Trends in the prevalence and incidence of diabetes : non-insulin-dependent diabetes mellitus / Hilary King & Paul Zimmet

- 190 - TRENDS IN THE PREVALENCE AND INCIDENCE OF DIABETES: NON-INSULIN-DEPENDENT DIABETES MELLITUS Hilary King a & Paul Zimmet b In contrast to insulin-dependent diabetes (IDDM), non- insulin-dependent diabetes (NIDDM) generally has its onset in later life. The two forms of diabetes are now seen as distinct disorders, both etiologically and patho- logically, and this distinction has been of considerable importance in understanding their respective epidemio- logies. Whilst IDDM is rare in developing countries, NIDDM reaches its highest prevalence in non-European commu- nities. Genetic predisposition to NIDDM appears to vary between populations, and in susceptible subjects certain potentially modifiable precipitants of the disease are strongly suspected. Of these, the three most important appear to be obesity, low levels of habitual physical activity, and aspects of the modern diet. The close asso- ciation between these factors and the imprecision of their measurement have hindered the exploration of their influence in different populations. Although there has been considerable research activity in the field of the epidemiology of NIDDM in the present decade, there has been a regional imbalance in this regard, and our knowledge of the subject remains very inadequate for large areas of the world. Epidemiological considerations A serious constraint upon the interpretation of reports of the frequency of diabetes is that criteria for the diagnosis of the disease have varied widely in the past. Many reports failed to record their criteria clearly, and many also failed to distinguish between NIDDM and IDDM. For diabetes epidemiology, therefore, one of the major achievements of the present decade has been the pro- vision of clear and unambiguous guidelines for the clas- sification and diagnosis of the disease ( 1 ). Since it is well known that considerable discrepancies can occur in esti- mates of disease frequency when study methods and diagnostic criteria vary, this review will concentrate on some of the recent studies which have attempted to use the criteria recommended by WHO ( 1 ). For convenience, migrant communities, including the large non-indigenous populations in North America, Australia and New Zealand, will be considered together with other popu- lations in their region of origin. Most of the evidence regarding the frequency of NIDDM in populations comes from surveys carried out at a single point in time. This approach may be used to determine • Consultant, Division of Noncommunicable Diseases, World Health Organization, Geneva. b Director, WHO Collaborating Centre for the Epidemiology of Dia· betes Mellitus, Lions International Diabetes Institute, Caulfield South. Victoria. Australia. c Prevalence of IDDM appears to be so low in most non-industrialized societies that prevalence of diabetes may be taken as an approximation to that of NIDDM in such situations. NIDDM prevalence (i.e. the proportion of the population suffering from the disease at that point in time). The incidence of NIDDM (i.e. the number of new cases occur- ring in the population in a specified period of time) can only be calculated by monitoring the population contin- uously, or by repeated cross-sectional surveys. The resources required for ·such studies are often considera- ble. Furthermore, it is well known that a substantial pro- portion of subjects with NIDDM remain undetected in the community, and incidence estimates based upon routine data sources are much less reliable than they may be for IDDM. For these reasons, comparatively few estimates of inci- dence of NIDDM have been reported. In this review we will therefore consider prevalence estimates for NIDDM first, before discussing the few incidence estimates that are available. Unfortunately, prevalence estimates also present problems in interpretation, even when standard- ized study methods have been used, since prevalence depends on both incidence and survival, and the latter can vary between populations for many reasons. Since diabetes becomes more prevalent with advancing age in almost all communities, differences in age struc- ture between populations can also lead to misleading comparisons, unless these differences are allowed for statistically. Although this has been done in some cases (in a series of standardized surveys in