Data sources
The National Health and Nutrition Examination Survey (NHANES), a program by the National Center for Health Statistics of the Centers for Disease Control and Prevention [7], contains interviews and physical examinations and aims to assess the health and nutritional status of adults and children in the United States [7]. Given the dramatic increase in elderly population in the United States, NHANES play an important role with public health agencies to increase the knowledge of the health status of this population [7]. The interviews were conducted one person at a time at the participants’ homes [7]. The study team consisted of a physician, medical and health technicians, and dietary and health interviewers [7]. The interviewers used an advanced computer system to enter data in real time [7]. The average length of an interview was 2–3 h, but examinations varied, depending on the age of the participants [7].
Study design, setting, and participants
The estimated population proportion for the target outcome is 20%, and the number of elderly people with diabetes is 12,000,000 in the United States [8]. After calculation, the minimum number of necessary samples is 246 based on the 95% confidence interval (CI) that the real value is within ±5% of the measured/surveyed value. Using the data on diabetes from the NHANES between 2007 and 2016, we identified 1572 elderly participants for this cross-sectional population-based study. Demographic characteristics (sex, age, race, education, marital status, and family poverty index ratio), health conditions (general health condition, body mass index, cigarette smoking, and alcohol drinking), comorbidities (hypertension, hypercholesterolemia, coronary heart disease, chest pain, sleep disorders, and malignancy), HRQoL (depression, worse health compared with the past year, fever in the past year, asthma attack in the past year, and visits to mental health professionals in the past year), and medical resource use (routine place to go for healthcare, doctor’s office or health maintenance organization as most often place for healthcare, clinic or health center as most often place for healthcare, emergency department [ED] as most often place for healthcare, number of healthcare visits/year, hospitalized overnight in the past year, ED visit for asthma in the past year) were included for the analyses.
Definitions of variables and outcomes
The participants were categorized into following groups: (1) no exercise (n = 1119): no habit of exercise; (2) low-intensity exercise (n = 195): having a positive habit of exercise but have not reached the level of moderate-intensity exercise; (3) moderate-intensity exercise (n = 118): at least 150 min of moderate aerobic activity (e.g., cycling or walking) or 75 min of vigorous aerobic activity (e.g., running or playing basketball) every week; and (4) high-intensity exercise: at least 300 min of moderate aerobic activity or 150 min of vigorous aerobic activity every week. Family poverty index ratio was defined as the ratio of family income to poverty [9].
Ethics statement
The NHANES is a publicly available database and approved by the National Center for Health Statistics institutional review board. All participants provided written informed consents for their participation in the NHANES. The current study was also approved by the Institutional Review Board of Kaohsiung Medical University (IRB number: KMUHIRB-EXEMPT(I)-20,190,033).
Statistical analysis
We used χ2 test for categorical variables and analysis of variance for continuous variables to compare demographic characteristics, health conditions, comorbidities, HRQoL, and medical resource use among the four groups. Multivariate logistic regressions were used to compare HRQoL and medical resource use among the four groups by adjusting for sex, age, race, education, marital status, general health condition, family poverty index ratio, body mass index, cigarette smoking, alcohol drinking, hypertension, cholesterol, chronic heart disease, chest pain, sleep disorders, and cancer. SAS 9.4 (SAS Institute Inc., Cary, NC, USA) was used for data analysis. Significance level was set at p < 0.05 (two-tailed).