NEW YORK - Some herbal supplements may boost the levels of lead in the blood of women, new research shows.

Among 12,807 men and women age 20 and older, Dr. Catherine Buettner, at Beth Israel Deaconess Medical Center in Boston, Massachusetts, and colleagues found blood lead levels about 10 percent higher in women, but not men, who used specific herbal supplements.

When they examined herbal supplement use among women of reproductive age (age 16 to 45 years old), "the relationship with lead levels was even stronger, with lead levels 20 percent higher overall, and up to 40 percent higher among users of select herbal supplements compared to non-users," they report in the Journal of General Internal Medicine.

Lead accumulates in the body over time and may pass from a woman's placenta and breast milk to developing fetuses and infants. The U.S. Food and Drug Administration does not specify safe lead limits, or even routinely test for this toxin in herbal supplements.

Buettner's team found that women using Ayurvedic or traditional Chinese medicine herbs had lead levels 24 percent higher than non-users, while those using St. John's wort and "other" herbs had lead levels 23 percent and 21 percent higher, respectively, than non-users.

When combined with prior studies hinting at excess lead in specific supplements, the evidence strongly suggests use of specific herbal supplements may result in higher lead levels among women, Buettner said.

In the current study, Buettner was reassured to find "no evidence of lead toxicity," she told Reuters Health in an email.

The researchers point out that the use of some herbal supplements among study participants was low, which limited the power to detect associations among specific herbal supplements.

They also emphasize that the current study does not prove that herbal supplements cause higher lead levels. They urge further studies to analyze how other lead exposures, calcium intake, or use of other dietary supplements alter lead levels.

Dr. Adriane Fugh-Berman, at Georgetown University Medical Center in Washington, D.C. concurs in an editorial on the study, and also cautions, "let us not use too broad a brush to tar all herbal products."

Specific analyses of specific herbal products or the blood of users, Fugh-Berman writes, should be used to establish products containing problematic amounts of lead.