Should we be taking salt reduction messages with a pinch of salt?

How Salt Impacts Your Health

Matt Whitaker – Researcher and Trainer in Public Health/23 March 2017

What is salt?

Salt is arguably one of the most used ingredients worldwide. It is harvested from salt mines or through evaporating sea water or mineral rich water. Salt is used to enhance flavours of food and to aid in their preservation, as it prevents the growth of bacteria, thus extending shelf life. Salt is also known as sodium chloride. Consisting of sodium (40%) and chloride (60%). This means when you see ‘sodium’ listed by weight on food packaging you should multiply this figure by 2.5 to calculate the products salt content.

Salt is absolutely essential for life. It is used to regulate fluid balance and to control the functioning of the muscles and nerves. Meaning it is essential in contractions and nerve signalling to and from the brain. Without salt we would die, simple. Salt has been demonised due to its impact on blood pressure, although I’m going to park this for now and introduce the main different types of salt.

The different types of salt

Salt varies depending on how it is harvested and processed. As a result of this, different salts have slightly different micronutrient profiles (see table 1 for a comparison).

Table salt is the most consumed variant of salt. It is highly refined through heavy grinding, removing most of the impurities and trace minerals. Iodine is often added to table salt.

Sea salt is similarly processed to table salt although is not ground as heavily and may have a slightly more noteworthy micronutrient profile.

Himalayan salt is usually pink in colour due to its trace content of iron oxide (rust). It is unrefined and has more minerals than table salt, and its unique colour may help with the aesthetic appeal of a meal.

Maldon salt is usually crystallised, giving it a pleasant crunch on roast and baked foods, although it can cost nearly ten times more than conventional salt.

Kosher salt can be less dense than other salts, meaning you may not need as much for a similar flavour enhancement, its flaky texture means it is easily sprinkled on top of food.

Celtic salt is greyish in colour due to its higher magnesium content. It is an unrefined salt found on the coastal areas of France.

Table 1. Mineral content of different types of salt (1).

Salt may vary slightly in flavour, with the less refined salts having larger crystals meaning flavour may be more predominant and intense. Certain salts may be the optimal choice when considering cooking compared to baking compared to sprinkling on foods, although I feel that is a topic best covered by a chef as opposed to myself.

From a nutritional perspective all salts are generally comparable and to my understanding there is no research comparing consumption of different types of salt on health outcomes. All seem very similar, so I would say personal preference prevails when choosing your salt.

Salt recommendations

It is currently advised to have no more than 6g salt/day (2) with a high salt food being defined as containing  more than 1.5g/100g and a low salt food as less than 0.3g/100g product. Salt has a significant presence in most processed foods such as ready meals, which may partly explain its negative reputation. The adverse health outcomes of  high consumptions of processed foods are likely due to a multitude of factors such as the processing itself, the refined carbohydrate, the polyunsaturated fats, the artificial additions etc. It would be an unfair judgement to mark salt as a contributor to the same extent as these other factors. Despite this salt still receives a bad press and is advised against by healthcare bodies all over the world due to its impact on blood pressure.

Salt intake and health

The mechanism of action behind why salt increases blood pressure is a result of a rise of sodium in the blood. The more sodium the more water it binds. As blood pressure is elevated the heart naturally works harder to pump blood around the body which may increase strain on arteries and some organs. It is understood hypertension (high blood pressure) is a direct risk factor for several diseases, particularly cardiovascular diseases (CVD) and kidney failure.

Salt intake has been studied extensively in normotensive (healthy blood pressure) and hypertensive (high blood pressure) individuals. One Cochrane review of eight randomised controlled trials (gold standard of research) showed no statistically significant correlations between salt intakes on all-cause or CVD mortality (death) and thus does not support restricting salt intake in either individuals with normal blood pressure or high blood pressure individuals (3).

A separate Cochrane review, again in normotensive and hypertensive individuals, showed reducing salt intake marginally reduced blood pressure on average of -1.1mmHg (systolic) and -0.6mmHg (diastolic). These minimal changes failed to reach any clinical importance and despite a follow up period of up to seven years salt intake showed no relationship with all-cause mortality or CVD events (4).

Similar results have been shown in a separate meta-analysis in normotensive individuals (5) and some observational research has even shown a risk reduction in all-cause mortality with a slightly increased salt intake in patients with Type 2 diabetes. The authors did state this is a conclusion that has not been met with other literature and thus more research is required to establish its reliability (6).

