Epidemiology of Type 2 Diabetes
Epidemiology of type 2 Diabetes
Epidemiology of diabetes mellitus in South Africa
| SEMDSA 2017 RECOMMENDATIONS |
The estimated national prevalence of diabetes (based on HbA1c) in persons older than 15 years was 9.5% (2012), and about 45% of these individuals were undiagnosed. An additional 9% of the South African population had abnormal glucose regulation defined by an HbA1c between 6.0 and 6.4% |
The Asian and Coloured populations have the highest prevalence of diabetes in South Africa |
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The prevalence of diabetes in rural dwellers appears to be increasing rapidly
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The number of people living with diabetes in Africa is predicted to increase by 140% by the year 2040 |
The number of deaths globally from diabetes exceeded the combined mortality from HIV/AIDS, tuberculosis and malaria in 2015 |
There are clearly modifiable risk factors driving the diabetes epidemic; the rising prevalence of obesity is one of the most important |
BACKGROUND AND INFORMATION 1,2
Sub-Saharan Africa (SSA)
Diabetes mellitus (diabetes) affects people worldwide and poses major public health and socio-economic challenges. The disorder was previously thought to be rare or undocumented in rural Africa, but over the past few decades it has emerged as an important non-communicable disease (NCD) in sub-Saharan Africa (SSA). After the introduction of standardised diagnostic criteria, King and Rewers showed in 1993, that diabetes in adults was a global disorder and that populations of developing countries, minority groups and disadvantaged communities in industrialised nations faced the greatest risk. Subsequently, several reports on global estimates and projections confirmed the diabetes epidemic and indicated that the numbers of people with diabetes and prevalence of both diabetes and impaired glucose tolerance (IGT) will rise. The increases are expected to be largest in developing regions of the world because of population ageing and urbanisation.1
Estimates from 2015 by the International Diabetes Federation (IDF) (Table) suggest that the number of adults with diabetes in the world will increase by 55% in 2040. The greatest increase is anticipated for the Africa region, with a 140.9% projected increase. IGT in SSA is expected to rise in the same period, by 126.4%; this will likely contribute to the higher burden of future diabetes. Therefore, the proportionate increase for SSA is more than double the predicted global increase for both IGT (51.3%) and diabetes (54.7%).2
The regional prevalence of diabetes for the Africa region for 2015 was 3.2% (2.1-6.7%) and expected to increase to 3.7% (2.6- 7.3%) by 2040. This region has the highest proportion (66.7%) of undiagnosed diabetes. The majority (58.8%) of people with diabetes live in cities, although the population in the region is predominantly (61.3%) rural; as urbanisation increases and populations age, type 2 diabetes will pose an increasing threat. Nearly half of all adults with diabetes in the region live in the four most populous countries: South Africa (2.3 [1.2-4.6] million), Democratic Republic of Congo (1.8 [1.5-2.2] million), Nigeria (1.6 [1.2-3.8] million) and Ethiopia (1.3 [0.8-3.5] million).2
In 2015, there were 321 100 deaths attributable to diabetes for the Africa region, with more than 79% occurring in the economically productive age group i.e. age < 60 years, the highest proportion of any region and 1.7 times higher in women than in men. Globally approximately 5.0 million people aged between 20 and 79 years died from diabetes in 2015, equivalent to one death every six seconds. This is higher than the combined number of deaths from HIV/AIDS (1.5 million), tuberculosis (1.5 million), and malaria (0.6 million) in 2013. Close to half
(46.6%) of deaths due to diabetes are in people under the age of 602
In 2015, the estimated health expenditure on diabetes in Africa was USD 3.4 billion, accounting for 0.5% of the global expenditure, the lowest for any region; this is equivalent to 7.0% of the region’s total health budget and to USD 24.3 - 419 person / year.
In addition to the present challenges of resource depletion, countries in SSA face the double burden of communicable diseases (e.g. HIV/AIDS, tuberculosis) and non-communicable diseases (NCD) and their risk factors (e.g. diabetes).
