1 March 2015

Are we ingesting too much aluminium?

Takeaway bread
Naan wrapped in aluminium foil.

Aluminium in the diet has become an increasing concern ever since the metal was implicated in causing Alzheimer's disease in the mid 1960s. The metal can come from a variety of sources, including foods cooked or stored in aluminium or clay crockery and aluminium packaging; foods that naturally contain aluminium, like tea, and foods that are made with aluminium-based additives, such as baked goods.

Yes, you can get your daily dose of aluminium from cakes and tea. One study found that aluminium levels are generally low in unprocessed foods, typically under 1 ppm and rarely exceeding 10 ppm*, but the story is different for tea leaves. The same study noted that the richest natural sources of aluminium for Chinese food in Harbin are tea leaves, Chinese prickly ash (Sichuan pepper) and mustard*. Another study which focused on teas in Sichuan noted that brick teas, which are chiefly composed of old leaves, have the highest aluminium concentrations of all types of tea.

Drinking tea itself may be a negligible source of dietary aluminium however. Studies have found that there is little increase in the level of aluminium found in blood plasma or in urine after drinking black or green tea, with milk or lemon juice.

What about aluminium leaching from aluminium pots and pans, dishes or packaging, then? A 1992 study from Food Additives and Contaminants studied just that and found that very small or undetectable levels of aluminium actually leached out of aluminium containers into food, but, as always, 'it depends'. 

1993 study, done in Harbin and published in the Chinese Journal of Preventive Medicine (Zhonghua Yu Fang Yi Xue Za Zhi), concluded that Chinese people in Harbin consume an average of 4 to 15 mg, and rarely up to 20 mg of aluminium in the daily diet.  According to the study, tea leaves can contain between 300 to 1,800 ppm of aluminium, and 16 to 20% of this aluminium can be extracted from the leaves. Foods can contain 10 to 30 ppm of aluminium after processing and handling, the researchers added.

Foods made with aluminium-containing food additives contain extremely high level of aluminium, however. Such additives** may include E523, aluminium ammonium sulphate, used in industrial baking powder, or E541, sodium aluminium phosphates (acidic and basic) which may be used in the production of baked goods, cheese products, confectionery, frozen fish, minced meat, and stews. Other additives include and are not limited to E554, which is sodium aluminosilicate, E556, calcium aluminium silicate, and E559, aluminium silicate. According to the Chinese researchers, people can consume more than 100 mg of aluminium daily from their diet due to intake of foods made with aluminium-containing food additives.

The Science of the Total Environment also contains a 1997 study from India which agrees with the Chinese study. It noted that baking powder is a rich source of aluminium. A kg of cake prepared with one to three teaspoons of baking powder may contain 2 to 12.7 mg of aluminium in a 25g serving, the Indian researchers said.

The question is how much is too much. The Agency for Toxic Substances and Disease Registry, which is part of the US Department of Health and Human Services, has a toxicological profile for aluminium that lists minimum risk levels for exposure to the metal. Oral exposure should be no more than1 mg of aluminium per kg of body weight per day. Through staying away from baked goods and possibly medications that contain aluminium, we are all probably within safe levels. To be on the safer side, we can also minimise aluminium intake based on what we know so far.
A 2003 study in Environmental Geochemistry and Health conducted in Hong Kong has some advice on minimising aluminium from tea consumption:

  • Go for younger tea leaves
  • Indian tea varietals grown in the same place as Chinese tea varietals have less aluminium 
  • Green tea has less aluminium content than black tea
  • Steep the tea in the pot - more aluminium is released with the repeated tea infusion method (emptying the teapot once the tea is brewed and then adding fresh boiling water to make another pot of tea) compared to the continuous infusion method (leaving the tea to steep in the pot).
What about cooking?
  • Don't worry about boiling neutral porridge. Boiling neutral (non-alkali and non-acidic) porridge in aluminium pans causes no migration of aluminium out of the pan into the porridge***
  • Relatively small amounts of aluminium come through with milk. Milk causes leaching of 0.2 to 0.8 mg/kg***
  • Don't boil tap water in aluminium pans for too long. 
    • Bringing water to boil causes leaching of 0.54 to 4.3 mg/l. This increased with increasing boiling time, to 6.3-17 mg/l, perhaps explaining why adding more boiling water to tea also raises aluminium levels***
    • A different study was more precise: boiling water in aluminium pans caused aluminium concentrations to rise to 2.6 mg/l after 15 minutes****
  • Beware of cooking acidic foods in aluminium pans
    • Aluminium dissolved in foods based on acidic fruit juice registered at 2.9 to 35 mg/kg when the foods were boiled in aluminium pans*** 
    • The highest aluminium concentration of 170 mg/kg was measured in rhubarb juice prepared in the steaming vessel***
    • Tomato sauce made from mashed tomatoes cooked in non-coated aluminium pans contained 10-15 mg/kg of aluminium after an hour of cooking****

And what about storing foods and liquids in aluminium containers? Some studies throw light on this:
  • Coffee seems safe. Coffee, strangely enough, had lower levels of aluminium than in the tap water that was used in its preparation****.
  • Relatively little aluminium is poured out with Coca-Cola that has been stored in internally lacquered aluminium cans (levels of below 0.25 mg/l)****
  • Stay away from acidic liquids stored in aluminium containers. Lime blossom tea acidified with lemon juice stored in non-coated aluminium camping bottles for five days (up to 7 mg/l)****

Editor's note: Aluminium content is reported directly from the research reports. Some are in parts per million, others in mg per litre (l), while yet others are in mg per kg. It is not possible to compare these measurements directly. With water however the mg/l and mg/kg figures would be the same as 1 g of water has a volume of 1 ml. 

*These figures come from a 1993 study done in Harbin and published in the Chinese Journal of Preventive Medicine (Zhonghua Yu Fang Yi Xue Za Zhi).

**Some of these additives are banned in different countries.

***These figures come from a 1992 study from Food Additives and Contaminants.

****These figures come from a 1993 study published in Zeitschrift für Lebensmittel-Untersuchung und -Forschung.