Salt and health

Table salt, the salt that we, and the food processing industry, add to our food to enhance its flavor and to satisfy the human physiologically innate hunger for salt,   consists, in its familiar solid granulated form, of the crystalline ionic compound of sodium cations (Na⁺) and chloride anions (Cl^-), referred to as sodium chloride, chemical formula, NaCl. Added to water, the salt dissolves, the compound dissociates into its constituent cations and anions, each ion encased in a dynamically changing shell of water molecules, forming an aqueous solution.

Consumption of NaCl is necessary for the survival of humans, the amount required depending on physiological conditions. Under ordinary physiological conditions, the amounts required fall in the category of a 'low-salt' diet.

Human populations have demonstrated the capacity to survive at extremes of sodium intake from less than 0.2 g (10 mmol)/day of sodium in the Yanomamo Indians of Brazil to over 10.3 g (450 mmol)/day in Northern Japan. The ability to survive at extremely low levels of sodium intake reflects the capacity of the normal human body to conserve sodium by markedly reducing losses of sodium in the urine and sweat. Under conditions of maximal adaptation and without sweating, the minimal amount of sodium required to replace losses is estimated to be no more than 0.18 g (8 mmol)/day.

The amounts of NaCl consumed influence the concentrations and total amounts of sodium and chloride in cellular and extracellular fluids, critical determinants of optimal physiological functioning, in part through their effect on cellular and extracellular fluid volume and osmolarity. Accordingly, physiological homeostatic and allostatic systems carefully regulate those variables.

Most of the NaCl we consume, nearly 80%, derives from the processed/canned foods that we eat. Under steady-state conditions, sodium chloride excretion, predominantly by the kidneys, balances sodium chloride consumption.

Salt-related conditions

Too much or too little salt in the diet can lead to muscle cramps, dizziness, or even an electrolyte disturbance, which can cause severe, even fatal, neurological problems.

It has been suggested that excessive salt consumption might be linked to the following conditions:

• asthma A study concludes, "Our results suggest that large increases in dietary sodium result in physiological deterioration and increased morbidity in male asthmatic patients." For exercise-induced asthma (EIA), a study suggests that salt intake and EIA are related.
• heartburn.
• osteoporosis One paper states, "These data suggest that an effect of reducing bone loss equivalent to that achieved by a daily dietary increase of 891 mg (22 mmol) Ca can also be achieved by halving daily sodium excretion." One report shows that a high salt diet does reduce bone density in girls.. Yet "While high salt intakes have been associated with detrimental effects on bone health, there are insufficient data to draw firm conclusions." (, p3)
• Gastric cancer (Stomach cancer) is associated with high levels of sodium, "but the evidence does not generally relate to foods typically consumed in the UK." (, p18) However, in Japan, salt consumption is higher. A study conducted in Puerto Rico concluded, "A statistically significant dose response for the index of salt exposure and gastric cancer was also found."
• prehypertension (high normal blood pressure between 120/80 and 140/90)
• hypertension (blood pressure is persistently at or above 140/90): "Since 1994, the evidence of an association between dietary salt intakes and blood pressure has increased. The data have been consistent in various study populations and across the age range in adults." ( p3). A large scale study from 2007 has shown that people with high-normal blood pressure who significantly reduced the amount of salt in their diet decreased their chances of developing cardiovascular disease by 25% over the following 10 to 15 years. Their risk of dying from cardiovascular disease decreased by 20%.
• left ventricular hypertrophy (cardiac enlargement): "Evidence suggests that high salt intake causes left ventricular hypertrophy, a strong risk factor for cardiovascular disease, independently of blood pressure effects." ( p3) "…there is accumulating evidence that high salt intake predicts left ventricular hypertrophy." (, p12) Excessive salt (sodium) intake, combined with an inadequate intake of water, can cause hypernatremia. It can exacerbate renal disease.
• edema (BE: oedema): A decrease in salt intake has been suggested to treat edema (fluid retention).
• duodenal ulcers and gastric ulcers
• Severe premenstrual syndrome
• Vertigo of Meniere’s disorder
• Acute salt poisoning
• Chinese restaurant syndrome
• Idiopathic oedema
• Congestive heart failure
• Carpal tunnel syndrome
• Glaucoma
• Diabetic retinitis
• macular degeneration (wet type)
• Calcium kidney/bladder stones "In men with recurrent calcium oxalate stones and hypercalciuria, restricted intake of animal protein and salt, combined with a normal calcium intake, provides greater protection than the traditional low-calcium diet."
• Pulse wave velocity "This is prima facie evidence that reduced salt intake has a beneficial effect in improving distensibility of the central aorta and large peripheral arteries, which is independent of its antihypertensive action."
• Aggregation of erythrocytes
• Helicobacter pylori infection
• Crohn’s disease
• microalbuminuria
• Diabetic nephropathy
• Ingestion of large amounts of salt in a short time (about 1 g per kg of body weight) can be fatal through hypernatremia. Salt solutions have been used in China as a traditional suicide method, and deaths have also resulted from attempted use of salt solutions as emetics, forced salt intake, and accidental confusion of salt with sugar in child food.

