To prevent hypertension in Africans: do we need to eat more vegetables?

Graphical Abstract

Vegetable servings with odds of hypertension.

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This editorial refers to ‘Frequent vegetable consumption is inversely associated with hypertension among indigenous Africans', by O.M. Akpa et al., https://doi.org/10.1093/eurjpc/zwac208.

So Daniel said to the steward…. please test your servants for ten days, and let them give us vegetables to eat and water to drink. Then let our appearance be examined before you, and the appearance of the young men who eat the portion of the king’s delicacies; and as you see fit, so deal with your servants. So he consented with them in this matter, and tested them ten days. And at the end of ten days their features appeared better and fatter in flesh than all the young men who ate the portion of the king’s delicacies.

—Daniel 1:11-15 NKJV

A cornerstone for lowering the incidence and prevalence of hypertension, a global health problem irrespective of age, ethnicity, and income status, is primordial and primary prevention.^1–4 Hypertension usually co-exists with insulin resistance, a precursor of diabetes, and dyslipidaemia which are premises for the pathological process of cardiovascular diseases and their sequelae.^1,5–8 Modifiable risk factors for hypertension include high sodium intake, low potassium intake, alcohol, smoking, poor diet, sedentary behaviour, low physical activity, air and noise pollution, poor sleep, and vascular stiffness.^1,4–8 Due to the rising prevalence of hypertension and cardiovascular diseases in low- and middle-income countries, there is an urgent need to attenuate the trend.^1,6

The dietary approach to preventing hypertension is well established⁹ and has led to several completed and ongoing clinical trials.¹⁰ However, the effect of vegan diet in preventing blood pressure remains uncertain.¹⁰ Similarly, a meta-analysis of prospective studies involving >94 000 participants from America, Asia, Australia, and Europe reported no dose-response association between the risk of hypertension and vegetable intake.¹¹ While a diet rich in fruits, vegetables, and low-fat dairy foods may reduce blood pressure, the specific role of vegetables in lowering blood pressure remains inconclusive.^8–11 A few cross-sectional studies^12,13 conducted in Africa have reported inverse relationships between vegetable consumption and the risk of hypertension. One study conducted in Congo among >6700 middle-aged adults reported a 35% increase odd of hypertension among participants who do not eat vegetables.¹³ Another study conducted in Ethiopia among >3500 middle-aged adults reported a two-fold increase odd of hypertension among participants who consumed vegetables less than or equal to 3 days per week.¹²

The present study, published in this issue of the European Journal of Preventive Cardiology, conducted across five African countries by Akpa et al.¹⁴ examined the potential dose–response relationship between vegetable consumption and hypertension. This cross-sectional study included diverse ethnic groups and cultures which increases the generalizability of the report across the African population.¹⁴ The study based on data from the Cardiovascular H3Africa Innovation Resource involved >16 400 (53% females) participants from Nigeria, South Africa, Kenya, Ghana, and Burkina Faso.¹⁴ The mean age of the study participants was 52 years, and >7000 participants (∼43%) were hypertensive.¹⁴ Vegetable consumption was characterized using a semi-quantitative food frequency questionnaire based on retrospective information detailing vegetable consumption in servings and the frequency consumed in a typical day/week/month in the last 12 months.¹⁴ Vegetable servings categories were ‘low’ (<6 servings), ‘moderate’ (6–11 servings), ‘sufficient’ (12–29 servings) or ‘high’ (≥30 servings).¹⁴ Hypertension was defined as a once-off or sustained systolic blood pressure ≥140 mmHg, diastolic blood pressure ≥90 mmHg, a prior diagnosis of hypertension, or use of antihypertensive medications. The study accounted for several risk factors such as smoking status, alcohol use, physical activity status, socioeconomic profile, obesity, glucose, glycated haemoglobin level or diabetes status, dyslipidaemia, and family history of cardiovascular disease.¹⁴

