Low Sodium and High Potassium Intake for Cardiovascular Prevention: Evidence Revisited With Emphasis on Challenges in Sub‐Saharan Africa

Abstract

Reduction in dietary salt intake and increase in potassium intake can make a major contribution to the prevention and control of hypertension and consequential cardiovascular disease, especially in sub‐Saharan Africa (SSA) where prevalence rates are highest. African populations are going through a westernization of their traditional eating patterns, with a shift towards a US/Western‐style diet, which contains an excessive amount of salt. Currently, the mean sodium intake in SSA populations is far above the recommended daily allowance. Besides, potassium intake is low, and, particularly, the supply of fruits and vegetables that are important sources of potassium is insufficient to meet current and growing population needs in SSA countries. Context‐relevant strategies are needed for population‐wide sodium intake reduction and increase in potassium intake.

Background

Hypertension is the leading cause of cardiovascular disease (CVD) and deaths worldwide. It is estimated that at least 1 billion adults have hypertension globally, and that hypertension is associated with more than 9 million deaths annually.1, 2 According to the World Health Organization (WHO), in 2008 sub‐Saharan Africa (SSA) had the highest prevalence of hypertension, with 46% of adults aged 25 and older affected in the region.2 What's more, SSA countries along with other low‐ and low‐middle income countries account for more than 80% of global deaths from CVD.2 The high cardiovascular mortality in these countries is fuelled by very low rates of awareness, treatment, and control of hypertension.3

In the past two decades, SSA is experiencing an epidemic of hypertension and consequential CVD, which is mainly a result of the region's epidemiologic transition driven by the breakdown of traditional ways of life, urbanization, physical inactivity, high salt and fat consumption, and population growth and aging.4 Although hypertension and CVD are increasingly receiving attention across SSA, public health response still remains low, in a context of scarce health resources, poor health system organization, and extreme workforce shortage.5 Context‐relevant strategies are urgently needed to increase the community awareness of hypertension and control of its modifiable risk factors and enhance early detection, adequate treatment and good control of the disease. Reduction in dietary salt intake and increase in potassium intake can make a major contribution to the prevention and control of hypertension.

Role of Sodium and Potassium Intake in CVD

Population studies have shown a strong association between dietary salt intake and blood pressure. Furthermore, several randomized clinical trials have demonstrated that increased dietary salt intake plays a significant role in the elevation of blood pressure as well as endothelial dysfunction, vascular remodeling and dysregulation, albuminuria, and kidney disease progression in the general population.6 On the other hand, several studies have shown a reduction of blood pressure with potassium intake by the consumption of more fruits and vegetables or supplementation. It has also been suggested that increased potassium intake may have a cardioprotective effect.6 Until recently, there was contentious evidence on the cause‐and‐effect relationship between sodium and potassium intake and cardiovascular event rates and mortality.

The Prospective Urban Rural Epidemiology (PURE) cohort study involving more than 150,000 adults in 17 high‐, middle‐, and low‐income countries, whose findings have recently been published,7, 8 has provided new evidence about the association between sodium and potassium intake, estimated on the basis of measured urinary excretion and blood pressure, death, and major cardiovascular events. In this study, an estimated 3 g to 6 g of daily sodium intake was associated with a lower risk of death and cardiovascular events than was either a higher or lower estimated level of intake. Moreover, as compared with an estimated potassium excretion <1.50 g per day, higher potassium excretion was associated with a lower risk of death and cardiovascular events.7

There is evidence that very low sodium intake may lead to increased risk of CVD and associated deaths. Although the effect of potassium supplementation and sodium reduction may not be additive, there is an interaction between sodium and potassium intakes. High potassium intake may have the greatest effect when salt intake is high because potassium supplementation did not reduce blood pressure in hypertensive men concomitantly maintained on a low‐salt diet.6 Indeed, the PURE study has shown an interaction between sodium and potassium intakes as demonstrated from measurements of excretion of these cations: high sodium excretion was more strongly associated with increased blood pressure in persons with lower potassium excretion.8 This suggests that instead of recommending aggressive sodium reduction alone, increased potassium intake alongside reasonable reduction in sodium intake may be more efficient. However, to date, there is no sufficient evidence to determine a lower limit for dietary sodium intake and an upper limit for potassium intake.