Salt is sometimes used as a health aid, such as in treatment of dysautonomia.

Salt intake and cardiovascular disease (CVD)

Low sodium diet may decrease blood pressure but increase morbidity.

A study published in 2008 concluded, "....for the general US adult population, higher sodium is unlikely to be independently associated with higher CVD [cardiovascular disease] or all-cause mortality." A group serving the "....the food, pharmaceutical, and consumer goods industries...." publicized the paper. Yet, the absence of evidence does not necessarily count as evidence of absence. The investigators used the term "unlikely" based on 'trends' suggested by the data, and could not render a more definitive conclusion because of lack of statistical significance, despite a very large sample-size in the analysis. They also used the phrase "independently associated" because they used statistical methods to 'adjust' for differences in other variables that might influence mortality due to cardiovascular disease during the interval of observation. Certain of those variables, however, might interact with dietary salt intake to influence cardiovascular mortality.

One such interacting variable, dietary potassium intake, comes out of a similar study carried out in Rotterdam, which likewise revealed "....no consistent association of urinary sodium [a marker of dietary sodium]....with CVD and all-cause mortality....". However, in participants initially free of CVD and hypertension, the investigators found that dietary potassium, a factor known to reduce body content of sodium through enhancing the efficiency of kidney sodium excretion, associated with a lower risk of all-cause mortality. In such participants who qualified as overweight, the higher amounts of urinary sodium relative to the amounts of urinary potassium, a marker of the dietary sodium-to-potassium ratio, associated with higher all-cause mortality.

The Rotterdam study raises the possibility that higher dietary potassium has a sodium countervailing effect in respect of the pathogenesis of CVD, or conversely, that lower dietary potassium exaggerates the effect of sodium, and suggests that individuals initially free of CVD can substantially improve their chances of living longer by increasing their dietary potassium intake.

In a 2011 publication of the Annual Review of Public Health, an in-depth review of the relation of cardiovascular disease (CVD) and sodium intake, data from published studies, concluded that men and women of all ages, ethnicities, and normotensives experience reduced CVD risk when consuming a lowered sodium intake. CVD denotes clinical effects on the heart or blood vessels, and accounts for approximately one-third of deaths in the U.S. The authors also conclude that:

Public health policy to reduce sodium intake in the United States would have significant cost-savings, far greater than the cost of intervention, and would also result in a significant gain in quality-adjusted life years.

Recommended intake

This section summarizes the salt intake recommended by the health agencies of various countries. Recommendations tend to be similar. Note that targets for the population as a whole tend to be pragmatic (what is achievable) while advice for an individual is ideal (what is best for health). For example, in the UK target for the population is "eat no more than 6 g a day" but for a person is 4 g.

Intakes can be expressed variously as salt or sodium and in various units.

