Primitive humans had much less tin in their bodies than modern humans. Tin has been used since the Bronze Age began more than 3,500 years ago (bronze contains copper and tin). It has been used for food storage for more than 200 years. Food does absorb tin from cans, and so we ingest this tin. Luckily for us, it is poorly absorbed from the gastrointestinal tract, probably less than 5 percent, so this is not likely to cause toxicity. Most excess tin is excreted in the feces. Some is eliminated in sweat and even less in urine.
Sources of Tin Toxicity
Tin is present in very low amounts in the soil and in foods. Canning, processing, and packaging often add some tin to food; the solder in iron or copper pipes contains tin; stannous fluoride in toothpaste may add more. Since we consider tin primarily as a contaminant, though fairly nontoxic, we should try to avoid it. Using few canned foods and avoiding toothpaste with tin are some ways to do this.
There are no known functions for tin in humans. If it has a function, it may be related to protein structure or oxidation and reduction reactions, though tin is generally a poor catalyst. Tin may interact with iron and copper, particularly in the gut, and so inhibit absorption.
No uses for tin are presently known other than in food storage, in industrial processes, and as a fluoride carrier in toothpaste.
Deficiency and Toxicity
Though tin is considered a mildly toxic mineral, there are no known chronic or serious diseases from tin exposure or ingestion. Studies in rats showed mainly a slightly shortened life span. I have found no cases of acute tin exposure; chronic low-level environmental and food contamination is more likely. Avoiding eating too much food from tin cans is probably the best we can do (oily foods seem to pick up more tin than others). In the United States, tin cans are now lacquered, which prevents some food absorption. Lacquered cans have a slight yellow coloring, while the unlacquered cans, which are more common with imported foods, are brighter metal. There are no known problems from tin deficiency in humans.
There is currently no RDA or any known requirement for tin. We should avoid any large or long-term exposure. The average diet may contain about 2 mg. per day, but this can vary from about 2-20 mg. per day, depending on the foods ingested. Tin is not likely to be found in many supplements other than occasional trace mineral formulae, and there is no current reason to add tin to any nutritional program.