Monday, September 13, 2021

Do salt substitutes improve mortality in persons at high risk of CVD?

 - Jennifer Middleton, MD, MPH

The current Dietary Guidelines for Americans recommend limiting daily sodium intake to 2,300 mg or less, but 90% of Americans aged 2 years and older consume more salt than this amount daily. The best evidence to date recommends lowering sodium intake to reduce the risk of cardiovascular disease (CVD), but given the pervasiveness of sodium in the American diet, lowering salt intake can be challenging. Replacing table salt with a lower-sodium product could be a more feasible change, and a large randomized controlled trial now suggests that doing so may decrease mortality from CVD in those persons at higher risk. 

The study researchers enrolled nearly 21,000 participants from 600 villages in rural China. The researchers randomized villages to either continued usual salt use or use of a provided salt substitute (75% sodium chloride and 25% potassium chloride). Participants either had a history of stroke or were at least 60 years of age with hypertension:

The mean duration of follow-up was 4.74 years. The rate of stroke was lower with the salt substitute than with regular salt (29.14 events vs. 33.65 events per 1000 person-years; rate ratio, 0.86; 95% confidence interval [CI], 0.77 to 0.96; P=0.006), as were the rates of major cardiovascular events (49.09 events vs. 56.29 events per 1000 person-years; rate ratio, 0.87; 95% CI, 0.80 to 0.94; P<0.001) and death (39.28 events vs. 44.61 events per 1000 person-years; rate ratio, 0.88; 95% CI, 0.82 to 0.95; P<0.001).  

The difference in adverse events due to hyperkalemia was not statistically significant between groups. 

Generalizing the results of this study may be risky; I would presume that most Americans, for example, consume more processed foods and foods prepared outside of the home than the rural Chinese participants in this study. Since "[m]ost sodium consumed in the United States comes from salt added during commercial food processing and preparation, including foods prepared at restaurants," simply decreasing sodium intake in foods prepared at home may not have as great of an effect among persons eating the standard American diet. Then again, even a small benefit could have a sizable effect on population outcomes, and salt substitutes are inexpensive and simple to incorporate into home cooking. Given the minimal harms associated with the salt substitute product in this study, recommending a salt substitute for home use still seems like a reasonable recommendation for our patients at higher risk of CVD.

Taking the time to discuss these recommendations with patients is worthwhile; the United States Preventive Services Task Force (USPSTF) gives a "B" grade to "Behavioral Counseling Interventions to Promote a Healthy Diet and Physical Activity for CVD Prevention in Adults with Cardiovascular Risk Factors." As with all behavior change, tailoring strategies to each patient's circumstances increases the likelihood of success. In addition to recommending salt substitutes, we can teach our patients to read food labels for sodium content, recommend low salt recipes, and discourage frequent restaurant meals. For patients having difficulty making changes, this 2018 AFP article on "Diets for Health: Goals and Guidelines" includes this table with suggestions for overcoming common barriers to eating a healthier diet.