• 1 g sodium = 1,000 mg sodium = 42 mmol sodium = 2.5 g salt

United Kingdom: In 2003, the UK's Scientific Advisory Committee on Nutrition (SACN) recommended that, for a typical adult, the Reference Nutrient Intake is 4 g salt per day (1.6 g or 70 mmol sodium). However, average adult intake is two and a half times the Reference Nutrient Intake for sodium. "Although accurate data are not available for children, conservative estimates indicate that, on a body weight basis, the average salt intake of children is higher than that of adults." SACN aimed for an achievable target reduction in average intake of salt to 6 g per day (2.4 g or 100 mmol sodium) — this is roughly equivalent to a teaspoonful of salt. The SACN recommendations for children are:

• 0–6 months old: less than 1 g/day
• 7–12 months: 1 g/day
• 1–3 years: 2 g/day
• 4–6 years: 3 g/day
• 7–10 years: 5 g/day
• 11–14 years: 6 g/day

SACN states, "The target salt intakes set for adults and children do not represent ideal or optimum consumption levels, but achievable population goals."

Republic of Ireland: The Food Safety Authority of Ireland endorses the UK targets "emphasising that the RDA of 1.6 g sodium (4 g salt) per day should form the basis of advice targeted at individuals as distinct from the population health target of a mean salt intake of 6 g per day."(, p16)

Canada: Health Canada recommends an Adequate Intake (AI) and an Upper Limit (UL) in terms of sodium.

• 0–6 months old: 0.12 g/day (AI)
• 7–12 months: 0.37 g/day (AI)
• 1–3 years: 1 g/day (AI) 1.5 g/day (UL)
• 4–8 years: 1.2/day (AI) 1.9 g/day (UL)
• 9–13 years: 1.5 g/day (AI) 2.2 g/day (UL)
• 14–50 years: 1.5 g/day (AI) 2.3 g/day (UL)
• 51–70 years: 1.3 g/day (AI) 2.3 g/day (UL)
• 70 years and older: 1.2 g/day (AI) 2.3 g/day (UL)

New Zealand

• Adequate Intake (AI) 0.46 – 0.92 g sodium = 1.2 – 2.3g salt
• Upper Limit (UL)) 2.3 g sodium = 5.8 g salt

Australia: NHMRC recommends an Adequate Intake (AI) and an Upper Limit (UL) in terms of sodium.

Adequate Intake (AI)

• 0–6 months 120 mg/day (5.2 mmol)
• 7–12 months 170 mg/day (7.4 mmol)
• 1–3 yr 200–400 mg/day (9–17 mmol)
• 4–8 yr 300–600 mg/day (13–26 mmol)
• 9–13 yr 400–800 mg/day (17–34 mmol)
• 14–18 yr 460–920 mg/day (20–40 mmol)
• Adults 460-920 mg/day (20-40 mmol)
• Pregnancy (all ages) 460-920 mg/day (20-40 mmol)
• Lactation (all ages) 460-920 mg/day (20-40 mmol)

Upper Level (UL)

• 0–12 months Not possible to establish. Source of intake should be through breast milk, formula and food only.
• 1–3 yr 1,000 mg/day (43 mmol)
• 4–8 yr 1,400 mg/day (60 mmol)
• 9–13 yr 2,000 mg/day (86 mmol)
• 14–18 yr 2,300 mg/day (100 mmol)
• Adults 19+ yr 2,300 mg/day (100 mmol)
• Lactation (all ages) 2,300 mg/day (100 mmol)

Another Australian government site gives a recommended dietary intake (RDI) is 0.92 g–2.3 g sodium per day (= 2.3 g–5.8 g salt)

USA: The Food and Drug Administration itself does not make a recommendation but refers readers to Dietary Guidelines for Americans 2005. These suggest that US citizens should consume less than 2,300 mg of sodium (= 2.3 g sodium = 5.8 g salt) per day.

France: "In 2002, Afssa recommended a 20% reduction in salt consumption over 5 years, i.e. to 6 to 8g a day on average."

Labelling

UK: The Food Standards Agency defines the level of salt in foods as follows: "High is more than 1.5g salt per 100g (or 0.6g sodium). Low is 0.3g salt or less per 100g (or 0.1g sodium). If the amount of salt per 100g is in between these figures, then that is a medium level of salt." In the UK, foods produced by some supermarkets and manufacturers have ‘traffic light’ colors on the front of the pack: Red (High), Amber (Medium), or Green (Low).

USA: The FDA Food Labeling Guide stipulates whether a food can be labelled as "free", "low", or "reduced/less" in respect of sodium. When other health claims are made about a food (e.g. low in fat, calories, etc.), a disclosure statement is required if the food exceeds 480mg of sodium per 'serving.'

