Adding Salt to Food Linked to Higher CVD Risk

A lower frequency of adding salt to food is associated with lower risk of cardiovascular disease, particularly heart failure and ischemic heart disease, a new study has found.

The study analyzed the association of adding salt to food and incident cardiovascular disease risk in 176,570 adults participating in the UK Biobank database.

Results showed that a lower frequency of adding salt to foods was significantly associated with lower risk of total cardiovascular events after adjustment for covariates and the DASH (Dietary Approaches to Stop Hypertension) diet. 

Compared with the group who always added salt to food, those who usually added salt had a 19% reduction in risk of cardiovascular events; those who sometimes added salt had a 21% reduction; and those who rarely or never added salt had a 23% reduction.  

Participants who combined a DASH-style diet with the lowest frequency of adding salt had the lowest cardiovascular risk.

“Our results indicate an additive role of lower salt preference and a healthier diet in cardiovascular disease prevention,” the researchers, led by Hao Ma, MD, School of Public Health and Tropical Medicine, Tulane University, New Orleans, Louisiana, conclude.

“Adding salt to foods (usually at the table) is a common behavior in the diet of some Western countries and is modifiable through health education,” they note. “Our findings also indicate that behavioral interventions to reduce adding salt to foods may improve cardiovascular health, even in those with a DASH-style diet.”

The study is published in the December 6 issue of the Journal of the American College of Cardiology, available online on November 28.

The authors explain that while there is substantial evidence supporting high sodium intake as a major cause of hypertension, previous epidemiologic studies investigating the relationship between dietary sodium intake and cardiovascular disease have generated conflicting results. An important reason for such conflicting results is the lack of valid and feasible methods for assessing long-term dietary sodium intake.

The recent large-scale Salt Substitute and Stroke Study (SSaSS) showed that using a salt substitute to replace the regular salt used in cooking generated significant benefits on cardiovascular events in a Chinese population.

Several previous studies have also found that the frequency of adding salt to foods may be considered as a surrogate marker for evaluating individual long-term sodium intake in the Western diet. But, until now, no study has assessed whether the frequency of adding salt to foods is associated with cardiovascular risk in prospective cohorts.

The researchers therefore conducted the current study to investigate the association between the frequency of adding salt to foods and cardiovascular disease risk in the UK Biobank, a large population-based, prospective study including more than 500,000 participants.

They also analyzed the joint association between the frequency of adding salt to foods and the DASH diet (a modified DASH score was used without considering sodium intake) in relation to risk for cardiovascular disease.

The current analysis included 176,570 participants from the UK Biobank database who had completed at least one 24-hour dietary assessment, had complete data on the frequency of adding salt to foods, and had no history of cardiovascular disease at the time of dietary assessment.

Information on the diagnosis of cardiovascular events was collected through medical history and linkage to data on hospital admissions as well as questionnaire and the death register data.

Results showed that during a median follow-up of 11.8 years, there were 9963 incident cardiovascular events.

For total cardiovascular events, after adjustment for sex, age, race, body mass index, smoking, alcohol drinking, regular physical activity, socioeconomic status, high cholesterol, chronic kidney disease, diabetes, cancer, total energy intake, and the modified DASH diet score, lower frequency of adding salt to foods was significantly related to lower risk of cardiovascular events.

The adjusted hazard ratios (HR) were 1.00 (reference — always add salt); 0.81 (usually add salt); 0.79 (sometimes add salt); and 0.77 (never/rarely add salt), showing a statistically significant trend.

For the subtypes of cardiovascular disease, the strongest association was with heart failure: compared with the group of always adding salt to foods, the adjusted HRs were 0.70; 0.65; and 0.63 across the groups of usually, sometimes, and never/rarely.

Lower frequency of adding salt to foods was also significantly associated with a lower risk of ischemic heart disease, but not associated with stroke.

The researchers say the lack of statistically significant association with stroke risk should be interpreted with caution, noting that the benefits of sodium reduction on stroke risk have been demonstrated in the SSaSS study, and the null association in the present study might be partly caused by the limited number of stroke cases.

Subgroup analyses showed that the association of adding salt to foods with risk of cardiovascular disease was stronger in current smokers and in participants with lower socioeconomic levels.

Noting that previous studies have shown that both lower socioeconomic level and current smoking are related to higher salty taste threshold, the authors say these results “highlight the importance of improving eating habits in the participants with high salt preferences.”

The study also found that higher modified DASH diet scores, without considering sodium intake, were significantly associated with lower risks of total cardiovascular events, and participants who combined the highest level of the DASH-style diet with the lowest frequency of adding salt had the lowest cardiovascular risk.

‘Encouraging Findings’

In an accompanying editorial, Sara Ghoneim, MD, University of Nebraska Medical Center, Omaha, points out that the effect of salt reduction on cardiovascular risk has been challenged by some observational studies in which investigators reported J-shaped or U-shaped associations, suggesting that both low and high salt intake were associated with increased risk. However, these studies had severe methodological limitations.

She notes that SSaSS was the largest clinical trial of salt reduction and cardiovascular events, and showed a reduced risk of stroke, major cardiovascular events, and even death from any cause in Chinese participants using salt substitute compared with those using regular salt.

“The present study builds on what was previously reported and alludes to the possible role that long-term salt preferences may have on the risks of total cardiovascular events and major subtypes of cardiovascular disease,” Ghoneim says. 

She lists limitations of the current study as the self-reported frequency of adding salt to food and the enrollment of participants only from the United Kingdom, limiting generalizability to other populations with different eating behaviors.

“Randomized trials are warranted to ascertain the results of this study. Nonetheless, the findings of the present study are encouraging and are poised to expand our understanding of salt-related behavioral interventions on cardiovascular health,” she concludes.

This study was supported by grants from the National Heart, Lung, and Blood Institute; the National Institute of Diabetes and Digestive and Kidney Diseases; the Fogarty International Center; and Tulane Research Centers of Excellence Awards. The authors reported no disclosures.

J Am Coll Cardiol. Published online November 28, 2022. Abstract; Editorial.

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