Chu, Chu-Pin

Clinical risk factors for nephropathy were assessed in a population-based study of Rochester, Minnesota, residents with diabetes mellitus initially diagnosed between 1945 and 1969 (incidence cohort). The 1031 Rochester residents with non-insulin-dependent diabetes mellitus (NIDDM) were followed through their complete medical records in the community to 1 January 1982. The prevalence of persistent proteinuria was 8.2% at the diagnosis of NIDDM. Among those initially free of persistent proteinuria, the subsequent incidence was 15.3/1000 person-yr. Twenty years after the diagnosis of diabetes, the cumulative incidence of persistent proteinuria was 24.6%. A proportional hazards model identified the following risk factors for persistent proteinuria in NIDDM: elevated initial fasting blood glucose (P < .01); older age at onset of diabetes (P < .01); male gender (P = .05); and presence of macrovascular disease (P = .05), diabetic retinopathy (P = .05), or glycosuria (P = .07) at the diagnosis of diabetes. Separate analyses controlling for attained age indicated no association between duration of NIDDM and the incidence of persistent proteinuria. Stratified analysis of the two most significant risk factors (fasting blood glucose and age) indicated that hyperglycemia was a stronger risk factor for proteinuria in younger diabetic subjects, perhaps because of a competing risk of death in the elderly diabetic patient. In contrast to a recently described decreasing secular trend of proteinuria in Danish insulin-dependent diabetes mellitus patients, there was no decrease over the past 40 yr in proteinuria risk in this NIDDM incidence cohort.

The incidence and prevalence of diabetes mellitus in residents of Rochester, Minnesota, for 25 years (1945 to 1970) were determined from available medical records. The over-all incidence rate for diabetes is 133 new cases per 100,000 population per year (age-adjusted to 1970 U.S. white population). The rate increased with age for both men and women and was higher among men over 30 years of age. The average annual incidence rates per five-year period for juvenile-onset diabetes mellitus were low and variable and showed little change. Polyuria, polydipsia, glycosuria, lean habitus, loss of weight, and high levels of fasting hyperglycemia at initial diagnosis occurred more frequently in younger than in older patients. The peak incidence in 1960 through 1964 and the decrease in the following five years may be a reflection of the introduction of the AutoAnalyzer method for blood glucose in 1958. The average annual incidence rates for 1955 through 1959 and 1965 through 1969 were essentially the same. The over-all prevalence for diabetes mellitus is 1.6 per cent, with a higher rate among men than among women over 40 years of age; among school children the rate is 0.1 per cent. Survivorship in the diabetic population is lower than that in the general population. The leading cause of death was coronary heart disease, the death rate from it being higher than for the general population.

Among the 1135 Rochester residents discovered to have diabetes in the period 1945–69, the prevalence of retinopathy was 2.6% at the time of initial diagnosis. Among those free of retinopathy at diagnosis of diabetes, the subsequent incidence of any retinopathy was 17.4 per 1000 person-years and for proliferative retinopathy alone was 1.6 per 1000 person-years, based on 12,000 person-years of follow-up. The incidence rate of retinopathy was almost three times greater among residents with insulin-dependent (IDDM) than with non-insulin-dependent diabetes (NIDDM); however, the actual number of retinopathy cases was over four times greater among the more numerous residents with NIDDM. By 20 yr after diagnosis of diabetes, the cumulative incidence of retinopathy approached 70% among IDDM subjects and was 30% and 36%, respectively, among the obese and nonobese NIDDM residents. The epidemiologic patterns for proliferative retinopathy were qualitatively similar to those for nonproliferative retinopathy. The risk of blindness was greater among those with proliferative than with nonproliferative retinopathy but was substantial even for those without retinopathy. Most blindness was caused by factors other than isolated diabetic retinopathy.

In a population-based investigation among the residents of Rochester, Minnesota, the diabetes mortality rate was 8.5 per 100,000 person-years with diabetes as the underlying cause of death, 31.5 per 100,000 person-years with diabetes as an underlying or contributory cause, and 82.7 per 100,000 person-years if all deaths among diabetic individuals were counted. Diabetes was not mentioned on the certificate in 62% of the 428 diabetic deaths during 1965–1974. When the clinical characteristics of the subgroup of mortality cases in 1969 were compared with those of the prevalence cases on 1 January 1970, it was found that mortality cases tended to be older, were more often on insulin therapy, and were more likely to have macro- and microvascular complications. Because mortality data are sometimes used to infer trends and characteristics for the diabetic population at large, it is important to recognize these biases.

In a population-based study in Rochester, Minnesota, the clinical characteristics of 1135 patients newly diagnosed with diabetes (1945–69) were compared with those of 810 residents with diabetes mellitus on prevalence day (1 January 1970). The prevalence patients were older and the male:female ratio was reduced from that seen among incidence cases. The prevalence patients were more likely to be on oral agents, had lower fasting blood glucose levels, were less likely to be symptomatic, but were more likely to have macrovascular and microvascular complications. These differences seemed to come about as a result of variation in survival rates among patients with specific characteristics, differential migration of certain groups of patients, and changes in the status of individuals.

The incidence of diabetes mellitus by clinical type was determined for the community of Rochester, Minnesota, 1945–69. Overall adjusted incidence rates per 100,000 person-years were 8.4 for IDDM, 80.1 for obese NIDDM, 45.6 for nonobese NIDDM, and 3.6 for secondary diabetes, using our definitions. Strict use of National Diabetes Data Group criteria would have reduced the apparent incidence of all diabetes by about 20% through the deletion of NIDDM cases. The National Diabetes Data Group classification improved the clinical homogeneity of IDDM patients compared with “juvenile-onset” diabetes but had little effect on NIDDM relative to “maturity-onset” diabetes, since essentially the same patients were included in both groups. Separation of NIDDM into obese and nonobese subcategories accomplished little in the way of defining two more homogeneous subgroups.