Modelling the potential impact of a sugar-sweetened beverage tax on stroke mortality, costs and health-adjusted life years in South Africa
Stroke is a major cause of disability and death worldwide. The Global Burden of Disease Study (GBD) shows that approximately 11.6 million cases of ischaemic stroke (65 % in low-to-middle income countries, LMICs) and 5.3 million of haemorrhagic stroke (80 % in LMICs) occurred worldwide in 2010. Sixty-four percent of the disability-adjusted life years (DALYs) due to ischaemic stroke and 86 % of DALYs due to haemorrhagic stroke were lost in LMICs [1]. In sub-Saharan Africa (SSA), more than 30 % of stroke patients die within the first month, less than 60 % of patients are alive after six months and by one year less than 50 % are still alive [2]. This global burden is projected to increase to 23 million first-ever strokes and 7.8 million deaths by 2030 [3].
The burden is also increasing in South Africa. In 2000, stroke (mostly haemorrhagic) was the third leading cause of death after HIV/AIDS and ischemic heart disease [4]. In 2008, a modelling study showed that 75 000 new cases of stroke occurred in that year, with a third of these being fatal within 28 days. Of the 350 000 stroke survivors, 35 % had moderate to severe disability due to the condition [4]. An estimated 33 500 strokes occurred in rural South Africa in 2011 [5].
Stroke poses a significant human and economic burden. The total direct and indirect cost of stroke for 2008 in the United States of America (USA) was estimated at USD65.5 billion, and 27 billion Euros in 27 European Union countries [6]. The estimated cost of care for stroke in SSA is USD157 per episode [2]. Direct costs include the cost of physicians and other health professionals, acute and long-term care, medications and other medical durables. Additional indirect costs include lost productivity resulting from morbidity and mortality and the costs of informal care by families and communities. Affecting mostly the economically productive age group especially in LMICs, stroke leaves about 65 % of its victims disabled leading to increased loss of manpower both at individual, household and societal levels [7] which adversely affects productivity and income, and hampers development. It also affects social relationships and economic status.
Hypertension is the most prevalent, independent and modifiable risk factor for stroke at the population level in SSA [3, 8] with over 50 % of stroke cases in South Africa attributable to hypertension [9]. Other risk factors for stroke include diabetes, smoking, dyslipidaemia, obesity and heavy alcohol consumption [2]. Increasing evidence however shows a significant link between excess sugar consumption, especially from sugar-sweetened beverages (SSBs), and risk of cardiovascular disease (CVD), including stroke. Data from the GBD estimates show that in 2010 approximately 184 000 deaths worldwide were attributable to SSB consumption, with almost 25 % of these due to CVD [10]. Further longitudinal evidence suggests a positive association between SSB consumption and increased stroke risk and mortality [11–13]. The relationship between SSB consumption and stroke may be mediated through weight gain and/or hypertension [14–18]. However, an independent effect may arise from the large amounts of highly absorbable sugars found in SSBs which contribute to high glycaemic load and may lead to inflammation and cardiovascular changes [16, 19, 20].
Globally, consumption of SSBs has increased alongside the increase in non-communicable disease (NCD) prevalence. Between 2005 and 2010, added sugar and sucrose-sweetened beverage consumption increased in both urban and rural areas in South Africa, with a corresponding increase in NCD risk factors [21]. The proportion of adults drinking SSBs in rural areas doubled from 2005–2010. Consumption of Coca-Cola products in South Africa increased from 183 per person per year in 2002 to 260 products in 2012 putting South Africa in the top ten consumers of Coca-Cola products [22]. These estimates are based on a USA eight fluid ounce serving or 250 ml. SA Euromonitor data also show a 16 % increase in soft-drink off-trade sales from 3,620 million to 4,206 million litres between 2008 and 2013 respectively [23].
A tax on SSBs is currently being advocated by policy makers and public health experts world-wide as an effective tool to reduce obesity. The South African National Department of Health (DOH), has included this as a cost effective policy intervention as part of its Strategic Plan for the Prevention and Control of NCDs, 2013–2017 [24]. Research shows that price changes due to taxation or subsidies can modify consumption and potentially lead to positive diet and weight outcomes [25, 26]. In addition, modelling evidence suggests that taxing SSBs has the potential to reduce obesity [27–30].
Mexico introduced a tax on SSBs in January 2014 and observational results show an average reduction of 6 % in the purchase of taxed SSBs during 2014 [31]. This reduction accelerated over the course of the year to reach 12 % by December 2014. Household SSB purchases decreased across all socioeconomic levels although the greatest decrease was among the lowest socioeconomic group which achieved a reduction of 17 % by the end of the year [31]. The amount of the tax was one peso ($.07 USD) per liter, roughly equivalent to a 10 % increase in price.
As a leader in promulgating tobacco taxes, the implementation of taxes on tobacco in South Africa has resulted in an aggregate decrease in cigarette consumption of 41 % and a per capita decrease of 66 % over two decades from 1990 [32]. This evidence suggests that fiscal levers, as part of a multi-pronged approach, can influence consumption. The aim of this study was to estimate the impact of an SSB tax on the burden of stroke in South Africa through the reduction of SSB consumption and reduction of population mean body mass index (BMI).