This study was done to assess the health outcomes of sodium levels in urine and whether it could predict the blood pressure of a person. Over 3600 participants were involved in the study over a span of seven to eight years. It was found that deaths due to cardiovascular diseases decreased with increasing excretion of sodium in urine. In another follow-up of 2096 participants, after the previous assessment lasting 6.5 years, the risk of hypertension did not increase with varying sodium excretion in urine. On further follow-up for six years, the systolic pressure alone was found to increase. It was concluded that lower sodium excretion in urine was associated with mortality due to heart disease and vascular diseases.
Several population-based and clinical studies have shown that salt intake is related to blood pressure. A few studies have revealed that reduction in dietary salt intake by 3 grams/day could reduce the incidence of heart diseases, thereby lowering medical costs. However, there was an inconsistency in these studies, mostly due to varying salt intakes. Although high salt content raises the blood pressure, the fact that less salt could lower blood pressure, has not been confirmed yet. This proposed hypothesis was based on a large European population sample. In this study, the incidence and mortality of heart diseases were studied with respect to the excretion of sodium in urine, giving thereby an estimate of the body salt content.
- A total of 3681 people participated in the study and were followed up for seven years. Baseline blood pressure and 24-hour urine sodium measurements were taken.
- Later, 3178 participants were followed-up after the initial study.
- Of these, 1499 were included in a study to correlate blood pressure with a 24-hour urinary sodium level estimation. Additionally, 2496 were included in the analysis of high blood pressure.
- In the initial assessment, deaths due to cardiovascular cause decreased with increasing levels of 24-hour urinary sodium excretion. The death rate was 4.1 percent when the sodium levels in urine were low and only 0.8 percent when they were higher.
- In the follow-up on hypertensive people, it was found that the urinary sodium excretion was not a good predictor of hypertension.
- In the follow-up for assessing blood pressure and 24-hour urinary excretion, an increase of urinary sodium by 100 mmol was found to increase the systolic pressure by 1.14 mm Hg.
- The diastolic blood pressure was independent of urinary sodium excretion.
Physiologically, both systolic and diastolic pressures increase with age. Thus, in this long term study, age-related changes in blood pressure could have altered the association between blood pressure and changes in 24-hour urinary sodium. The urinary sodium levels were assessed only once in this study and it also involved only Europeans. Thus, the finding might not apply to Asians or Africans.
Significant associations between systolic pressure and urinary sodium excretion were observed in this study. Diastolic blood pressure was not significantly associated with sodium levels and sodium levels could not be used as a predictor of high blood pressure. It was also found that lower sodium excretion could lead to higher death rates due to cardiovascular disorders. This study disagrees with previous studies involving computer models, which predicted that more lives could be saved and health care costs reduced with reduction in salt intake. Also, a generalized reduction of salt levels in the population would not alter the incidences of cardiovascular mortality. However, this study agrees with the fact that altering salt content in the diet could lower blood pressure in hypertensive patients.
For More Information:
Blood Pressure Changes in Relation to Urinary Sodium Excretion
Publication Journal: The Journal of the American Medical Association, May 2011
By Katarzyna Stolarz-Skrzypek, PhD; Tatiana Kuznetsova, PhD; University of Leuven, Leuven, Belgium
*FYI Living Lab Reports Are Summaries of the Original Research