Salt or sodium?
The only thing that differentiates table salt, sea salt, rock salt, Himalayan rock salt or organic salt is a few minerals and a marketing strategy – they are the same thing. Salt or sodium chloride is the primary source of sodium for the human body.
Sodium Chloride has two elements –
sodium (40%) and chloride (60%)
Sodium is a key component of our body for regulating fluids i.e. our blood volume. Too much sodium increases the volume of the blood (by attracting water) thereby adding stress to the blood vessels and heart (more blood to pump around) and resulting in increased blood pressure. The connection between high blood pressure and increased risk of strokes, cardiovascular disease has been firmly established (1).
What is the evidence?
Initially, it was the Intersalt observational study (2) which found the association between sodium and blood pressure. Since then many randomised controlled trials have been organised to test this association.
Evidence of sodium intake affecting blood pressure is definite. The World Health Organisation (WHO) conducted a meta-analysis and systematic review. The overall objective was to assess the effect of reduced sodium intake on blood pressure, kidney function and blood lipids. Other specific objectives include looking at the effect of consuming less salt compared with consuming more and reducing the salt by varying amounts to establish the best intake zone (3).
- in normotensive and more so in hypertensive people
- regardless of how much the salt reduction was and
- regardless of whether blood pressure medication was taken or not
A reduction in salt intake is able to reduce resting diastolic blood pressure.
For the greatest positive effect in systolic and diastolic pressure, the sodium intake was less than 2g (5g salt) per day,
The same meta-analysis also confirmed blood lipids (total cholesterol, HDL and LDL and triglycerides) were not affected by changes in salt (3).
The relationship between high salt intake and increased systolic blood pressure (and thereby cardiovascular disease) makes high salt intake a major population health concern. WHO considers reducing daily salt intake will have significant health and financial benefits to the global population. New Zealand modelling has found similar effects and NZ would benefit financially and in terms of life quality with population salt reduction.
1 gram of sodium chloride (salt) contains 390 mg sodium
The majority of sodium comes from processed foods and it is challenging to leave the salt out of food processing. Changing the salt content in the food affects many things – taste, texture, shelf life and food safety. Initiatives to reformulate food with this goal in mind has been undertaken globally. Incognito salt reductions have already been accepted by consumers, up to 40% and 70% of salt has been removed from bread and processed meats (9).
Salt in the United Kingdom
The United Kingdom has actively been reducing salt in their food since 2003. Voluntary salt reduction in food manufacturing, public awareness campaigns and mandatory labelling of high salt foods has resulted in a 15% reduction in salt intake since the work started (10).
Salt in Australia and New Zealand
The Healthy Food Partnership, comprising of the Australian Government, public health groups and the food industry is also working towards reducing salt by reformulating food. Voluntary targets were set in 2009 for 10 food categories. However, a 2017 study (11) found only 17 of 33 large Australian food manufacturers have publicly available strategies to reduce salt content in their foods. The authors conclude insufficient efforts were being made to make “significant and comprehensive positive (nutrition) changes” in relation to salt or healthier food products”.
New Zealand has no government-led salt reduction strategy. The New Zealand Heart Foundation (NZHF) has led the charge, urging voluntary reductions from manufacturers through the NZHF ‘Tick’, initiated in 1991. This front-of-pack nutrition logo helps consumers determine heart-healthy foods and encourages ‘Tick’ food manufacturers to produce heart-healthy products. Over a 12 month period (1998/1999) The Tick program resulted in 33 tonnes of salt being removed from food products (12).
In 2010, 50% of New Zealand and 72% of Australian bread had reduced sodium levels to below 450mg/100g or 1.1 g salt per 100 g of bread (13)). Another New Zealand study demonstrated a 12% reduction in salt content in 182 foods over the 10 years to 2013 (14). The graph below shows different food groups and changes in salt quantity from this study.
