A study in the Journal of General Internal Medicine. investigates the effects different herbal supplements on blood lead levels. Supplements with high heavy metals levels included Ayurvedic herbs, echinacea, ginseng, St. John’s wort, bee pollen, ginko, and nettle.

Lead exposure can result in medical complications, including high blood pressure, kidney disease, cancer, heart disease and peripheral artery disease. High blood lead levels also pose a risk for women planning to become pregnant. Lead can lead to pregnancy complications for both the mother and the developing child.

“Among adults, the potential implications of low-level lead exposure are most relevant to women of child-bearing age,” study authors write. “As lead is especially harmful to developing nervous systems of fetuses and children and passes through the placenta and breast milk.”

Researchers recruited 6,712 Unites States women in good health who were of reproductive age—20 or more years old. Participants self-reported their vitamin regimen for 30 days, and were divided into groups based on the type of supplements they used.

Women who took these supplements had significantly higher lead levels than women who took other herbal medicines. Blood lead levels of women who took Ayurvedic supplements were 24 percent higher than non-users. St. John’s wort wasn’t far behind with 23 percent higher levels.

Greater lead levels were not seen in individuals who used other supplements, such as garlic. Researchers acknowledge that these supplements can have some beneficial effects on personal health, but recommend firmer regulations.

“Our data suggest testing guidelines for herbal supplements,” they write, “and regulations limiting lead in supplements are needed.”