The only way to accurately determine whether or not you're lacking any essential minerals is a blood test. Hair analysis, which is widely promoted to determine or monitor trace minerals or toxins in the body, is not reliable. The results don't necessarily correlate with actual levels in the body. To begin with, exposure of hair to substances in shampoos or hair dyes can distort results. Furthermore, some mineral levels can be affected by your hair's color, diameter, growth rate, the season of the year, your geographic location, and your age and gender.
Beyond all that, normal ranges of minerals found in hair have not been defined, and no correlation has been established between hair levels and other indicators of nutrition status. This means that the concentration of a mineral in your hair could be high even though you may actually be deficient in that mineral. Or vice versa.
Finally, there are no standards for hair analysis, which means that you could get completely different results if you sent hair samples from the same person, taken at the same time, to more than one laboratory.
Some alternative practitioners recommend hair analysis to assess vitamin and mineral levels in the body and then prescribe dietary supplements on the basis of the results. I would be suspicious of any nutritional deficiency or disease diagnosed via this method alone. If you suspect that you might be deficient in some vitamin or mineral, check with your physician. A blood test can set your mind at ease or demonstrate any need to increase your intake of specific nutrients.
Andrew Weil, M.D.