limitation was examined among community-dwelling US adults aged 70–79 years at baseline (1997–1998) in the Health, Aging and Body Composition Study (n = 2,845). Body mass index was calculated by using recalled weight at ages 25 and 50 years and measured weight at ages 70–79 years. Mobility limitation (difficulty walking 1/4 mile (0.4 km) or climbing 10 steps) was assessed semiannually over 7 years of follow-up and was reported by 43.0% of men and 53.7% of women. Men and women who were overweight or obese at all 3 time points had an increased risk of mobility limitation (hazard ratio = 1.61, 95% confidence interval: 1.25, 2.06 and hazard ratio = 2.85, 95% confidence interval: 2.15, 3.78, respectively) compared with those who were normal weight throughout. Furthermore, there was a significant graded response (P < 0.0001) on risk of mobility limitation for the cumulative effect of obesity in men and overweight and/or obesity in women. Onset of overweight and obesity in earlier life contributes to an increased risk of mobility limitation in old age.

Keywords: aged, mobility limitation, obesity, overweight

The proportion of older adults in the United States is expected to grow to 20% of the population by the year 2030 (1). In addition, adults are, on average, increasingly heavier than earlier generations, with approximately one-third classified as obese (body mass index (BMI) ≥30 kg/m2) (2). Obesity has been consistently associated with increased risk of cardiovascular disease, diabetes, and several cancers, as well as other chronic conditions (3, 4). Obesity in middle-aged and older adults also increases the risk of physical disability (510), possibly as a result of these obesity-related chronic conditions or by other mechanisms. Thus, the growing prevalence of obesity, particularly among younger age groups, could reverse the recent declines in disability rates among future generations of older adults (1113).

Although the association between obesity in middle and late adulthood and physical disability is established (58, 10), few studies have examined the effect of obesity among younger adults (14, 15) or the cumulative effect of obesity from young adulthood (9, 16) on disability in older adults. In the National Health and Nutrition Examination Survey Epidemiologic Follow-up Study, being obese or becoming obese over 20 years of follow-up was associated with higher levels of disability (9). Among Finnish adults aged 55 years or older, earlier onset of obesity and obesity duration based on recalled weights at ages 20, 30, 40, and 50 years increased the likelihood of reporting walking limitations (16). However, neither of these studies included a measure of incident disability.

In the Health, Aging and Body Composition (Health ABC) Study, we previously showed that, compared with those of normal weight, men and women who reported being overweight or obese at ages 25, 50, and 70–79 years had significantly worse physical performance at study baseline (ages 70–79 years) based on objective measures (17), predictive of subsequent mobility disability (18). The primary objective of the present study was to examine the association of overweight and/or obesity in young, middle, and late adulthood, as well as the cumulative effect of overweight and/or obesity across all 3 time points, with incident mobility limitation in men and women in their 70s and 80s.

MATERIALS AND METHODS

Study population

Data for this analysis were derived from the Health ABC Study, a prospective cohort study investigating the associations among body composition, weight-related health conditions, and incident functional limitations in older adults. The Health ABC Study enrolled 3,075 community-dwelling male and female blacks and whites aged 70–79 years between April 1997 and June 1998. Participants were recruited from a random sample of white and all black Medicare-eligible residents in the Pittsburgh, Pennsylvania, and Memphis, Tennessee, metropolitan areas. Participants were eligible if they 1) reported no difficulty walking one-fourth of a mile (0.4 km), climbing up 10 steps, or performing activities of daily living; 2) were free of life-threatening illness; 3) planned to remain in the geographic area for at least 3 years; and 4) were not enrolled in lifestyle intervention trials. All participants provided written informed consent, and all protocols were approved by the institutional review boards at both study sites.

Participants who were missing data on recalled weight at age 25 years (n = 75) or age 50 years (n = 68) or data on recalled height at age 25 years (n = 39) were excluded. Participants with an extremely low body weight (BMI <15 kg/m2) at ages 25, 50, or 70–79 years (n = 15) or an absolute weight change of more than 100 pounds (45.4 kg) from age 50 to ages 70–79 years (n = 8) were also excluded. Participants who were missing information on mobility limitation during follow-up (n = 2) as well as other pertinent baseline covariates (n = 23) were also excluded. The final analysis sample was 2,845 participants.

