Lead in Calcium Supplements
Authors: Robert P. Heaney
Journal: JAMA (2000)

LEAD IS AN ELEMENT THAT EVERYONE CAN SAFELY BE against. Lead causes anemia, hypertension, and brain and kidney damage, and in children stunts growth and causes permanent cognitive impairment and increased aggressive behavior. For human health, lead clearly causes harm and does no good. Ironically, virtually all the lead in the environment is there as a result of human activity. Under premetallurgical conditions, lead in the earth’s crust was locked safely away in deep ore deposits or in marine calcareous beds. As technology advanced, lead was mined and smelted and was a workable and useful metal, finding its way into such diverse applications as Roman water conduits, medieval cathedral roof sheathing, fine crystal, paints with a superior covering characteristic, solders, antiknock compounds for automotive fuels, and, of course, ammunition—ammunition by the countless ton over the last several hundred years. All that lead was transferred through human activity, from deep ore deposits to the superficial layers of the earth’s crust in which food is grown. Because of recent awareness of the dangers posed by lead, lead-based paints and leaded gasoline have been eliminated in the United States, producing a substantial reduction in daily exposure. Blood lead levels in the US population have declined by as much as 80% or more in the past 25 years, averaging today in the range of 0.10 to 0.14 μmol/L (2-3 μg/dL). The lowest observed adverse effect level (LOAEL) is 0.48 μmol/L (10 μg/dL) in children and 1.4 μmol/L (30 μg/dL) in adults, leaving a comfortable margin of safety for most people. Unfortunately, inner-city children of low socioeconomic status still have an unacceptably high prevalence of blood lead values above the LOAEL, with long-term adverse effects for both the children involved and for society. It seemed to have come as somewhat of a surprise 7 years ago when Bourgoin et al reported that many calcium supplements contained appreciable quantities of lead. However, this finding should not have been unexpected. Lead, in its predominant divalent cationic form, follows calcium, both metabolically and geochemically. The ancient marine calcareous deposits that are mined for calcium supplements inevitably contain some lead. Lead content of supplements can be reduced by chemical processing, but that increases the cost of the product to the consumer. Nevertheless, supplement manufacturers have responded by using deposits with lower lead levels or chemical refining or both. Given this background, it is important to place the findings reported by Ross et al in this issue of THE JOURNAL— that there is still some lead in some marketed calcium supplements—in proper perspective. The authors view their findings, that 8 of 22 calcium supplements they tested had measurable lead content, with alarm, citing a need for “public health concern over the health risks . . . of popular [supplement] . . . products.” Certainly, their recommendation that it would be better for patients to choose products specifically labelled as having been tested for lead content is sound. However, their assertion that the calcium supplements with the highest lead content represent a “public health concern” is arguable. There is, actually, more reason to be concerned about alarming the public unnecessarily. A backlash against calcium supplements—evoked by a lead scare—would unquestionably do far more harm, for health generally and for lead poisoning specifically, than would continued ingestion of current supplements. Several facts are needed to put the lead content of calcium supplements in perspective. If there is any place in the food chain in which small quantities of lead may be safe, it is in sources with high calcium content. The reason is that calcium both blocks intestinal lead absorption and reduces access to endogenous lead deposits. The British lead mining industry recognized this protection a century ago and supplied free milk to its miners— not out of largesse, but because it prevented lead poisoning. (Without a doubt, the dairy herds grazing near those mining towns would have produced lead-laced milk. Still, it was protective.) Lead, as Pb, is absorbed with 20% to 50% efficiency from low calcium sources, but in the presence of coingested calcium, absorption is reduced by roughly a factor of 10 (depending on the amount of calcium), both because of simple dilution of lead in the much larger mass of calcium, and by down-regulating active calcium transport. Further protection is provided by the calciuria of highcalcium diets, which decreases the body burden by increasing urinary lead excretion. Additionally, calcium supplements constitute only a minor source of lead in most contemporary diets. Various foods, particularly raisins, grapes, berries, wine, and salad greens, all contain appreciable amounts of lead—often 1 or 2 orders of magnitude higher than what is found in supplements. For example, a luncheon of mixed salad greens and