Limit dark chocolate consumption in pregnancy to avoid excess heavy metals
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Key takeaways:
- Several brands of dark chocolate bars have levels of lead and cadmium unsafe for pregnant women and children.
- More research is needed on effects of lower levels of heavy metals on a developing fetus.
Consumer Reports in December warned of high levels of lead and cadmium in certain dark chocolate bar brands. These heavy metals, even in small concentrations, can have adverse consequences for pregnant people and developing fetuses.
Lead and cadmium can have negative effects on vulnerable populations, such as children and pregnant women, including neurologic issues, low birth weight, gestational hypertension, preeclampsia and spontaneous abortion. It is important to make consumers aware of brands with increased levels of heavy metals and encourage them to purchase products with lower levels.
Pregnant people should consume dark chocolate in moderation and maintain a well-balanced diet to offset potential risks. More research is needed on processing cacao and the effects of lead and cadmium on a developing fetus.
We reviewed current literature to best counsel patients on safe food choices during pregnancy. Consumer Reports found that 15% of people consume chocolate daily. Generally, at obstetric intake visits, providers counsel patients on foods to avoid during pregnancy. To date, dark chocolate has been on the approved-to-consume list. In fact, some studies have shown potential benefits of dark chocolate consumption in pregnancy, including improved blood vessel function, reduced inflammation and a reduction in cholesterol levels linked to the presence of antioxidants. Any moderation warnings associated with dark chocolate consumption are tied to limiting the amount of caffeine and sugar intake.
Adverse effects of heavy metal exposures
Exposure to heavy metals during pregnancy is certainly a concern, and consuming contaminated food is the primary pathway for these substances to pass into the body. ACOG discusses the risk of lead poisoning due to environmental factors and states that chronic low levels of lead exposure can lead to cognition issues, hypertension and other CV problems, as well as decreased renal function and adverse reproductive outcomes in adults. In August 2022, WHO published that there is no known safe blood lead concentration pertaining to children, and even levels as low as 3.5 µg/dL could be associated with decreased intelligence, behavioral and learning difficulties. In one study, each 1 µg/dL increase in umbilical cord blood lead level was found to be associated with an incremental reduction in mental development index scores (Bayley Scales of Infant Development) within 6 months of life. In contrast, another study showed the relationship is not linear, and more data are needed to draw any conclusions.
During pregnancy, lead in bone is released into the blood and can become a source of exposure to the developing fetus. Lead also crosses the placenta and can lead to pregnancy issues, including gestational hypertension, spontaneous abortion and low birth weight. As of Dec. 23, the FDA’s interim lead reference level was 2.2 µg per day for children and 8.8 µg per day for females of childbearing age. ACOG recommends that if a pregnant person’s blood lead level is greater than 5 mg/dL, the source of lead exposure should be identified and removed due to concern for potential adverse effects.
A study published in Nature in 2021 outlined how cadmium exposure is a growing concern because it is primarily found in foods grown in contaminated soil. Contaminated foods mentioned include lettuce, spinach, potatoes, grains, peanuts, soybeans, sunflower seeds and tobacco leaf. However, dark chocolate as a source for cadmium toxicity has not been well publicized, and there are few studies regarding this topic.
The WHO states the tolerable weekly intake of cadmium is 7 µg/kg body weight per week. The Environmental Protection Agency recommends less than 1,000 mg/kg body weight per day. Due to physiologic alterations in the gastrointestinal system during pregnancy, dietary cadmium is easily absorbed, and a fetus is especially at risk for adverse effects of heavy metal exposure due to the high rate of cell division. Studies show that even in low concentrations, cadmium may affect the function of the placenta, particularly zinc homeostasis, and has been shown to increase rates of pregnancy-related hypertension and preeclampsia.
A direct correlation has been established between the cadmium level in pregnant women’s urine and a reduction of birth weight, height and cranial circumference of the newborn. There is also an association with developmental issues due to cadmium in breast milk and evidence of spontaneous abortion with higher levels of cadmium.
Heavy metals in dark chocolate
Consumer Reports evaluated 28 dark chocolate bars and found that for 23 of these bars, eating only 1 oz per day would increase levels of lead and cadmium in an adult to a level that may be harmful. It is established that elevated levels of these heavy metals may cause serious health effects in children and a developing fetus.
Dark chocolate bars generally contain at least 65% cacao by weight. According to Consumer Reports, these chocolate bars likely have increased levels of heavy metals due to how the plants are grown and processed. For example, cacao plants absorb cadmium from the soil, and lead contaminates the cacao after beans are harvested due to the heavy metal deposits on the outer shell of the cacao.
Figures 1A through 1D highlight the results of the Consumer Reports study. California’s maximum allowable dose level of lead (0.5 µg) and cadmium (4.1 µg) were used as a cutoff because at the time of the study there were no federal limits for lead and cadmium that are safe for most foods to contain and this standard is the most protective available. For reference, a chocolate bar generally ranges from 1.5 oz to 3.5 oz.
