Do we need to use iodized salt

Do we need to use iodized salt?

Pawel Malczewski
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Short summary

Whether iodized salt is required or not, depends on whether you belong to one of the iodine deficiency risk groups. If you live in an area where iodine is abundant in the soil or if you consume iodine-rich foods, such as seafood, you may not need to consume an iodized salt. Actually, if that happens you may even be over the safe limit, in which case using iodized salt would not be necessary. Nevertheless, using iodized salt contributes only a small fraction of the overall iodine (10%) to potential toxicity. For a quick answer click here.

Explanation

BACKGROUND INFORMATION

How much iodine do we need?

150 micrograms per day of iodine levels is a daily physiological requirement for adults, out of which 120 micrograms is used by the thyroid for the production of thyroid hormones. (read more..)

Why do we need Iodine?

(1)Kabir M, Oppert JM, Vidal H, Bruzzo F, Fiquet C, Wursch P, Slama G, Rizkalla SW. Four-week low-glycemic index breakfast with a modest amount of soluble fibers in type 2 diabetic men. Metabolism. 2002 Jul;51(7):819-26. Available here. (2)Wolever TM, Jenkins DA. Effect of Dietary Fiber and Foods on Carbohydrate Metabolism. In: Spiller GA, ed. CRC Handbook of Dietary Fiber in Human Nutrition. 3rd ed. Boca Raton: CRC Press; 2001:321-360. Available here. (3)Bingham SA, Day NE, Luben R, Ferrari P, Slimani N, Norat T, et al. Dietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study. Lancet. 2003 May 3;361(9368):1496-501. Available here. (4)Park Y, Hunter DJ, Spiegelman D, Bergkvist L, Berrino F, van den Brandt PA, et al. Dietary fiber intake and risk of colorectal cancer: a pooled analysis of prospective cohort studies. JAMA. 2005 Dec 14;294(22):2849-57. Available here. (5)Trock B, Lanza E, Greenwald P. Dietary fiber, vegetables, and colon cancer: critical review and meta-analyses of the epidemiologic evidence. J Natl Cancer Inst. 1990 Apr 18;82(8):650-61. Available here. (6)Howe GR, Benito E, Castelleto R, Cornée J, Estève J, Gallagher RP, et al. Dietary intake of fiber and decreased risk of cancers of the colon and rectum: evidence from the combined analysis of 13 case-control studies. J Natl Cancer Inst. 1992 Dec 16;84(24):1887-96. Available here.
Iodine levels of 50 micrograms per day or lower are associated with goiter – a very visible sign of iodine deficiency.
Iodine levels of 30 micrograms per day or lower during pregnancy are associated with cretinism.

How much Iodine should we take?

The upper limit of iodine levels for adults has been established at 1,100 micrograms per day. For children or adolescents the upper limit is between 200 and 900 micrograms, depending on the age. (7)Oregon State University. Micronutrient Information Center. Case-control study. Definition. Available here.

How much iodine do we get from foods?

Daily intake of iodine depends greatly on the type and source of the foods we consume. Some of the best sources of iodine are oysters, seaweed, canned salmon, snapper, cheddar cheese and eggs. (8)Kabir M, Oppert JM, Vidal H, Bruzzo F, Fiquet C, Wursch P, Slama G, Rizkalla SW. Four-week low-glycemic index breakfast with a modest amount of soluble fibers in type 2 diabetic men. Metabolism. 2002 Jul;51(7):819-26. Available here. (9)Wolever TM, Jenkins DA. Effect of Dietary Fiber and Foods on Carbohydrate Metabolism. In: Spiller GA, ed. CRC Handbook of Dietary Fiber in Human Nutrition. 3rd ed. Boca Raton: CRC Press; 2001:321-360. Available here. (10)Bingham SA, Day NE, Luben R, Ferrari P, Slimani N, Norat T, et al. Dietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study. Lancet. 2003 May 3;361(9368):1496-501. Available here. (11)Park Y, Hunter DJ, Spiegelman D, Bergkvist L, Berrino F, van den Brandt PA, et al. Dietary fiber intake and risk of colorectal cancer: a pooled analysis of prospective cohort studies. JAMA. 2005 Dec 14;294(22):2849-57. Available here. (12)Trock B, Lanza E, Greenwald P. Dietary fiber, vegetables, and colon cancer: critical review and meta-analyses of the epidemiologic evidence. J Natl Cancer Inst. 1990 Apr 18;82(8):650-61. Available here. (13)Howe GR, Benito E, Castelleto R, Cornée J, Estève J, Gallagher RP, et al. Dietary intake of fiber and decreased risk of cancers of the colon and rectum: evidence from the combined analysis of 13 case-control studies. J Natl Cancer Inst. 1992 Dec 16;84(24):1887-96. Available here.
The level of iodine in some foods also depends on how rich in iodine the soils are. There are regions with low iodine level soils where deficiency may be common (e.g. Australia) and areas where iodine levels are high enough to be toxic and induce hyperthyroidism (such as Brazil). See map below (14)World Health Organization (WHO). Summary tables and maps on iodine status worldwide. Available <a href=”http://www.who.int/vmnis/database/iodine/iodine_data_status_summary/en/” target=”_blank”>here</a>.
WHO world iodine deficiency map

Some iodine related Statistics: (15)Schatzkin A, Lanza E, Corle D, Lance P, Iber F, Caan B, et al. Lack of effect of a low-fat, high-fiber diet on the recurrence of colorectal adenomas. Polyp Prevention Trial Study Group. N Engl J Med. 2000 Apr 20;342(16):1149-55. Available here.