the various com- munities of the Western Pacific, for example), world- standardized rates are not yet available for NIDDM, and most estimates reported here are crude figures. To date, few reports of incidence or prevalence of NIDDM have included confidence intervals or other esti- mates of precision. This creates further difficulties in the interpretation of population comparisons. It is important to be aware of all these constraints when reviewing global patterns of a disease such as NIDDM. Prevalence of NIDDM Some recent estimates of the prevalence of NIDDM, c using the WHO criteria, are summarized in Table 1. Africa Population-based reports of diabetes in Africa are un- common, though a few have appeared recently. Ahren & Corrigan (2) determined the prevalence of dia- betes according to WHO criteria in the north-western part of the United Republic of Tanzania. Prevalence in subjects over the age of 20 was 1.6%. Three separate communities were included in the study, two of which were in rural locations. Interestingly, prevalence was 2.5% in the rural-dwelling Haya tribe, as compared with 0.5% in the rural Sukuma. Prevalence in the urban area of Rapp. trimest. statist. sanit. mond., 41 (1988) - 191 - TABLE 1. SOME RECENT ESTIMATES OF THE PREVALENCE (PER CENT POPULATION) OF NON-INSULIN-DEPENDENT DIABETES (NIDDM) IN VARIOUS POPULATIONS USING CRITERIA RECOMMENDED BY WHO• TABLEAU 1. ESTIMATIONS RECENTES DE LA PREVALENCE (POURCENTAGE DE LA POPULATION) DU DIABETE SUCRE NON INSULINO-DEPENDANT (DSNID) DANS DIFFERENTES POPULATIONS, EN APPLIQUANT LES CRITERES RECOMMANDES PAR L·oMs• Region of origin/population Region d'origine/population Africa - Afrique Bantu - bantoue mixed (rural) - differentes ethnies (rurale) . . . . . mixed (rural) - differentes ethnies (rurale) black - noire . . . . . . Americas - Ameriques Pima .......... . Mapuche ........ . Country - Pays United Rep. of Tanzania - Republique-Unie de Tanzanie Mali Togo United States - Etats-Unis United States - Etats-Unis Chile - Chili South-East Asia - Asie du Sud-Est Indian - indienne rural - rurale . . . . urban - urbaine . . . Indian (urban) - indienne (ur- baine) Indian - indienne Malay - malaise Chinese - chinoise Indonesian (urban) - lndonesie (urbaine) .......... . Europe rural - rurale white - blanche white - blanche Fiji - Fidji South Africa - Afrique du Sud Singapore - Singapour Singapore - Singapour Singapore - Singapour Indonesia - lndonesie Italy - ltalie United States - Etats-Unis Australia - Australie Eastern Mediterranean - Mediterranee orientale Arab - arabe . . Tunisia - Tunisie rural - rurale urban - urbaine Western Pacific - Pacifique occidental Micronesian - micronesienne Micronesian - micronesienne rural - rurale . . . . . . urban - urbaine Polynesian - polynesienne Melanesian (AN)c - melane- sienne (AN) c . . . . . . . . rural - rurale . . . . . . . . urban - urbaine . . . . . . . Melanesian (NAN) d - melane- sienne (NAN) d . . . . . . . . Melanesian (NAN) - melane- sienne (NAN) rural - rurale urban - urbaine Aboriginal (urban) - aborigene (urbaine) ..... . • Reference (1) - Reference (I). Nauru Kiribati Rarotonga Niue Wallis Island - Wallis Fiji - Fidji Papua New Guinea highlands - Papouasie-Nouvelle-Guinee, montagnes Solomon Islands - lies Salomon Australia - Australie b Note discrepancies in age ranges - Observer les difMrences de tranches d'lge. c AN: Austronesian ancestry - d'ascendance austronesienne. d NAN: non-Austronesian ancestry - d'ascendance non austronltsienne. Mwanza was 1.9%. Whilst the authors considered that these differences had implications for the planning of national health services, it appears from the report (2) that the differences between the three groups were not in fact statistically significant after allowing for differ- ences in their age/sex distribution. This emphasizes the Wld hlth statist. quan .. 