Loprinzi PD, Brodowicz GR, Sengupta S, Solomon SD, Ramulu PY. Accelerometer-Assessed Physical Activity and Diabetic Retinopathy in the United States. JAMA Ophthalmol. 2014;132(8):1017-1019. doi:10.1001/jamaophthalmol.2014.402
Hemoglobin A1c (HbA1c) and blood pressure currently represent the only reversible risk factors associated with diabetic retinopathy.1 Physical activity (PA) is another potential modifiable risk factor for preventing diabetic ocular complications, although studies investigating this association have produced conflicting results.2 These studies have relied exclusively on self-report to quantify PA, which is prone to considerable error. Herein, we assess whether accelerometer-defined PA is associated with more advanced retinopathy independent of HbA1c level and blood pressure in a nationally representative sample of patients with diabetes mellitus.
Data from the 2005 to 2006 National Health and Nutrition Examination Survey were used. All study procedures were approved by the National Center for Health Statistics review board, and all participants provided written informed consent.
Diabetes was defined by self-report of a previous diabetes diagnosis, use of insulin or diabetes medications, an HbA1c level of 6.5% of total hemoglobin or higher (to convert to proportion of total hemoglobin, multiply by 0.01), or a fasting glucose level of 126 mg/dL or higher (to convert to millimoles per liter, multiply by 0.0555).
Retinal imaging was performed using the Canon Nonmydriatic Retinal Camera CR6-45NM, with details reported elsewhere.3 The presence and severity of nonproliferative diabetic retinopathy (NPDR) (none, mild, or moderate to severe) was determined using the Early Treatment Diabetic Retinopathy Study grading criteria.4
The participants’ PA was measured during waking hours in participants with at least 4 days of 10 h/d or more of accelerometer wear time using the Actigraph 7164 accelerometer. Activity counts of 2020/min or greater were classified as moderate to vigorous PA.
Analyses were performed with Stata version 12.0 statistical software (StataCorp LP) using survey data procedures. Multinomial regression was used to examine the association between PA (independent variable) and presence of NPDR, with no retinopathy serving as the reference group. Analyses were stratified by sex, with race/ethnicity, comorbid illness, smoking status, visual acuity, mean arterial pressure, serum cholesterol level, HbA1c level, homocysteine level, and functional disability included as covariates.
Analyzed participants (n = 282) were older than those excluded owing to missing accelerometer or covariate data (n = 162) (mean age, 62.2 vs 58.5 years; P = .01), but differences with respect to the other variables were not identified (P > .05 for all) (Table 1).
Post hoc analyses were computed separately for each sex. After adjustments, the odds ratio (OR) for moderate to vigorous PA for men with moderate to severe NPDR was 0.98 (95% CI, 0.95-1.01) (Table 2); when expressed as 10- and 20-minute changes, men were 16% (OR = 0.84; P = .25) and 29% (OR = 0.71; P = .25) less likely to have moderate to severe NPDR, respectively. Compared with those with no retinopathy, moderate to vigorous PA was associated with moderate to severe NPDR for women (OR = 0.86; 95% CI, 0.76-0.98) (Table 2). When expressed as 10- and 20-minute changes, women were 76% (OR = 0.24; P = .02) and 94% (OR = 0.06; P = .02) less likely to have moderate to severe NPDR, respectively.
To our knowledge, this is the first study to examine the association between objectively measured PA and NPDR. Women with more PA had reduced odds of more advanced diabetic retinopathy, and this association persisted even after adjusting for visual acuity (known to predict less activity) and other predictors of prevalent retinopathy, including a higher HbA1c level and higher blood pressure.
Physical activity benefits vascular endothelial function,5 and these benefits may be partially independent of blood pressure and HbA1c level, providing a biological explanation for our findings. Only women showed a statistically significant association between PA and retinopathy, while men demonstrated a nonsignificant association in the same direction. Other reports have also shown a stronger association between PA and health for women.6 Our cross-sectional design cannot exclude the possibility that diabetic retinopathy may have influenced PA through unmeasured factors (eg, fatigue, neuropathy). Longitudinal studies are required to establish whether PA can indeed protect against retinopathy and to determine whether PA regimens can help improve ocular outcomes in patients with diabetes.
Corresponding Author: Paul D. Loprinzi, PhD, Department of Exercise Science, Bellarmine University, Donna and Allan Lansing School of Nursing and Health Sciences, Louisville, KY 40205 (firstname.lastname@example.org).
Author Contributions: Dr Loprinzi had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Loprinzi, Brodowicz.
Acquisition, analysis, or interpretation of data: Loprinzi, Sengupta, Solomon, Ramulu.
Drafting of the manuscript: Loprinzi, Brodowicz.
Critical revision of the manuscript for important intellectual content: Loprinzi, Sengupta, Solomon, Ramulu.
Statistical analysis: Loprinzi.
Administrative, technical, or material support: Solomon.
Study supervision: Ramulu.
Conflict of Interest Disclosures: None reported.