Of the total population of >16 400 participants, 41% had ‘low’ vegetable consumption, and 11% had high vegetable consumption. The prevalence of hypertension among participants with ‘low’ and high vegetable consumption was 46 and 39%, respectively.¹⁴ Paradoxically, participants with high vegetable consumption had an unhealthy lifestyle and a higher prevalence of risk factors for hypertension such as smoking and alcohol use, dyslipidaemia, and family history of cardiovascular disease and diabetes.¹⁴ In the general population (Graphical Abstract) and particularly among males, consuming sufficient and high vegetable servings were associated with a 20% lower odds of hypertension. Importantly, high vegetable consumption was not associated with lower odds of hypertension in females.¹⁴ An age-specified analysis revealed that among <60 years old vegetable consumption was associated with a lower odds of hypertension but not among those >60 years old.¹⁴

These cross-country and reasonably continent-wide findings provide evidence for recommending frequent vegetable consumption for the primary prevention of hypertension among African young and middle-aged men. It is likely that if high vegetable consumption is complemented by healthier lifestyle choices, the risk of hypertension may be further reduced.^9–11 The studied population¹⁴ may be at a high risk of hypertension based on genetic inheritance. Thus, vegetable consumption could be a cost-effective approach to preventing hypertension. High flavonoid content in vegetables may increase endothelium-dependent microvascular reactivity, plasma nitric oxide, decreased C-reactive protein, inhibit platelet aggregation, and prevent hyperhomocysteinaemia, which is essential in the development of hypertension.^4,5,15 However, the study by Akpa et al.¹⁴ did not identify the type of vegetables consumed, their molecular contents, and whether they could be classified as fruits or green leafy vegetables, cruciferous vegetables, and dark and yellow vegetables.¹⁶ Furthermore, the study did not account for salt intake, red meat consumption, the quantity of cigarettes smoked, or alcohol consumed which are independent predictors of hypertension^4,5,7,9,10 and could attenuate the relationship between vegetable consumption and hypertension.

It is important to note that the prevalence of dyslipidaemia >50% was high in the African population, irrespective of the included country, and particularly among those who consumed high vegetable servings.¹⁴ However, whether dyslipidaemia mediated or suppressed the relationship between high vegetable consumption and hypertension remains unexamined, although the authors included dyslipidaemia as a covariate. The temporal association of high vegetable intake with the risk of dyslipidaemia and hypertension in this population is not known, and whether participants’ dyslipidaemia level enhances more vegetable consumption or preparation of vegetable diet includes a high proportion of saturated fat is unclear.¹⁶ Future research in the African population is therefore warranted since dyslipidaemia and hypertension are complementary comorbidities in cardiovascular disease sequelae.⁸

Early prevention of hypertension is key to mitigating the public health burden of cardiovascular diseases, since consuming sufficient or high vegetable servings among >60-year-olds was not associated with decreased odds for hypertension.¹⁴ It is known that aging is a non-modifiable risk factor for hypertension and that vascular adaptation to blood pressure changes decreases in later life.^4,5,7,11 Comorbid disease conditions which are prevalent with advancing age may attenuate the effect of high vegetable intake on hypertension. The sex disparity in the Akpa et al.¹⁴ study where a high vegetable intake was not associated with lower odds for hypertension among females has been reported a decade earlier in a long-term prospective study of American women.¹⁶ A plausible reason for the results may be that 57% of hypertensive participants were females and the proportion of females who consumed high vegetable servings among 8893 females was 10%.¹⁴ However, 22% females of the 8893 females consumed sufficient vegetable servings, and sufficient vegetable servings was associated with 20% lower odds of hypertension in females.¹⁴ Hence, more consumption of vegetable servings is warranted among African females to attenuate the higher prevalence of hypertension. Akpa et al.¹⁴ did not present the proportion of males and females who were overweight/obese and had dyslipidaemia, important risk factors for hypertension, which may further explain the sex difference in results.^5,8

In conclusion, the growing body of cross-sectional evidence regarding the associations between high vegetable intake and lower odds of hypertension in middle-aged and young African adult males and potentially in African females (Graphical abstract) represents a relevant step towards hypertension prevention, but prospective studies are warranted.

References

Author notes