Salt and health

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Table salt, the salt that we add to our food to enhance its flavour, mainly consists of the molecule sodium chloride. Chloride and sodium ions, the two major components of salt, are necessary for the survival of all creatures, including humans. Because the extracellular concentration of sodium chloride is critical for the proper functioning of all cells, the concentration of sodium chloride in the blood has to be regulated very carefully. We ingest sodium chloride in just about everything that we eat, and excrete the excess, mainly in our urine. How much sodium is excreted in our urine is regulated by several physiological processes, including by hormones such as aldosterone and atrial natriuretic hormone, and by the antidiuretic hormone vasopressin. As the concentration of sodium in blood depends on the total sodium content and on the total water content, an excess of salt can lead to water retention and volume expansion, which can put an increased strain on the cardiovascular system. Conversely, inappropriate water retention can lead to hyponatremia (low plasma sodium concentration) with potentially fatal consequences.

Some isolated cultures, such as the Yanomami in South America, have been found to consume little salt, possibly an adaptation originated in the predominantly vegetarian diet of human primate ancestors.[1]

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.[2]

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."[3] For exercise-induced asthma (EIA), a study suggests that salt intake and EIA are related.[4]
  • heartburn[5].
  • 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."[6] One report shows that a high salt diet does reduce bone density in girls.[7]. Yet "While high salt intakes have been associated with detrimental effects on bone health, there are insufficient data to draw firm conclusions." ([8], 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." ([8], p18) However, in Japan, salt consumption is higher.[9] A study conducted in Puerto Rico concluded, "A statistically significant dose response for the index of salt exposure and gastric cancer was also found."[10]
  • hypertension (high blood pressure): "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." ([8] 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%.[11]
  • 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." ([8] p3) "…there is accumulating evidence that high salt intake predicts left ventricular hypertrophy." ([12], p12) Excessive salt (sodium) intake, combined with an inadequate intake of water, can cause hypernatremia. It can exacerbate renal disease.[2][13]
  • edema (BE: oedema): A decrease in salt intake has been suggested to treat edema (fluid retention).[14][2]
  • duodenal ulcers and gastric ulcers[15]
  • Prehypertension
  • Hypertension
  • Severe premenstrual syndrome[16][17]
  • Vertigo of Meniere’s disorder[16][17]
  • Acute salt poisoning[16][17]
  • Chinese restaurant syndrome[16][17]
  • Idiopathic oedema[16][17]
  • Congestive heart failure[16][17]
  • Carpal tunnel syndrome[16][17]
  • Glaucoma[16][17]
  • Diabetic retinitis[18][17]
  • macular degeneration (wet type)[18][17]
  • 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."[19]
  • 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."[20]
  • Aggregation of erythrocytes[18][17]
  • Helicobacter pylori infection[21]
  • Crohn’s disease[18][17]
  • microalbuminuria[22]
  • 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.[2] 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.[23]

Salt is sometimes used as a health aid, such as in treatment of dysautonomia.[24]

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."[8]

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."([12], 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)[25]

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[26]

Australia: The recommended dietary intake (RDI) is 0.92 g–2.3 g sodium per day (= 2.3 g–5.8 g salt)[27]

USA: The Food and Drug Administration itself does not make a recommendation[28] 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. [29]

France: "In 2002, Afssa recommended a 20% reduction in salt consumption over 5 years, i.e. to 6 to 8g a day on average."[30][31]

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).[32]

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.'[33]

Campaigns

In 2004, Britain's Food Standards Agency 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).[34] The Advertising Standards Authority did not uphold the SMA complaint in its adjudication.[35]. 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.[36]

Consensus Action on Salt and Health (CASH)[37] 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.[38]

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.[39] 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.[40]

Some advocates for sea salt assert that unrefined sea salt is more healthy than refined salts.[41] 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.[42]

Other additives

In some European countries where drinking water fluoridation is not practised, 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[43] 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

