Prenatal Heavy Metals Exposure and Multi-Vitamins: What a Mother Needs to Know

For women who spend little time thinking about nutrition, pregnancy usually changes that. In fact, for many women, especially if they are healthy, a prenatal multi-vitamin/mineral formula might be the first supplement they ever take. 

So, if you are taking a prenatal multi to ensure the good health of your baby, then it would be very troubling to learn that supplement might contain a heavy metal, such as lead. A 2023 report¹ published by the U.S. Government Accountability Office brought attention to this issue of prenatal heavy metal exposure, although in truth it is not a new issue. 

Why is there lead in prenatal vitamins (and other supplements) anyway?

Virtually all risk of prenatal heavy metals contamination in supplements is associated with minerals. 

Minerals get their start as part of the Earth’s crust. In nature, you don’t just have piles of pure calcium or magnesium or zinc lying around – they tend to be all mixed together. And heavy metals are minerals too, so the good and bad are naturally present together. 

In addition, minerals that have similar electrical charges tend to cluster together – meaning that heavy metals like lead and cadmium tend to be found mixed with nontoxic minerals like calcium and magnesium. 

For their use in foods or supplements, minerals are refined or processed in various ways. More processing tends to result in a “cleaner” product with fewer contaminants.²

It is the responsibility of the supplement manufacturer to ensure that levels of heavy metals are risk-acceptable for the ingredients being used and for the final product. Ingredients or products in excess of acceptable limits should be disposed of, although this does not always happen.

It should be understood, however, that even with the best manufacturing methods, it’s impossible to get rid of 100% of the heavy metals – although you can get pretty close.

What are the limits on prenatal exposure to heavy metals and lead in multis and other supplements?

The United States Pharmacopeia (USP) sets the federal limits for lead and other toxic elements (such as mercury, arsenic, and cadmium) in supplements. The USP sets two limits:  one that is acceptable for an ingredient, and one for daily intake. 

Separately, the State of California has stricter limits under the regulation known as Proposition 65. 

Proposition 65 limits are significantly lower than federal guidelines, so it is often the case that supplements that are below federal limits still require a Proposition 65 warning notice when sold in California.

California’s Proposition 65 limits for lead are 0.5 mcg per day

The GAO report tested 12 prenatal supplements for percent of the label amount of nutrients and for heavy metal contaminants (lead, arsenic, mercury, and cadmium) found in measurable amounts. Of the 12 supplements, which were not identified in the report, only six had trace amounts of lead or cadmium, “but not in amounts likely to cause a health concern based on metrics used by the Food and Drug Administration (FDA).”¹ 

What’s more, all the products that were tested for lead in the GAO report remained well below California’s strict Proposition 65 standard; all of the products had acceptable lead limits per federal USP guidelines.

Most often the numbers provided for defining limits of exposure are given in measures like parts per million (ppm) – which is pretty hard to relate to in daily life. The following table shows you the limits set for “safe” daily intake of various heavy metals such as lead, comparing the USP limits to California’s Proposition 65 limits.

Note that the State of California has never set a safe limit for mercury, although the limits of 0.3 mcg/day and 3.0 mcg/day for methylmercury and mercury, respectively, have been proposed by California’s Office of Environmental Health Hazard Assessment.³

What’s the risk from lead in prenatal vitamin supplements?

Lead is a known toxin to the developing fetus, to children, and to adults. Lead can accumulate in a woman’s body and then cross the placenta, with potentially harmful effects on fetal development. Prenatal exposure to lead can have lasting adverse effects on intelligence, behavior, memory, and more.⁴

According to the Centers for Disease Control and Prevention,⁵ the biggest risk factors for exposure to high concentrations of lead are old paint; drinking water that comes through lead pipes; cosmetics; and workplace exposures. Environmental factors such as pollution can sometime be a source, too. 

Can you help protect yourself from heavy metal exposure?

One piece of good news is that a high intake of other nutrients is actually protective – especially calcium, iron, and vitamin C. That’s right – while calcium can have some naturally occurring lead present in it, it also competes with lead for absorption and binding, and calcium helps to keep other minerals (including heavy metals like lead) from being mobilized from bone. Iron has a similar function, as well,⁶ and possibly zinc.

So, having higher levels of these nutrients from supplements and foods helps lower overall risk. In fact, supplementing with calcium has specifically been shown to help lower blood levels of lead during pregnancy and nursing.⁷ 

Are some prenatal vitamins “cleaner” than others? 

Testing of the raw materials and further testing of finished goods is the responsibility of the supplement manufacturer. Some supplement companies take this responsibility much more seriously than others.

Testing for heavy metals is time consuming and costly – so it’s not uncommon for companies to take shortcuts to save time and money. 

At Thorne, our standards aren’t industry standards — they are much higher. At Thorne, we test every batch of every ingredient for heavy metal contaminants before its mixed into a product, ensuring the highest level of quality in every lot and bottle.

Our name stands for quality and trust – a reputation built over more than 40 years and a reputation that we seek to protect each and every day. 

What about Thorne's prenatal supplement and lead?

Because we test our products extensively, we are confident in what they contain. Here are the heavy metal testing results from a recent batch of our Basic Prenatal vitamin supplement and how we measured up against the federal and California limits on lead:

As you can see, the levels consumed in one day’s use of Basic Prenatal fall far below even the strict levels set by the State of California – and not just for lead, but also for the other heavy metals as well.

Another common supplement taken by women during pregnancy is additional folate (folic acid). Folate is naturally less of a concern, because it is not a mineral, but it’s good to know Thorne’s 1 mg 5-MTHF also conforms to these strict standards.

At Thorne, product quality is our number one concern. It’s not just our reputation – it’s your health. We truly appreciate that you trust us with your health. We know our products cost a little more than other brands, but we hope you see it as we do – as an investment. We do what we do so you can be confident about what you take – and feel better taking it. 

References

1. U.S. Government Accountability Office. “Prenatal Supplements: Amounts of Some Key Nutrients Differed from Product Labels.” GAO-24-106689; 2023. https://www.gao.gov/products/gao-24-106689 [Accessed October 31, 2024]
2. Scelfo GM, Flegal AR. Lead in calcium supplements. Environ Health Perspect. 2000;108(4):309-313.
3. Steven D. Gillett v. Madison One Acme Inc., a Company doing business as Solstice Medicine Company, 2008. https://oag.ca.gov/system/files/prop65/settlements/2007-00033S800.pdf. [Accessed October 31, 2024]
4. Shah-Kulkarni S, Ha M, Kim B, et al. Neurodevelopment in early childhood affected by prenatal lead exposure and iron intake. Medicine (Baltimore) 2016;95(4). doi:10.1097/MD.0000000000002508
5. Health NC for E. CDC – Lead – At risk populations – pregnant women. https://www.cdc.gov/lead-prevention/risk-factors/pregnancy.html [Accessed October 31, 2024]
6. Choi JW, Kim SK. Association between blood lead concentrations and body iron status in children. Arch Dis Child. 2003;88(9):791-792. doi: 10.1136/adc.88.9.791. 
7. Ettinger AS, Hu H, Hernandez-Avila M. Dietary calcium supplementation to lower blood lead levels in pregnancy and lactation. J Nutr Biochem. 2007;18(3):172-178. doi: 10.1016/j.jnutbio.2006.12.007.