Moderate reductions in the amount of salt people eat doesn't reduce their likelihood of dying or experiencing cardiovascular disease. This is the main conclusion from a systematic review published in the latest edition of The Cochrane Library.
The study is published in the May 4 issue of The Journal of the American Medical Association. It included 3,681 middle-aged Europeans who did not have high blood pressure or cardiovascular disease and followed them for an average of 7.9 years.
The researchers assessed the participants’ sodium consumption at the study’s start and at its conclusion by measuring the amount of sodium excreted in urine over a 24-hour period. All the sodium that is consumed is excreted in urine within a day, so this method is the most precise way to determine sodium consumption.
The investigators found that the less salt people ate, the more likely they were to die of heart disease — 50 people in the lowest third of salt consumption (2.5 grams of sodium per day) died during the study as compared with 24 in the medium group (3.9 grams of sodium per day) and 10 in the highest salt consumption group (6.0 grams of sodium per day). And while those eating the most salt had, on average, a slight increase in systolic blood pressure — a 1.71-millimeter increase in pressure for each 2.5-gram increase in sodium per day — they were no more likely to develop hypertension.
"What we wanted to see was whether this dietary change also reduced a person's risk of dying or suffering from cardiovascular events," says Taylor.
An earlier Cochrane review of dietary advice published in 2004 could not find enough evidence to allow the researchers to draw any conclusions about the effects of reducing salt intake on mortality or cardiovascular events. In Taylor's newly published research, however, the team managed to locate seven studies that together included 6,489 participants. This gave a sufficiently large set of data to be able to start drawing conclusions. Even so, Taylor believes he would need to have data from at least 18,000 individuals before he could expect to reveal any clear health benefits.
Most experts are agreed that consuming too much salt is not good for you and that salt reduction is beneficial in people with normal and high blood pressure. "We believe that we didn't see big benefits in this study because the people in the trials we analyzed only reduced their salt intake by a moderate amount, so the effect on blood pressure and heart disease was not large," says Taylor. He believes that health practitioners need to find more effective ways of reducing salt intake that are both practicable and inexpensive.
Many countries have government-sanctioned recommendations that call for reduced dietary sodium. In the UK, the National Institute of Health and Clinical Guidance (NICE) has recently called for an acceleration of the reduction in salt in the general population from a maximum intake of 6g per day per adult by 2015 to 3g by 2025.
"With governments setting ever lower targets for salt intake, and food manufacturers working to remove it from their products, it's really important that we do some large research trials to get a full understanding of the benefits and risks of reducing salt intake," says Taylor.