Heavy metals and female hormones: what cadmium and lead can do

You are sitting in the consulting room, and I ask you whether you smoke. Then whether you used to smoke. Then about your ferritin, and after that how heavy your period is. Meanwhile you are here because of cycle complaints, because of fibroids or endometriosis. And you think to yourself: what does one have to do with the other?

It has more to do with each other than most guides tell you. And less than some elimination blogs claim. This text sits in between.

Cadmium and lead are not exotic poisons from a chemical accident. They are everyday: cigarette smoke, grains, vegetables, organ meats, shellfish, cocoa. And some of them can dock where estrogen otherwise docks. That is a well measured mechanism. What follows from it for your menstrual cycle is an entirely different question.

This article is for the woman who wants to know after the appointment why I ask these questions. And for the woman who read online that cadmium raises the endometriosis risk 3.4-fold and has felt bad ever since. That number does not appear here, because I could not find its source. What I did find is here in full, including where it contradicts environmental medicine.

These four colours will accompany you through the text. In this field, almost everything depends on whether a sentence comes from a petri dish, from a rat or from a woman. That is the most common mistake online, in both directions.

Metalloestrogen: what the term means and where it ends

Imagine a lock. The lock on a door behind which the building instructions for the uterine lining, the mammary gland and part of your mood are kept. The key is called estradiol, and your body makes it itself, in the rhythm of your cycle.

And now the uncomfortable part. This lock is not particularly choosy. Other molecules fit into it as well. Some from plants, some from plastics, some from moulds. And some are simply metal ions.

The word metalloestrogen comes from a review by Darbre from 2006, published in the Journal of Applied Toxicology. It brings together metal ions that bind to estrogen receptors and can trigger an estrogen-like response there in the laboratory. The list is longer than you would expect: aluminium, antimony, arsenite, barium, cadmium, chromium, cobalt, copper, lead, mercury, nickel, selenite, tin and vanadate.

Here is the first distinction, and it matters. A metalloestrogen is something different from a xenoestrogen made of plastic. Xenoestrogens are organic molecules, often from packaging, cosmetics or pesticides, and they carry their own cluster of questions. We already have a separate text on that, so I will not go into it here and instead point you to xenoestrogens in everyday life. And there is a third family, the mycoestrogens from moulds, above all zearalenone. We have a separate article on that too: zearalenone and hormones.

So why does this article exist at all? Because the word has had a strange career online. On agency websites it does not appear, there the subject is kidney values. On elimination blogs it is a magic word with a therapy standing right behind it. The two sides talk past each other, and in between sits a woman with cycle complaints.

And now you know why I pause briefly at the word metalloestrogen in the consulting room instead of acting straight away. It is a good starting point for a conversation and a poor starting point for a treatment.

Cadmium at the estrogen receptor: cell culture, animal model and the line between them

When you read online that cadmium mimics estrogen, that sentence almost always traces back to two papers. Both are well done, neither was carried out in humans, and both are almost never cited with that label attached.

The first is from 2000, from the Lombardi Cancer Center at Georgetown University in Washington. A team around Stoica measured how tightly cadmium sits on estrogen receptor alpha.

The second paper is the more famous one. In 2003, Nature Medicine published an experiment showing that this does not only play out in a dish. Ovariectomised rats, meaning rats without ovaries and therefore without their own estrogen source, were given cadmium.

In 2020 the same effect was added for arsenite, in a paper in Carcinogenesis. There too the increase could be blocked with an antiestrogen, and after additional exposure to a carcinogen, tumours appeared more often and earlier. What is interesting is what was not different: total number, multiplicity and volume of the tumours did not differ. Such distinctions show how limited an effect can be, even when it is statistically there.

And then there is one more finding that is particularly interesting for this topic. At the US environmental institute NIEHS, work was done in 2021 on human fibroid cells, meaning cells from a uterine leiomyoma line.

And now you know why, with the sentence cadmium mimics estrogen, I always ask in which species. It is correct. It is just not about humans.

What has been measured in humans: menstrual cycle, hormone levels, ovarian reserve

Many women know this pattern. The period comes irregularly, the second half of the cycle feels sluggish, and the values that were taken all sit somewhere within the reference range. Then the thought appears that it could be environmental exposure. A legitimate question. It even has data behind it.

The best work on cycle hormones and metals is called BioCycle and comes from Buffalo, New York. It is so good because it did not take blood once, but up to eight times per cycle.