Mobility limitation

Occurrence of mobility limitation during follow-up was assessed during annual clinic visits alternating with telephone interviews every 6 months. Persistent mobility limitation was defined as 2 consecutive reports of having any difficulty walking one-fourth of a mile (0.4 km) or climbing up 10 steps without resting because of health or a physical problem. Follow-up included incident cases ascertained through 6.9 years of follow-up, with a mean follow-up of 4.2 (standard deviation, 2.4) years.

BMI history

At the baseline visit, participants were asked to recall their usual body weight (women were instructed to answer for a time when not pregnant) and height (without shoes) at age 25 years and to recall their usual body weight at age 50 years. Body weight at study baseline (ages 70–79 years) was measured in kilograms by using a standard balance beam scale, and height was measured in millimeters by using a Harpenden stadiometer (Holtain Ltd., Crosswell, United Kingdom). BMI at ages 25 and 50 years was calculated by using recalled weight at age 25 or 50 years and recalled height at age 25 years, while BMI at ages 70–79 years was calculated by using measured weight and height. BMI was categorized as normal weight (<25.0 kg/m2), overweight (25.0–29.9 kg/m2), and obese (≥30.0 kg/m2). Additional analyses that excluded underweight (BMI <18.5 kg/m2) participants at ages 25, 50, and 70–79 years were similar to those that included them with the normal-weight group (data not shown).

To assess the cumulative effect of overweight and/or obesity across all 3 time points, the following categories were created: normal weight/nonobese at ages 25, 50, and 70–79 years; overweight and/or obese at ages 70–79 years but not at ages 25 or 50 years; overweight and/or obese at ages 70–79 and 50 years but not at age 25 years; overweight and/or obese at all 3 time points; and overweight and/or obese at age 50 years but not at ages 70–79 years. Other BMI history patterns were categorized as other. For these analyses, recalled height at age 25 years was used to calculate BMI at ages 70–79 years in addition to BMI at ages 25 and 50 years to minimize possible misclassification bias due to systematic differences between recalled height at age 25 years and measured height at study baseline. Results were similar when measured height at study baseline was used to calculate BMI at ages 25, 50, and 70–79 years (data not shown).

Potential confounders

Demographic characteristics (age, gender, race, and education), smoking status, alcohol consumption, and physical activity were ascertained by an interviewer-administered questionnaire at study baseline. The time and intensity of self-reported physical activities performed in the past 7 days, including walking for exercise, other walking, climbing stairs, aerobic dance, weight training, and other high- and medium-intensity activities, were summed (kcal/week). Because BMI history may affect mobility as a consequence of weight-related health conditions, prevalent health conditions at study baseline were examined as potential mediators of the associations. The prevalence of diabetes, coronary heart disease, congestive heart failure, stroke, chronic obstructive pulmonary disease, and knee pain were determined by using algorithms based on self-report and medication use at study baseline; participants with definitive health conditions were coded as “yes.” The 20-item Center for Epidemiologic Studies Depression Scale was used as an indicator of depressed mood, and persons scoring 16 or higher were classified as depressed (19). The Modified Mini-Mental State Examination was used as an indicator of general cognitive status, with a minimum score of zero and maximum score of 100 (best) (20). Because mean scores on the Modified Mini-Mental State Examination vary by education, a cutpoint of <75 for individuals with less than a high school education and a cutpoint of <80 for individuals with a high school education were used to classify participants as cognitively impaired.

Statistical analyses

Cox proportional hazards regression models were used to examine the associations between BMI status at ages 25, 50, and 70–79 years and risk of incident mobility limitation with SAS version 9.1 software (SAS Institute, Inc., Cary, North Carolina). The cumulative effect of overweight and/or obesity across all 3 time points and incident mobility limitation was also examined. Participants who survived with no evidence of incident mobility limitation were censored at their next-to-last 6-month contact. Participants who died and had no evidence of incident mobility limitation were censored at their time of death, and those who were lost to follow-up were censored at their last visit. Two-way interactions between gender and BMI status at ages 25, 50, and 70–79 years were tested, and interactions were found at the significance level of α = 0.10. Interactions between race and BMI status at ages 25, 50, and 70–79 years within gender group were also tested but were not significant. Thus, in this paper, all analyses are presented for men and women separately, with race groups combined. Models were adjusted for age, race, field center, education, smoking, alcohol consumption, and physical activity at study baseline. Additional models were also adjusted for prevalent health conditions at study baseline. Proportional hazards assumptions were assessed by examining log(−log S(t)) plots as well as testing interactions of each variable with time in the model. The proportional hazards assumptions were not violated. All P values were 2 sided.