Situation and Challenges in SSA

The WHO recommends that adults should consume <2 g of sodium (5 g of salt) and at least 3.51 g of potassium per day.9, 10 The Global Burden of Diseases Nutrition and Chronic Diseases Expert Group (NutriCoDE) estimated the global sodium consumption and its effect on cardiovascular mortality using modeling techniques. The global mean sodium intake in 2010 was 3.95 g/d, with 1.65 million deaths from cardiovascular causes that occurred the same year attributed to sodium consumption above the WHO recommended limit of 2.0 g/d. Sodium intakes in SSA (<3.3 g/d) and cardiovascular mortality attributed to excessive sodium consumption were among the lowest globally. However, estimates about sodium consumption in SSA was uncertain as a result of limited data, stressing the need for large population studies bearing on this matter in the region.11

High sodium intake in most industrialized countries is mainly explained by the US/Western‐style diet, which contains excessive amounts of salt. If no action is taken in SSA, increase in sodium consumption and consequential cardiovascular disease is expected in the region, owing to the nutrition transition occurring driven by economic growth, industrialization, and globalization. Indeed, African populations are going through a westernization of lifestyles, especially their traditional eating patterns.12 Trendy fast foods, soft drinks, and meat products are replacing traditional ethnic foods. Consumption of high sodium content foods are increasing across SSA. The spread of ready meals within global supermarket chains and fast‐food restaurants is reinforcing these trends.

Studies on sodium and potassium content of local foods are scarce in SSA. Some studies have revealed that bread is one the most important contributors to overall sodium intake in SSA populations as in most populations worldwide.13 For instance, a study in South Africa showed that local diet is high in salt, with bread contributing to 25% to 40% of sodium intake.14 Other studies in Nigeria and Mozambique have shown that the sodium content of bread from bakeries and traditional markets was far above the recommended daily allowance.15, 16 These findings call for measures to regulate the sodium content in bread in order to reduce sodium intake at the population level. Interestingly, one study has shown that a 50% reduction in salt content of bread does not decrease bread consumption or increase sodium intake by the choice of sandwich fillings.17 Other foodstuffs contribute significantly in nondiscretionary sodium intake, including meat products, margarines, gravy and soup powders, meat and vegetable extracts, and products containing sodium monoglutamates. Thus, regulation of sodium content must be extended to all the food and beverage industry. However, it remains an issue related to discretionary salt added during domestic food preparation and at the table. Discretionary sodium intake has been shown to represent up to 45% of salt intake in some populations in South Africa.14 Assuming that discretionary sodium intake is as important in other SSA populations as in South Africa, initiatives for intense public education on the necessity to reduce salt added during cooking and at the table will be crucial for population‐wide reduction in sodium intake.

Since salt in SSA countries is fortified with iodine to optimize population level of iodine, a concern has been expressed that salt‐lowering initiatives may compromise iodine intakes. However, a study in South Africa has shown that a reduction of iodinated salt intake to 5 g per day as recommended by the WHO will not lead to iodine deficiency.18

There is dearth information on potassium intake in SSA. Studies in some populations suggest that potassium consumption may be insufficient.14 Furthermore, a study on the global consumption of fruits and vegetables that are important sources of potassium has shown that in most SSA countries surveyed, there was low fruit and vegetable consumption, defined by the WHO as consuming fewer than five servings (<400 g) of fruits and/or vegetables daily.19 Because fresh fruits, vegetables, and beans are high in potassium, an increased intake of potassium can be achieved without increasing caloric intake and without the need for specially formulated food and beverage products, if these foods replace those lower in potassium levels in the diet.10 A recent study has revealed that the supply of fruits and vegetables is insufficient to meet current and growing population needs in select SSA countries, thereby emphasizing the need to find innovative ways to increase fruit and vegetable production and consumption to meet population health needs.20

Conclusions

Overall, to achieve the recommended increase in dietary potassium intake and reduction of sodium intake in SSA countries, there is a need for concerted action from governments, civil society, public health experts, academia, and food and beverage industries. National programs to implement a population‐wide increase in dietary potassium and sodium intake reduction should be put in place. Strategies should include intensive public education emphasizing fruit and vegetable consumption and salt reduction during cooking and at the table; regulation of sodium content of industrially produced foods through mandatory legislation with sodium reduction targets and defined timelines; and evaluation and monitoring of population sodium and potassium consumption and sources in the diet. The experience of countries where salt reduction initiatives are successful should be capitalized by SSA countries.

Disclosures

The authors declare no conflict of interest.

J Clin Hypertens (Greenwich). 2015;17:81–83. © 2014 Wiley Periodicals, Inc.