Dietary sodium restriction, an established method for reducing blood pressure (BP), may also improve endothelial function in the conduit (brachial) artery and arterial microvascular circulation. A new study published on Nov. 7 in the Journal of the American College of Cardiology found that reduced sodium intake improves endothelial function by increasing nitric oxide (NO) and tetrahydrobiopterin (BH4, needed for endothelial NO synthase) bioavailability.

The study involved 17 men and women with a mean age of 62 years and moderately elevated systolic blood pressure (130-159 mm Hg) maintaining a low-sodium diet with a sodium target of 1,200 mg/day as recommended in the DASH (Dietary Approaches to Stop Hypertension) diet for 10 weeks. During this 10-week study period, patients were instructed to take 10 tablets throughout the day. For five weeks, these tablets were slow-release sodium chloride, and, for the other five weeks, a placebo. The distribution of tablets was randomized and double-blinded. The sodium chloride tablets returned sodium levels to normal (approximately 3,600 mg/day, the current average in the U.S.).

Additional Resources   Full Study Journal Scan  CardioSmart for Your Patients: How to Eat a Low Sodium Diet

Results showed that sodium restriction was associated with an average decrease of 12 mm Hg in systolic BP, and endothelial function improved in the conduit artery and microvascular circulation. Low sodium intake was also associated with an improved endothelium-dependent dilation in the large arteries. These improvements were associated with increased NO and BH₄ bioavailability, and reductions in oxidative stress.

The investigators concluded that the vascular effects were not "related to changes in BP, other dietary factors, clinical characteristics or humoral influences. Overall, the findings support the emerging concept that maintaining low dietary sodium intake exerts 'vasculoprotective' effects beyond those attributable to BP lowering."

In an accompanying editorial, David S. Celermajer, DSc, and Bruce Neal, PhD, Royal Prince Alfred Hospital, Sydney, Australia, wrote that this "elegant" study provides "novel insights into the vascular effects of controlled dietary sodium reduction in mildly hypertensive vasculoprotective middle-aged and older adults. Studies such as that by Jablonski et al. remind us that a simple molecule such as sodium can assault our vessels in complex maladaptive ways. Our next challenge is to translate this knowledge derived from vascular biology into effective and appropriate public health strategy."

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