Researchers followed 500 pregnant women to see if metals in their blood during early pregnancy were connected to their body composition (how much fat versus muscle they had) in their 50s. They measured harmful metals like arsenic and mercury, as well as helpful metals like zinc and magnesium. Surprisingly, higher levels of certain harmful metals were linked to less body fat in midlife. The study also found that folate (a B vitamin) seemed to change how arsenic affected obesity risk. These findings suggest that what pregnant women are exposed to and their nutrition may work together to influence body weight decades later.

The Quick Take

  • What they studied: Whether metals in a pregnant woman’s blood are connected to how much body fat she has when she reaches her 50s
  • Who participated: 500 women from Project Viva (a long-term health study) who were measured during early pregnancy (around 10 weeks pregnant, average age 33) and then followed up about 20 years later when they were around 51 years old
  • Key finding: Women with higher levels of arsenic, cesium, and mercury during pregnancy had less body fat in midlife, which was unexpected. However, folate (a B vitamin) changed this pattern—arsenic only increased obesity risk when folate levels were low
  • What it means for you: This research suggests that metal exposure during pregnancy may have long-term effects on body composition, but the relationship is complex and depends on nutrition. If you’re pregnant or planning pregnancy, focus on good nutrition (including folate-rich foods) and reducing exposure to harmful metals. However, this is one study and more research is needed before making major changes

The Research Details

This was a prospective cohort study, which means researchers followed the same group of people over time. They started by measuring metals in the red blood cells of 500 pregnant women during their first trimester (around 10 weeks of pregnancy). They also measured folate levels in their blood at the same time. Then, approximately 20 years later when these women were in their 50s, researchers measured their body composition using two methods: BMI (body mass index, a basic weight-to-height measurement) and DXA scans (a special X-ray that shows exactly how much fat, muscle, and bone someone has). The researchers used statistical models to look at whether the metal levels from pregnancy predicted the body composition measurements decades later.

This study design is valuable because it follows people forward in time, which helps establish whether early exposures might cause later health changes. Rather than just looking at one moment in time, this approach allows researchers to see if pregnancy metal exposure actually predicts midlife body composition. The use of DXA scans is particularly important because they measure actual fat distribution, not just overall weight, which gives a more complete picture of health than BMI alone.

This study has several strengths: it followed real people over 20 years, it measured metals directly in blood (not just estimated exposure), and it used precise body composition measurements. However, readers should know that 500 people is a moderate sample size, and the study only included people from one geographic area who participated in Project Viva. The results may not apply equally to all populations. Additionally, the researchers adjusted their analysis for diet and other factors, which strengthens the findings, but there could be other unmeasured factors that influenced the results.

What the Results Show

The most surprising finding was that higher levels of three harmful metals—arsenic, cesium, and mercury—during pregnancy were actually associated with lower amounts of body fat in midlife. This seems counterintuitive because these metals are generally considered harmful to health. The association remained even after researchers accounted for diet during pregnancy. The study also found that the combination of essential metals (helpful metals like zinc, magnesium, and selenium) tended to be associated with lower BMI and lower obesity risk in midlife.

A particularly interesting discovery involved folate, a B vitamin important during pregnancy. The relationship between arsenic and obesity depended on folate levels. When women had low folate levels during pregnancy, higher arsenic was linked to higher obesity risk in midlife. However, when women had adequate or high folate levels, higher arsenic was actually linked to lower obesity risk. This suggests that folate may protect against some of arsenic’s harmful effects.

The study measured both harmful metals (arsenic, barium, cadmium, cesium, mercury, and lead) and essential metals (copper, magnesium, manganese, selenium, and zinc). While the harmful metals showed unexpected associations with lower body fat, the essential metals showed more expected patterns—higher levels were generally associated with healthier body composition. The researchers also looked at different measures of body fat, including total body fat percentage, total fat mass, and trunk fat (fat around the middle), and found consistent patterns across these different measurements.

Previous research has generally shown that metal exposure during pregnancy can harm fetal development and increase disease risk later in life. However, most prior studies focused on birth outcomes or childhood health, not long-term body composition in adulthood. This study’s finding that certain metals are associated with lower body fat is unexpected and somewhat contradicts the general understanding that metal exposure is harmful. This contradiction suggests that the relationship between metal exposure and health may be more complex than previously thought, and that other factors like nutrition (particularly folate) may modify these effects in important ways.

Several important limitations should be considered. First, this study only shows associations, not proof of cause and effect—we cannot say that the metals caused the body composition changes. Second, the study population was relatively homogeneous (similar in many ways), so results may not apply to all groups equally. Third, metal exposure was measured only once during early pregnancy, so we don’t know if exposure changed throughout pregnancy or later in life. Fourth, the study couldn’t measure all possible factors that might influence body composition over 20 years. Finally, the unexpected finding that harmful metals were associated with less body fat needs to be confirmed by other studies before we can trust it fully.

The Bottom Line

Based on this research, pregnant women should focus on: (1) Ensuring adequate folate intake through diet (leafy greens, legumes, fortified grains) or prenatal vitamins—this appears to modify how metals affect long-term health; (2) Reducing exposure to harmful metals through safe drinking water, avoiding certain fish high in mercury, and minimizing exposure to lead-based products; (3) Maintaining overall good nutrition with essential minerals like zinc, magnesium, and selenium. However, these recommendations are based on one study, so discuss specific concerns with your healthcare provider. Confidence level: Moderate—the findings are interesting but need confirmation from other studies.

This research is most relevant to pregnant women and women planning pregnancy, as well as healthcare providers who advise them. It’s also important for public health officials thinking about environmental exposure limits. People who are not pregnant should not be overly concerned about these specific findings, though the general principle of reducing harmful metal exposure applies to everyone. If you have specific concerns about metal exposure (such as living near industrial areas or having high fish consumption), discuss this with your doctor.

The effects described in this study developed over approximately 20 years, from early pregnancy to midlife (age 50s). This means any changes from reducing metal exposure or improving folate intake would likely take years or decades to show up in body composition. Don’t expect short-term changes; think of this as a long-term health investment.

Want to Apply This Research?

  • If you’re pregnant or planning pregnancy, track folate intake daily (aim for 400-800 micrograms per day) and note any potential metal exposures (fish consumption, water quality concerns, occupational exposures). Record these weekly to identify patterns and discuss with your healthcare provider.
  • Start a simple food diary focusing on folate-rich foods (spinach, broccoli, lentils, chickpeas, asparagus, avocado) and track consumption. Set a goal to include at least one folate-rich food daily. Also track fish consumption, noting types and frequency, to monitor mercury exposure. Use the app to set reminders for prenatal vitamin intake if recommended by your doctor.
  • Create a long-term health profile in the app that tracks: (1) Folate intake through food and supplements monthly; (2) Fish/seafood consumption patterns; (3) Any known metal exposures or environmental concerns; (4) Body composition measurements (weight, BMI) at regular intervals. Review this data annually with your healthcare provider to identify trends and adjust nutrition or exposure reduction strategies as needed.

This research describes associations between metal exposure during pregnancy and body composition in midlife, but does not prove that metals cause these changes. The findings are from one study and should not be used to make medical decisions without consulting your healthcare provider. If you are pregnant or planning pregnancy and have concerns about metal exposure or nutrition, discuss these concerns with your obstetrician or primary care doctor. This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.