How much salt is too much
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How much salt is too much?

If you have a heart condition, your doctor has probably told you to limit your salt intake. As it is impossible and undesirable to eliminate salt completely, it is important to know much salt is too much?

Sodium vs salt

Sodium is a mineral and what we know as salt (the one we use for seasoning our food) is sodium chloride. Therefore, the amount of salt we consume does not equal the amount of sodium we consume. Sodium in food manifests in other forms, not just as the salt that is added for seasoning.

Sodium is involved in many processes in the body, including maintenance of plasma volume, acid-base balance, transmission of nerve impulses and normal cell function (1).

Sodium is found naturally in a variety of unprocessed foods (e.g. milk, meat and shellfish) (1), however most of the sodium in our diets comes from processed foods, about 80% as estimated by FSANZ (1, 2). The foods that contribute the most to sodium intake in the Australian diet are bread and bread rolls, meat (including processed meat), and cereal products and cereal-based dishes (e.g. biscuits and pizza) (2). Other foods that contain high amounts of sodium include snack foods, condiments and monosodium glutamate (1).

How much salt is too much?

The Australian Dietary Guidelines, the World Health Organization (1) and the Heart Foundation recommend that adults limit their salt intake to 5g per day (which is equivalent to 2000mg of sodium per day) (1, 3, 4) In addition, the WHO recommends to consume only iodised salt (1).

Is there such thing as too little salt?

In short, yes. Sodium, as many other substances, has a U or J-shaped relationship, meaning that both too little and too much sodium can cause problems. In fact, meta-analyses have found that both lower and higher intakes of sodium are associated to increased risk of all cause mortality and cardiovascular disease. While these effects seem to be stronger for high intakes, when data are adjusted for confounders the strength seems to be equivalent for both ends of the spectrum (5, 6).

Low-salt diets can have small to moderate effects in blood pressure reduction depending on the baseline blood pressure of the individual. However they have also been shown to increase uric acid, blood lipids (LDL-cholesterol, total cholesterol, triglycerides), hormones (renin, aldosterone, noradrenaline), creatinine, inflammation, etc., and decrease HDL-cholesterol (6, 7).

The adverse outcomes of restricting sodium too much seem to appear when daily intake is below 2300mg (5.75g salt) (7), and optimal intake of sodium has been suggested to be 2645–4945mg (6).

How much sodium do we eat?

The sodium intake for most of the population has been estimated to be 2620-4830mg per day (equivalent to 6.6-12.2g of salt per day) (6).

In Australia, FSANZ has estimated that the average salt intake is 5.5g per day for individuals over 2 years old (2). Obviously, children have a much lower intake, so adults are likely consuming a lot more than the average.

A comprehensive review estimated salt consumption in Australia using different methods, with the following results: (8)

Estimation methodSalt intake (g/day)Sodium intake (mg/day)
24-hour urine collections8.7-9.6 (10.07 for males, 7.34 for females)3480-3840 (4028 for males, 2936 for females)
Food frequency questionnaires6.762704
Dietary recalls6.692676
Diet diaries6.49g2596

Beyond sodium

Like sodium, potassium is also involved in body fluid and pH balance, and cell function (1). Potassium opposes the effect of sodium on blood pressure. In fact, analyses of populations that consume higher than average amounts of sodium but also consume high levels of potassium (in an approximate 1:1 ratio) have shown those populations do not have hypertension (7).

Furthermore, populations that consume high sodium but low refined sugar do not develop hypertension either (7).

Potassium is found in fruits and vegetables, indicating that a diet high in unprocessed foods including several serves of vegetables and fruits is key for preventing risk of cardiovascular disease and all cause mortality.

References

  1. World Health Organization. Salt reduction [Internet]. 2020 [cited 2023 May 6]. Available from: https://www.who.int/news-room/fact-sheets/detail/salt-reduction
  2. Food Standards Australia New Zealand. How much sodium do Australians eat? [Internet]. 2015. Available from: https://www.foodstandards.gov.au/consumer/nutrition/salthowmuch/pages/howmuchsaltareweeating/howmuchsaltandsodium4551.aspx
  3. Council NH and MR. Nutrient Reference Values for Australia and New Zealand Including Recommended Dietary Intakes [Internet]. 2017. Available from: https://www.eatforhealth.gov.au/sites/default/files/2022-04/sodium_chapter.pdf
  4. National Heart Foundation of Australia. Heart Healthy Eating [Internet]. 2018. Available from: https://www.heartfoundation.org.au/getmedia/defa5336-0bc0-4915-ae05-98ba05bdf0a6/190729_Nutrition_Position_Statement_-_Salt2.pdf
  5. Graudal N, Jürgens G, Baslund B, Alderman MH. Compared with usual sodium intake, low- and excessive-sodium diets are associated with increased mortality: a meta-analysis. Am J Hypertens. 2014 Sep;27(9):1129–37.
  6. Graudal N. A Radical Sodium Reduction Policy is not Supported by Randomized Controlled Trials or Observational Studies: Grading the Evidence. Am J Hypertens. 2016 May;29(5):543–8.
  7. DiNicolantonio JJ, O’Keefe JH. Salt and hypertension: what do we know? Curr Opin Cardiol. 2018 Jul;33(4):377–81.
  8. Land M-A, Neal B, Johnson C, Nowson C, Margerison C, Petersen KS. Salt consumption by Australian adults: a systematic review and meta-analysis. Med J Aust. 2018;208(2):75–81.

[Photo by Jason Tuinstra on Unsplash]

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