Ten percent less FSH sounds like a lot. It is not. Within a single woman's cycle, FSH swings by a multiple of that. A ten percent difference between two groups is a statistical signal, not a finding you would feel in yourself. Which hormone value is meaningful and when is covered in hormone testing in women.

The second big question is ovarian reserve, usually measured as anti-Muellerian hormone. There is a paper on this from the SWAN cohort, one of the best long-term studies on the menopausal transition anywhere.

And now the counter-finding that appears in no elimination blog. In western France, four fertility centres examined whether women with diminished ovarian reserve have higher metal values than women without. 139 cases, 153 controls.

And now you know why, with cycle complaints, I do not start with a metal test but with thyroid, iron, stress and sleep. Metals come later, if they come at all.

Endometriosis and fibroids: the contradictory evidence, honestly sorted

This is the section many women find this article for. And the one in which I choose my words most carefully. Not out of reticence, but because the data demand it.

First a sentence that stands above everything. Endometriosis and fibroids are medical diagnoses. They belong in gynaecological care for assessment, and an indicated operation or laparoscopy is not replaced or postponed by any environmental thought. The environmental question comes on top. You will find the larger context under endometriosis seen integratively.

Endometriosis: two studies, two directions

In 2023, Human Reproduction published an analysis from four NHANES cycles, meaning from the large US health survey. It is the source for almost all German articles on the topic.

Now the other study. The ENDO study secured the diagnosis surgically: 473 women who were being operated on anyway, plus a population cohort with MRI diagnosis. That removes the largest source of error, self-report.

Fibroids: somewhat more consistent, but weak

With fibroids the picture is a little more uniform. The same surgical cohort found an adjusted odds ratio of 1.44 with 1.02 to 2.04 for whole blood cadmium, 1.31 with 1.02 to 1.69 for whole blood lead and 1.31 for urinary cobalt. The catch: cadmium and lead in urine were not associated. When blood and urine give different answers, that is a warning sign.

The study group itself considers that a fibroid could also be a reservoir for these elements. So not the metal makes the fibroid, but the fibroid binds the metal. That is reverse causality, and here it is not an excuse but a serious possibility.

The best prospective work so far is from 2025 and comes from the SELF cohort in the Detroit area. Prospective means: first the measurement, then the waiting, then the look at who newly develops a fibroid. Ultrasound at the start and after 20 months.

For context, one more reassuring finding. In a Danish cohort of 23815 postmenopausal women, the incidence rate ratio per additional 10 micrograms of dietary cadmium per day was 0.99 for breast cancer, 1.08 for endometrial cancer and 1.15 for ovarian cancer, each with intervals that include 1. So nothing.

And now you know why, with fibroids and endometriosis, I talk first about the gynaecological treatment, about bleeding intensity, about iron and about pain. And only afterwards, if at all, about metals. If the estrogen metabolism behind it interests you, you will find it under understanding estrogen dominance.

Menopause: what the numbers say about the timing of the final period

One sentence has been travelling through German health websites for years: that cadmium brings menopause forward. I considered it plausible myself for a long time. It fits the mechanism narrative and sounds logical.

The most recent work on it shows the opposite.

Why a cross-section is such a large problem here

A cross-section measures everything at the same time. So today's metal value and yesterday's age at menopause. That is roughly like measuring adults' shoe sizes and concluding from that how fast they ran as children.

With lead there is an additional twist. Lead sits in bone, and bone is remodelled faster after menopause because estrogen is missing. If more lead is in the blood afterwards, that can mean lead accelerated menopause. It can just as well mean menopause released the lead. Both explanations produce the same number.

Alongside this there is something better documented that gets mentioned less often: in human observational studies smoking itself counts as a factor for earlier menopause. And smoking is at the same time the largest cadmium source.

What actually becomes a topic in this phase of life we describe in detail elsewhere: perimenopause and when it begins as well as the question of what may ease things during menopause. And because the iron store is often a blind spot in this phase, it is also worth a look at iron deficiency in menopause.

And now you know why I no longer use that one sentence from the internet. Not because environmental medicine were unimportant. But because the most recent number points the other way, and then you say so.

Lead: fertility, pregnancy and the bone store

Lead is the quieter candidate. It does not bind to the estrogen receptor as spectacularly as cadmium and therefore appears less often in guide texts. In the human data, however, it is the metal with the most robust signals. That reversal surprised me too.

Time to pregnancy: a couple matter

The LIFE study is one of the best papers on environmental factors and fertility. 501 couples were followed from the moment they stopped contraception, with diaries and tests, for up to twelve months.