RESULTS

The mean age of the study population was 73.6 years, 50.6% were women, and 39.7% were black. Participants excluded from the present analysis (n = 230, 7.5%) were more likely to be female, black, and older; have less than a high school education; have a higher BMI at ages 70–79 years; and report incident mobility limitation during follow-up (P < 0.01). The descriptive characteristics of the study population by gender and incident mobility limitation are shown in Table 1. Approximately 43.0% of men and 53.7% of women reported becoming limited in mobility over the 7 years of follow-up. Participants who reported incident mobility limitation were more likely to be black, have less than a high school education, report being a current smoker and a former drinker, engage in less physical activity, and report prevalent chronic conditions than those who did not report incident mobility limitation. Overweight and obesity at ages 25, 50, and 70–79 years were more prevalent among those who reported incident mobility limitation. Participants who reported mobility limitation were less likely to be normal weight or nonobese at all 3 time points.

Table 1.
Participant Characteristics at Study Baseline (Ages 70–79 Years) by Incident Mobility Limitation in Men and Women, the Health, Aging and Body Composition Study, 1997–1998a

The hazard ratios and 95% confidence intervals of incident mobility limitation by BMI status at ages 25, 50, and 70–79 years for men and women are shown in Table 2. Men who were obese at age 25 years and overweight or obese at ages 50 and 70–79 years were at significantly increased risk of incident mobility limitation compared with men who were normal weight at ages 25, 50, and 70–79 years, respectively. For women, those who were overweight at age 25 years and overweight or obese at ages 50 and 70–79 years were at significantly increased risk of incident mobility limitation compared with women who were normal weight at each of the 3 time points. Adjusting for prevalent health conditions at study baseline attenuated the associations between BMI status at ages 25, 50, and 70–79 years and incident mobility limitation slightly, but, in general, the associations remained significant.

Table 2.
Incident Mobility Limitation Among Men and Women by Body Mass Index at Ages 25, 50, and 70–79 Years, the Health, Aging and Body Composition Study, 7 Years of Follow-upa

Figures 1 and and22 show the hazard ratios and 95% confidence intervals for incident mobility limitation associated with overweight and/or obesity from age 25 to ages 70–79 years. Compared with that for those of normal weight at all 3 time points, the risk of incident mobility limitation appeared to increase by duration of overweight or obesity (BMI ≥25 kg/m2) for those who were overweight or obese at ages 70–79 years (Figure 1). Although fewer participants reported being obese at age 50 years or earlier, similar associations were seen for duration of obesity (BMI ≥30 kg/m2), particularly among men (Figure 2). After excluding participants who were overweight and/or obese at age 50 years but not at ages 70–79 years and those who had a BMI history pattern of “other,” we found a significant graded response for the cumulative effect of obesity in men (P for trend < 0.0001) and overweight and/or obesity in women (P for trend < 0.0001) on risk of mobility limitation. Women who reported being overweight and/or obese at age 50 years but not at ages 70–79 years were at increased risk of incident mobility limitation compared with those who were normal weight or nonobese at all 3 time points. Men who reported being obese at age 50 years but not at ages 70–79 years were also at increased risk of incident mobility limitation. Further adjustment for prevalent health conditions at study baseline attenuated the associations slightly, but, in general, the associations remained significant.

Figure 1.
Hazard ratios and 95% confidence intervals for incident mobility limitation among men (A) and women (B) by history of overweight or obesity (body mass index ≥25 kg/m2), the Health, Aging and Body Composition Study, 7 years of follow-up. Models ...
Figure 2.
Hazard ratios and 95% confidence intervals for incident mobility limitation among men (A) and women (B) by history of obesity (body mass index ≥30 kg/m2), the Health, Aging and Body Composition Study, 7 years of follow-up. Models were adjusted ...

