Author + information
- Prakash Deedwania, MD⁎ ()
- ↵⁎Reprint requests and correspondence:
Dr. Prakash Deedwania, Cardiology Division, VA Central California Heath Care System/University of California, San Francisco, 2615 East Clinton Avenue, Fresno, California 93703
Diabetes mellitus (DM) and cardiovascular disease (CVD) have become major public health challenges around the world. Both DM and CVD are leading causes of death and disability in developed nations. Recent data indicate that with rapidly rising rates of obesity and metabolic syndrome globally, both DM and CVD have become the leading chronic disorders affecting populations across the world. Of the estimated 16 million deaths resulting from CVD in 2001, the vast majority (13 million) occurred in low- and middle-income countries (1). The alarming increases observed in the rate of DM and CVD in developing nations represent a major threat to human health and have become serious public health concerns of enormous magnitude.
Although the prevalence of DM has increased globally, there seem to be disproportionally higher rates of development of DM in racial and ethnic minority populations (1,2). For example, people of South Asian origin (both in their native countries as well as migrant populations) have one of the highest rates of developing DM, and India is now labeled as the diabetes capital of the world, having in excess of 50 million people with DM. Similarly, the rate of DM is expected to increase by 150% in sub-Saharan Africa in the next 10 to 15 years (1–3). This rapid explosion in the rates of DM is likely to be associated with significant increases in the rates of coronary heart disease (CHD) and strokes across the world in people of various ethnic backgrounds. The available data indicate that although the presence of DM is associated with significant increase in the overall death rate, its impact on CHD events and strokes and the related morbidity and mortality indeed may differ based on ethnicity (1–3). Therefore, it is critical to examine and evaluate the impact of various racial and ethnic differences on the development of DM and CVD risk profiles and the related CV disease burden to understand better and to explore opportunities to narrow down the existing health-related racial, ethnic, and gender disparities.
The paper by Tillin et al. (4) in this issue of the Journal highlights the importance of these ethnic differences by examining the impact of DM and other metabolic risk factors on incident CVD in people of 3 different ethnic backgrounds during a 20-year follow-up evaluation in the SABRE (Southall and Brent Revisited) study. This was a tri-ethnic community-based cohort study from northwest London in which 4,196 middle-aged subjects (mean age: 52 years) who were enrolled originally for assessment for DM and other cardiometabolic risk factors in the SABRE study were evaluated after a mean of 20 years for mortality and incident CVD by chart reviews and health care authority data, and survivors were invited for follow-up evaluation. Although most subjects were of European descent (n = 2,049), there were 1,517 South Asians and 630 people of African Caribbean origin.
The main results of this study showed that there were significant differences in the phenotypic patterns in the 3 ethnic cohorts. As expected, there was higher prevalence (almost 3-fold) of DM in South Asians and African Caribbeans along with more central obesity and atherogenic dyslipidemia in South Asians than in the African Caribbean cohort (4). Compared with Europeans, the incidence of CHD events was higher in South Asians, but lower in African Caribbean subjects. In contrast, both South Asians and African Caribbean cohorts experienced more stroke events compared with subjects of European descent. This study does provide interesting data regarding the difference in the prevalence of DM and other metabolic risk factors as well as the impact of these parameters on incident CVD (4). However, before further discussion of these differences and the plausible explanation for the difference, it is important to note that there are some inherent problems and limitations in the study (4).
First, it should be noted that there were a disproportionate number of subjects with the 3 ethnicities. It is also important to recognize that the data from South Asians living in Southall do not represent all South Asians, because the primary population in Southall is of Punjabi and Sikh descent, whereas South Asians as a whole are a heterogeneous group with varying dietary habits and lifestyles. Similarly, the African Caribbean cohort in this study does not represent all people of African descent. Therefore, the results of this study may not be applicable to all South Asians and people of African descent. The authors contend that there was no sex and ethnicity interaction (4). However, this may not be an accurate assessment because of the smaller number of women, especially in the South Asian cohort. A major limitation of the data in this study is that the evaluation for DM and other metabolic risk factors was only made at the beginning of the study, and there is no information regarding the changes (improvement, deterioration, as well as new onset) in these parameters (which are quite likely given the nature of these variables) during the long follow-up period of 20 years. With a mean age of 52 years in the overall cohort, it is certain that there were considerable change(s) in the risk profile during this long period. Furthermore, some recent findings suggest that changes do occur in these parameters over time because of changing lifestyles, improving dietary patterns, as well as healthcare interventions (5). The lack of information about the changes in risk profile during the 20 years of follow-up lead me to question the authors inference that differences in CVD between ethnic groups remained even after adjustment for conventional cardiometabolic risk factors. The authors themselves contend in their conclusion that changes in these parameters across the life course of subjects indeed may be the key (4).
The lack of information regarding the treatment received by the study subjects for important risk factors such as diabetes, hypertension, and dyslipidemia also makes it difficult to put these data in proper perspective. With the well-known efficacy of statins in reducing CVD and stroke rates especially in DM, it is likely that many subjects did indeed receive such therapy, which certainly would alter the natural history of CVD and the subsequent outcome. Finally, it is also important to realize that because of the limited number of events, many of which were soft events (such as angina and coronary interventions), the study has limited power and there is a possibility for spurious findings, thereby limiting the usefulness of these findings for reliable conclusions and clinical implication.