  • Approximately 70% of the salt consumed in the U.S. is from processed foods, which is mostly not iodized.
  • In the U.S., only about 50% of people chose iodized salt for their home use.
  • Iodized salt contains approximately 77 micrograms per gram of iodine in the U.S.
  • If the salt in processed products is also fortified with iodine, than the iodine should be around 20 milligrams per kilo of salt.
  • Some other examples of iodine usage: In Switzerland, 25 milligrams is added per kilo of salt. For the purpose of this article, I will be using the current average daily intake of salt of 8.5g which is equivalent to 213 micrograms of iodine. (16)Schatzkin A, Lanza E, Corle D, Lance P, Iber F, Caan B, et al. Lack of effect of a low-fat, high-fiber diet on the recurrence of colorectal adenomas. Polyp Prevention Trial Study Group. N Engl J Med. 2000 Apr 20;342(16):1149-55. Available here.
  • The World Health Organization (WHO) suggests that, for areas with iodine deficiency, the range of iodine added to salt should be between 20-40 milligrams per kilo of salt in order to reach the recommended iodine intake of 150 micrograms per day. This amount takes into account that about 40% of iodine is lost either through cooking or on the way from production site to the household. (17)World Health Organization, ICCIDD, UNICEF. Recommended iodine levels in salt and guidelines for monitoring their adequacy and effectiveness. Available here. (18)World Health Organization. Vitamin and Mineral Nutrition Information System (VMNIS). Degree of public health significance of iodine nutrition. Available here.

Iodine-deficiency risk groups:

  • If you are you a pregnant woman (pregnant women need about 50% more iodine).
  • If you do not consume foods rich in iodine (see table).
  • If your diet in unbalanced and you consume mostly goitrogen rich foods such as cruciferous vegetables (goitrogens interfere with iodine in the body) (19)Oregon State University. Micronutrient Information Center. Case-control study. Definition. Available here.
  • If you live in an area with low levels of iodine in the soil, consume no seafood and only locally produced food (see the regions with Iodine levels above).

Calculation
According to statistics we consume on average 8.5 grams of salt per day (read more..). See also daily recommended sodium intake (read more..).

If we assume that an average adult consumes 8.5 grams of iodized salt per day and knowing that iodized salt in the U.S contains approximately 77 micrograms per gram of iodine then:

77 micrograms of iodine * 8.5 grams of salt = 655 micrograms of iodine.

If we now assume that 40% of iodine is lost, as per the above WHO stats, we will get 393 micrograms, which is higher than the recommended daily intake but still much lower than the upper limit of 1,100 micrograms.

In reality, most (75%) of the salt consumed per day out of the 8.5 grams of salt comes from processed foods, which don’t contain iodized salts.

That means that only 25% of the 393 micrograms is consumed as table salt that contains Iodine. 25% of 393 micrograms is 98 micrograms of iodine.

This means that if an average American consumes 8.5g of salt per day, the actual iodine consumed will be 98 micrograms, which is below the recommended daily intake. Nevertheless, this amount may be higher if some of the processed products, such as bread, are fortified.

Provided that you are in an iodine deficiency risk group, the amount of iodine that you would be getting from the iodized salt would not increase your chances of toxicity. Actually, it would only top-up the iodine levels you need and still remain far from the upper limit.

The iodine toxicity from using extra iodized salt would occur if your diet consisted of foods high in iodine. To reach a toxic state, you would have to intake over 1,000 micrograms of iodine daily. 98 micrograms from extra iodized salt represents only approximately 10% of this upper safe limit.
What this means is that toxicity wouldn’t be caused by the extra iodized salt but by rather an overall diet high in iodine rich foods. Therefore, your primary concern would have to be to reduce these foods from your diet.

Conclusion

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I believe that it is important to see if some of the above points apply to your specific case and only then make an informed decision whether you need iodized salt or not.

Some governments enrich certain foods with iodine and add iodine to salt to prevent a widespread deficiency and associated health problems.
The individual situation may vary. If you are concerned about taking extra iodine or not having enough you should consider these questions:

  • Do you live in an iodine deficient area?
  • Do you consume foods rich in iodine such as seafood and seaweed?
  • Do products that you consume every day contain fortified iodized salt (such as bread)?
  • Lastly, if your diet is rich in iodine, whether because you live in a iodine rich area or you consume foods high in iodine, you should consider not only avoiding iodized salt but, more importantly, reducing iodine rich foods from your diet.