41 ( 1988) Reference - Reference Ahren & Corrigan (2) Fisch et al. (3) Teuscher et al. (4) Harris et al. (5) Knowler et al. (7) Larenas et al. (9) Zimmet et al. (15) Omar et al. (16) Thai et al. (19) ibid. ibid. Waspadji et al. (20) Verrillo et al. (12) Harris et al. (5) Glatthaar et al. (14) Papoz et al. (11) Zimmet et al. (24) King et al. (25) King et al. (26) ibid. Taylor et al. (2 7) Zimmet et al. (15) King et al. (28) Eason et al. (29) Cameron et al. (30) Age range 0 Tranche d'Age 0 (years/ans) ~ 20 ~ 15 all ages tous ages 20-74 ~ 20 ~ 20 ~ 20 ~ 15 ~ 18 ~ 18 ~ 18 ~ 15 ~ 18 20-74 ~ 25 ~ 20 ~ 20 ~ 20 ~ 20 ~ 20 ~ 20 ~ 20 ~ 20 ~ 18 ~ 20 M (%) 1.3 0.8 0.0 8.6 32.6 0.4 12.7 14.1 7.6 12.5 9.1 4.3 1.8 6.6 5.5 5.1 2.3 4.6 24.6 3.6 8.1 5.5 5.3 1.4 1.7 4.8 0.0 0.0 0.0 16.7 F (%) 1.8 1.0 0.0 11.0 37.2 1.4 12.9 12.3 13.5 4.8 6.1 3.6 1.5 6.8 7.3 3.7 0.6 3.5 23.9 3.6 7.4 8.0 9.1 3.5 1.7 8.2 0.0 1.4 1.5 14.6 need for careful evaluation of apparent differences in rates of disease. A further constraint in this study, which the authors acknowledged, was that fasting blood- glucose concentration was used as an initial screening test for glucose intolerance. This is known to be a rela- tively insensitive measure, as compared with the blood- - 192 - glucose concentration after an oral glucose challenge, and the prevalence of diabetes could therefore have been underestimated. Another study which used the WHO criteria, but was based entirely upon fasting blood-glucose estimation, estimated prevalence of diabetes as 1 % in rural Mali (3). A further report from Western Africa, using WHO cri- teria and random blood-glucose estimation, failed to identify any diabetic subjects among 517 survey respondents in rural Togo (4). However, diabetes was known at the local hospital. These three studies suggest that the prevalence of NIDDM is low in rural Africans at the present time. Although the difficulties attending field surveys in such areas should not be forgotten, these reports also illus- trate some persisting discrepancies in study methods. A report based upon the National Health and Nutrition Examination Survey (NHANES 2) suggests that NIDDM is more prevalent in black than in white North Americans in the United States, with approximately 10% of the former suffering from the disease (5). Thus, it may be that Afri- can genes carry greater underlying susceptibility to NIDDM than do Caucasian genes, and there may be a potential for a rise in the prevalence of NIDDM in Africa, as nations become more industrialized. There was the opposite suggestion, however, from the Mali data (3). In that survey, negroid ethnic groups appeared to be less affected than Caucasian or part-Caucasian communities. This raises the possibility that Caucasian genetic admix- ture might, in part, be responsible for the increased sus- ceptibility of blacks in the United States. A clinic-based report from Soweto (6) suggested a pre- valence of known diabetes of only 0. 1 %. It also found approximately half of the diabetic subjects to be treated with insulin. Taken together, these two findings may suggest considerable under-ascertainment of milder cases of NIDDM in South African blacks. Thus, the real status of NIDDM in the public health of Africa is far from clear. Further population surveys, par- ticularly of urban communities and incorporating the recommended 75 g oral glucose challenge (1) could yield much useful information. The Americas There is abundant evidence that indigenous North Americans are highly susceptible to NIDDM. The com- munity with the highest reported prevalence of NIDDM in the Americas is the Pima Indians of Arizona (7) in which approximately one-third of all adults are affected. It also appears that for indigenous North Americans, susceptibility to NIDDM is related to proportional Amer- indian genetic admixture, with subjects of mixed ethnic- ity having a risk of NIDDM intermediate between that of full-blood American Indians and Caucasians (8). There is some evidence to suggest that the prevalence of NIDDM is increasing in many North American Indian commu- nities and that the Aleuts (related to the Eskimos) who were formerly thought to be relatively resistant to NIDDM, may now be suffering from it also. The picture in South America is not so clear, and in many ways resembles the state of our knowledge of NIDDM in Africa. The prevalence of diabetes in the indigenous Mapuches of Chile was recently estimated as only 1 % (9). A prevalence of 5% has been reported from La Plata City (Argentina) (10) and this may have been an underestimate, since the survey was based upon a 50 g oral glucose challenge. Urban communities throughout Latin America would benefit from further investiga- tion. The Eastern Mediterranean Little information is available on NIDDM in this Region also. A study in Tunisia, using WHO criteria, has recently estimated age-standardized prevalence as a percentage of the population to be 4.6 in males and 3.5 in females in urban Tunis, as compared with 2.3 in males and 0.6 in females