The cumulative effect of overweight and/or obesity on incident mobility limitation may partly be explained by attained BMI at ages 70–79 years. Participants who reported being overweight or obese at age 50 years or earlier had higher BMIs in late adulthood compared with those not classified as being overweight or obese until ages 70–79 years (30.8 kg/m2 vs. 28.0 kg/m2, P < 0.0001). Thus, we examined the cumulative effect of overweight or obesity in analyses limited to those who were overweight or obese at ages 70–79 years, adjusting for age, race, education, field center, smoking, alcohol consumption, and physical activity at study baseline. Among men, the hazard ratios of incident mobility limitation were 1.22 (95% confidence interval: 0.96, 1.54) for those who were overweight or obese at ages 25, 50, and 70–79 years and 1.15 (95% confidence interval: 0.92, 1.44) for those who were overweight or obese at ages 50 and 70–79 years compared with those who were overweight or obese at ages 70–79 years but not at ages 50 or 25 years (P for trend = 0.15). Among women, the hazard ratios of incident mobility limitation were 1.71 (95% confidence interval: 1.30, 2.23) for those who were overweight or obese at all 3 time points and 1.23 (95% confidence interval: 1.02, 1.47) for those who were overweight or obese at ages 50 and 70–79 years compared with those who were overweight or obese at ages 70–79 years but not earlier (P for trend = 0.0002). Further adjustment for prevalent health conditions at study baseline attenuated the associations slightly; however, the trend remained significant for women.

DISCUSSION

For both men and women, overweight and/or obesity in young, middle, and late adulthood were associated with an increased risk of incident mobility limitation in late adulthood compared with normal weight. The risk of incident mobility limitation was approximately 2.8-fold higher for women and 1.6-fold higher for men who were overweight or obese at ages 25, 50, and 70–79 years compared with being normal weight at all 3 time points. For men, the risk of incident mobility limitation was approximately 2.4-fold higher among those who were obese compared with nonobese at all 3 time points. Although not significant, there was a trend for women who were obese at all 3 time points to have a 1.7-fold higher risk of mobility limitation compared with those who were nonobese throughout. Furthermore, the risk of incident mobility limitation appeared to increase with duration of overweight and/or obesity. Among those who were normal weight at ages 70–79 years, having a history of overweight and/or obesity in midlife was associated with an increased risk of incident mobility limitation compared with those who were normal weight or nonobese at all 3 time points. Thus, being overweight and/or obese at any time during adulthood increased the risk of mobility limitation later in life, and, the longer the duration of overweight and/or obesity, the greater the risk. This finding extends prior work showing that overweight and obesity in young and middle-aged adults predicts physical disability in late life (1416).

Overweight and obesity may lead to joint wear and tear, reduced exercise capacity, and a higher rate of chronic disease such as cardiovascular disease, diabetes, and arthritis, thus resulting in physical disability. The onset of overweight or obesity in young and middle adulthood may result in lower physical activity levels, contributing to decreased muscle strength and cardiovascular fitness and greater declines in physical function because of longer duration of excess body weight and earlier onset of chronic disease. In the National Health and Nutrition Examination Survey Epidemiologic Follow-up Study, being obese or becoming obese over 20 years of follow-up was associated with higher levels of upper- and lower-body disability among adults aged 25–74 years at baseline (9). Among Finnish adults aged 55 years or older, those who reported being obese at age 30, 40, or 50 years had a 4-fold or higher increased likelihood of walking limitations, and there was a significant linear trend between duration of obesity and walking limitations (16). However, reverse causality cannot be ruled out because neither of these studies included a measure of incident disability. In the Health ABC cohort, participants who had a history of being overweight and/or obese at ages 25, 50, and/or 70–79 years had an increased risk of incident mobility limitation compared with those who were normal weight at all 3 time points. Adjustment for prevalent diabetes, cardiovascular disease, pulmonary disease, and knee pain attenuated the associations slightly; however, the associations between BMI history and incident mobility remained.

Whether overweight and/or obesity in young and middle adulthood are independent of overweight and/or obesity in late adulthood is difficult to untangle. In the Health ABC cohort, recalled BMI at ages 25 and 50 years and measured BMI at ages 70–79 years were moderately correlated (r = 0.33 and r = 0.64, respectively). This finding raises the issue of whether BMI in earlier life or attained BMI at ages 70–79 years was the driving force behind the associations seen between recalled BMI at ages 25 and 50 years and mobility limitation in late adulthood. Thus, caution must be exercised when interpreting the results. Participants who reported being overweight or obese in midlife or earlier were heavier in late adulthood than those who became overweight or obese later in life. Nonetheless, there appeared to be a graded response between age at onset of overweight and/or obesity and increased risk of mobility limitation, particularly for women. Furthermore, a history of overweight and/or obesity in midlife or earlier was associated with increased risk of incident mobility limitation among those who were normal weight at ages 70–79 years.

