Efficacy of Dietary Sodium Restriction of Improving Vascular Endothelial Function in Middle Aged and Older Adults

Not Applicable

Completed

Brief Summary: The investigators hypothesize that reducing salt in the diet will improve the function of blood vessels in middle aged and older adults with moderately elevated systolic blood pressure, by increasing the amount of BH4 and nitric oxide in your blood vessels and reducing the amount of oxidative stress.

Detailed Description: The improvement in blood vessel function will be determined over a 10 week period. Subjects will be randomly assigned to either a 'low salt' condition (placebo pills + 1200 mg dietary sodium) or a 'normal salt' condition (2300 mg sodium chloride pills + 1200 mg dietary sodium) and monitored for 5 weeks. After the initial set of 5 weeks, the subjects are switched into the opposite condition, completing the cross-over study design. During weeks 1-4 and 6-9, subjects are monitored weekly with 24 hour urine collections and diet logs. The assessment of the primary outcome (blood vessel function) is completed during weeks 5 and 10. BH4 and ascorbic acid are also administered during weeks 5 and 10 to measure the effects of sodium intake on endogenous BH4 levels and vascular oxidative stress.

Recruitment & Eligibility

Inclusion Criteria

Exclusion Criteria

Have been sick with an infection in the past two weeks
Are currently sick or have ongoing health problems such as kidney or CVD
Have lost more than 11 lbs. in the last 3 months
Are taking any type of antioxidants
Smoke or have alcohol problems
Have blood glucose levels higher than 126 mg/dL
Have resting SBP below or less than 100 mmHg or greater than 159 mmHg
Have a resting diastolic blood pressure greater than 99 mmHg
Have a BMI greater than 40 kg/m^2
Are presently consuming less than 9 or greater than 18 grams of salt / day
Have a baseline FMD of greater than 6%
Are taking any of the following types of drugs: blood thinners, anti-seizure medications, ant-inflammatory drugs
Participate in any high endurance athletic training
Taking Hormone Replacement Therapy
Have not been post-menopausal for at least 1 year

Arm && Interventions

Group	Intervention	Description
Normal sodium	Slow sodium tablets	Subjects on a 1200 mg sodium diet are given 2300 mg sodium in the form of slow sodium tablets to bring them back up to a normal salt intake. Subjects then cross-over to the low sodium condition in the second half of the study.
Low sodium	placebo	Subjects on a 1200 mg salt diet are given placebo pills in order to maintain them on a low salt diet. Subjects then cross-over to the normal sodium condition in the second half of the study.

Primary Outcome Measures

Name	Time	Method
Improved Flow Mediated Dilation	Week 5 (after first condition of low salt or normal salt), Week 10 (after second condition, opposite to first)	FMD is analyzed at weeks 5 and 10 or after each condition in this cross-over study design. Subjects are randomly assigned to a low salt or normal salt condition for the first set of 5 weeks and then crossed over to the other condition for the second set of 5 weeks.

Secondary Outcome Measures

Name	Time	Method
Vascular Oxidative Stress	Immediately following acute infusion of ascorbic acid on Weeks 5 and 10	Change in FMD following acute infusion of ascorbic acid (a dose known to scavenge superoxide) is measured at the end of 5 weeks of sodium condition (low and normal intake) as an index of vascular oxidative.
BH4 Bioavailability	Immediately following acute administration of BH4 on Weeks 5 and 10	Change in FMD following acute oral tetrahydrobiopterin (BH4) is measured at the end of 5 weeks of sodium condition (low and normal intake) as an index of BH4 bioavailability.