References

  1. ↑ Yanomami Indians in the INTERSALT study, (accessed13 January,2007)
  2. ↑ 2.0 2.1 2.2 2.3 Australia: Better Health Channel (Australia, Victoria) Salt
  3. ↑ O J Carey, C Locke, and J B Cookson Effect of alterations of dietary sodium on the severity of asthma in men Thorax 1993 July; 48(7): 714–718
  4. ↑ Exercise-induced asthma more clearly linked to high-salt diet
  5. ↑ Everybody Study adds salt to suspected triggers for heartburn
  6. ↑ Devine A, Criddle RA, Dick IM, Kerr DA, Prince RL. A longitudinal study of the effect of sodium and calcium intakes on regional bone density in postmenopausal women American Journal of Clinical Nutrition 1995;62:740–45
  7. ↑ High salt diet reduces bone density in girls
  8. ↑ 8.0 8.1 8.2 8.3 8.4 Scientific Advisory Committee on Nutrition (SACN) Salt and Health (PDF)
  9. ↑ Salt raises 'stomach cancer risk'
  10. ↑ CRUZ M NAZARIO, MOYSES SZKLO, EARL DIAMOND, ANGEL ROMÁN-FRANCO, CONSUELO CLIMENT, ERICK SUAREZ; and JOSE G CONDE Salt and Gastric Cancer: A Case-Control Study in Puerto Rico International Journal of Epidemiology Volume 22, Number 5 Pp. 790-797
  11. ↑ Cook NR, Cutler JA, Obarzanek E et. al. Long term effects of dietary sodium reduction on cardiovascular disease outcomes: observational follow-up of the trials of hypertension prevention (TOHP). BMJ. 2007;334(7599):885. PMID 17449506 Free full-text
  12. ↑ 12.0 12.1 Food Safety Authority of Ireland Salt and Health: Review of the Scientific Evidence and Recommendations for Public Policy in Ireland
  13. ↑ R. E. Schmieder Salt intake is related to the process of myocardial hypertrophy in essential hypertension JAMA Vol. 262, Issue 9, 1187-1188, September 1, 1989 PMID: 2527319
  14. ↑ Australia: Better Health Channel (Australia, Victoria) Fluid retention
  15. ↑ BBC High-salt diet link to ulcer risk 22 May 2007
  16. ↑ 16.0 16.1 16.2 16.3 16.4 16.5 16.6 16.7 Beard TC. Salt Matters: the killer condiment. Sydney: Hachette Livre; 2007
  17. ↑ 17.00 17.01 17.02 17.03 17.04 17.05 17.06 17.07 17.08 17.09 17.10 17.11 Menzies Research Institute Salt-related health problems
  18. ↑ 18.0 18.1 18.2 18.3 Hawkins WR. Eat right—electrolyte: a nutritional guide to minerals in our daily diet New York: Prometheus Books; 2006
  19. ↑ Borghi L, Schianchi T, Meschi T, Guerra A, Allegri F, Maggiore U, Novarini A. Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria N Engl J Med 2002 Jan 10;346(2):77-84
  20. ↑ AP Avolio, KM Clyde, TC Beard, HM Cooke, KK Ho and MF O'Rourke Improved arterial distensibility in normotensive subjects on a low salt diet Arteriosclerosis, Thrombosis, and Vascular Biology 1986;6:166-169
  21. ↑ Hanan Gancz, Kathleen R. Jones, and D. Scott Merrell Sodium chloride affects Helicobacter pylori growth and gene expression J. Bacteriol doi:10.1128/JB.01728-07
  22. ↑ George L. Bakris, and Amy Smith [Effects of Sodium Intake on Albumin Excretion in Patients with Diabetic Nephropathy Treated with Long-Acting Calcium Antagonists] Annals of Internal Medicine 1 August 1996 Volume 125 Issue 3 Pages 201-204
  23. ↑ Elisabeth Elena Türk, Friedrich Schulz, Erwin Koops, Axel Gehl and Michael Tsokos. Fatal hypernatremia after using salt as an emetic—report of three autopsy cases. Legal Medicine 2005, 7, 47-50. DOI:10.1016/j.legalmed.2004.06.005
  24. ↑ Cleveland Clinic Health Information Center Dysautonomia page
  25. ↑ Health Canada Dietary Reference Intakes (look for Sodium)
  26. ↑ Auckland District Health Board Public Health Nutrition Advice (PDF)
  27. ↑ Better Health Channel (Australia, Victoria) Salt
  28. ↑ U. S. Food and Drug Administration A Pinch of Controversy Shakes Up Dietary Salt
  29. ↑ Department of Health and Human Services (HHS) and the Department of Agriculture (USDA) Dietary Guidelines for Americans 2005 "Sodium and Potassium"
  30. ↑ afssa Salt
  31. ↑ afssa Report on Salt: Evaluation and recommendations 2002
  32. ↑ Understanding labels
  33. ↑ Food and Drug Administration A Food Labeling Guide--Appendix A
  34. ↑ Salt Manufacturers Association press release New salt campaign under attack
  35. ↑ Advertising Standards Authority Broadcast Advertising Adjudications: 20 April 2005 (PDF)
  36. ↑ Salt TV ads
  37. ↑ CASH Consensus Action on Salt.
  38. ↑ My Blood Pressure.
  39. ↑ Iodized Salt
  40. ↑ Iodized Salt
  41. ↑ Susan Dearing Sea Salt is good for you and is made in Colima!
  42. ↑ Iodine in non-iodized sea salt
  43. ↑ LoSalt Advisory Statement (PDF)

External links

Government bodies

Many other government bodies are listed in the References section above.

Medical authorities

Charities and campaigns

Journalism

Salt industry

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