The impact of dietary sodium on cerebral blood flow regulation
Date
2020
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
The American Heart Association and the Dietary Guidelines for Americans recommend
2,300 mg of sodium (Na+) per day, but the American Heart Association further
recommends lowering dietary Na+ intake to 1,500 mg of Na+ per day for optimal health.
Americans continue to consume on average 3,400-3,600 mg of Na+ per day, and about
a third of Americans report eating at a restaurant every day where many menu items
exceed the daily recommended Na+ intake. High Na+ intake increases stroke risk by
23%. Data from rodent studies suggest that high Na+ consumption impairs cerebral
blood flow regulation, which has been associated with strokes. However, it remains
unknown how dietary Na+ affects cerebral blood flow regulation in humans.
PURPOSE: To examine the impact of high dietary Na+ on cerebrovascular reactivity
and cerebral autoregulation in healthy young individuals. HYPOTHESIS: High
dietary sodium intake will impair cerebrovascular reactivity and dynamic cerebral
autoregulation compared to low dietary sodium. METHODS: These hypotheses were
tested using two experimental protocols. In the first protocol, we provided participants
with a low (138 mg; LSM) - and high (1,495 mg; HSM) -sodium soup. Transcranial
doppler ultrasound was used to measure middle cerebral artery velocity. We measured
cerebrovascular reactivity to hypercapnia and hypocapnia, and dynamic cerebral
autoregulation to spontaneous and inducible changes in blood pressure prior to- and
post-meal consumption. In the second protocol, participants were placed on a chronic
controlled feeding study. Participants consumed a low (1,000 mg Na+/day)-, medium
(2,300 mg Na+/day)-, and high (7,000 mg Na+/day)-sodium diet for ten days. On the
tenth day of the diet, we assessed cerebrovascular reactivity and dynamic cerebral
autoregulation. RESULTS: The acute high dietary sodium meal increased serum
sodium compared to the low sodium meal (HSM: D1.6±1.2 mmol/l vs LSM: D0.7±1.2
mmol/l; time: P<0.001, meal: P=0.03, interaction: P=0.02). Despite the increases in
serum sodium, cerebrovascular reactivity to hypercapnia (meal: P=0.41) and to
hypocapnia (meal: P=0.65) were not different. Dynamic cerebral autoregulation in the
low frequency band was modestly reduced following the HSM and increased following
the LSM as indicated by postprandial phase (interaction: P=0.04). The controlled
feeding diets increased urinary sodium excretion (P=0.007). There was a trend for a
difference in cerebrovascular reactivity to hypercapnia (P=0.06), but there was no
difference in cerebrovascular reactivity to hypocapnia (P=0.57) between the three diets.
There was no difference in dynamic cerebral autoregulation in any metric between the
diets. CONCLUSIONS: Acute high dietary sodium does not impact cerebrovascular
reactivity in healthy, young adults but may modestly impair dynamic cerebral
autoregulation. Chronic low dietary sodium may increase cerebrovascular reactivity to
hypercapnia but chronic high dietary sodium does not impair dynamic cerebral
autoregulation. These data indicate that acute and chronic dietary sodium may impact
cerebral blood flow regulation in healthy, young adults providing additional rationale
for lowering salt intake recommendations in the United States to improve the health of
the cerebrovasculature.
Description
Keywords
Acute, Cerebral autoregulation, Cerebrovascular reactivity, Chronic, Sodium