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Low salt may lower blood pressure, but not CVD death risk

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A new population-based study by researchers of the University of Leuven in Belgium suggests that eating low dietary salt or chemically known as sodium chloride may lower systolic blood pressure, but may boost risk of death from cardiovascular disease (CVD).

The study found the risk of cardiovascular death for subjects who had highest urinary excretion of sodium, which is indicative of lowest intake of salt, was at lowest risk for cardiovascular death, compared with those who had highest excretion.

The study, led by K. Stolarz-Skrzypek and colleagues who were European Project on Genes in Hypertension (EPOGH) Investigators was meant to examine the correlation between a 24-hour urinary excretion, and blood pressure and health outcomes.

They followed for an average 7.9 years 3681 men and women enrolled in the Flemish Study on Genes, Environment, and Health Outcomes from 1985 to 2004 and the European Project on Genes in Hypertension from 1999 to 2001. Sodium excretion was measured at baseline and last follow-up between 2005 and 2008.

Of 3681 participants, 50 CVD deaths were identified in the group with low sodium excretion (107 nmol), 24 in the group with the medium excretion (168 nmol) and 10 in the group with high excretion (260). This means the CVD death rate in the low sodium group is 4.1 percent, compared to 0.8 percent in the high sodium group.

The inverse association between sodium excretion and risk of CVD death was statistically significant. And those who had low sodium excretion were found 56 percent more likely to die from cardiovascular disease.

The researchers found sodium excretion did not predict the risk of total death risk nor the risk for fatal and non-fatal CVD events.

Among 2096 participants who were followed for 6.5 years, increased excretion of sodium was not associated with increased risk of hypertension or high blood pressure.

Further multi-variable-adjusted analyses found an increase of 100 nmol sodium excreted was associated with an increase of 1.71 mm Hg in systolic blood pressure, but not diastolic blood pressure.

The researchers concluded "In this population-based cohort, systolic blood pressure, but not diastolic pressure, changes over time aligned with change in sodium excretion, but this association did not translate into a higher risk of hypertension or CVD complications. Lower sodium excretion was associated with higher CVD mortality."

The study was published in the May 4, 2011 issue of Journal of American Medical Association.

The study has one important limitation.   It is unknown whether any subjects in the study knew they suffered some cardiovascular condition and they opted to lowr their intake of salt. Controlling salt intake because of pre-existing conditions may cause some bias in the study.

Low salt intake has been associated with low blood pressure.  But salt is not the only thing that people need to consider when they want to lower their blood pressure to say the least.

One early study in the New England Journal of Medicine as reported by CNN suggests that eating a low fat diet can also lower systolic blood pressure.

Dr. Frank Sacks at Harvard Medical School and colleagues studied 412 men and women and found the following:

Among people with normal blood pressure, using low sodium and a low-fat diet led to a reduction of systolic blood pressure by 7.1 mm Hg.  Eating a low fat diet alone reduced systolic blood pressure by 3 mm and eating low salt alone lowered systolic blood pressure by 6.7 mm Hg.

Among those who had high blood pressure or hypertension, eating low salt and a low fat diet reduced blood pressure by 11.5 while eating low salt alone reduced blood pressure by 8.3 mm and eating a low fat diet lowered blood pressure by 5 mm.

The current study seems to suggest that low sodium may lower systolic blood pressure, but may not cut the risk of cardiovascular death.

By David Liu

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