The IDF report also highlighted the paucity of data sources for the Africa region with a total of 13 sources from 12 countries selected. More than three quarters of countries lacked nation- wide data; only a few SSA countries (Kenya and South Africa) had data sources based on oral glucose tolerance test (OGTT); diabetes prevalence figures for other countries in the region were based on studies that used self-reports, fasting blood glucose, were older than five (5) years and may be underestimates. The report highlighted the urgent need for further epidemiological research and improved data collection systems in the region
Table: IDF Estimates for 2015 and 20402
| Number of adults (20-79 years) with diabetes: | |||
| Number (million) [uncertainty range] | Projected increase | ||
| 2015 | 2040 | ||
| World | 415 [340-536] | 642 [521-829] | +55% |
| Africa | 14.2 [9.5-29.4] | 34.2 [23.7-67.7] | +140.9% |
| Number of adults (20-79 years) with IGT | |||
| SSA | 34.9 [21.0 - 96.8] | [48.3-222.3] | +126.4% |
South Africa
South Africa is ranked as an upper middle-income economy by the World Bank and the United Nations (UN). It has one the largest economies in Africa. It is a country of contrasts, with wide divides between the “haves” (privileged) and the “have-nots” (underprivileged), where at least a quarter of the population is unemployed and lives on USD 1.25 per day. It is a country where traditional values grapple with the onslaught / entrenchment of the technological age and which has undergone rapid socio- political changes over the past two decades.
From the most recent (2011) population census, the total population is 51.770,560 million, living in nine (9) provinces with 11 official languages; >60.0% live in urban areas. Africans (Blacks) constitute 79.2% (41 million) of the total population; South Africa has the largest European, Asian Indian and Mixed Ancestry communities in Africa.
Against this background, this section provides an overview of the burden (epidemiology) of type 2 diabetes in non-pregnant adults in South Africa.
EPIDEMIOLOGY OF DIABETES MELLITUS IN SOUTH AFRICA
IDF Estimates
Based on the most recent 2015 IDF estimates for South Africa, there were 2.286 (1.1637-4.6206) million adults (20-79 years) with diabetes; the national prevalence was 7.0% (3.6-14.1) with a comparative prevalence of 7.6% (3.1-14.7). Of the 2.3 million people with diabetes, 1.3968 (0.603-2.3944) million (61.1%) were undiagnosed. The mean health expenditure per person with diabetes was USD 918.9 USD (1736.1 international dollars); and there were 57,319 diabetes related deaths.2
The following will provide a brief overview of the epidemiology studies undertaken from the 1960’s to the present.
A.Early studies (prior to standardised criteria)
Before the introduction of standardised WHO criteria for glucose tolerance and since the early 1960’s, several studies examined the prevalence of diabetes in South Africa. However, such studies involve different study populations, methodologies and criteria for the diagnosis of diabetes. Despite these limitations, such studies showed prevalence rates ranging between 0.6 - 3.6% in urban communities.1,3,4,5
B.Studies using standardised WHO/ADA criteria
Appendix 1 summarises the studies on diabetes prevalence undertaken from the 1980’s1,3,4,5,6. Since the introduction of standardised WHO criteria and methodology for the diagnoses of diabetes in 1985, there have been several studies undertaken in South Africa in urban, peri-urban and rural communities; the majority of the published studies have used the 1985 WHO criteria. In these studies, from three provinces (KwaZulu Natal, Western Cape and Free State), the age standardised prevalence was 4.8% in peri-urban and 5.3-8.0% in urban Africans (Blacks), 10.8% in Mixed ancestry (Coloured) communities, and 13.0% in Asian Indians. All the studies reported age-standardised prevalence rates.
Using current (1998 WHO) criteria, moderate prevalence (3.9%) has been reported in rural KwaZulu Natal and high rates in urban Africans in Cape Town (13.1%) and Durban (12.9%) and in Mixed ancestry populations in the Western Cape (26.3%) (Epidemiology Diabetes Surveys in South Africa)1,3,4,5,6.