in a rural area (11). Since these figures could be conservative.due to the use of fasting blood-glucose estimation only. NIDDM would appear to be of potential public health concern in urban populations in this Region also. Europe, and populations of European origin In Europeans, NIDDM is a relatively common disorder, but it does not reach the frequency seen in high-risk communities in the developing world. There have been surprisingly few population studies of NIDDM using WHO criteria in Europe itself. A survey in rural Italy ( 12) estimated the prevalence of diabetes as 6.8% in females and 6.6% in males. A sur- vey in Finland, a country with the highest reported pre- valence of IDDM in the world, suggested that approxi- mately one-third of elderly male Finns may have NIDDM (13). Recent information from Malta (A. Schranz, personal communication) suggests a prevalence of 10% in the total adult population of the island. For whites in the United States, data on the prevalence of NIDDM were obtained nationwide during the NHANES 2 survey (5). This estimated the prevalence of diabetes in the 20-75 years age range as 6.6%, according to WHO criteria, which is very close to the Italian figure (12). Approximately one-half of subjects were undiagnosed prior to the survey. Prevalence rose from 2% in the 20- 44 years age range, to 18% in the 65-74 years age range. Thus, at the present time, almost one-fifth of white North Americans can expect to develop NIDDM if they live to the seventh decade of life. This somewhat alarming find- ing highlights the potential for an escalation in prevalence of NIDDM in European communities, as a result of the increasing longevity which most industrialized societies are experiencing at present. A somewhat lower estimate of the prevalence of NIDDM has been reported for white Australians (14). South-East Asia Present evidence suggests that there is a spectrum of underlying genetic susceptibility to NIDDM in Asian populations. Several surveys of migrants from the Indian subcontinent have suggested that Indians are the most susceptible. According to WHO criteria, prevalence has been reported as 12-14% in Indian migrants to Fiji (15). A high prevalence has also been reported in Indians living in South Africa (16) and Suriname (17). A number of population studies of diabetes have been reported from South-East Asia itself, but study methods have varied widely. These reports have been reviewed elsewhere (18). Rapp. trimest. statist. sanit. mond .. 41 (19881 - 193 - A recent study in Singapore (19) found prevalence to be lowest in Chinese, highest in Indians and intermediate in Malays. There was also a suggestion of an apparent secular increase in prevalence since a previous survey a decade earlier. A survey in urban Jakarta (Indonesia) (20) found a pre- valence of only 1.6%, slightly lower than the figure of 2. 7% reported for migrant Indonesians in Suriname (17). As already noted for Indians, it is not uncommon for migrant communities to show a higher prevalence of NIDDM than those they leave behind, since migration is often accompanied by socioeconomic advancement. As in the Singapore study, the conclusions of the major- ity of comparative studies in South-East Asia have been that Chinese have the lowest prevalence of diabetes in the Region, with other populations having rates interme- diate between the high rates of the Indians and the low rates of the Chinese. However, recent reports from Taiwan (21) and Hong Kong (22) have recorded a preva- lence of approximately 10% in urban Chinese over the age of 60 years, suggesting that Chinese may be more susceptible than was formerly supposed. The Western Pacific There have been a number of studies of diabetes in the Western Pacific using the WHO criteria, and our knowl- edge of the prevalence of NIDDM in this Region is becom- ing relatively complete. This large data base will be of great value in due course, for monitoring temporal trends and evaluating the effects of interventions aimed at pri- mary and secondary prevention of the disease. Age- standardized prevalence according to WHO criteria in adults in 17 communities from 10 Pacific nations have been published elsewhere (23). The highest prevalence of NIDDM in the Western Pacific has been reported from the Micronesian population of Nauru (24) where approximately one-quarter of all adults are affected. Other Micronesian populations are also very susceptible. In