Campaigns

In 2004, Britain's Food Standards Agency (FSA) started a public health campaign called "Salt - Watch it", which recommends no more than 6g of salt per day; it features a character called Sid the Slug and was criticised by the Salt Manufacturers Association (SMA). The Advertising Standards Authority did not uphold the SMA complaint in its adjudication.. In March 2007, the FSA launched the third phase of their campaign with the slogan "Salt. Is your food full of it?" fronted by comedienne Jenny Eclair.

In July 2008, the FSA published evidence that showed the UK’s average daily salt consumption has fallen from 9.5g to 8.6g since 2000. It launched a public consultation on proposals that will make its voluntary 2010 salt reduction targets stricter.

Consensus Action on Salt and Health (CASH) established in 1996, actively campaigns to raise awareness of the harmful health effects of salt. The 2008 focus includes raising awareness of high levels of salt hidden in sweet foods and marketed towards children.

In 2008, Gateshead council and other councils started the distribution of five-hole salt shakers (compared with a typical 17-hole model) to try to reduce the amount of salt sprinkled on food by customers in chip shops and takeaways.

Additives to salt

Iodized salt

Iodized salt (BrE: iodised salt) is table salt mixed with a minute amount of potassium iodide, sodium iodide, or iodate. Iodized salt is used to help reduce the chance of iodine deficiency in humans. Iodine deficiency commonly leads to thyroid gland problems, specifically endemic goitre. Endemic goitre is a disease characterized by a swelling of the thyroid gland, usually resulting in a bulbous protrusion on the neck. While only tiny quantities of iodine are required in a diet to prevent goitre, the United States Food and Drug Administration recommends (21 CFR 101.9 (c)(8)(iv)) 150 micrograms of iodine per day for both men and women, and there are many places around the world where natural levels of iodine in the soil are low and the iodine is not taken up by vegetables.

Today, iodized salt is more common in the United States, Australia and New Zealand than in the United Kingdom. Table salt is also often iodized—a small amount of potassium iodide (in the US) or potassium iodate (in the EU) is added as an important dietary supplement. Table salt is mainly employed in cooking and as a table condiment. Iodized table salt has significantly reduced disorders of iodine deficiency in countries where it is used. Iodine is important to prevent the insufficient production of thyroid hormones (hypothyroidism), which can cause goitre, cretinism in children, and myxedema in adults.

The amount of iodine and the specific iodine compound added to salt varies from country to country. In the United States, iodized salt contains 46-77 ppm, while in the UK the iodine content of iodized salt is recommended to be 10-22 ppm.

Some advocates for sea salt assert that unrefined sea salt is more healthy than refined salts. However, completely raw sea salt is bitter due to magnesium and calcium compounds, and thus is rarely eaten. The refined salt industry cites scientific studies saying that raw sea and rock salts do not contain enough iodine salts to prevent iodine deficiency diseases.

Other additives

In some European countries where drinking water fluoridation is not practiced, fluorinated table salt is available.

Another additive, principally for pregnant women, is Folic acid (Vitamin B9), which gives the table salt a yellow colour.

Salt substitutes

Salt intake can be reduced simply by reducing salty foods in one's diet, without recourse to salt substitutes. Salt substitutes have a taste similar to table salt and contain mostly potassium chloride, which will increase potassium intake. Excess potassium intake can cause hyperkalemia. Various diseases and medications may decrease the body's excretion of potassium, thereby increasing the risk of hyperkalemia. If you have kidney failure, heart failure or diabetes, seek medical advice before using a salt substitute. A manufacturer, LoSalt, has issued an advisory statement that people taking the following prescription drugs should not use a salt substitute: Amiloride, Triamterene, Dytac, Spironolactone (Brand name Aldactone), Eplerenone and Inspra.

Further reading

• Department of Health, Dietary Reference Values for Food Energy and Nutrients for the UK: Report of the Panel on DRVs of the Committee on the Medical Aspects of Food Policy , The Stationery Office.
• MacGregor, Graham A and De Wardener, Hugh Edward Salt, Diet and Health: Neptune's Poisoned Chalice: the Origins of High Blood Pressure Cambridge University Press; (1998) ISBN-10: 0521635454 ISBN-13: 978-0521635455