Principal findings

Our evaluation of three population-wide salt reduction interventions for CVD prevention shows that these interventions not only could result in substantial health gains, that is, reducing incident CVD and related deaths, but also are very cost-effective. When future net healthcare costs are taken into account, the interventions have very high probabilities of being cost-saving, ranging from 85% to 99% compared with doing nothing over the remaining life course of adult Cameroonians. Even after multiple scenario/sensitivity analyses, our findings were largely robust. Health impacts and probabilities of being cost-effective or cost-saving were greatest for the reduced sodium salt substitute’s intervention followed by a school-based education programme targeting children (with their families) and least for MMC.

Comparison with other studies

In a global cost-effectiveness analysis of government-led salt reduction policy that included industry agreements to reduce sodium content of processed foods and a public health campaign, authors found that such a policy over a 10-year time horizon was highly cost-effective, with ICERs in almost all countries reported at less than the GDP per capita.30 There is limited evidence from individual countries in Africa regarding economic evaluation of salt reduction strategies. In South Africa, the government recently legislated to reduce nationwide salt intakes, among others by reducing salt in processed foods and via media campaigns to reduce discretionary salt use.31 Watkins and colleagues, in an extended cost-effectiveness analysis evaluating this salt policy, found that in addition to resulting in large healthcare savings to the South African government, this salt policy could save households over US$4 million in out-of-pocket expenses, as well as prevent 2400 cases of catastrophic health expenditures annually.32

Several modelling studies, mostly out of Africa, have evaluated the health and economic impacts of various salt reduction interventions, in which majority were found to be cost-saving or very cost-effective.25 33 34 For example, Mason et al modelled the impact of health promotion campaign, labelling food packaging and mandatory reformulation across four Eastern Mediterranean countries. Compared with ‘no policy’, these interventions over a 10-year time horizon were found to be potentially cost-saving and resulted in substantial gains in life years, especially when combined.34 Among the three interventions they assessed, the health promotion campaign had comparatively lower health and economic gains, which is somewhat on par with our analysis. However, in their healthcare costs estimates, the authors did not take into account future costs due to other unrelated disease, which may have inflated their estimate of the benefits.35 Nevertheless, other studies that accounted for these costs still found the majority of population salt reduction interventions were highly cost-effective or dominant.25 33

Studies evaluating pharmacological strategies for CVD prevention reported mixed results. The polypill was shown to be highly cost-effective in LMICs.36 In Tanzania, pharmacological strategies were cost-effective for individuals at moderate or high CVD risk; however, for individuals at low CVD risk, with or without diabetes, medical management was not cost-effective.37 In a study from Ethiopia, most pharmacological interventions assessed for treatment of CVD events were not cost-effective. Similarly, for primary prevention, treatment for elevated cholesterol (at >6.2 and >5.7 mmol/L) and high blood pressure (>160 and >140 mm Hg) were not cost-effective. Treatment following the absolute risk approach was mostly cost-effective, with the lowest ICERs for those with greater than 35% 10-year CVD risk. These results were, however, sensitive to different willingness to pay thresholds (with higher thresholds improving the cost-effectiveness of these interventions).38 Taken together, these findings on the cost-effectiveness of salt reduction strategies and pharmacological interventions for CVD bring to context Geoffrey Rose’s perspective. He advocated that interventions that shift the risk factor distribution of whole populations were likely to result in larger population health gains compared with interventions targeting just the high-risk individuals.39