neighbouring Kiribati, approximately 8% of urban residents of both sexes were found to have NIDDM, as compared with 4% of residents of a more traditional island (25). When standardized for age, the risk for urban dwellers was threefold that of the rural community. For Polynesia, a recent report estimated prevalence as approximately 5% in males and 8% in females in both Rarotonga (Cook Islands) and Niue (26). Taylor et al. (27) have demonstrated a low prevalence among traditional- living Polynesians on Wallis Island. There is still some uncertainty as to the true susceptibil- ity of Melanesians to NIDDM. Though the majority (of Austronesian ancestry) may be as susceptible as Poly- nesians (15), there is some evidence that the few Mela- nesian communities that lack Austronesian genetic an- cestry (nonAustronesians) may be relatively resistant to NIDDM (28, 29). NIDDM is now common in urbanized Australian Abori- gines (30). Incidence of NIDDM There have been very few population-based estimates of NIDDM incidence, due to the practical difficulties of ascertaining occurrence of NIDDM in populations, when a substantial proportion of subjects meeting the WHO criteria for the disease remain asymptomatic. For the Wld hlth statist. quart., 41 (1988) United States, an estimate of physician-diagnosed dia- betes-which may be expected to underestimate total incidence by as much as 50% (5)-gave an incidence of 117 per 100 OOO person-years for three communities in Minnesota (31 ). This figure concurs with a previous report from Rochester, Minnesota. Both the Pima Indians of Arizona and the Nauruans of Micronesia have been intensively studied with respect to NIDDM, and incidence estimates are available for each. For the Pimas (7) incidence was reported as 1.85 per 100 person-years at all ages, and for the Nauruans (32) 1 . 6 per 100 person-years in subjects aged 20 years and older (note the thousand-fold difference in the denomi- nator, compared with the Minnesota estimate). From the data published (7) incidence in Pimas aged 25 and over could be calculated as 4.6 per 100 person-years. These high incidence estimates mirror the very high prevalence of NIDDM in these two unusual populations. Since prevalence is the product of average incidence and average duration of disease, and considering their re- spective incidence and prevalence rates, average survi- val with established NIDDM may be calculated as ap- proximately 15 years for the Nauruans, but only 8 years for the Pimas. The reason for the lower apparent life expectancy of Pima diabetics is not at all clear, and this should stimulate further comparisons between longitudi- nal studies of NIDDM in different populations. These may not only lead to further etiological insight, they may also provide greater understanding of important public health aspects of the disease. Impaired glucose tolerance The WHO classification of glucose intolerance ( 1) in- cludes a category that is intermediate between normal tolerance and diabetes mellitus, called impaired glucose tolerance (IGT). Subjects in this range, whilst not con- sidered to be suffering from diabetes, are known to be at substantially higher risk of developing the disease and its complications than are persons who have glucose toler- ance in the normal range. IGT has an unpredictable course, and is thought to repre- sent a heterogeneous group of subjects, some of whom may be in progress towards frank diabetes, some of whom may have a transient abnormality and be destined to return to normality, and some of whom may continue in a steady IGT state. Surveys which have used a 75 g oral glucose challenge and have estimated the two-hour blood-glucose value (but not those which have only studied the fasting, or random blood-glucose value) can assess the prevalence of IGT according to the WHO criteria. Several reports already discussed here with respect to NIDDM have also produced corresponding figures for IGT (Table 2). None of the three African studies mentioned earlier included estimates of IGT. However, for the black popu- lation of the United States (5) NHANES 2 data indicate a prevalence of IGT of 13%, i.e. slightly higher than that of NIDDM. From the same study, prevalence of IGT in the white population was estimated as 11 %, close to the figure for blacks, despite the whites' relatively lower prevalence of NIDDM. The surveys of rural Italians ( 12) and white Austral- ians (14) estimated prevalence of