Think Before You Shake: UK Biobank Data Link Added Salt to Long-term CVD Risks

Frequently adding salt to food can set people up for an increased long-term risk of cardiovascular disease, especially heart failure and ischemic heart disease, new data suggest.

“For the first time, we found an eating behavior—adding salt to foods (usually at the table)—was related to risk of cardiovascular diseases,” senior author Lu Qi, MD, PhD (Tulane University School of Public Health and Tropical Medicine and Harvard T.H. Chan School of Public Health, Boston, MA), told TCTMD via email.

Compared with those who always added salt to their food before eating (not including salt used in cooking), individuals who never or rarely added salt had a 23% lower risk of long-term total CVD events, a 26% lower risk of ischemic heart disease, and a 37% lower risk of HF. People whose dietary habits most closely resembled a Dietary Approaches to Stop Hypertension (DASH) eating plan and who reported rarely or never adding salt to their food had the lowest overall risk of total CVD events.

Qi said the study, published this week in the Journal of the American College of Cardiology, suggests that most of the general population can benefit from cutting back on adding salt to their foods, or by using a salt substitute. 

The data add to prior work by Qi and colleagues that found that the risk of premature death (before age 75) was greater in those who reported adding salt to their food often compared with those who rarely or never did. But the evidence of the impact of dietary salt on outcomes has been conflicting, with some studies showing a direct linear relationship between intake and all-cause mortality, and others actually showing an inverse relationship. Data in support of salt substitutes have come from the SSaSS (Salt Substitute and Stroke Study) trial in Chinese participants, which found that using a substitute was associated with fewer strokes, major CV events, and all-cause deaths than regular use of table salt.

In an accompanying editorial, Sara Ghoneim, MD (University of Nebraska Medical Center, Omaha), says lowering sodium intake is thought to prevent CVD by modifying sympathetic activity and autonomic neuronal modulation of the CV system, which reduces both blood pressure and risk of end-organ damage. She concludes that the new study is “promising,” adding that it “builds on what was previously reported and eludes to the possible role that long-term salt preferences may have on the risks of total CVD events and major subtypes of CVD.”

Ghoneim further notes that recent data suggest that how often a person adds salt to their food “may not only represent the discretionary sodium intake of some individuals, but can also reflect the person’s long-term taste preference.”  

Less Salt, Fewer Events

Qi and colleagues, led by Hao Ma, MD, PhD (Tulane University, New Orleans, LA), examined data of more than 175,000 participants (mean age 56 years; 55% female) from the UK Biobank who were initially free of CVD and who were followed over a median of 11.8 years. Participants completed a questionnaire at baseline on the frequency of adding salt to foods (never or rarely, sometimes, usually, or always), provided dietary information used to calculate a DASH diet score, and had 24-hour sodium excretion estimates calculated from casual spot urinary concentrations. The DASH diet, which was originally developed to prevent hypertension, emphasizes eating fruit, vegetables, whole grains, low-fat dairy, nuts, and legumes and limiting intake of red and processed meats as well as sweetened beverages.

Over the follow-up period, there were 9,963 total CVD events (ischemic heart disease, stroke, and heart failure), with 6,993 diagnoses of ischemic heart disease, 2,007 strokes, and 2,269 diagnoses of heart failure. The strongest association between lower salt intake and CVD subtypes was for HF. Compared with those who always adding salt to food, those who usually did had a 30% reduction in risk of HF, while those who sometimes and those who never/rarely added salt saw even greater risk reductions (HR 0.65; 95% CI 0.54-0.79 and HR 0.63; 95% CI 0.52-0.76, respectively; P for trend < 0.001). An association was also seen between lower frequency of salt use and risk of CAD (P for trend < 0.001).

In subgroup analyses, the association between added salt and CVD risk was stronger in participants with lower versus higher socioeconomic status (P for interaction = 0.003) and in current smokers versus nonsmokers (P for interaction = 0.03). Additionally, greater adherence to the modified DASH eating plan (without considering sodium intake) was associated with significantly lower risks of total CVD events, CAD, stroke, and HF.

“A major limitation of the study is the self-reported frequency of adding salt to foods and the enrollment of participants only from the United Kingdom, limiting generalizability to other populations with different eating behaviors,” Ghoneim notes. She adds that randomized trials are warranted to replicate the study results. The study authors agree, pointing out that unmeasured or residual confounding cannot be excluded.