Letters to the Editor
Cardiovascular Risk Factors in Elderly Diabetics
1. The subjects improved their glucose intolerance by weight reduction etc. 2. The diagnosis was made prior to 1979, and would have been labelled as impaired glucose tolerance today [4], 3. T h e subjects were not properly classified initially.
S. CROXSON
Department of Geriatric Medicine, Northern General Hospital, Sheffield S5 7AU 1. Maggi S, Bush TL, Hale WE. Diabetes mellitus and other cardiovascular risk factors in an elderly population. Age Ageing 1990;19:173-8. 2. WHO Study Group. Diabetes mellitus. WHO Tech Rep Ser 727. W.H.O.; Geneva: WHO, 1985. 3. Harris MI, Hadden WC, Knowler WC, Bennett PH. Prevalence of diabetes and impaired glucose tolerance and plasma glucose levels in U.S. population aged 20 74 yr. Diabetes 1987;36:523 34. 4. Jarrett RJ. Do we need IGT? Diabetic Med 1987;4:5445. 5. Mather HM, Keen H. The Southall diabetes survey: Br l:\0%\ 3.
On the other hand, is the non-diabetic group truly The above letter was referred to Dr Maggi and non-diabetic? In the Southall diabetes survey, colleagues who offer the following reply: approximately 16° o of patients attending a diabetic SIR Dr Croxson hypothesizes that we found no clinic were not identified when surveyed at their differences in cholesterol levels and body weight front door [5]. NHAXES 2 found prevalences of between our diabetic and non-diabetic population diabetes in white Caucasians aged 65 to 74 of 8.9°O because diabetes status may have been misclassified. previously diagnosed and 9.0° o newly diagnosed by That is, some of our diabetic patients may not have G T T . Thus it is highly likely that about 9 ° o of the been 'truly' diabetic, and some of our non-diabetic authors' non-diabetic group were diabetic and the patients may have had diabetes. Several reports are remainder would include those with impaired glu- cited documenting that misclassification of diabetes cose tolerance (IGT) (prevalence 23° O in NHANES status can occur in studies. This issue of misclassifi2) which is itself associated with vascular disease. cation is an important one and theoretically could The prevalence of undiagnosed diabetes and I G T explain the lack of an association in our study. is much lower in younger populations [3]; here, However, we believe that misclassification of diatherefore, the association between diabetes and betes status in our report is low for reasons listed hypercholesterolaemia is not confounded by many below. young subjects with undiagnosed glucose intolerFirst, as noted, there is nearly perfect agreement ance. But in the present study [1] the lack of between the self-report of diabetes on our annual Age and Ageing 1991 ;20:70-71
Downloaded from http://ageing.oxfordjournals.org/ at University of Sussex on June 7, 2016
SIR—S. Maggi et al. [1] were puzzled that their diabetic group had lower cholesterol levels and weights than their non-diabetic group. I may have an explanation. The diagnosis of diabetes appears to have been based on the patients' beliefs; the authors state that in the majority of cases a diagnosis of diabetes was 'noted in the medical records'. This is what one would expect; it is normal for patients to get information about their medical conditions from their doctors. However, we are not told whether there were any records of plasma glucose values diagnostic of diabetes in these subjects [2]. The NHANES 2 survey examined the prevalence of diabetes across the USA [3]; of 100 self-reported non-insulindependent diabetics, 19 (on diet alone) were completely normal on performing a glucose tolerance test ( G T T ) . There are three possible reasons for this paradox:
associations with diabetes may well be that the glucose tolerance status of the diabetic and nondiabetic groups is not quite what the authors believe it to be. Other explanations for the lack of association do include a possible bias of the healthier diabetics to migrate to Dunedin, and/or to participate in healthscreening surveys.
Cardiovascular Risk Factors in Elderly Diabetics
1. The subjects improved their glucose intolerance by weight reduction etc. 2. The diagnosis was made prior to 1979, and would have been labelled as impaired glucose tolerance today [4], 3. T h e subjects were not properly classified initially.
S. CROXSON
Department of Geriatric Medicine, Northern General Hospital, Sheffield S5 7AU 1. Maggi S, Bush TL, Hale WE. Diabetes mellitus and other cardiovascular risk factors in an elderly population. Age Ageing 1990;19:173-8. 2. WHO Study Group. Diabetes mellitus. WHO Tech Rep Ser 727. W.H.O.; Geneva: WHO, 1985. 3. Harris MI, Hadden WC, Knowler WC, Bennett PH. Prevalence of diabetes and impaired glucose tolerance and plasma glucose levels in U.S. population aged 20 74 yr. Diabetes 1987;36:523 34. 4. Jarrett RJ. Do we need IGT? Diabetic Med 1987;4:5445. 5. Mather HM, Keen H. The Southall diabetes survey: Br l:\0%\ 3.
On the other hand, is the non-diabetic group truly The above letter was referred to Dr Maggi and non-diabetic? In the Southall diabetes survey, colleagues who offer the following reply: approximately 16° o of patients attending a diabetic SIR Dr Croxson hypothesizes that we found no clinic were not identified when surveyed at their differences in cholesterol levels and body weight front door [5]. NHAXES 2 found prevalences of between our diabetic and non-diabetic population diabetes in white Caucasians aged 65 to 74 of 8.9°O because diabetes status may have been misclassified. previously diagnosed and 9.0° o newly diagnosed by That is, some of our diabetic patients may not have G T T . Thus it is highly likely that about 9 ° o of the been 'truly' diabetic, and some of our non-diabetic authors' non-diabetic group were diabetic and the patients may have had diabetes. Several reports are remainder would include those with impaired glu- cited documenting that misclassification of diabetes cose tolerance (IGT) (prevalence 23° O in NHANES status can occur in studies. This issue of misclassifi2) which is itself associated with vascular disease. cation is an important one and theoretically could The prevalence of undiagnosed diabetes and I G T explain the lack of an association in our study. is much lower in younger populations [3]; here, However, we believe that misclassification of diatherefore, the association between diabetes and betes status in our report is low for reasons listed hypercholesterolaemia is not confounded by many below. young subjects with undiagnosed glucose intolerFirst, as noted, there is nearly perfect agreement ance. But in the present study [1] the lack of between the self-report of diabetes on our annual Age and Ageing 1991 ;20:70-71
Downloaded from http://ageing.oxfordjournals.org/ at University of Sussex on June 7, 2016
SIR—S. Maggi et al. [1] were puzzled that their diabetic group had lower cholesterol levels and weights than their non-diabetic group. I may have an explanation. The diagnosis of diabetes appears to have been based on the patients' beliefs; the authors state that in the majority of cases a diagnosis of diabetes was 'noted in the medical records'. This is what one would expect; it is normal for patients to get information about their medical conditions from their doctors. However, we are not told whether there were any records of plasma glucose values diagnostic of diabetes in these subjects [2]. The NHANES 2 survey examined the prevalence of diabetes across the USA [3]; of 100 self-reported non-insulindependent diabetics, 19 (on diet alone) were completely normal on performing a glucose tolerance test ( G T T ) . There are three possible reasons for this paradox:
associations with diabetes may well be that the glucose tolerance status of the diabetic and nondiabetic groups is not quite what the authors believe it to be. Other explanations for the lack of association do include a possible bias of the healthier diabetics to migrate to Dunedin, and/or to participate in healthscreening surveys.
