Disease of stealth: Diabetes is still slipping through the cracks of SA's health-care system
A so-called lifestyle disease, diabetes is still concentrated among the rich, although evidence suggests that this is changing. HSRC lead researcher Chipo Mutyambizi and her team set out to discover the factors behind the differences in prevalence across socioeconomic groups, and how this might help the government to combat the rising tide of diabetes in the country. Andrea Teagle reports.
Almost 4 in 10 people in South Africa with diabetes are unaware that they have the disease. And there are no significant differences in rates of undiagnosed diabetes across the socioeconomic spectrum, suggesting that knowledge of diabetes and diabetes screening remains low, even among higher-income groups.
Once primarily affecting developed countries, type 2 diabetes and other so-called lifestyle diseases are increasing across developing countries, particularly in sub-Saharan Africa.
Using data from the HSRC’s 2012 national health and nutrition study, SANHANES-1, a team of researchers at the HSRC led by Chipo Mutyambizi undertook to explore the distribution of diabetes across socio-economic groups and the factors behind it. Using self-reported data (a measure of diagnosed diabetes), and clinical data (results from diabetes blood tests), the team found a prevalence of 11% across the adult population.
Concentrated among the rich…
The study, titled Lifestyle and socio-economic inequalities in diabetes prevalence in South Africa: A decomposition analysis, found that total diabetes figures, including self-reported and undiagnosed cases, were concentrated among the rich. This suggested that higher recorded rates of the disease among higher-income individuals were not just reflecting differences in access to health care and diagnostic tests.
While type 1 diabetes is largely hereditary, the far more common type 2 diabetes develops over time as a result of biological and other factors. The short explanation is often “insulin resistance”, but type 2 diabetes only occurs if the pancreas is unable to produce sufficient insulin to compensate for its lower absorption rate. Insulin acts as a key to “unlock” muscle cells for glucose to enter and be stored or used as energy. If this system malfunctions, blood-sugar levels increase, which can cause blood-vessel damage, heart failure and other complications.
Mutyambizi and her team investigated the factors driving the different rates of diabetes across richer and poorer households in South Africa, which is important for devising targeted interventions.
Spreading from rich to poor
If lifestyle is a significant driver, then, as lifestyles change across the socioeconomic spectrum, the distribution of diabetes is likely to change too, which research suggests is already happening. Diabetes is rising rapidly in lower and middle-income countries, as populations become more urbanised and sedentary and subsist increasingly on diets high in sugar and unsaturated fats.
Meanwhile, in developed countries, diabetes and other lifestyle diseases are now more common among the poor, for whom healthy lifestyle choices are constrained. In the absence of government interventions, the spread of diabetes from rich to poor is likely to occur in South Africa too.
Among other factors, changes in diabetes distribution could be a result of diabetes awareness or education programmes influencing the adoption of healthier lifestyles, says Mutyambizi.
She and her team explored various lifestyle factors associated with diabetes that might differ across the socio-economic spectrum, such as physical exercise, body mass index (BMI), level of fruit and vegetable consumption, smoking and drinking, and whether participants lived in towns or rural areas. To measure the true contribution of these factors, the study accounted for the possible impact of age, race and family history. The latter was important because the survey did not differentiate between type 1 and type 2 diabetes, which the authors noted as a limitation of the study. In addition, the self-reported data could be distorted by social desirability biases due to individuals giving inaccurate answers for fear of judgement.
Collectively, lifestyle factors explained 35% of the inequalities in the total number of diabetes cases. In other words, if everyone in the sample ate the same amount of fresh produce, exercised the same amount, etc., the differences in diabetes across the wealth spectrum would be reduced by just over a third. Of course, other lifestyle factors that were not included in the study could be contributing to the skewed distribution.
Obesity is the most significant lifestyle factor associated with type 2 diabetes. (Very simply, fatty acids compete with insulin for absorption into cells, leading to insulin resistance.) Although obesity is on the rise nationally, it is still more common among the rich.
It is useful to think of obesity and diabetes as a result of living in an environment that makes it difficult to lead a healthy lifestyle. In cities particularly, starchy, processed foods are often cheaper than fresh alternatives and an easier way for households to meet their energy needs. So, while education is important to empower individuals, interventions also need to focus on making healthier options more affordable, accessible and appealing.
Diabetes missed in rural areas
Place of residence – whether an individual lived in a rural or urban area – explained about a third of the difference in reported diabetes across wealth groups, suggesting a discrepancy in diagnosis in rural versus urban areas. A 2017 study on the prevalence of diabetes, also drawing from data from SANHANES-1, and involving researchers from the HSRC and the University of Boston, showed that the proportion of unscreened South Africans is far greater in rural and informal urban areas (68% and 65% respectively) than formal urban areas (44%).
Most of the respondents whose diet did not include much fresh produce were in the lowest wealth quintile. The authors also found, surprisingly, that individuals eating more than four portions of fruit and vegetables a day were more, not less, likely to have the disease.
Mutyambizi explains that not all fruit and vegetables are beneficial: individuals should favour those with higher roughage and less sugar content. It is also possible that participants reporting more portions of fruit and vegetables might be eating more in general, or more of other types of food like refined foods and sugary beverages, as well.
Creating a healthier environment
Diet and exercise are among the most effective known preventative measures for type 2 diabetes. Exercise was not found to be a major driver of the differences in diabetes across wealth quintiles in South Africa. However, the higher risk faced by inactive individuals, and the high levels of sedentariness nationally – 57%, according to a recent HSRC study using 2012 data – underscore the importance of creating safe, accessible recreational spaces and encouraging exercise.
Last year, results from the same survey helped to propel the introduction of the national tax on sugary beverages. The tax, which came into effect in April 2018, was widely endorsed by health practitioners as an important step – if coupled with other interventions – in creating an environment conducive to healthier choices.
Mutyambizi emphasises the importance of screening across the population, and designing policies that enable healthy lifestyles.
Author: Andrea Teagle, HSRC science writer
Lead researcher of the study: Chipo Mutyambizi