According to Johns Hopkins Medicine toxicologist Andrew Stolbach, MD, MPH, in an interview with National Public Radio following publication of the Consumer Reports study, the safety levels for lead and cadmium are very protective, and going beyond these cutoffs by a small amount should not be concerning. He also discusses the importance of maintaining a balanced diet that is sufficient in calcium and iron to prevent absorption of some of the lead and cadmium. ACOG agrees that it is important to maintain adequate dietary intake of calcium, iron, zinc and vitamins C, D and E, as these are known to decrease lead absorption.
Unfortunately, this new finding in cacao may be a preview into a much larger environmental issue. According to an article in Time magazine in response to the Consumer Reports study, there are many foods that contain detectable heavy metals and labeling as such is not currently required. This makes identification of these foods and products challenging for consumers. Heavy metals such as lead and cadmium are finding their way into food at increased levels, at least in part by human activity, such as farming, transportation, industry, urbanization and pollution.
Consumer Reports calls for cacao manufacturers to reevaluate the way beans are processed to decrease lead levels and to survey cadmium soil levels in areas where cacao is being grown. This requires the development of strategies that restrict processing these metals near farming areas and stringent assessment and restriction of cadmium in fertilizers. Co-authors of the study recommend reducing wet cacao bean contact with soil during fermentation and drying and blending high cadmium content beans with those with lower levels, identifying areas of contamination, and conducting more robust testing prior to distribution.
ACOG advocates for policies that will reduce harmful exposures and protect the health of pregnant individuals and their children.
Consumers should be aware of brands with increased levels of heavy metals and, given that there are options for products with lower levels, consider purchasing the latter. Pregnant people should consume dark chocolate in moderation and maintain a well-balanced diet to offset potential risks. More research is needed on processing cacao and the effects of lower levels of lead and cadmium on a developing fetus.
References:
- ACOG. Lead screening during pregnancy and lactation. Committee Opinion. August 2012. Available at: www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2012/08/lead-screening-during-pregnancy-and-lactation. Accessed March 17, 2023.
- ACOG. Reducing prenatal exposure to toxic environmental agents. Committee Opinion. July 2021. Available at: www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2021/07/reducing-prenatal-exposure-to-toxic-environmental-agents. Accessed March 22, 2023.
- Ahn A. Dark chocolate might have health perks, but should you worry about lead in your bar? NPR. Published Dec. 17, 2022.
- Amegah AK, et al. J Expo Sci Environ Epidemiol. 2021;doi:10.1038/s41370-021-00289-6.
- Blum JL, et al. J Toxicol Environ Health A. 2015;doi:10.1080/15287394.2015.1026622.
- CDC. Cadmium toxicity: What are the U.S. standards for cadmium exposure? 2013. Available at: www.atsdr.cdc.gov/csem/cadmium/Safety-Standards.html#:~:text=The%20ATSDR%20MRL%2C%20which%20states,based%20on%20its%20renal%20effects. Accessed March 22, 2023.
- Espart A, et al. Metallomics. 2018;doi:10.1039/C8MT00174J.
- FDA Center for Food Safety and Applied Nutrition. Lead in food, foodwares, and dietary supplements. Available at: www.fda.gov/food/environmental-contaminants-food/lead-food-foodwares-and-dietary-supplements. Published March 1, 2023. Accessed March 17, 2023.
- Katz DL, et al. Antioxid Redox Signal. 2011;doi:10.1089/ars.2010.3697.
- Law T. What to know about dark chocolate and heavy metals. Time. Published Dec. 22, 2022.
- Loria K. Lead and cadmium could be in your dark chocolate. Consumer Reports. Available at: www.consumerreports.org/health/food-safety/lead-and-cadmium-in-dark-chocolate-a8480295550/?EXTKEY=YSOCIAL_IG. Published Dec. 15, 2022. Accessed March 17, 2023.
- WHO. Lead poisoning. Available at: www.who.int/news-room/fact-sheets/detail/lead-poisoning-and-health. Published Aug. 31, 2022. Accessed March 17, 2023.
- Yan X, et al. Sustainability. 2018;doi:10.3390/su10020338.
For more information:
Ashley Zeilenga, DO, is an OB/GYN PGY4 resident through the Michigan State University College of Osteopathic Medicine Statewide Campus System at Garden City Hospital. She can be reached at ablanchard@primehealthcare.com.
Hamid Sanjaghsaz, DO, is OB/GYN faculty and adviser through the Michigan State University College of Osteopathic Medicine Statewide Campus System and is employed at Advanced Obstetrics and Gynecology in Dearborn, Michigan.
Melina Henderson, DO, is an OB/GYN PGY4 resident through the Michigan State University College of Osteopathic Medicine Statewide Campus System at Garden City Hospital.