A later overview from the same research group confirmed this: for lead in the man the fecundability odds ratio was 0.83 with 0.70 to 0.98, after adjustment for the partner's values.

Pregnancy: pre-eclampsia, honestly placed

On lead and pre-eclampsia there is a meta-analysis from 2022 that pools 21 studies. It compared 1533 women with pre-eclampsia against 10998 healthy pregnant women. The standardised mean difference was 1.06 with a confidence interval of 0.69 to 1.43.

Sounds unambiguous. It is not. Heterogeneity was 96.4 percent, a value at which, strictly speaking, one should no longer pool. The association has been found repeatedly. That single number still does not carry. Pre-eclampsia has many causes and is a core topic of antenatal care, with blood pressure measurement, urine testing and ultrasound. Nothing in this article changes that.

The bone store: the underestimated point, with both sides

Lead behaves in the body somewhat like calcium. It is built into bone and stays there, with half-lives measured in decades. Part of your current lead burden comes from a time when petrol still contained lead.

And now the thought I consider underestimated. Bone is not a safe, it is an account. Where bone is remodelled, stored lead can return to the circulation. Two such phases are pregnancy and breastfeeding, a third is menopause.

One paper is practically the most important in this article for me, because it is randomised. Chance decides who gets what, and therefore something can be said about cause and effect instead of only about associations.

What lead otherwise does in the body and which values are considered abnormal in Germany is covered under lead: symptoms and sources. Pregnancy and childhood follow their own rules: heavy metals in pregnancy and childhood.

And now you know why I sometimes ask women in the menopausal transition about calcium supply, without it being only about bone density.

Mercury, thyroid and arsenic: the indirect routes

Not every route from metal to hormone runs through the estrogen receptor. Two detours are better documented than the direct route: one through the thyroid, the other through blood sugar.

Mercury and the thyroid

Your thyroid is the pacemaker hardly anyone has on their radar when the cycle goes off track. It co-regulates cycle length, bleeding intensity, ovulation and the binding protein your sex hormones hang on. When the thyroid tips, the cycle tips with it.

A finding from the Spanish INMA birth cohort with 1407 pregnant women fits with this. Mercury in cord blood was borderline inversely associated with total T3, with a beta of minus 0.05 and an interval of minus 0.10 to 0.01. The association was clearer in the women who supplemented iodine, there minus 0.08 with minus 0.15 to minus 0.02. So the effect depends on iodine status. Exactly these interactions explain why studies in this field so often point in different directions.

How thyroid and female hormones interact is covered under thyroid and female hormones. On metals and Hashimoto there is heavy metals and Hashimoto, on mercury itself understanding mercury.

Arsenic and gestational diabetes

The second detour runs through sugar metabolism, and that is more tightly interlocked with your hormones than it sounds. Insulin co-regulates androgen production in the ovaries and can influence the binding protein SHBG in the liver. That is why the blood sugar axis turns up in almost every hormone topic, described under insulin resistance and hormones in women.

On arsenic and gestational diabetes there are two independent meta-analyses. The first from 2020 from the San Raffaele Institute in Milan pooled nine papers with 1984 cases, pooled risk 1.56 with 1.23 to 1.99, heterogeneity moderate at 64 percent. The second from 2024 from Shenyang covered 13 studies with 2575 cases, odds ratio 1.47 with 1.11 to 1.95.

Two groups, two datasets, the same direction, a similar order of magnitude. For this field that is remarkably consistent. The heterogeneity, however, has to be judged separately: in the 2020 paper it was in the moderate range, while the 2024 paper reports considerable heterogeneity. On top of that, the diagnostic criteria differ between countries.

And now you know why, with me, a thyroid panel and a look at blood sugar often stand at the beginning instead of a metal profile. The path runs through the systems I can actually observe.

Where cadmium and lead come from, and how to read measured values

Up to here the question was whether metals could have something to do with your hormones. Now the question that brings more in everyday life: where do they come from, and what does a test show.

The sources, sorted by weight

One source towers above all others: tobacco smoke. The tobacco plant accumulates cadmium from the soil, and the lung takes it up far more efficiently than the gut.

I write this without a wagging finger. Smoking is not a character flaw, it is a dependency, and quitting is hard. But leaving this number out would make the whole rest of the article dishonest. It is the largest single lever in this topic.

Through food the distribution is broader and the amounts are smaller. The Austrian agency for health and food safety compiled measured values for this from the years 2010 to 2017: algae around 1800 micrograms per kilogram, cocoa about 179, seafood 136, mushrooms 128, oilseeds 110, organ meats 41 and grains around 30.