Reduce salt intake

Recommendations to reduce salt intake are supported by the conclusion of a separate, massive Cochrane review of 34 randomised controlled trials on 3230 individuals. An average reduction in salt intake of -4.4g/day seemingly led to a mean reduction in blood pressure of -4.18mmHg (systolic) and -2.06mmHg (diastolic). This reduction was far more apparent in hypertensive individuals with reductions of -5.39mmHg (systolic) and -2.82mmHg (diastolic) compared to normotensive individuals who showed reductions of -2.42mmHg (systolic) and -1.00mmHg (diastolic) (7).

Now to get my critical head on. This reduction in people with normal blood pressure would be like going from 130/80mmHg to 128/78 which is clearly minimal, at the cost of such a dramatic reduction in salt intake. Additionally the two largest studies in this review showed minimal effect when examined in isolation and these two studies included 1773 of the 3230 subjects, that’s 55% of all subjects!

It is also interesting to note reductions in salt led to increased levels of serum renin, serum aldosterone and noradrenaline which may potentially increase the risk of coronary heart disease and in fact many medications dedicated on the treatment of CVD focuses on reducing these. Lastly the reduction in salt did slightly decrease blood pressure but that is not ultimately what we’re interested in. We want to know about CVD events and all-cause mortality, which were not reported on.

Dramatically reducing salt intake may be harmful to health as too little sodium has been associated with detrimental impacts on blood lipid profile (8), insulin resistance (9) and even (ironically) heart failure (10) where individuals who restricted their salt intake had a staggering 160% increased risk of death.

Too little salt

Lastly limiting your salt intake can dilute sodium levels to a dangerous extent and may induce a state of hyponatremia (too little sodium in circulation) which is very dangerous in itself (11).

Conclusion

To conclude, reducing salt intake only seems consistently beneficial for hypertensive individuals and whether this effect translates to reduced CVD risk or reduced all-cause mortality remains to be determined. Decreasing intake of processed foods, particularly refined carbohydrates, which is very advisable will automatically result in a reduced salt intake. Individuals following a low carbohydrate dietary approach may need to add additional salt to their foods to remain within healthy blood sodium levels.

Basically, take any advice to dramatically reduce salt intake with a pinch of salt.

References

1. Drake SL, Drake MA. Comparison of Salty Taste and Time Intensity of Sea and Land Salts from around the World. Journal of Sensory Studies. 2011;26(1):25-34.

2. British Nutrition Foundation. Nutrition Requirements. Revised 2015.

3. Adler AJ, Taylor F, Martin N, Gottlieb S, Taylor RS, Ebrahim S. Reduced dietary salt for the prevention of cardiovascular disease. The Cochrane database of systematic reviews. 2014(12):CD009217.

4. Hooper L, Bartlett C, Davey SG, Ebrahim S. Advice to reduce dietary salt for prevention of cardiovascular disease. The Cochrane database of systematic reviews. 2004(1):CD003656.

5. Graudal N, Hubeck-Graudal T, Jürgens G, McCarron DA. The Significance of Duration and Amount of Sodium Reduction Intervention in Normotensive and Hypertensive Individuals: A Meta-Analysis. Advances in Nutrition: An International Review Journal. 2015;6(2):169-77.

6. Ekinci EI, Clarke S, Thomas MC, Moran JL, Cheong K, MacIsaac RJ, et al. Dietary salt intake and mortality in patients with type 2 diabetes. Diabetes Care. 2011;34(3):703-9.

7. He FJ, Li J, Macgregor GA. Effect of longer-term modest salt reduction on blood pressure. The Cochrane database of systematic reviews. 2013(4):CD004937.

8. Jürgens G, NA G. Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterols, and triglyceride. The Cochrane database of systematic reviews. 2003;1:CD004022.

9. Rajesh Garg, Gordon H. Williams, Shelley Hurwitz, Nancy J. Brown, Paul N. Hopkins, Adler GK. Low-salt diet increases insulin resistance in healthy subjects. Metabolism – Clinical and Experimental. 2011;60(7):965–8.

10. Taylor RS, Ashton KE, Moxham T, Hooper L, Ebrahim S. Reduced dietary salt for the prevention of cardiovascular disease: a meta-analysis of randomized controlled trials (Cochrane review). American journal of hypertension. 2011;24(8):843-53.

11. Rosner MH, Kirven J. Exercise-associated hyponatremia. Clinical journal of the American Society of Nephrology : CJASN. 2007;2(1):151-61.