IGT as 6.4% and approximately 4% respectively. In the Western Pacific, the prevalence of IGT in Fiji Indians (15) and Nauruans (24)-approximately 10% - 194 - TABLE 2. SOME RECENT ESTIMATES OF THE PREVALENCE (PER CENT POPULATION) OF IMPAIRED GLUCOSE TOLERANCE (IGT) IN VARIOUS POPULATIONS USING CRITERIA RECOMMENDED BY WHO• TABLEAU 2. ESTIMATIONS RECENTES DE LA PREVALENCE (POURCENTAGE DE LA POPULATION) DE L'ABAISSEMENT DE LA TOLERANCE AU GLUCOSE (ATG) DANS DIFFERENTES POPULATIONS, EN APPLIQUANT LES CRITERES RECOMMANDES PAR L'OMS" Age rangeb Population Country - Pays Reference - R616rence Tranche M F d'Age 0 (%) (%) (years/ans) black - noire United States - Etats-Unis Harris et al. ( 5) 20-74 11.3 13.6 white - blanche United States - Etats-Unis Harris et al. ( 5) 20-74 10.2 11.1 rural - rurale .. Italy - ltalie Verrillo et al. ( 12) ~ 18 5.1 7.7 white - blanche Australia - Australie Glatthaar et al. ( 7 4) ~ 25 4.3 3.3 Indian - indienne Fiji - Fidji Zimmet et al. ( 15) ~ 20 rural - rurale 10.4 10.8 urban - urbaine 9.4 11.2 Micronesian - micronesienne Nauru Zimmet et al. (24) ~ 20 18.4 18.3 Micronesian - micronesienne Kiribati King et al. (25) ~ 20 rural - rurale ... . . . 12.5 14.3 urban - urbaine ..... 15.0 16.9 Polynesian - polynesienne .. Rarotonga King et al. (26) ~ 20 9.7 10.0 Polynesian - polynesienne Niue ibid. ~ 20 6.6 7.2 Polynesian - polynesienne .. Wallis Island - Wallis Taylor et al. (27) ~ 20 4.0 9.3 Melanesian (AN)C - melane- sienne (AN) c Fiji - Fidji Zimmet et al. ( 7 5) ~ 20 rural - rurale ...... 6.2 10.2 urban - urbaine .. . . . . . . 8.0 13.8 Melanesian (NAN)d - melane- Papua New Guinea highlands - sienne (NAN) d .. Papouasie-Nouvelle-Guinee, montagnes King et al. (28) ~ 20 3.5 1.2 Melanesian (NAN) - melane- Solomon Islands - lies Salo- sienne (NAN) . .... . . . man Eason et al. (29) ~ 18 rural - rurale ........ 0.2 0.7 urban - urbaine 0.0 0.0 Aboriginal. urban - aborigene. urbaine ... Australia - Australie Cameron et al. (30) ~ 20 0.7 4.2 'Reference ( 7) - R616rence ( 7). O Note discrepancies in age ranges - Observer les diff6rences dans les tranches d'Age. c AN: Austronesian ancestry - d'ascendance austron~sienne. d NAN: non-Austrones1an ancestry - d'ascendance non austronesienne. and 18% respectively-reflects the high prevalence of NIDDM in these two populations. Prevalence of IGT in several other Pacific populations of Micronesian, Polynesian and Melanesian ancestry (15, 25-30) varied widely. from almost total absence in the Solomon Islands (29) to 17% in urban females in Kiribati (25). IGT was present in the Papua New Guinea highland- ers, although there was an absence of NIDDM (28). Com- pared with the high prevalence of NIDDM, IGT was sur- prisingly uncommon in an urban Australian Aboriginal population (30). Thus, there is a wide variation in the prevalence of IGT in populations, which to some extent mirrors their preva- lence of NIDDM. However, this relationship is not entirely consistent, and the implications of the prevalence of IGT in the emergence of NIDDM in populations are intriguing, and not fully understood. SUMMARY The revision of the classification of diabetes mellitus, to differentiate clearly between insulin-dependent (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM). and the provision of unambiguous guidelines for diagno- sis (1) constitute important recent developments in dia- betes epidemiology. However. our knowledge even of the prevalence of NIDDM remains surprisingly incom- plete for many areas of the world. Whilst NIDDM may still be uncommon in rural Africa, prevalence has been reported as approximately 10% in blacks in the United States, indicating a need for more information regarding the prevalence of NIDDM in urban Africa. There is also little information with regard to urban communities in Latin America. The highest prevalence of NIDDM is found in certain indigenous North American and Western Pacific socie- ties. In extreme cases approximately one-third of the adult population now suffers from the disease. NIDDM is also common (prevalence approximately 5%) in Europe and in communities of European origin. Data from the United States suggest that approximately one- fifth of white North Americans can expect to develop NIDDM if they live to the seventh decade of life. Of populations of South-East Asian ethnicity, Indians appear to be the most susceptible. Indian migrants to Fiji, South Africa and South America all demonstrate