Possible deleterious hormonal changes associated with low-sodium diets

Impact of Dietary Sodium Reduction on the Development of Obesity and Type 2 Diabetes in db/db Mice

The impact of dietary sodium reduction on mouse models of type 2 diabetes is not well understood. Therefore, we analyzed the effect of a low-salt diet on obesity and parameters of type 2 diabetes in db/db mice. Five-week-old male db/db and lean db/m mice were fed a normal salt (0.19% Na⁺, NS) or a low-salt diet (<0.03% Na⁺, LS) for 5 weeks. Body and organ weight and parameters of glucose and insulin tolerance were analyzed. Plasma levels of steroids were determined by liquid chromatography tandem mass spectrometry. Body weight, glucose, and insulin tolerance were not affected by LS. The amount of gonadal adipose tissue showed a trend to be increased by LS whereas liver, pancreas, kidney, heart, and adrenal weight remained unaffected. LS reduced urinary sodium-to-creatinine ratio but did not affect plasma Na⁺ levels in both genotypes. Plasma and urinary potassium-to-creatinine ratio did not differ in all groups of mice. Aldosterone as a major determinant of changes in dietary sodium remained unaffected by LS in db/db mice as well as further investigated steroid hormones. The present study showed reduced sodium-to-creatinine ratio, but no additional effects of dietary sodium reduction on major metabolic parameters and steroid levels in obese and hyper-glycemic db/db mice.

Simple dietary advice reduces 24-hour urinary sodium excretion, blood pressure, and drug consumption in hypertensive patients

Sodium intake should be restricted to 100 mEq, that is, about 2.3 grams per day. Strict diets, however, are often cumbersome and seldom matched by rigorous compliance. We studied 291 patients on antihypertensive treatment, 240 of whom were instructed to avoid salty foods, such as cheese and cured meats, and to switch from regular bread to salt-free bread. The remaining 51 matched patients constituted a control group and received only generic dietary advice. Na[U]/24h, K[U]/24h, and office BP (automated repeated measurements) were recorded before dieting started and after 9 ± 1 weeks of dieting. Our intervention group showed a significant decrease in body weight (71.75 ± 14.0 to 70.54 ± 13.33 kg, P < .0001), sodium excretion (153.1 ± 44.61 to 133.5 ± 37.1 mEq/24h, P < .05), systolic and diastolic BP (134.16 ± 16.0 to 126.5 ± 10.53 mm Hg, P = .014 and 80.59 ± 11.47 to 75.9 ± 8.72 mm Hg, P = .026, respectively), and drug consumption (1.71 ± 0.91 to 1.49 ± 0.84 DDD, P < .05). The rate of responders to antihypertensive therapy increased (51.4% to 79.5%). In the control group neither significant nor substantial changes were seen. Our data suggest that even a minimal reduction in the apparent sodium intake (∼0.5 grams per day) can improve both BP values and responder rates in treated hypertensive patients, while reducing the consumption of antihypertensive drugs.

Longitudinal Change of Perceived Salt Intake and Stroke Risk in a Chinese Population

BACKGROUND AND PURPOSE

Data for a relationship between salt intake and stroke have been inconsistent. This inconstancy could be because of the majority of studies evaluated salt intake at a single time point, which may be insufficient to accurately characterize salt intake throughout the observation period.

METHODS

Included were 77 605 participants from the Kailuan study. We assessed perceived salt intake via questionnaire in 2006, 2008, and 2010. Salt intake trajectories from 2006 to 2010 were identified using latent mixture models. Incident stroke cases were identified from 2010 to 2015 and confirmed by review of medical records. Cox proportional hazards model was used to examine the association between salt intake trajectories and stroke risk after adjusting for possible confounders, including age, sex, lifestyle, social economic status, body mass index, use of medicines, blood pressure, and lipoprotein profiles.

RESULTS

Identified were 5 distinct salt intake trajectories: moderate-stable (n=59 241), moderate-decreasing (n=9268), moderate-increasing (n=2975), low-increasing (n=2879), and high-decreasing (n=3242). During the 5-year follow-up period, there were 1564 incident strokes cases. Compared with individuals with the moderate-stable salt intake trajectory, individuals with moderate-decreasing salt intake trajectory had significantly lower cerebral infarction stroke risk (adjusted hazard ratio, 0.76; 95% confidence interval, 0.63-0.92) but not intracerebral hemorrhage risk (adjusted hazard ratio, 0.84; 95% confidence interval, 0.55-1.29). Further adjustment for 2006 or 2010 perceived salt intakes generated similar results. When baseline perceived salt intake only was used as the exposure, a significant dose-response relationship between higher perceived salt intake and higher stroke risk was observed (P trend=0.006).

CONCLUSIONS

Change in salt intake was associated with the stroke risk. These data support the dietary recommendation to the reduction of salt intake.

Low-salt diet increases NO bioavailability and COX-2 vasoconstrictor prostanoid production in spontaneously hypertensive rats

AIMS

The ability of dietary sodium restriction to reduce the incidence of cardiovascular mortality and improve vascular function in hypertension still remains poorly understood. The aim of this study was to observe the effects of a long period of salt restriction on the vascular reactivity of mesenteric resistance arteries of SHRs.

METHODS

Male SHRs received either standard-salt diet (0.3% NaCl) or low-salt diet (0.03% NaCl) for 28weeks. Vascular reactivity was studied in mesenteric artery segments and the influence of cyclooxygenase-2 (COX-2), reactive oxygen species (ROS) and participation of the renin-angiotensin system were analyzed.

KEY FINDINGS

Decreased salt intake did not affect phenylephrine-induced vasoconstriction but increased acetylcholine-induced vasodilatation and also increased the response to phenylephrine after inhibition of NO synthase by L-NAME (100μM) and iNOS protein expression was elevated. Cyclooxygenase inhibitor indomethacin (10μM) and COX-2 inhibitor NS 398 (1μM) decreased the reactivity to phenylephrine in low-salt-treated group, and COX-2 protein expression was elevated in low-salt group. The effects of apocynin (10μM); superoxide anion scavenger, tiron (1mM); hydrogen peroxide scavenger, catalase (1000UmL(-1)); and ACE and AT1 receptor blockers, enalapril (10μM) and losartan (10μM) on vascular reactivity were not different between two groups. The levels of AT1 protein expression were similar in both groups.

SIGNIFICANCE

Low-salt diet modulates mesenteric vascular responses via increased NO bioavailability suggested by increased iNOS protein expression and vasoconstrictor prostanoid production via COX-2 pathway, in SHRs. Neither ROS nor the local renin-angiotensin system is involved in these responses.