Hidden Salt in Food

Researchers at VicHealth and Deakin University compared how much salt people thought they consumed with how much salt they really had consumed and found that Australians were not only eating too much salt, but were also eating more salt than they thought they were!

Australians were found to be consuming between 8 and 10 grams of salt per day, about twice the amount recommended by the World Health Organisation (WHO) that recommends adults should eat less than 5 g of salt (a bit less than a teaspoon) per day. The "salt" they are referring to is "table salt" which has the chemical name "sodium chloride" and the chemical formula NaCl. Sodium chloride is actually an ionic substance made up of sodium ions (Na⁺) and chloride ions (Cl^-) in a ratio of 1:1 and it is the sodium ions (Na⁺) that are the cause for concern because elevated levels of sodium ions increase a person's risk of high blood pressure, heart disease and stroke. Unfortunately, non-Chemists often refer to this as elevated "sodium" levels rather than as elevated "sodium ion" levels.

If you want to reduce your sodium chloride intake, the first thing you can do is NOT add "table salt" to your food when you eat it. However, only about 20% w/w of our daily intake of sodium ions comes from adding sodium chloride to our food at the table before we eat it. The other 80%  w/w of the sodium ions we consume is already present in our food, either naturally or because it has been added during processing.

Natural sources of sodium ions in our food include:

• milk and cream: 50 mg of sodium ions per 100 g
• eggs: 80 mg of sodium ions per 100 g
• carrot: 69 mg of sodium ions per 100 g
• spinach: 79 mg of sodium ions per 100 g
• green beans, potatoes: 6 mg of sodium ions per 100 g
• pumpkin: 1 mg sodium ions per 100 g
• apple, banana, pear: 1 mg sodium ions per 100 g

By far the greatest source of sodium ions in our diet comes from eating processed foods:

• 1 slice of white bread (30 g) can contain 140 mg Na⁺
• 1 slice of cheddar cheese (20 g) can contain 140 mg Na⁺
• 1 foil pack of butter (7 g) can have 55 mg of Na⁺
• 1 small bowl of breakfast cereal (30 g) can have 140 mg of Na⁺
• 1 small packet of potato chips (45 g) can have about 300 mg of Na⁺
• 1 can (12 fl oz, about 350 mL) diet coke has 40 mg of Na⁺
• tap water contains about 20 mg Na⁺ per 1 L

Food you buy in packets from a supermarket will have a list of ingredients and you can read this to find the amount of sodium ions (Na⁺) present in the food.

However, there are many foods we buy that do not come in a packet which tells us how much sodium ion is present. These foods make up our "hidden salt intake". You may find this information on company websites, such as

• 1 McDonalds Big Mac contains 859 mg of Na⁺
• 6 KFC chicken nuggets with sauce has 1040 mg of Na⁺
• 1 slice (¹/₈ ^th) of medium pan Pizza Hut Meat Lover's pizza has 740 mg of Na⁺
• 1 Taco Bell black bean burrito contains 1030 mg of Na⁺

Many people forget that sodium ions are also present in many medicines. Effervescent medicines contain sodium hydrogen carbonate (or sodium bicarbonate) which helps them dissolve in water.
For example,:

• 1 effervescent Berocca tablet contains about 280 mg of Na⁺ while the film-coated Berocca tablet contains only 1.85 mg of Na⁺
• 1 Gaviscon Advance tablet contains 55 mg Na⁺ but 10 mL of liquid Gaviscon contains 141 mg of Na⁺
• 1 Panadol Actifast caplet contains 173 mg Na⁺ but 1 Panadol soluble tablet contains 428 mg of Na⁺

So, if you want a diet that's low in sodium, eat lots of fresh fruit and vegetables, drink lots of water, and avoid packaged food and "fast food", and, remember to choose "low sodium" medicines.

Reference:
http://www.abc.net.au/news/2016-03-24/reducing-salt-intake-could-save-thousands-of-lives-each-year/7274140

Further Reading:
Mass Conversions
Percent by Mass

Suggested Study Questions:

