Ohio death certificate index

OBJECTIVE--To determine whether impaired pulmonary function is a significant predictor of the incidence of diabetes.

RESEARCH DESIGN AND METHODS--Using data from the National Health and Nutrition Examination Survey Epidemiologic Follow-Up Study, a cohort study of a representative sample of U.S. adults, we examined the prospective associations between pulmonary function and incidence of diabetes. Our analyses included 4,830 U.S. men and women aged 23-74 years who had a baseline interview and examination (including spirometry) from 1971 through 1975 and were followed through 1992-1993. Incident diabetes (n = 443) was based on self- or proxy reports, hospitalization, or death certificates.

RESULTS--After multiple adjustment, forced expiratory volume in 1 s (FE[V.sub.1]), forced vital capacity (FVC), percentage of predicted FE[V.sub.1], and percentage of predicted FVC were significantly and inversely associated with the incidence of diabetes, but the ratio of FE[V.sub.1] to FVC was not. Obstructive lung disease (defined by the Global Initiative for Chronic Obstructive Lung Disease classification) was not significantly associated with the incidence of diabetes, but restrictive lung disease was (hazard ratio = 1.45, 95% CI 1.04-2.03). The association did not differ significantly by smoking status.

CONCLUSIONS--Although several prospective studies have found that impaired pulmonary function may increase the risk for developing diabetes, additional research is needed to better understand these relationships and their possible implications.

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Lung function may predict the development of insulin resistance or diabetes (1-4). In the Normative Aging Study (2), forced vital capacity (FVC), forced expiratory volume in 1 s (FE[V.sub.1]), and maximal mid-expiratory flow rate (MMEF) were associated with insulin resistance over a period of 20.9 years. In addition, three Swedish studies with follow-ups of 6-13.9 years found that impaired lung function predicted the development of diabetes (1,3,4). In all three studies, low levels of FVC were associated with increased risk; in one, FE[V.sub.1] was inversely associated with incidence.

To provide another perspective on the possible association between lung function and incidence of diabetes, we analyzed data from the National Health and Nutrition Examination Survey Epidemiologic Follow-Up Study (NHEFS), a cohort study. We studied possible prospective associations between measures of pulmonary function, including FE[V.sub.1], FVC, percentage of predicted FE[V.sub.1], percentage of predicted FVC, and the ratio of FE[V.sub.1] to FVC, and incidence of diabetes. In addition, we examined the association between different forms of lung disease--chronic obstructive pulmonary disease as classified by the Global Initiative for Chronic Obstructive Lung Disease (GOLD), restrictixe lung disease, and respiratory symptoms--and the incidence of diabetes.

RESEARCH DESIGN AND METHODS--In 1971-1975, a representative sample of the U.S. civilian population received a baseline examination and interview as part of the first National Health and Nutrition Examination Survey (NHANES I). The sample was selected using a complex sampling design so that results would be representative of the noninstitutionalized civilian population. Participants aged 25-74 years (n = 14,407) were followed up through 1992-1993 and thus became part of the NHEFS. Details of the NHANES 1 and the NHEFS are available elsewhere (5-11).

During the follow-up study, up to four attempts were made to contact participants or their surrogates in person and, during later follow-ups, by telephone as well: this occurred in 1982-1984, 1986 (only participants aged [greater than or equal to] 55 years), 1987, and 1992-1993. Permission was requested to obtain hospital records. Deaths were identified through searches of the National Death Index, enrollee files of the Health Care Financing Administration, and other tracing mechanisms. A participant was considered deceased only if a death certificate had been received or a proxy interview had been completed to verify the death. Death certificates have been obtained for 97% of participants who died through 1993.

Participants had incident diabetes if 1) during any of the four follow-up contacts, they reported that they had ever been told by a doctor that they had diabetes; 2) a hospitalization record listed the ICD-9-CM code 250 as any 1 of 10 diagnoses on the hospital discharge sheet; or 3) the death certificate included the ICD-9 code 250. Participants who reported that they had diabetes were asked the year of disease onset. The midpoint of that year was designated as the date of onset. For participants who did not report a year of onset, we assigned the midpoint between the last date of known contact and the date of the most recent interview. The date of onset was chosen as the date the condition was first reported or recorded on institutional records or death certificates.

Participants who reported at baseline that they had diabetes were considered prevalent cases, as were participants who during later follow-up contacts reported a date of onset that occurred in the year of their baseline interview or earlier, and they were excluded from the analyses.

The pulmonary symptoms included in the analysis, which were used to define an asymptomatic subset of the population to calculate equations for lung function and define a subset of the cohort with only respiratory symptoms, were cough (defined as a positive response to "Have you ever had a cough first thing in the morning in the winter?" or "Have you ever had a cough first thing in the morning in the summer?"), sputum (defined as a positive response to "Have you ever had any phlegm from your chest first thing in the morning in the winter?" or "Have you ever had any phlegm from your chest first thing in the morning in the summer?"), and wheeze (defined as a positive response to "Have you ever had wheezy or whistling sounds in your chest?").

Spirometry was obtained by using an Ohio Medical Instruments 800 spirometer. The procedures used have been documented previously (6). Individuals were excluded from this analysis if they either did not perform spirometry or had results that were not reliable. We included data from participants who did not have "reproducible" measures (12). (To be reproducible the FE[V.sub.1] and FVC from two reliable measurements had to be within 5% for most participants.) Values used in this analysis included the FVC, FE[V.sub.1], and the FE[V.sub.1]-to-FVC ratio. We determined predicted values of FE[V.sub.1] and FVC by performing linear regression (stratified by sex and by using age and height as predictors) on a subgroup of participants who were white never smokers who did not report respiratory symptoms or physician-diagnosed lung disease. The results from these regression models (men: FE[V.sub.1] = -4.3806 - age x 0.031767 + height x 0.13827, [r.sub.2] = 0.626, and FVC = -7.49837 - age x 0.03071 + height x 0.19794, [r.sup.2] = 0.589; women: FE[V.sub.1] = -0.75683 - age x 0.02475 + height X 0.07131, [r.sup.2] = 0.539, and FVC = -2.2086 - age x 0.02394 + height x 0.10381, [r.sup.2] = 0.451) were applied to the data from all participants to obtain predicted values of FE[V.sub.1] and FVC. We used an adjustment factor of 0.88 to estimate predicted values for African-American participants.

Using the percentage of predicted FE[V.sub.1], percentage of predicted FVC, the FE[V.sub.1]-to-FVC ratio, and the presence of respiratory symptoms, we used a modification of the GOLD criteria to classify participants as having chronic obstructive pulmonary disease (COPD). Participants had mild COPD if they had a FE[V.sub.1]-to-FVC ratio <0.70 and a percentage of predicted FE[V.sub.1] [greater than or equal to] 80%). Because too few participants had severe or very severe COPD, we combined them and participants who had moderate COPD into a single group (FE[V.sub.1]-to-FVC ratio <0.70 and percentage of predicted FE[V.sub.1] <80%). In addition, we assigned participants as having restrictive lung disease (RLD) (FE[V.sub.1]-to-FVC ratio [greater than or equal to]0.70 and FVC <80% predicted), symptoms only (presence of respiratory symptoms in the absence of any lung function abnormality), and no lung disease. As per GOLD criteria, we assigned participants who met the criteria for having both COPD and RLD to the COPD group.