Heavy Metals in Supplements: What Labs Check

Quick answer

In supplement testing, heavy metals usually means four contaminants: lead, arsenic, cadmium and mercury. They reach ingredients from soil, water and processing. FDA's 2007 manufacturing rule was written partly to keep supplements free of contaminants such as heavy metals, and it makes each maker set contaminant limits for every finished batch (21 CFR 111.70).^1,2,3

Key facts

FDA says that finding a metal in a food does not necessarily mean the food should be avoided, because the effect depends on the amount, how often it is eaten and who eats it.^1,4
Results are usually given as a concentration, such as micrograms per gram, so the daily amount depends on the size of the serving.⁵
In a 2008 study of 193 Ayurvedic products bought online, 20.7% contained detectable lead, mercury or arsenic.⁶
FDA has set numbers for these metals in certain foods, such as limits for bottled water and action levels for some foods for babies, while the supplement rule has each maker set its own limits.^1,3
Supplements have been recalled for heavy metal contamination, one of the problems FDA cited when it wrote its 2007 rule.²

Where the metals come from

Metals occur naturally in rock and soil, and human activity adds more. Plants take them up and pass them into ingredients, so levels depend on where a crop was grown. Lead, for example, is still in the environment from its past use in paint, gasoline and plumbing.¹

Some ingredient types stand out. FDA notes that seaweed can be a source of arsenic and cadmium, that cadmium in chocolate depends on the growing area and the share of cocoa solids, and that nearly all fish and shellfish carry traces of methylmercury.^7,8

Traditional formulas can be a special case. Some Ayurvedic preparations combine herbs with metals and minerals by design, and in the 2008 study these rasa shastra products were more than twice as likely to contain metals as other Ayurvedic products.⁶

How labs measure them

A common method is inductively coupled plasma mass spectrometry (ICP-MS), which FDA's own manual uses to measure arsenic, cadmium, lead, mercury and other elements in food.⁹

For arsenic and mercury the chemical form matters. A standard result is the total. Telling inorganic from organic arsenic, or methylmercury from other mercury, takes a separate speciation method.^4,9

Every method has a floor below which it cannot report a reliable number. A result given as below a limit tells you the amount is under that floor, not that it is absent.¹⁰

Turning a result into a daily amount

A concentration only means something next to a serving size. The same result per gram matters more in a large scoop of powder than in a small capsule, which is why California's Proposition 65 rules calculate exposure from the concentration and the amount an average user takes.⁵

Daily benchmarks then give a point of comparison, such as FDA's reference levels for lead content in the diet, its reference range for cadmium and California's safe harbor levels.^1,7,11

Why the limits exist

These metals are toxic at high or prolonged exposure. FDA links lead to harm to brain development in children and to kidney effects and hypertension in adults, inorganic arsenic to skin, bladder and lung cancers, cadmium to kidney and bone damage, and methylmercury to effects on the developing nervous system.^1,4,7,8

Pregnancy, infancy and early childhood are the most sensitive times, according to FDA, because the brain is developing and young children are small and growing fast.^1,8

Questions people ask

Which supplements tend to contain heavy metals?

Any ingredient from soil or sea can carry some. FDA data and studies point to seaweed for arsenic and cadmium, cocoa for cadmium, fish for methylmercury, some mineral ingredients for lead, and some traditional Ayurvedic formulas for several metals at once.^6,7,8,12

Is there a safe amount of heavy metals?

For lead, FDA says no safe level of exposure has been identified, so the aim is to keep exposure as low as possible. For the others, agencies use reference levels of daily intake, such as FDA's range for cadmium.^1,7

Does good manufacturing practice mean a product is low in heavy metals?

Not by itself. In the 2008 study of Ayurvedic products sold online, three in four of the products found to contain lead, mercury or arsenic claimed good manufacturing practices.⁶

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Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.