Salt and the metabolic syndrome

Background and aims: High blood pressure in subjects with the metabolic syndrome (MS) is largely related to dietary salt. We investigated in free-living men and women whether increase in dietary salt intake is associated with the presence and severity of the MS. Methods and results: A total of 766 subjects (251M, 515F) of 44.9 ± 0.5 years/age and SBP/DBP of 120 ± 0.6/77 ± 0.4 mmHg were studied. Twenty-four hour urinary sodium (UNa+) and potassium (UK+) excretions were 143±2.5 mmol (median: 131.5) and 48 ± 0.9 mmol (median: 44). UNa+ was higher in men than in women (median: 155.5 vs. 119.8 mmol/day; P < 0.0001). UK+ (r = 0.34; P < 0.0001), measures of obesity (r = 0.26; P < 0.0001) and BP (r = 0.15; P < 0.0001) were significantly associated with UNa+. The association with BP was lost after adjusting for weight. Of the 766 subjects, 256 (33.4%) met the NCEP-ATPIII criteria for the MS. Median UNa+ in men and women with no traits of the MS was 140 and 116.7 mmol/day, respectively (P < 0.001), increasing to 176 in men and 135 mmol/day in women with 4-5 components of the syndrome (P < 0.001). Weight, BMI and waist increased significantly across the quartiles of UNa+ both in men and women; whereas, age, lipids and fasting glucose did not. SBP and DBP were associated with UNa+ in men but not in women. UK+ correlated with age in men and women (r = 023; P < 0.0001) and with obesity in women (r = 0.14; P = 0.001). Conclusions: UNa+ a measure of dietary sodium intake in free-living subjects was markedly increased in subjects with the MS. Higher UNa+ was associated with obesity and higher BP, but not with age, dyslipidemia or fasting glucose.