C.Longitudinal studies
To date, the only longitudinal studies which have examined the incidence of diabetes or the natural history of intermediate stages of glucose intolerance (IFG, IGT) in South Africa, have been in Asian Indians in Durban. There was a high risk of progression to diabetes in Indians with IGT (50.4% over four (4) years; rate of progression: 12.6% per annum). In a 10-year follow-up study, the age and sex adjusted cumulative incidence of diabetes was 8.3% (rate of progression 0.95% per annum; incidence density 8.3/1000 person years).1,3,4,5,
D.South African National Health and Nutrition Examination Survey (SANHANES) 2012 (Appendix 2)
The Human Science Research Council embarked on the SANHANES to recruit and establish a nationally representative cohort of 5 000 South African households to be followed up over the coming years. The first cross-sectional examination (SANHANES-1) was completed in 2012 and reported in 2014.7
The final population sample included 25 532 people from 6 305 households who were interviewed, and then subsequently invited to a clinic examination and blood biomarker analyses for lipid profiling and HbA1c. The results for the prevalence of HbA1c and other metabolic abnormalities are summarised in South African National Health and Nutrition Examination Survey-1.
The national prevalence of abnormal glucose regulation (as defined by the cut-points used) was 18.6%. The prevalence figures are more startling when the analysis is confined to individuals older than 45 years where 16-25% of the population had diabetes and an additional 11-20% had sub-diabetic but abnormal HbA1c. It is noteworthy that HbA1c in the range 6.1 to 6.4% is not equivalent to IFG or IGT; it is known to underestimate intermediate hyperglycaemia (IFG and IGT). Nevertheless it is well established as a risk factor for progression to diabetes8,9,10. In SANHANES-1 only 5% of individuals knew that they had diabetes implying that 45% of diabetes was previously undiagnosed. It is also worrying that no sector of society appeared to be protected; the highest prevalence of diabetes was found in rural informal dwellers (11.9%) and urban formal dwellers (11.3%). The prevalence of diabetes was equal among Blacks and Whites (just over 8%), higher among Coloureds (13.4%) and peaked at 30% for Asians.
Africans (Blacks)
A.Prevalence
Both from earlier and recent studies, whatever criteria are used and when compared with other studies using oral glucose tolerance test (OGTT), both rural and urban prevalence in South Africa are higher than in other parts of SSA and comparable with that found in developed countries.1,2,3,4,5
Regarding intermediate hyperglycaemia, IGT rates are moderate (4.8%) in rural communities but high in urban Xhosa in whom the prevalence of IGT has increased by 67%, from 7.0% in the 1990’s to 11.7% in 2009. IFG prevalence was low both in rural (1.5%) and urban (1.2%) studies. A high prevalence of total disorders of glycaemia has been reported in both urban and rural communities. The foregoing also underscores the need for OGTT in epidemiology studies in SSA to identify those with IGT when estimating future trends in diabetes; IGT and IFG are not interchangeable and denote different abnormalities of glucose regulation.
More importantly, there is now clear evidence of an increase in the prevalence over the past few decades. Studies from the urban Cape Town study showed that when 1995 WHO criteria are applied, there has been a 52.5% increase, from 8.0% in the 1990’s to 12.2% in the recent study in 2009, both in men and women, and across age groups. similar findings are shown in the recent study in Durban (5.3% in 1984 vs. 12.9 % in 2014).
B.Risk factors for diabetes
South Africa as for the rest of SSA, is at grave risk for an increase in NCD especially diabetes, because of the many different and interrelated risk factors both modifiable and non-modifiable. These include the high proportions of undiagnosed diabetes in rural South Africans, the urban-rural differences and impact of urbanisation, ageing and peak prevalence in the older age group, the association with positive family history, adiposity, diminished physical activity and psycho social factors, as well as the impact of HIV/AIDS. In addition the global prevalence of obesity, a major risk factor for diabetes, is rising rapidly and in SSA, rates of obesity are among the fastest growing in the world.2,11 Since 1980, WHO estimates that the worldwide prevalence of obesity has more than doubled, with significant increases seen in every region. In sub-Saharan Africa, the number of overweight children grew from 4 million in 1990 to 10 million in 2012.12
Summary
The data on the epidemiology of type 2 diabetes in South Africa has confirmed moderate to high diabetes prevalence and higher than in other SSA countries using the same methodology and comparable with those in developed countries; it explodes the previously held myth that diabetes is rare on this continent and there is now confirmatory evidence that the prevalence has increased over the past few decades. Diabetes prevalence is higher in urban and migrant populations and they are clearly identifiable and modifiable risk factors for its development.
Author: Ayesha A. Motala
Editor: Aslam Amod
References
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