Measuring: what each test answers and what it does not

This is where serious and unserious handling of the topic part ways. Not in whether measuring happens, but in which question a measured value is trusted to answer.

How closely dietary intake and measured value hang together was examined in a Swedish paper at the Karolinska Institute. 57 non-smoking women collected duplicate portions of their food over four days, while blood and urine were measured in parallel. The partial correlation between dietary cadmium and urine was 0.43. And now the sentence that matters: taking iron status into account, it rose to 0.54. Two women with the same plate can carry different amounts of cadmium in the body.

In Germany there are official assessment values for cadmium in urine. The human biomonitoring commission of the Federal Environment Agency works in two steps: below the first level, no health impairment is to be expected according to current knowledge, above the second level an impairment is possible and environmental medical care is indicated. I deliberately do not name concrete numbers, because the values circulating online come from secondary sources and assessment values are adjusted over the years. They belong in the discussion of your results. Which test makes sense when is covered under measuring heavy metals in blood or urine.

With the provocation test the situation is similarly clear. A chelating agent such as DMPS or DMSA raises metal excretion in urine in every person, even without elevated exposure, and established comparison values for this situation do not exist. The American College of Medical Toxicology positioned itself explicitly against the use of this test for diagnostics in 2010, because the predictive value is not documented. We cover both procedures in detail under hair mineral analysis in review and DMPS and the provocation test.

And now you know why I sometimes forgo a test even though it would be technically available. A result from which no action follows produces mainly one thing: worry.

What may actually lower intake, and where keeping perspective begins

If you have read this far, you know my position. The mechanisms are good, the human data inconsistent, and the only randomised study in the entire field concerns calcium and blood lead. There is no randomised study in humans showing that lowering the metal burden changes hormonal complaints. Everyone reading about this topic should know that sentence.

Even so, the order in which one can act is not arbitrary. It follows the strength of the evidence, and it is remarkably unspectacular.

First: avoiding sources

The largest lever is quitting smoking. Not the second largest, the largest. It is not comparable to any dietary change. If it is not possible right now, it may be possible later, and everything else stays sensible regardless. Quitting deserves support, and there are good services for that.

With food it is not about a ban list but about variety. Anyone who eats grains from different sources, who treats organ meats and shellfish as an occasion rather than a habit, has understood the point. With dried algae products, deliberate restraint can genuinely be worthwhile, because the contents there are orders of magnitude higher.

Second: iron status. The practical core of the whole topic

This is the paragraph I wrote this article for. The gut has a transporter for divalent metals, DMT1. It is actually meant for iron, but it is not choosy, and cadmium, manganese and cobalt fit through it as well.

Now the decisive point. When your iron store falls, your body builds more of these transporters in order to catch more iron. And with the iron, more cadmium can come along. The body is not doing anything wrong. It is prioritising.

A small Japanese paper on 25 young women found the same pattern: blood and urine cadmium behaved inversely to haemoglobin, serum iron and ferritin. Too small to build anything on, but it fits the picture.

How to interpret your iron status is covered under iron deficiency and the right blood values. Why heavy periods are the most common reason for low stores, under iron deficiency through menstruation. A second ferritin guide helps nobody, so I will not repeat that here.

Third: zinc and calcium, honestly placed

Zinc is the partner of metallothionein, that sulphur-rich protein which binds cadmium. From this it is often concluded that plenty of zinc protects against cadmium. The evidence for that comes from the rat model and is thinner than assumed.

With calcium the situation is better, because there the randomised evidence exists. There too the effect was moderate and limited to a subgroup. In pregnancy and while breastfeeding, every supplement belongs under medical supervision.

What deliberately does not appear here

And now the paragraph that matters most to me

Environmental medicine has a side effect that is talked about too rarely. It can create fear. And fear looks for control.

I see this regularly. Someone reads about cadmium in grains and cuts out whole grains. Then about lead in spices, cuts out spices. Then about mercury, cuts out even more. In the end the plate is small, the worry large and the nutrient supply worse than before.

And now you know why, in the consulting room, I ask about smoking, ferritin and bleeding intensity before I talk about metals. Not because metals were irrelevant. But because the questions before decide more about your everyday life than any laboratory value after.

Common questions from the consulting room

Where this topic connects to the rest of your system

Metals are one puzzle piece. They hang on your iron status, on your thyroid, on your blood sugar and on how you handle uncertainty. Here are the texts that carry on at each of those points.