GAINESVILLE, Fla. — Many calcium supplements contain small but detectable levels of lead, needlessly boosting consumers’ exposure to the toxic heavy metal, according to a University of Florida study published in this week’s Journal of the American Medical Association.
For most people, there is little if any danger in taking very low doses of calcium — and indeed, there are substantial bone-building benefits to the practice. But UF researchers say the lead in some supplements may cause problems in the long run for those who ingest several times the normal daily requirement of calcium.
Moreover, they say the naturally occurring contamination would be an avoidable risk if manufacturers would begin indicating lead content on their products.
"We don’t want people to give up on the proven benefits of taking calcium supplements," said Dr. Edward A. Ross, lead author of the paper, who conducted the study with toxicology experts Ian R. Tebbett and Nancy J. Szabo from UF’s College of Veterinary Medicine. "The levels of lead we’re talking about here are very small and would only potentially be a problem after many years. But we also believe that the less lead anyone is exposed to the better, especially since there are many calcium products on the market without detectable quantities.
"So while people are taking their pills, they should try to find a source with little or no lead," said Ross, director of the UF College of Medicine’s End-Stage Renal Disease Program. "And we hope the industry will respond by labeling their products and finding better raw materials for their supplements."
The UF research comes at a time when lead poisoning has been receding as a major public health threat, in large part because of efforts to limit exposure to lead-containing paints, gasoline, and food and beverage containers. One measure of the success: Average daily dietary ingestion of lead has dropped from more than 30 micrograms to less than 5 between the two study periods of 1982-1984 and 1994-1996, according to the U.S. Food and Drug Administration. Average blood levels of lead also have dropped dramatically, but poor children in particular remain at risk for lead poisoning.
The levels found in the tested calcium samples were up to 3 micrograms for doses up to the 1,500 milligrams of elemental calcium recommended for women trying to prevent or treat osteoporosis. Groups with even more significant calcium needs, such as dialysis patients, would be exposed to even higher amounts.
It is impossible to avoid the substance completely. The heavy metal, which can lead to learning and behavioral difficulties in children and cardiovascular and kidney disease in adults with excessive exposure to it, occurs naturally in the air, water, soil and many foods. Thus, it can be present in the mineral beds that provide calcium sources for supplements. Because lead is so ubiquitous, UF researchers say it is important to avoid lead when possible.
"We probably would not have done this study 20 or 30 years ago. People then were exposed to many times the amount of lead in these supplements," Ross said. "But with progress in environmental controls, we can now ask, ‘How low do you have to go to ensure safety?’ No entirely safe level of lead has ever been established."
The UF scientists are not the first to raise the issue of lead in calcium supplements, but they sought to quantify how much products currently contain, especially in light of physician recommendations in recent years to increase calcium intake.
For the study, staff at the Analytical Toxicology Core Laboratory based at the College of Veterinary Medicine tested lead levels in calcium supplements corresponding to doses recommended for children, women and patients on dialysis. They examined 21 formulations of over-the-counter calcium carbonate, as well as one brand of prescription-only calcium acetate. They did not test any calcium citrate formulations.
Just two of the products listed lead on their labels, asserting that they were "essentially lead-free." Researchers could not detect any in those samples.
Overall, eight products, all nonprescription, had detectable levels of lead. These products included name brands, as well as both refined and "natural" varieties derived from oyster shells.
If taken in normal daily dose ranges — 800 milligrams for children or 1,500 milligrams for women trying to prevent bone loss – the supplements would fall below the 6 microgram total daily exposure limit suggested by many experts. The UF team as well as other investigators believe it’s reasonable to expect the supplements to contribute no more than 1 microgram of lead to the daily exposure limit.
Of the products tested, a children’s dose could result in a maximum of 1.8 microgram of lead, and the women’s dose 3 micrograms.
But people with failing kidneys, who often are directed to consume many times the normal dose calcium, could find themselves taking in as much as 20 micrograms of lead daily, according to the study. Also at risk for higher lead ingestion are people who greatly exceed recommended calcium doses in the mistaken belief that the more they take, the better off they will be.
For consumers, picking a lead-free brand is difficult without additional help from manufacturers.
"Just because a product is a name brand produced by a nationally recognized pharmaceutical company does not mean it has a lower lead content than a generic brand," said Tebbett, director of the Analytical Toxicology Core Laboratory. "One cannot even assume that a given brand is uniformly safe, in that some of their products may have high lead levels, and others, low lead levels."
"We don’t want people to assume from our tables in the JAMA article that any one brand would continue to be safe or toxic," Ross said. "On samples from a different lot, the results could flip-flop. That’s why we need manufacturers to voluntarily obtain better raw material, measure the amount of lead and label their products."
At the small but detectable levels present in some of the calcium supplements, any potential dangers for adults, such as vascular disease, would develop over years, rather than immediately, Ross said. "That should not be a reason to stop taking calcium supplements, but it should be a reason to look for better ones," he said.
The risk for children is similarly small, Ross said, but he noted that children tend to absorb lead at a higher rate than adults.
"Children who are on calcium supplements usually really need them for growth because they are lactose-intolerant or have another problem," Ross said. "It would be much riskier to stop the supplements immediately. Instead, parents should verify that children are taking a product that has the appropriate quality controls and ask their pediatrician to determine the risk at the particular dose prescribed."
The UF researchers say the medical community has a particular obligation to make sure calcium supplements are as safe as possible.
"Calcium is unique among nutritional supplements, which are not regulated by the Food and Drug Administration, in that it is perceived as more mainstream than other remedies such as St. John’s wort or ginkgo biloba," said Tebbett, a pharmacist. "This perception is perpetuated by the medical community, which has been on record recommending the intake of calcium at higher and higher doses, particularly among certain groups of people."
Source: University of Florida. September 2003.