Strengths and limitations

This study had a number of weaknesses. Our model does not include changes in population demographics and fertility rates over time. In addition, trends in disease incidence or mortality were not accounted for in the model. Forecasts from the GBD suggest that between 2016 and 2040, age-standardised mortality rates for IHD and stroke in Cameroon could decline annually by 0.58% and 1.37%, respectively, while HHD rates increase by 0.15% annually. In their worst-case scenario, IHD and HHD mortality rates were projected to increase annually by 0.65% and 1.78%.40 Furthermore, high blood pressure and high body mass, which strongly influence incidence of CVD, were projected to worsen by 2040. Therefore, it is likely that these trends in IHD and stroke could reduce our modelled health gains, while the projected increasing trends in HHD, blood pressure and BMI could increase them, the balance of this future trends being unclear. Second, we rely on salt consumption data obtained in 2010 for our modelling. It is highly likely that these may have changed (increased) a decade later, given the current growth in urbanisation and accompanied nutrition transition, with worsening dietary patterns such as increasing sugar and energy-dense food consumption41 reportedly related with high salt intake.42 Third, in our base analyses, we assume full intervention effects (and costs) over the lifetime, which could seem unrealistic. However, in sensitivity analyses, we test alternate scenarios limiting the intervention effect to the first 20 years and then decay of 50% for the remaining lifetime and another with zero benefits after 20 years (but maintain full costs throughout the life course). In addition to applying higher discounting, which further penalises future benefits, we also modelled scenarios with a shorter time horizon of 10 years. As expected, there were proportionate reductions in health outcomes and costs, but ICERs were largely robust to these alternative assumptions. Fourth, other diseases that are linked to excess salt intake, such as gastric cancer, osteoporosis and kidney disease, were not modelled. This was mainly because the causal evidence linking them to salt is not as strong as that for CVD. While this omission suggests that our modelled population health gains are probably underestimated, implying the interventions are likely even more economically attractive than currently presented, some of these benefits could be balanced by the harmful effect of potassium-rich salt substitutes on people with chronic kidney disease. Fifth, the school education intervention modelled here is based on cluster randomised trial evidence from China. This study reported both absolute and relative salt reductions for children and for adults. Even though most of the salt in the Chinese and Cameroonian diets are discretionary or added at table or during cooking, the differences in culture and baseline salt consumption levels between the two countries made it seem more reasonable to apply the relative intervention effect. This effect was scaled to the general adult population, and we recognise that some adults in the population do not have children. However, we anticipate that the overall impact of this assumption might have been attenuated by the non-inclusion of adults who were less than 30 years old. Finally, our modelling focused on those 30 years old and above. Given that we model into the future (lifetime), younger populations are likely to age out 30 years and more into the future. Not including them similarly indicates our modelled health gains are conservative and would have reduced our ICERs, making the interventions more economically attractive.

This study also has number of strengths. First, contrary to previous salt modelling studies that have focused on just coronary heart disease and all stroke, we explicitly modelled both major forms of stroke separately, given their varied relationship with blood pressure, as well as modelled HHD that has seldom been modelled. Second, most of the input data, especially on risk factors, was obtained locally for direct applicability of findings. In addition, intervention and healthcare costs used an ingredients approach to estimate total costs using local unit costs and resource use, which made our results more context-specific and policy-relevant to the Ministry of Health. Third, our modelling approach accounts for certain heterogeneities such as sex, age and hypertensive status, for which CVD risk differs. In addition, we test multiple scenarios and sensitivity analyses to ascertain the robustness of our study results. Finally, this study is the first of its kind from Cameroon and contributes to the very scant evidence from Africa on the cost-effectiveness of salt reduction interventions for CVD prevention.

Implications for policy and future research

We have evaluated just three salt reduction strategies. While this may seem interesting, there is a need for the evaluation of other salt reduction strategies such as a salt tax for foods high in sodium content, evaluation of the impact of reducing salt in specific foods such as bread, which also constitute important sources of salt in the diet. Second, future studies should also consider broader health and distributional or equity (by socioeconomic status, rural vs urban) impacts, as well as financial risk protection afforded by health policies. Third, there is a need for evaluation of interventions for other risk factors for NCDs such as physical activity, smoking, alcohol and body mass, as suggested in the broader WHO best-buys. This would provide more evidence for policy makers to decide on the optimal mix of interventions for NCD prevention.

In this study, we use a healthcare system perspective; future studies should consider using a wider societal perspective. There is evidence that productivity costs due to CVD mortality is likely to lead to significant economic returns from investment in preventive health.43 This may provide additional information for policy makers as they grapple with resource allocation decisions. The interventions modelled may not be an exhaustive list, and given most of the salt in the diet is discretionary especially added during cooking, and acknowledging the challenge of changing behaviours, health policy makers may consider implementation of low-sodium salt substitutes. This requires no conscious behaviour change on the part of the consumer; hence, it is likely to be sustainable and has the largest health gains with almost 100% probability of being cost-saving. These economic returns could be reinvested in other much needed health interventions or invested in other non-health sectors. These may, however, need to be evaluated in the context of political feasibility and budget impact.