There are genetic differences that may contribute to slight differences in blood pressure response to sodium and potassium intake. These genetic differences may vary among races. They may explain the difference among races in the diseases resulting from a poor sodium potassium ratio, such as hypertension and stroke. There are studies showing a higher rate of hypertension and stroke in African-Americans than in Caucasian Americans. Does a difference in the sodium potassium ratio explain the racial difference in hypertension, stroke and death rate? The study to be discussed today looked at the sodium potassium ratio of the diets of African-Americans and Caucasian Americans to see if the ratio explained the differences.
Sodium Potassium Ratio Study
In the publication (1) to be discussed, the researchers looked at the REGARDS study participants to try to find the reason for racial differences in the United States in stroke. More African-Americans than Caucasians suffer strokes. Some studies have found that African-Americans get more sodium and less potassium in their diet. The researchers sought to find out whether this was the reason for the increased prevalence of salt sensitive hypertension and strokes in African-Americans.
The researchers looked at whether the dietary ratio of sodium to potassium (inverse of the potassium to sodium ratio that we prefer) was associated with the racial differences in salt sensitive hypertension, stroke and death. They used data from the REGARDS study. The researchers in the REGARDS study restricted participants to people who were older than 45 years of age at enrollment into the study. They collected data from history, physical examination and blood tests.
In addition to this data, the researchers in the present report phoned the participants, did home visits to measure blood pressure and to deliver a self-administered food questionnaire, which the participants filled out. The questionnaire was a food frequency questionnaire from which the researchers estimated the sodium and potassium intake. They followed the participants for a mean follow-up period of 4.9 years. The researchers obtained follow-up concerning health status, hospitalizations and death every 6 months during this period.
The original participant group had 30,000 participants, but this was reduced to just over 21,000 participants. A participant was eliminated if the food frequency data was not complete enough to evaluate or if the participant had an extremely high energy intake. The researchers divided the study population along racial lines and gender lines, and then into 5 groups based on the sodium potassium ratio.
Findings About Diet
The sodium potassium ratio of the diet was similar for blacks and whites in all 5 groups. In the lowest ratio group both races had approximately the same ratio of sodium to potassium, 0.56 (1.8 potassium to sodium ratio) for blacks and 0.57 (1.75 K:Na) for whites. In the highest ratio group blacks had a ratio of 1.36 (0.74 K:Na) and whites had a ratio of 1.18 (0.85 K:Na).
Findings About Disease
The researchers were able to show a significantly increased risk of death for both racial groups as the sodium potassium ratio increased. The highest ratio group had a 52% higher risk of death than the lowest ratio group. There also was an increased risk of stroke for both racial groups, but the increase did not reach significance. The highest ratio group had a 29% higher risk of stroke than the lowest ratio group.
However there was no significant racial difference in disease rates within each group having the same sodium potassium ratio. The researchers did not find a large difference in the prevalence of hypertension between the 2 races. Nor did they find a significant difference between races for stroke or death. Within each group, the sodium potassium ratio for one race was close to the ratio for the other race. This would imply that the dietary sodium potassium ratio was more significant than any genetic differences in determining hypertension, stroke or death from any cause.
Limitations Of The Study
When discussing the limitations of the study the researchers pointed out that because this was an observational study they could only show an association and not show causation. Another weakness of the study was that they used a food frequency questionnaire rather than using the urinary potassium and sodium values. It is well known that these questionnaires have approximately a 25% level of inaccuracy. Furthermore, people tend to under-report the sodium that they take in and over-report consuming foods that would be a source of potassium.
This reporting discrepancy was likely present in this study, since the ratio in the highest group was the only one not better than the ratio of the average American diet. When 4/5 of the population reports a better than average ratio, the reported ratio will appear to be better than it actually is. The true potassium sodium ratio will be smaller than the reported ratio (sodium potassium ratio will be greater than reported). This kind of error weakened the ability of the study to find the effect of the potassium sodium ratio.
What It Means To You
Despite this weakened ability, this study did find a significant difference in death rate corresponding to the sodium potassium ratio. So the study, despite an important weakness, supports an important principle. Even though you may have genetic differences that can result in a higher prevalence of hypertension, stroke, and cardiovascular disease, your risk of these diseases can be reduced by improving your potassium sodium ratio. In this particular study, both blacks and whites had a lower incidence of disease when they had an improved ratio, and their risk of death was significantly reduced.
So no matter what your race or genetics, there is still much that you can do as an individual to reduce your risk. As an individual you can reduce your risk of hypertension, stroke, and cardiovascular disease by changing your diet to include less sodium and more high potassium foods. To find links to tables of high potassium foods, click on the tab labelled “Links To Food Potassium Tables” at the top of the page.
1. High sodium:potassium intake ratio increases the risk for all-cause mortality: the REasons for Geographic And Racial Differences in Stroke (REGARDS) study. Judd SE, Aaron KJ, Letter AJ, Muntner P, Jenny NS, Campbell RC, Kabagambe EK, Levitan EB, Levine DA, Shikany JM, Safford M, Lackland DT. J Nutr Sci. 2013 Apr 23;2:e13. doi: 10.1017/jns.2013.4. eCollection 2013.