Despite these limitations, the study is important because it is a moderately sized community study of 3 different ethnic groups living in a similar environment and it does provide reasonable comparison of the impact of DM and other metabolic risk factors on incident CVD during a long follow-up period (4). The findings of this study are important because there is paucity of data comparing cardiometabolic risk profiles in various ethnic groups and their relationship to incident CVD. The differences observed in the phenotypic patterns and incident CVD and stroke rates in the SABRE study are interesting. One of the main findings was that compared with Europeans, both South Asians and African Caribbeans had more DM and hypertension despite lower body mass index. This may well be related to more prevalent central obesity in South Asians and African Caribbeans (6). It is now well recognized that visceral adipose tissue (rather than subcutaneous fat) is a greater harbinger of insulin resistance (6,7). Visceral adipose tissue is considered by many to be an endocrine organ because of its ability to release a variety of hormonal substances and inflammatory mediators responsible for insulin resistance and increased cardiovascular risk. The pathogenesis of DM in South Asians and African Caribbeans also may be different because there is evidence of more insulin resistance in South Asians, whereas African Caribbeans may have beta-cell dysfunction (7). It is conceivable that such a higher prevalence of insulin resistance may well account for a higher incidence of CHD events in South Asians when compared with both European and African Caribbean cohorts in this study. It is important to recognize that insulin resistance is associated with atherogenic dyslipidemia and changes in balance between intrinsic prothrombotic and thrombolytic milieu that also may account for differences in the impact of DM in various cohorts in this study. The authors note that high-density lipoprotein and low-density lipoprotein cholesterol levels did not account for the protection from CHD in African Caribbeans. However, without data about the functionality and particle characteristics of these lipoproteins, it is difficult to evaluate their role. It is known that South Asians have a heterogenic lipid profile because of the predominance of small, dense low-density lipoprotein cholesterol particles along with low high-density lipoprotein cholesterol levels, whereas African Caribbeans usually have a more favorable lipid profile, which can account for difference in the rate of CHD events. Future studies should evaluate these parameters and functionality of lipoproteins to ascertain better the ethnic differences in the incidence of CHD.
Although DM was predictive of an increased risk of stroke in all ethnic groups, its effect was most profound in African Caribbeans. The increased risk of stroke in African Caribbeans should not be surprising given that the risk of stroke is closely related to hypertension, which was significantly more prevalent in African Caribbeans than in either Europeans or South Asians. The duration of hypertension also is important, and although no data are given regarding the duration of hypertension, it is quite likely that blood pressure abnormalities were present for a longer period and were more profound in those with DM. Also, the control rates of hypertension have been reported generally to be lower in African Caribbeans, and that also may have contributed to the increased risk of stroke. It is known that hypertension develops in many subjects in the prediabetic phase, and often there is minimal to no physiologic nocturnal dip in blood pressure in presence of DM. Recent data also show that the prevalence of hypertension is increasing in South Asians as well (8). It therefore is likely that despite relatively lower prevalence of hypertension in South Asians at baseline, there was a significant increase in both prevalence of hypertension as well as systolic blood pressure levels during the 20-year follow-up period secondary to advancing age as well as development of new-onset DM, which would indeed explain the high risk of stroke in South Asians as well.
The difference in the rates of incident CVD and stroke in various ethnic subgroups in the United Kingdom have been reported previously nearly 20 years ago (1–3). The persistence of these ethnic differences in the cardiovascular risk factors and incident CVD during such a long period is quite concerning because of the growing magnitude of problem. There is an urgent need for more concerted efforts to identify the reasons for the differences in the prevalence of cardiovascular risk factors, their control rates, and subsequent relationship with CVD in various ethnic cohorts. Diabetes and CVD already have become the leading causes of death and disability in minority populations and various ethnic cohorts across the world, often affecting younger people in many developing nations such as India (1,9,10). There is an urgent need to devote adequate resources toward research in these areas and to implement appropriate public health measures to prevent the oncoming tsunami of chronic, debilitating, and deadly disorders like diabetes and cardiovascular disease around the world (9,10).
Dr. Deedwania has reported that he has no relationships relevant to the contents of this paper to disclose.
↵⁎ Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology.
- American College of Cardiology Foundation
- Mathers C.D.,
- Salomon J.A.,
- Ezzati M.,
- Begg S.,
- Vander-Hoorn S.,
- Lopez A.D.
- Cappucino F.P.,
- Cook D.G.,
- Atkinson R.W.,
- Strazzullo P.
- Chaturvedi N.,
- Fuller J.H.
- Tillin T.,
- Hughes A.D.,
- Mayet J.,
- et al.
- Mathews G.,
- Alexander J.,
- Rahemtulla T.,
- Bhopal R.
- Banerji M.A.,
- Lebovitz H.E.
- Gupta R.,
- Deedwania P.C.,
- Achari V.,
- et al.