When the dietary guidelines were first introduced about 40 years, one of the key recommendations was the population intake of sodium should be reduced. Effectively sodium was identified as a “baddy” and that efforts should be made to keep the amount consumed as low as possible. This remains the official position here in the UK today.

Based on the report of the Scientific Advisory Committee on Nutrition (SACN) of 2003 (1), the UK Government has recommended is that the maximum intake of salt for adults and children over 11 years should be 6g per day. The food industry has been encouraged by the Government to reformulate processed food products in order to reduce the salt content. This programme has certainly had an impact. The results of surveys show that the mean intake for adults aged 19 to 64 years has fallen from 8.0g per day in 2005/6 to 7.1g per day in 2014 (2).

The doubts emerge

So while the authorities continue to push for a reduction in salt intake, there evidence appearing, which suggests that some people may not be consuming adequate amounts. One of the problems in determining the recommendations on the maximum (and minimum) amounts of any nutrient to be consumed is that the information available can be very limited. Hence assumptions are made that turnout to be faulty. The most effective way to check if the recommendations are sound is to follow people who comply with them and monitor their health. In an ideal world, it would be possible to continue until death. Essentially this has been the approach in the Prospective Urban Rural Epidemiology (PURE) study coordinated by the Population Health Research Institute, Hamilton Health Sciences, Hamilton, Ontario, Canada. A paper published in 2014, provided valuable insights into the optimum intakes of salt (3).

In total there are 156,424 persons being monitored. They are aged 35 to 70 years, residing in 628 urban and rural communities in 17 low-, middle-, and high-income countries (Argentina, Bangladesh, Brazil, Canada, Chile, China, Colombia, India, Iran, Malaysia, Pakistan, Poland, South Africa, Sweden, Turkey, United Arab Emirates, and Zimbabwe). For the work on sodium and potassium, data were obtained for 101,945 participants, who provided urine sample that could be analysed to assess the 24-hour intake of these nutrients.

The mean estimated sodium excretion, which reflected the intake over the previous 24 hours was 4.93g sodium (12.3g salt). The mean follow-up period was 3.7 years. Information was collected for 95% of the participants. During this time, 3317 died or had a major cardiovascular event. There were 1976 participants who died (650 from cardiovascular causes), 857 had myocardial infarction, 872 had stroke, and 261 had heart failure.

The most interesting result is that the lowest death rates occur in those who are consuming 4-7g sodium per day which is equivalent to 10-17.5g per day of salt. There were higher death rates for those who consumed both higher and lower intakes. On average, those who consumed less than 8g salt per day had a death rate 38% higher than those consuming 10-17.5g per day.

It is this result that should set the alarm bells ringing because here in the UK we are being advised that 6g salt is the maximum intake. Therefore it follows that those who comply with the official advice on salt intake are probably not deriving any benefit and may well have reduced their life expectancy. Furthermore the research also shows that there is a graded response, which means that the lower the intake the more the death rate is increased. The irony is that if the results of this PURE study are reliable, then all these initiatives to lower salt intake have not improved health and are likely to have been damaging. This study also shows that intakes have to be higher than 1.5g per day before any increase in death rate is recorded. In practice, this is probably restricted to those who consume a high proportion of processed foods.

How have we got into such a mess?

If we go back and look at the official report from SACN, what is immediately apparent is the obsession with blood pressure (BP). For example the opening paragraph of the Summary is:

“Increased blood pressure, or hypertension, is the most common outcome that has been associated with high levels of salt intake. Hypertension is a major risk factor in the development of cardiovascular disease. The relative risk of cardiovascular disease increases as blood pressure rises even within what is considered the normal range of blood pressure, indicating that large numbers of people are at risk.”

For the advice to have any validity, it would have to be established that a reduction in BP would actually be beneficial. Yet the report admits:

“There are insufficient reliable data on long-term effects of salt on cardiovascular disease outcomes to reach clear conclusions.”

Basically what this means is that the group preparing the report is operating on a wing and a prayer. What is equally unfortunate is that the degree of BP reduction that can be achieved by reducing salt intake is relatively small and that greater reductions can be achieved by increasing consumption of fruit and vegetables.

What is unbelievable is the cavalier approach to assessing the minimum intake of sodium. There is no question that sodium is an essential nutrient. Therefore if the intake is inadequate, the body will not be able to function properly. There is very little effort to determine how much is needed and how that requirement can be fulfilled. There is a small section dealing with the physiological requirements. It is recognised that there in warm climates there is an additional need for salt but concludes rather complacently that:

“There is little evidence that, in a temperate climate such as that of the UK, salt intakes of 4-6g per day (70-100 mmol/1.6-2.4g sodium) would have any adverse physiological effects on a healthy population.”

Conclusion

The reality is that this aspect has just been treated superficially and there has been a total failure to appreciate that any recommendation to lower salt will inevitably mean that some people will have intakes which are much lower than the maximum specified. In the event there has been so much emphasis on the need to reduce salt, we have lost sight of the fact that sodium has a vital function. All of the worst fears have been confirmed by the PURE study. What is unforgivable is that the establishment continue to promote a strategy that fatally flawed and causing unnecessary ill-health, especially among those who take the advice seriously.

References

  1. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/338782/SACN_Salt_and_Health_report.pdf
  2. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/509399/Sodium_study_2014_England_Text_final.pdf
  3. http://www.nejm.org/doi/full/10.1056/NEJMoa1311889