A limitation of the work presented here is the use of recalled weight and height from the distant past. However, previous studies have shown high correlations (r ≥0.80) between recalled and measured weight in young adulthood among middle-aged and older men and women (2123). In the Health ABC cohort, self-reported and measured weight at study baseline (ages 70–79 years) was highly correlated (r = 0.98). The correlation between recalled height at age 25 years and measured height at study baseline was also high (r = 0.93; mean difference, 3 cm). Other studies have also shown high correlations between self-reported and measured height among older adults (r ≥0.77), with a mean difference of approximately 2–3 cm (24, 25). However, the overreporting of height by older adults may be due, in part, to loss of height associated with aging (26) and may more accurately reflect height in younger adulthood. Results were similar when measured height at study baseline was used in the analysis in place of recalled height at age 25 years to calculate BMI.

Important characteristics of the Health ABC cohort limit generalization of these findings. First, participants were recruited to be well functioning and free of mobility limitation at study baseline. Thus, selection bias may have weakened the association between BMI history and incident mobility limitation because persons with a history of overweight and/or obesity may have developed mobility limitation prior to study entry and were excluded from the study. Another limitation is the use of self-reported mobility limitation as the primary endpoint. However, previous studies have shown that self-reported mobility limitation is valid and has clinical significance (27). Furthermore, the use of 2 consecutive reports of mobility limitation reduces the influence of transient mobility limitation. Use of BMI as a surrogate of body fatness is also a limitation of these analyses. Although BMI is correlated with body fatness in young and middle-aged adults, changes in body composition that accompany aging alter the relation between BMI and body fatness in older adults such that older adults have more body fat for a given BMI compared with younger adults (28). Finally, the observational nature of our study did not enable us to evaluate a causal association between BMI history and mobility limitation. It is biologically plausible that a history of overweight and/or obesity may result in mobility limitation. However, although the analyses were adjusted for behavioral characteristics such as smoking and physical activity and for prevalent health conditions at study baseline, overweight and/or obesity may serve as a proxy measure for other relevant participant characteristics that may lead to both overweight and obesity and mobility limitation.

In conclusion, overweight and obesity in young, middle, and late adulthood was associated with increased risk of incident mobility limitation in this well-functioning cohort of older adults. Those with a history of overweight and/or obesity in midlife or earlier but not in late adulthood also tended to have an increased risk of incident mobility limitation compared with those who were normal weight throughout. Furthermore, there appeared to be a graded response between age at onset of overweight and/or obesity and risk of mobility limitation. These data suggest that interventions targeting prevention of overweight and obesity in young and middle-aged adults may be useful in preventing or delaying the onset of mobility limitation later in life.

Acknowledgments

Author affiliations: Sticht Center on Aging, Wake Forest University School of Medicine, Winston-Salem, North Carolina (Denise K. Houston, Jingzhong Ding, Barbara J. Nicklas, Stephen B. Kritchevsky); Laboratory of Epidemiology, Demography, and Biometry, National Institute on Aging, Bethesda, Maryland (Tamara B. Harris); Department of Foods and Nutrition, University of Georgia, Athens, Georgia (Jung Sun Lee); Department of Epidemiology and Biostatistics, University of California, San Francisco, California (Michael C. Nevitt, Susan M. Rubin); and Department of Preventive Medicine, University of Tennessee Health Science Center, Memphis, Tennessee (Frances A. Tylavsky).

This work was supported in part by the Intramural Research Program of the National Institute on Aging, National Institutes of Health; National Institute on Aging, National Institutes of Health (contracts N01-AG-6-2101, N01-AG-6-2103, and N01-AG-6-2106); and the Wake Forest University Claude D. Pepper Older Americans Independence Center (grant P30-AG21332 to D. K. H.).

Conflict of interest: none declared.

Glossary

Abbreviations

BMI
body mass index
Health ABC
Health, Aging and Body Composition

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