Preference for salt contributes to sympathovagal imbalance in the genesis of prehypertension.

BACKGROUND/OBJECTIVES: As salt preference is known to cause hypertension (HTN), the present study was conducted to assess the impact of preference for salt on sympathovagal imbalance in prehypertensives by spectral analysis of heart rate variability (HRV).

SUBJECTS/METHODS: Body mass index (BMI), basal heart rate, blood pressure (BP), rate pressure product and spectral indices of HRV such as total power (TP), normalized low frequency power (LFnu), normalized high frequency power (HFnu), ratio of low frequency power to high frequency power (LF-HF ratio), mean heart rate, square root of the mean squared differences of successive normal to normal (NN) intervals, the number of interval differences of successive NN intervals >50 ms (NN50) and the proportion derived by dividing NN50 by the total number of NN intervals were assessed in 555 subjects divided into four groups: Group 1, normotensives no-salt-preference subjects (n=260); Group 2, normotensives salt-preference subjects (n=185); Group 3, prehypertensives no-salt-preference subjects (n=25); and Group 4, prehypertensives salt-preference subjects (n=89). Sympathovagal balance was analyzed and contribution of individual factor to sympathovagal imbalance was assessed by regression analysis.

RESULTS: LFnu was significantly increased (P=0.009), whereas TP and HFnu were significantly decreased (P=0.024 and 0.007, respectively) in the salt-preference groups compared with the no-salt-preference groups. LF-HF ratio, the sensitive indicator of sympathovagal balance, was significantly increased (P<0.0001) in salt-preference subjects compared with no-salt-preference subjects. In regression analysis, the link of LF-HF ratio to HTN status was found to be more prominent in the salt-preference group (P=0.000) compared with the no-salt-preference group (P=0.004). BMI had no significant contribution (P=0.818) to LF-HF ratio in salt-preference subjects.

CONCLUSIONS: Salt preference is associated with sympathovagal imbalance caused by sympathetic overactivity and vagal withdrawal. Sympathovagal imbalance is more intense in salt-preferring prehypertensives compared with salt-preferring normotensives. Sympathovagal imbalance in salt-preferring subjects is independent of BMI. Thus, salt-preferring subjects should be encouraged to restrict salt intake to maintain their sympathovagal balance and BP homeostasis.