1. Convert the following masses in grams to masses in milligrams:
   • 5 g
   • 8 g
   • 10 g
   • 30 g
   • 100 g
2. Convert the following masses in milligrams to masses in grams:
• 1.85 mg
• 55 mg
• 69 mg
• 173 mg
• 859 mg
• 1040 mg
3. Calculate the percentage of sodium ions and the percentage of chloride ions in sodium chloride.
4. Use the information in the article to calculate the mass of sodium ions each adult Australian currently consumes as a result of :
   • adding table salt to food before eating it
   • table salt that is naturally present or is added to food during preparation
5. 100 g of milk contains 50 mg of Na⁺ . What is the percentage by mass of sodium in the milk?
6. One 30 g slice  of white bread contains 140 mg Na⁺. What is the percentage by mass of sodium in white bread?
7. For lunch, a student ate a sandwich made up of 2 slices of white bread, 2 foil packs of butter and a slice of cheddar cheese. She also ate a 200 g banana, and washed it all down with 250 mL of plain, unflavoured milk.
   • Calculate the mass of sodium ions the student consumed for lunch.
   • Calculate her consumption of sodium ions as a percentage of the WHO recommended daily intake of sodium ions.
8. A different student consumed a Big Mac, 1 can of diet coke, and a 200 g packet of potato chips.
• Calculate the mass of sodium ions the student consumed for lunch.
• Calculate her consumption of sodium ions as a percentage of the WHO recommended daily intake of sodium ions.
9. For her birthday, a Chemistry Teacher's class gave her a 500 g block of dairy milk chocolate. The label included the information that the block of chocolate contained 82 mg of sodium per 100 g.
   • What is the mass of sodium ions in the block of chocolate?
   • If each person in the class of 22 received an equal share of the block chocolate, what mass of sodium ions would each person consume?
10. In Australia, the maximum recommended dose of paracetamol (the active ingredient in panadol tablets) is 4000 mg per day. 1 soluble Panadol tablet contains 500 mg of paracetamol.
    • What is the maximum number of soluble Panadol tablets per day that an adult Australian should consume?
    • If an adult Australian consumed the maximum recommended dose of soluble panadol tablets in 1 day, what mass of sodium ions would they have consumed?
    • What percentage of the WHO recommended maximum intake of sodium would this amount of panadol be?

Salts of Drugs a Health Risk

Many studies have shown that excess salt is harmful to heart health, but many commonly prescribed medicines have sodium added to improve their absorption into the body, but the effect of doing this has not been known. For example, 1 Alka-Seltzer tablet contains 324 mg of aspirin (the drug) and 445 mg of sodium.
University of Dundee and College of London researchers have found that a person taking the maximum, daily dose of some medicines would exceed the recommended daily dietary intake limits for sodium. In Australia, the total maximum recommended limit of sodium for adults should be less than 2300 mg per day (less for children). The label on the Alka-Seltzer tablets carries a warning that you should not take more than 8 tablets per day.
In the study, the researchers found that patients taking the sodium-containing medication had a 16% increased risk of a heart attack, were 7 times more likely to develop high blood pressure, and, were 28% more likely to die, compared with patients who took the non-sodium containing versions of the same drug.

So why do we add sodium to drugs if it is potentially harmful?

We do this because many drugs are actually insoluble in water. The cells in your body are made up mostly of water, so if you want to be able to transport a drug around the body, and have it absorbed into cells, it is beneficial if the drug is soluble in water.

How do we add sodium to drugs?

If the drug is, for example, a weak acid like aspirin, then it is not very soluble in water.
Being a weak acid, though, aspirin can undergo a proton transfer (neutralisation) reaction with a base such as sodium hydroxide. The product of a neutralisation reaction are salt and water.
acid + base → salt + water

aspirin + sodium hydroxide → sodium salt of aspirin + water

The sodium salt of aspirin readily dissolves in water by dissociating into positive sodium ions and negative "aspirin" ions.


Reference:
BMJ-British Medical Journal (2013, November 26). High salt levels in medicines increase risk of cardiovascular events. ScienceDaily. Retrieved November 28, 2013, from http://www.sciencedaily.com­ /releases/2013/11/131126191557.htm 

Further Reading
aspirin
mass conversions 
ppm
molarity
neutralisation
proton transfer reactions
acid dissociation constants

Suggested Study Questions: 

1. Convert these masses in milligrams to masses in grams
• 324 mg
• 445 mg
2. The label on the Alka-Seltzer packet recommends dissolving 2 tablets in water. For these two tablets, calculate the mass in milligrams of
• aspirin
• sodium
3. If you were to take the maximum number of tablets, 8, in a day, how much of each of the following substances would you be ingesting?
• aspirin
• sodium
4. Would you be exceeding the recommended daily dietary intake limits for sodium in Australia? Explain your answer.
5. A low salt food is one that contains less than 120 mg of sodium per 100 g of food. If Alka-Seltzer were to be considered a low salt food, what would the mass of each tablet need to be?
6. Aspirin has the molecular formula C₉H₈O₄. What is the molar mass of aspirin?
7. The sodium salt of aspirin has the molecular formula C₉H₇O₄^-Na⁺. What is the molar mass of the sodium salt of aspirin?
8. Calculate the mass of sodium in 1 Alka-Seltzer tablet due to the sodium salt of aspirin.
9. Compare the mass of sodium calculated above to the actual mass of sodium present in 1 Alka-Seltzer tablet according to the package. How would you explain the difference in the two masses?
10. If a person dissolved 2 Akla-Seltzer tablets in 150 mL of water, what is the concentration of sodium ions in the water in
    • mol/L
    • mg/L
    • ppm
11. Recommendations for the daily intake of potassium are higher than those for sodium at 4700 mg day, so one way to alleviate the sodium problem in aspirin tablets might be to replace the sodium with potassium. Describe one way that you could produce the potassium salt of aspirin.