References   [ + ]

1. Kabir M, Oppert JM, Vidal H, Bruzzo F, Fiquet C, Wursch P, Slama G, Rizkalla SW. Four-week low-glycemic index breakfast with a modest amount of soluble fibers in type 2 diabetic men. Metabolism. 2002 Jul;51(7):819-26. Available here.
2. Wolever TM, Jenkins DA. Effect of Dietary Fiber and Foods on Carbohydrate Metabolism. In: Spiller GA, ed. CRC Handbook of Dietary Fiber in Human Nutrition. 3rd ed. Boca Raton: CRC Press; 2001:321-360. Available here.
3. Bingham SA, Day NE, Luben R, Ferrari P, Slimani N, Norat T, et al. Dietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study. Lancet. 2003 May 3;361(9368):1496-501. Available here.
4. Park Y, Hunter DJ, Spiegelman D, Bergkvist L, Berrino F, van den Brandt PA, et al. Dietary fiber intake and risk of colorectal cancer: a pooled analysis of prospective cohort studies. JAMA. 2005 Dec 14;294(22):2849-57. Available here.
5. Trock B, Lanza E, Greenwald P. Dietary fiber, vegetables, and colon cancer: critical review and meta-analyses of the epidemiologic evidence. J Natl Cancer Inst. 1990 Apr 18;82(8):650-61. Available here.
6. Howe GR, Benito E, Castelleto R, Cornée J, Estève J, Gallagher RP, et al. Dietary intake of fiber and decreased risk of cancers of the colon and rectum: evidence from the combined analysis of 13 case-control studies. J Natl Cancer Inst. 1992 Dec 16;84(24):1887-96. Available here.
7. Oregon State University. Micronutrient Information Center. Case-control study. Definition. Available here.
8. Kabir M, Oppert JM, Vidal H, Bruzzo F, Fiquet C, Wursch P, Slama G, Rizkalla SW. Four-week low-glycemic index breakfast with a modest amount of soluble fibers in type 2 diabetic men. Metabolism. 2002 Jul;51(7):819-26. Available here.
9. Wolever TM, Jenkins DA. Effect of Dietary Fiber and Foods on Carbohydrate Metabolism. In: Spiller GA, ed. CRC Handbook of Dietary Fiber in Human Nutrition. 3rd ed. Boca Raton: CRC Press; 2001:321-360. Available here.
10. Bingham SA, Day NE, Luben R, Ferrari P, Slimani N, Norat T, et al. Dietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study. Lancet. 2003 May 3;361(9368):1496-501. Available here.
11. Park Y, Hunter DJ, Spiegelman D, Bergkvist L, Berrino F, van den Brandt PA, et al. Dietary fiber intake and risk of colorectal cancer: a pooled analysis of prospective cohort studies. JAMA. 2005 Dec 14;294(22):2849-57. Available here.
12. Trock B, Lanza E, Greenwald P. Dietary fiber, vegetables, and colon cancer: critical review and meta-analyses of the epidemiologic evidence. J Natl Cancer Inst. 1990 Apr 18;82(8):650-61. Available here.
13. Howe GR, Benito E, Castelleto R, Cornée J, Estève J, Gallagher RP, et al. Dietary intake of fiber and decreased risk of cancers of the colon and rectum: evidence from the combined analysis of 13 case-control studies. J Natl Cancer Inst. 1992 Dec 16;84(24):1887-96. Available here.
14. World Health Organization (WHO). Summary tables and maps on iodine status worldwide. Available <a href=”http://www.who.int/vmnis/database/iodine/iodine_data_status_summary/en/” target=”_blank”>here</a>.
15. Schatzkin A, Lanza E, Corle D, Lance P, Iber F, Caan B, et al. Lack of effect of a low-fat, high-fiber diet on the recurrence of colorectal adenomas. Polyp Prevention Trial Study Group. N Engl J Med. 2000 Apr 20;342(16):1149-55. Available here.
16. Schatzkin A, Lanza E, Corle D, Lance P, Iber F, Caan B, et al. Lack of effect of a low-fat, high-fiber diet on the recurrence of colorectal adenomas. Polyp Prevention Trial Study Group. N Engl J Med. 2000 Apr 20;342(16):1149-55. Available here.
17. World Health Organization, ICCIDD, UNICEF. Recommended iodine levels in salt and guidelines for monitoring their adequacy and effectiveness. Available here.
18. World Health Organization. Vitamin and Mineral Nutrition Information System (VMNIS). Degree of public health significance of iodine nutrition. Available here.
19. Oregon State University. Micronutrient Information Center. Case-control study. Definition. Available here.