Lead in Calcium Supplements: Title and subTitle BreakCause for Alarm or Celebration?

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).¹ 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,² 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 al³ 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 al⁴ 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.⁵ (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.⁶ Further protection is provided by the calciuria of high-calcium 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.^{7 - 8} For example, a luncheon of mixed salad greens and a glass of Chardonnay will contain from 10 to more than 50 times as much lead as could be ingested in a typical calcium supplement tablet. Absorption of lead from such a meal would be relatively high as well, because these foods contain little calcium. Adding a slice of cheese, a glass of milk, or even one of the higher lead-containing supplements described by Ross et al⁴ would sharply reduce total lead absorption from the meal, even though each of these calcium sources could contribute slightly to the ingested lead load.

Ross et al⁴ do not demonstrate the dangers they fear. They do not report measurements of blood lead in persons taking supplements, nor is it likely that, if they had made the measurements, they would find the hazard to which they wish to draw clinicians' attention. Essentially all reports that have addressed this issue have found that blood lead levels vary inversely with calcium intake,^{9 - 10} even though (as is usually the case) dietary calcium sources would contribute to the ingested lead load in their own right.

Moreover, Ross et al fail to mention the remarkable extent to which the supplement industry has reduced the lead content of the calcium supplements now on the US market. While Bourgoin et al³ found measurable quantities of lead in most of the 70 brands of supplements on which they reported 7 years ago, Ross et al found that lead content was below the detection limit in two thirds of the 22 products on which they now report. All of the products they tested had lead content less than both the 1992 Food and Drug Administration and the 1996 Food Chemicals Codex standards,¹¹ and two thirds were less than the much more stringent California Proposition 65 standards.¹²

The aggregate national effort at reducing lead from environmental sources has been so effective that one of the principal sources of lead for most North American adults, particularly the elderly, currently is not their supplements, but their own skeletons, which have sequestered most of the lead absorbed over a lifetime of high exposure. There is roughly 5 to 10 times as much lead per unit of calcium in the bones of the elderly than in any of the current calcium supplements,¹³ and because this lead is already in the body, there is no blocking its absorption, as with orally ingested lead.

Dietary calcium utilization efficiency declines with age, and the bodies of the elderly turn increasingly to bone for the calcium they need to offset daily losses. That is the reason recommended calcium intakes increase with age,^{14 - 15} and the reason low calcium intakes contribute to skeletal fragility. While this skeletal mobilization provides the calcium the elderly need (although at a skeletal cost), it also doses them with lead, which was not harming them as long as it was locked up in bone, but which is now introduced into the bloodstream. Exactly how much harm that released lead could do in its own right is unclear. Bogden et al¹⁶ argue for widespread calcium fortification and supplementation of the human diet, precisely to keep bone lead locked away. Certainly, if older adults were to avoid calcium supplements of whatever sort or for whatever reason, their blood lead levels would increase—both because of increased absorption of currently ingested lead from food sources and because of increased release of sequestered skeletal lead.

Important work is still necessary to eliminate the unacceptable problem of lead poisoning in underprivileged, inner-city children. However, that is not a calcium supplement problem, but rather is a problem compounded of poor nutrition and high environmental lead exposure. While environmental clean-up needs to continue, a more cost-effective approach to prevention, not just of lead intoxication in these children, but of the other problems to which they are prone, is better nutrition overall. The US Department of Agriculture's former "special milk program" was a nearly ideal way of dealing with this problem,¹⁷ and it needs to be reinstated. Even though calcium supplements would be helpful, these children need more than just calcium. They need the total nutrition, for example, of milk.

In the final analysis, one must wonder why there has been so much concern about calcium supplements. These agents contribute only a small fraction of the total daily lead intake, most of even that lead is not absorbed, and the supplemental calcium blocks absorption of lead from other foods. In truth, this is not bad, but good news: the calcium sources available today are generally very safe.