Heavy Metals in Supplements: What We Found When We Started Building Biosphere

When we started Biosphere nearly a decade ago, the goal was straightforward: build the magnesium supplement we would actually want to take ourselves every day. Best forms. Best ingredients. Therapeutic doses. Nothing compromised. What we did not expect was that sourcing a clean raw ingredient would become one of the most important decisions we made.

New Zealand manufacturing standards are genuinely high. But being made in New Zealand only tells you where a product was assembled, not where the raw ingredients came from. The mineral inside the capsule, the botanical extract in the powder, the amino acid in the tablet - these are almost always sourced internationally. And that is where quality can diverge enormously.

The first batch of magnesium glycinate we were offered came back from testing with mercury levels that immediately ruled it out. The supplier was credible. The price was competitive. The label would have said "Made in New Zealand" and that would not have been wrong. But we would have known what was really in it, and we were not willing to take that every day. We would not have recommended it to anyone we cared about.

That experience changed how we think about ingredient sourcing. The country of manufacture matters. The country of origin of the ingredient matters more.

Heavy metals are not an adulterant added to supplements. They are naturally present in soil, water, and rock, which means they are present in every mineral and botanical ingredient on earth at some level. Lead, arsenic, cadmium, and mercury are the four of primary concern: they accumulate in the body over time, they have no beneficial function at any dose, and they are toxic to multiple organ systems.

A 2024 analysis by researchers from the FDA and NIH's Office of Dietary Supplements, published in the Journal of AOAC International, tested 38 botanical dietary supplement reference materials for arsenic, cadmium, lead, and mercury. The study found meaningful variation across ingredients and extraction methods, and importantly noted that extraction processes do not reliably reduce heavy metal content - and can in some cases increase mass fraction levels. You cannot assume a processed or extracted ingredient is cleaner than its raw source material.

The practical implication is that ingredient origin and supplier testing matter. Not all magnesium glycinate is the same. Not all ashwagandha root extract is the same. The same ingredient from different suppliers in different growing regions can have dramatically different heavy metal profiles.

A single dose of a supplement with trace heavy metals is not a meaningful health concern. That is true. But it is not the right framing.

We built Biosphere to be taken every day. That was the point: consistent, therapeutic nutrition, not occasional supplementation. When you take something daily for years, trace amounts compound. A dose that seems trivial once a day becomes substantial across 3,650 days. And most people taking supplements are not taking just one. Stack three or four products with sub-optimal heavy metal profiles and the combined daily load starts to look very different from any single product's label.

The research supports this concern. A 2022 study published in Biology examined the effects of different lead exposure paradigms and found that duration of exposure was the primary driver of adverse outcomes - more so than the timing or intensity of any single exposure event. Chronic, low-level lead exposure was associated with hypertension, long-term memory impairment, neuroinflammation, and autonomic dysfunction. The longer the exposure continued, the more pronounced the effects.

Cadmium is arguably the more insidious concern for daily supplement users. Unlike lead, cadmium has a biological half-life of 10-30 years in the kidney - meaning it accumulates relentlessly with no meaningful clearance pathway. A study in Dose-Response found that even very low-level chronic cadmium exposure produced persistent renal tubule damage and fibrosis that continued progressing long after exposure stopped. The kidney damage outlasted the exposure itself.

This is the argument for caring about heavy metal levels in supplements you take daily. Not because a single serving will harm you, but because daily use over years is the entire premise of supplementation. It applies even more when you are taking therapeutic doses - if the goal is to take 400mg of magnesium every single day for years, the standard of what is in that dose has to be set accordingly.

The first magnesium glycinate we tested came with a certificate of analysis from the supplier. The heavy metal specifications listed were: Heavy Metal (total) ≤20 ppm, Mercury ≤1 ppm, Cadmium ≤0.5 ppm. The results showed total heavy metals <20 ppm and mercury <1 ppm. On paper, it passed the supplier's own standards.

The problem was those standards. A mercury specification of "less than 1 ppm" tells you almost nothing useful. It could mean 0.001 ppm or 0.99 ppm. That is a thousand-fold difference, and the document does not distinguish between them. Total heavy metals at "less than 20 ppm" has the same problem. For a product we planned to take every single day, indefinitely, that level of imprecision was not acceptable. We walked away.

After weeks of contacting bulk mineral suppliers around the world, requesting certificates of analysis and rejecting batches that did not meet the bar we had set for ourselves, we found what we were looking for.

The difference was immediately visible. Specific quantified results, not directional thresholds. Lead: 0.4 ppm. Arsenic: 0.1 ppm. Cadmium: 0.01 ppm. Mercury: 0.01 ppm. Those numbers mean something. Mercury at 0.01 ppm is less than one hundredth of what the first supplier's specification would have permitted. That is the gap we were trying to close.

This is the batch we built Biosphere Magnesium around. We have been taking it ourselves every day since - coming up on ten years.

Not all COAs are equally informative. Here is what to look for, and what should make you pause.

In the absence of universally mandated supplement-specific heavy metal limits, a practical grading framework has emerged in the testing community to give context to what individual results actually mean. Our Biosphere Magnesium Glycinate scores A++ for mercury and cadmium, A++ for arsenic, and B for lead - the latter driven by the fact that lead is the hardest of the four to eliminate from mineral sources entirely.

For reference, the USP (United States Pharmacopoeia) standard for oral dietary supplements taken at up to 10g per day sets limits of 5 ppm for lead and cadmium, 15 ppm for arsenic, and 15 ppm for mercury. Our ingredient comes in at a fraction of these limits across all four metals. The relevant question is not just whether a product passes a minimum standard, but how far below it the actual results sit.

Most people who take one supplement take several. Magnesium, fish oil, a greens powder, a protein supplement. Each product contributes its own heavy metal load. If each individual product sits near the top of permissible limits, the combined daily intake from four or five products can be meaningfully higher than any single one suggests.

Minerals are particularly relevant here because they are extracted from the earth directly. A magnesium supplement, a zinc supplement, an iron supplement - these all carry some natural mineral burden. Botanical ingredients, anything derived from roots, leaves, or fungi, are the other high-risk category because plants bioaccumulate heavy metals from soil. A cross-sectional study published in BMC Complementary and Alternative Medicine tested 200 health supplement products and found that cadmium daily intake exceeded or approximated the tolerable daily intake in three of them - each within permissible limits individually, but the combined load across a full supplement stack was not assessed. If you take a greens blend, an ashwagandha extract, and a mineral supplement daily, the sourcing quality of each matters.

The short version: ask for a certificate of analysis, look for individual quantified results for each of the four major heavy metals, and favour suppliers who test at the ingredient level rather than just the finished product. Our magnesium supplement buying guide covers the full evaluation framework, and the same principles apply to our astaxanthin and every other product in the range.

• Ask for the certificate of analysis. Any reputable supplement company should be able to provide one for the ingredients in their products. If they cannot or will not, that tells you something.
• Look for quantified individual results. "Less than X ppm" for total heavy metals is insufficient. You want individual figures for lead, arsenic, cadmium, and mercury.
• Check the country of origin of ingredients, not just where the product was manufactured. Raw minerals from certain regions consistently show higher contamination than others.
• Consider your total supplement load. If you take multiple products daily, the cumulative heavy metal profile across all of them is what matters, not any single product in isolation.
• Prioritise products you take every day. A supplement you take occasionally carries far less cumulative risk than one you take for years. Set higher sourcing standards for your daily stack. For a full checklist of what to look for, see our guide to what makes the best magnesium supplement.