Even though Australia and New Zealand have voluntary salt reduction programmes (and have seen some results in the food chain) they have not yet reported reductions in population salt intake and it is considered that the WHO global target will not be met in 2025 (15). This is not the case everywhere, 12 countries have reported reduced salt intakes in their population – will this correspond to reduced blood pressures?
New Zealand has a strong and committed non-government organisation, New Zealand Heart Foundation, to lead the salt reduction initiatives using food reformulation, front-of-pack labelling and consumer education but is this enough? Do we need a government led salt reduction programme to provide more resources and maybe even legislate?
- Lewington S, Clarke R, Qizilbash N, Peto R, Collins R. Age-specific relevance of usual blood pressure to vascular mortality: a meta-analysis of individual data for one million adults in 61 prospective studies. The Lancet 2002;360(9349):1903-13.
- Intersalt Cooperative Research G. Intersalt: An International Study Of Electrolyte Excretion And Blood Pressure. Results For 24 Hour Urinary Sodium And Potassium Excretion. BMJ: British Medical Journal 1988;297(6644):319-28.
- World Health Organization. Effect of reduced sodium intake on blood pressure, renal function, blood lipids and other potential adverse effects. 2012.
- World Health Organisation. Global action plan for the prevention and control of NCDs 2013-2020. Geneva: World Health Organisation, 2013.
- Land M, Neal B, Johnson C, Nowson C, Margerison C, Petersen K. Salt consumption by Australian adults: a systematic review and meta-analysis. Medical Journal of Australia 2018;208(2):75-81. doi: 10.5694/mja17.00394.
- McLean R, Edmonds J, Williams S, Mann J, Skeaff S. Balancing Sodium and Potassium: Estimates of Intake in a New Zealand Adult Population Sample. Nutrients 2015;7(11):5439.
- Hoy M, Goldman J, Murayi T, Rhodes D, Moshfegh A. Sodium intake of the U.S. population, NHANES 2007-2008. In: Group FSR, ed. Dietary Data Brief: Food Surveys Research Group Dietary Data Brief No 8, 2011.
- Bates BC, L; Maplethorpe, N; Mazumder, A; Nicholson, S; Page, P; Prentice, A; Rooney, K; Ziauddeen, N; Swan, G. National Diet and Nutrition Survey: assessment of dietary sodium. Adults (19-64 years) in England 2014. London: Department of Health, 2016.
- Jaenke R, Barzi F, McMahon E, Webster J, Brimblecombe J. Consumer acceptance of reformulated food products: A systematic review and meta-analysis of salt-reduced foods. Critical Reviews in Food Science and Nutrition 2017;57(16):3357-72. doi: 10.1080/10408398.2015.1118009.
- Webster J, Trieu K, Dunford E, Hawkes C. Target Salt 2025: A Global Overview of National Programs to Encourage the Food Industry to Reduce Salt in Foods. Nutrients 2014;6(8):3274.
- Lindberg R, Nichols T, Yam C. The Healthy Eating Agenda in Australia. Is Salt a Priority for Manufacturers? Nutrients 2017;9(8):881.
- Young L, Swinburn B. Impact of the Pick the Tick food information programme on the salt content of food in New Zealand. Health Promot Int 2002;17(1):13-9.
- Dunford E, Eyles H, Mhurchu CN, Webster J, Neal B. Changes in the sodium content of bread in Australia and New Zealand between 2007 and 2010: implications for policy. The Medical Journal of Australia 2011;195(6):346-9. doi: 10.5694/mja11.10673.
- Monro D, Mhurchu C, Jiang Y, Gorton D, Eyles H. Changes in the Sodium Content of New Zealand Processed Foods: 2003–2013. Nutrients 2015;7(6):4054.
- Trieu K, Eyles H, Webster J. Salt reduction in Australia and New Zealand: How do we compare with the rest of the world? Journal of Nutrition & Intermediary Metabolism 2016;4:26-7.