Canned foods play an important role in food storage. But substances used in making tin cans are strictly controlled to make sure they don't get into the food itself.
Most foods contain very low concentrations of tin. Canned foods may contain higher levels because the tin coating used to protect the steel body of the can from corrosion can slowly transfer into the food.
The resins that are used to coat the insides of some food cans contain the chemical bisphenol-A. This coating allows canned food to be heated to kill off bacteria without the metal in the can getting into the food contents.
Health issuesNo long-term health effects are associated with consuming tin. But it can cause stomach upsets such as nausea, vomiting, diarrhoea, abdominal cramps and bloating in some sensitive people at levels above 200 milligrams per kilogram. This is the maximum legal amount of tin that can be present in canned foods.
There are also limits for tin for particular categories of cans:
- 100mg/kg for drinks
- 50 mg/kg for infant and baby foods
- 50 mg/kg for dietary foods for special medical purposes intended specifically for infants
Bisphenol-A is one of a large number of substances that may have the potential to interact with our hormone systems.
These substances are referred to as 'endocrine disrupters'. Research is still going on to establish whether or not bisphenol-A could have this effect in people. Particular concern has focused on the sex hormones, the female oestrogens and male androgens, because of their important roles in the development of the reproductive system.
Although there is evidence that some wildlife species have been affected by exposure to endocrine disrupters, there is still no conclusive evidence of a link between harmful effects on human reproductive health and exposure to these chemicals.
Rules to keep canned food safeThere are regulations in place that lay down the general safety requirements for all food contact materials and articles. In England they are called The Materials and Articles in Contact with Food (England) Regulations 2005. Scotland, Wales and Northern Ireland have their own similar regulations.
These regulations also make sure that substances such as tin and bisphenol-A do not change the nature, substance or quality of the food.
The Food Standards Agency has worked with industry and enforcement officials to make sure measures are introduced to minimise the likelihood of high levels of tin in food. The most recent survey (2002) carried out found that levels of tin in canned foods were lower than five years previously. Of the canned fruit and vegetables and tomato-based products tested, 99.5% contained tin concentrations below the legal limit.
The regulations also require that can coatings containing bisphenol-A do not make food harmful. The Agency is encouraging the European Commission to develop European Union-wide controls on chemicals passing into food from can coatings. This international approach is needed because many canned foods are imported.
What you can doYou should not re-use empty cans or tins to cook or store food because this can increase the likelihood of the substances used to make the cans getting into the food.
Once a can is opened and the inside of the can comes into contact with oxygen in the air, corrosion, which is minimal while a can is sealed, becomes more rapid.
Half opened cans of any type of food should not be left in the fridge. It's best to place leftover food in a sealable container that can be stored in the fridge or freezer. This advice does not apply to those foods sold in cans with a re-sealable lid, such as golden syrup or cocoa.
To make sure your canned food is at its best:
- store cans in a cool dry place
- use your oldest cans first
- if a can is bulging or rusting, throw it away