The theory that high sodium diets cause hypertension is controversial. This is because while some studies do show that high sodium diets cause blood pressure rises in certain subgroups of the population as a whole, they are not able to consistently raise blood pressure in all individuals. The reason for this has been investigated and possible explanations have been presented. For example, some evidence (here) suggests that those individuals who have low birth weights have an increased risk of being salt sensitive and therefore are more likely to develop high blood pressure with a high sodium diet. Studies looking at the effects of high sodium diets on healthy individuals are inconsistent in their results, and recent evidence suggests that this is because high sodium diets only cause detrimental blood pressure changes in the presence of a low potassium intake. In fact, it is likely the the potassium to sodium ratio in the diet that is the determinant of blood pressure changes, rather than the absolute intake of either.
The optimal potassium to sodium ratio is not known and is likely to vary for each individual. However, eating a plant based diet with large amounts of fruits and vegetables can produce a potassium to sodium ratio of 100 to 1, as most fruits and vegetables are rich sources of potassium and poor sources of sodium. However, the potassium to sodium ratio of those eating a typical Western diet may be as low as 1 to 2. This reflects the lack of fruits and vegetables contained within typical Western foods. Because hypertension increases the risk of cardiovascular disease, the high potassium content of fruits and vegetables may go some way to explaining their cardioprotective effects. The fruit and vegetable intakes of populations are therefore of interest to researchers because it can allow an estimate of the potassium intake to be made. However, more recently studies have attempted to make objective measures of both fruit and vegetable intakes as well as potassium excretion in order to assess the association between the two variables objectively.
For example in one study, researchers1 measured the urinary excretion of an urban population living New York City and also collected data about the fruit and vegetable intakes of the subjects using self reported consumption. The authors then analysed the results in order to find associations with the socio economic status of the individual. The results of the study showed that the mean reported fruit and vegetable consumption was 2.5 portions per day which is well below the recommended intake. The mean urinary potassium excretion was 2180 mg per day, which is below the 3500 mg per day recommended for most individuals. As 75 % of the ingested potassium is excreted in the urine, the urinary potassium was used as a measure of potassium intake. The intake of potassium was 21 % lower in blacks compared to whites, 13 % lower in non-university graduates compared to university graduates, and 9 % lower in those with the lowest income compared to those with the highest income. This suggest that socioeconomic status may play a role in the mean excretion of potassium.
Dr Robert Barrington’s Nutritional Recommendation: The authors of this study suggested that the low intake of fruits and vegetables was largely responsible for the low potassium intake and that increasing fruit and vegetable intake above the 2.5 portions per day would improve potassium intake. Interestingly the majority of individuals in this study reported that fruits and vegetables were available to purchase within a distance that was less than 10 minutes walk away. This suggests that the low fruit and vegetable intake was not a result of an inability to access the produce. The lower potassium intake in those individuals with a low socioeconomic status is consistent with other findings that suggest that the poor have lower quality diets than the rich in Western nations.
RdB
