Salt intake was not associated with mortality or risk for cardiovascular disease (CVD) and heart failure (HF) in older adults based on self-reported estimated sodium intake, according to a researchers from Emory University in Atlanta.

However, the study, published online on 19 January 2015 by JAMA Internal Medicine, has been criticised by other experts on salt and health experts, who say the study is flawed and that a large body of existing evidence suggests salt is bad for health.

Contrary to these findings, the Australian National Heart Foundation has previously stated that “cutting salt could stop 5,800 heart attacks”.

Data on sodium restriction ‘scarce’, researchers

The Emory University researchers said data on sodium restriction among older adults are scarce, especially those with their blood pressure on target. They said achieving a sodium intake of less than 1,500 mg/day as currently recommended for adults over 50 also was difficult for older adults in part because of long-held dietary habits.

For these reasons, the researchers said the incremental benefit of restricting sodium to lower targets needed to be  evaluated.

Study method

Andreas P. Kalogeropoulos, M.D., M.P.H., Ph.D., of Emory University, Atlanta, and co-authors looked at the association between dietary sodium intake and mortality, CVD and HF in a group of 2,642 adults who ranged in age from 71 to 80 (51.2 percent of the participants were female and 61.7 percent were white). The authors analyzed 10-year follow-up data on the adults who were participating in this community-based study where dietary sodium intake was assessed at baseline with a questionnaire.

After 10 years, 881 of the participants had died, 572 had developed CVD and 398 had developed HF. Sodium intake was not associated with mortality, or new development of CVD or HF, according to study results. Ten-year mortality rates were 33.8 percent, 30.7 percent and 35.2 percent among participants consuming less than 1,500 mg/d, 1,500 to 2,300 mg/d, and greater than 2,300 mg/d of sodium, respectively.

“In conclusion, we observed that sodium intake estimated by FFQ [food frequency questionnaire] was not associated with mortality or risk for CVD and HF in a cohort of adults 71 to 80 years old,” the researchers wrote.

“Our data emphasise the need for stronger evidence, preferably from rigorous controlled trials testing additional thresholds for sodium intake, before applying a policy of further sodium restriction to older adults beyond the current recommendation for the general adult population (2,300 mg/d),” the researchers said.

This study was supported in part by grants from the Intramural Research Program of the National Institutes of Health and grants from the National Institute on Aging, the National Institute of Nursing Research and the National Center for Advancing Translational Sciences.

Study is ‘flawed’ say other experts

However, other experts have said the study had several limitations.

Professor Anna Domincza, Regium Professor of Medicine at the University of Glasgow said that several of the study’s limitations had been acknowledged by the authors.

“Firstly, food frequency questionnaires are not the optimal measure of sodium intake and have a poor correlation with the 24-hour urinary sodium excretion, which is a gold standard,” Professor Domincza said. “Therefore the association between dietary sodium intake and outcomes could have been attenuated,” she said.

“Secondly, the Health ABC Study was not designed to answer the question regarding appropriate dietary sodium intake,” Professor Domincza said. “This means that the analyses presented in the paper were secondary analyses not pre-specified when the study was originally designed.  Such secondary analyses are prone to confounding,” she said.

Professor Domincza said the study participants were volunteers with “good functional capacity and thus not fully representative of general older adult population”, and the lack of an association between dietary sodium intake and blood pressure or hypertensives status was “surprising”, as blood pressure increase is the main mechanism by which sodium intake leads to increased cardiovascular disease and heart failure risk. She said that in light of the limitations, the study’s recommendation that there was need for stronger evidence before the application of any policy of further sodium restriction was “correct and fully warranted”.

‘Healthy’ diet is a varied one, cardiovascular expert

Dr Tim Chico, Reader in Cardiovascular Medicine and consultant cardiologist at the University of Sheffield said the study highlights “how difficult it is to understand the relationship between lifestyle and health” and that “no single study can ever give a conclusive answer”.

“People are understandably confused by the conflicting results of scientific studies on the relationship between diet and health,” Dr Chico said. “Instead of concentrating on individual studies (which often only get attention if their results are unusual or surprising) it is much better to look at the overall message from all these studies,” he said.

“These are pretty clear; a healthy diet is varied, contains a high proportion of vegetables and a low amount of processed food, and does not provide more calories than needed to maintain a healthy weight,”Dr Chico said. “At the end of the day, most people don’t need a doctor or a scientist to tell them that an apple is almost certainly healthier than a packet of crisps.”

Study does not contradict current guidelines

Professor Jeremy Pearson, Associate Medical Director at the British Heart Foundation said the study did not contradict current dietary guidelines that people should consume less than 6g of salt per day.

“The study showed that risk of cardiovascular disease was not significantly different for people over 70 years old with a similar blood pressure but differing levels of salt intake,” Professor Pearson said. “However, blood pressure can be influenced by a number of factors and the finding that people with a similar blood pressure had a similar risk of cardiovascular disease is not surprising. More research is therefore needed before recommending further restrictions on salt intake for older adults,” he said.

“There is global agreement that lowering the amount of salt you consume will lower blood pressure which can significantly reduce your risk of cardiovascular disease,” Professor Pearson said.