preva- lence of NIDDM of 10% or more. Whilst it was formerly believed that Chinese were rarely affected by NIDDM, recent reports cast some doubt on this. Prevalence of NIDDM in the Western Pacific varies widely. However, with the possible exception of certain Melanesian populations, prevalence is high in all corn- Rapp. trimest. statist. sanit. mond., 41 (1988) - 195 - munities which have abandoned their traditional life- style. Very few estimates of the incidence of NIDDM have been published, largely because of the practical difficulties attending the estimation of incidence in this often asymptomatic disease. An intermediate category of impaired glucose tolerance (IGT) has been recommended recently, to define sub- jects whose glucose tolerance, though outside the nor- mal range, is not thought to be sufficiently deranged to warrant their being classified as diabetic. IGT appears to have an unpredictable course, though the risk of subse- quent diabetes is substantially higher than for subjects with normal glucose tolerance. Reports indicate that the prevalence of IGT in different populations varies as widely as does that of NIDDM. RESUME Tendances observees dans la prevalence et l'incidence du diabete: diabete sucre non insulino-dependant La revision de la classification du diabete sucre afin d'etablir clairement la difference entre diabete sucre insulino-dependant (DSID) et diabete sucre non insulino- dependant (DSNID). et la formulation de directives sans ambigurte pour le diagnostic (1) sont des faits notables recemment survenus dans l'epidemiologie du diabete. Toutefois, nos connaissances sur le DSNID dans de nombreuses parties du monde, s'agissant meme de sa prevalence, restent etonnament incompletes. Le DSNID est peut-etre encore rare dans les regions rurales de I' Afrique, mais sa prevalence est evaluee a environ 10% chez les noirs des Etats-Unis d' Amerique, ce qui indique qu'il faudrait reunir davantage de donnees sur sa prevalence dans les zones urbaines de I' Afrique. De meme, on possede peu de renseignements sur le DSNID dans les communautes urbaines en Amerique latine. C' est dans certaines societes indigenes d' Amerique du Nord et du Pacifique occidental que I' on enregistre la plus forte prevalence du DSNID. Dans les cas extremes, envi- ron un tiers de la population adulte est aujourd'hui atteinte de cette maladie. Le DSNID est egalement courant (prevalence d'environ 5%) en Europe et dans les communautes d'origine euro- peenne. Selan des donnees concernant les Etats-Unis, environ un cinquieme des Americains de race blanche peuvent s · attend re a developper un DSNID a partir de 70 ans. Parmi les populations de I' Asie du Sud-Est, les lndiens semblent etre les plus vulnerables. Chez les migrants indiens a Fidji, en Afrique du Sud et en Amerique du Sud, on observe une prevalence du DSNID de 10% ou plus. Alors que I' on pensait que les Chinois etaient rarement atteints de DSNID, de recents rapports remettent en cause cette opinion. La prevalence du DSNID dans le Pacifique occidental est extremement variable. Toutefois, a !'exception possible de certaines populations melanesiennes, elle est elevee dans toutes les communautes qui ont abandonne leur mode de vie traditionnel. Tres peu d'estimations de !'incidence du DSNID ont ete publiees du fait, essentiellement, des difficultes prati- ques que souleve I' evaluation de !'incidence de cette maladie souvent asymptomatique. II a ete recommande recemment d'introduire la categorie intermediaire d'abaissement de la tolerance au glucose (A TG) pour definir les sujets dont la tolerance au glucose se situe en dehors de la fourchette normale, sans etre suffisamment alteree pour qu'ils soient classes dans la categorie des diabetiques. L' ATG semble evoluer de maniere imprevisible, encore que le risque d'apparition d'un diabete soit nettement plus eleve que chez les sujets ayant une tolerance normale au glucose. Selan les rapports, la prevalence de I' ATG chez differentes popu- lations est tout aussi variable que celle du DSNID. REFERENCES - REFERENCES 1. WHO Technical Report Series No. 727. 1985 (Dia- betes mellitus: report of a WHO Study Group). OMS Serie de Rapports techniques N° 727. 1985 (Le diabete sucre: rapport d'un Groupe d'etude de l'OMS). 2. AHREN, B. & CORRIGAN, c. B. Prevalence of diabetes mellitus in North-Western Tanzania. Diabetologia, 26: 333-336 (1984). 3. FISCH. A. 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