<P> Not all elements which are found in the human body in trace quantities play a role in life . Some of these elements are thought to be simple bystander contaminants without function (examples: caesium, titanium), while many others are thought to be active toxics, depending on amount (cadmium, mercury, radioactives). The possible utility and toxicity of a few elements at levels normally found in the body (aluminium) is debated . Functions have been proposed for trace amounts of cadmium and lead, although these are almost certainly toxic in amounts very much larger than normally found in the body . There is evidence that arsenic, an element normally considered a toxin in higher amounts, is essential in ultratrace quantities, in mammals such as rats, hamsters, and goats . </P> <P> Some elements (silicon, boron, nickel, vanadium) are probably needed by mammals also, but in far smaller doses . Bromine is used abundantly by some (though not all) lower organisms, and opportunistically in eosinophils in humans . One study has found bromine to be necessary to collagen IV synthesis in humans . Fluorine is used by a number of plants to manufacture toxins (see that element) but in humans only functions as a local (topical) hardening agent in tooth enamel, and not in an essential biological role . </P> <P> The average 70 kg (150 lb) adult human body contains approximately 7027700000000000000 ♠ 7 × 10 atoms and contains at least detectable traces of 60 chemical elements . About 29 of these elements are thought to play an active positive role in life and health in humans . </P> <P> The relative amounts of each element vary by individual, mainly due to differences in the proportion of fat, muscle and bone in their body . Persons with more fat will have a higher proportion of carbon and a lower proportion of most other elements (the proportion of hydrogen will be about the same). The numbers in the table are averages of different numbers reported by different references . </P>

How many chemical elements in the human body
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