Dr. Gradual’s review of numerous short-term studies on salt reduction suggested that while reducing salt does modestly reduce BP, it might not reduce or could even increase the risk of CVD because of increases in other risk factors. Dr. Gradual reasoned that the small reduction in BP seen when salt intake was reduced may well be outweighed by modest increases in serum cholesterol and triglycerides and the renin/ angiotensin system and elevated levels of catecholamines and aldosterone . Of course the causal relationship between sodium intake and CVD events is better tested directly in long-term randomized clinical trials. However, no such long-term randomized trials have been done. The best data on salt reduction and CVD events comes from a follow-up study to the two Trials of Hypertension Prevention (TOPH). Back in the late 1980s and early 1990s two such randomized clinical trials (TOPH-I & TOPH-II) were conducted. Subjects in both these trials were 30-54 and all had prehypertension (120/80 to <140/90mmHg), no history of CVD, and were not taking anti-hypertensive medications. In both trials subjects were randomly assigned to either a control group or the interven- tion group. The intervention group of TOPH-I received comprehensive education and individual dietary counseling on sodium restriction for 18 months. In TOPH-II nutrition education on sodium reduction lasted at least 3 years. In TOPH-I the average reduction in sodium intake after 18 months for the intervention group was 44mmol (or 1012mg) and their BP was average 1.7/0.8mmHg less than that of the control group. In the TOPH-II the average sodium reduction after 3 years was reduced by an average 33mmol (or 759mg) per day and BP was 1.2/0.7mmHg lower on average. These small reductions in BP in the groups that received nutrition information on how to reduce salt/sodium intake were comparable to those reported by Dr. Gradual et al. in their meta-analysis of mostly much shorter clinical trials. Blood lipids, and changes in renin/angiotensin, catecholamines, and aldosterone were not measured but were likely similar to that seen in many shorter clinical trials. However, researchers followed up with the subjects in the two TOPH studies to see if sodium reduction impacted the risk of CVD events including stroke, heart attack, coronary revascualization, and CVD deaths.
Five to ten years after TOPH-I and TOPH-II ended the researchers found that there were 200 CVD events in the 2415 subjects. There were 25 to 30% fewer CVD events in those counseled to reduce sodium intake than in the control subjects.1 The results of this study demonstrated a significant 25%+ reduction in CVD events despite the rather modest reduction in salt intake and BP achieved in free-living subjects after 10-15 years.
Bottom Line: Clearly the results of the TOPH follow-up study conflict with Dr. Gradual’s thesis that increases in blood lipids and other hormones associated with salt reduction may eliminate any net benefit of a lower BP on the risk of CVD.
By James J. Kenney, PhD, FACN
1. Observational follow-up of the trials of hypertension prevention (TOPH). doi:10.1136/bmj39147.604896.55
Stephanie Ronco has been editing in a professional capacity for the past 10 years. In addition to her work as an editor, Ronco has also served as a ghostwriter and writing tutor. A voracious reader, Ronco loves watching language evolve and change. When she’s not delving into her latest project, Ronco can be found teaching acting classes, performing in community theater, or sailing with her husband.