Research Extracts: Heavy Metal Toxicity | Mercury | Lead | Cadmium
Welcome to the second edition of Thorne’s Research Extracts, our monthly update on the latest research that impacts your health or the health of your patients. Knowing that busy practitioners can’t always focus on the latest research, our medical team of NDs, MDs, PhDs, RDs, and MS (Biol) has extracted the essence of the very most interesting studies and provided a summary of each.
In this issue – a focus on heavy metals: (1) mercury toxicity and selenium deficiency; (2) deaths from lead exposure are 10 times higher than thought; (3) cadmium exposure and kidney stone risk; and (4) effects of cadmium on DNA methylation.
Mercury toxicity can result in a functional selenium deficiency
Contributed by Alan Miller, ND
Mercury is ubiquitous in our environment because 50 tons of this toxic heavy metal are released annually into the U.S. environment that makes its way into the air, water, soil, and food. Mercury binds to the sulfhydryl (sulfur-hydrogen) groups on molecules like glutathione and cysteine that are involved in mercury transport across cell membranes and in mercury excretion.
What has received little attention is how mercury binds to selenium-containing enzymes and other proteins, which permanently impedes their function. This binding causes cellular oxidative stress that can damage and even kill cells.
It has been thought that selenium can help protect against mercury toxicity.
This paper explains that mercury, by binding irreversibly to selenium-containing proteins, causes a functional selenium deficiency, which might be reversed by selenium supplementation. This finding highlights the importance of testing selenium levels along with mercury when assessing heavy metal burden in the body, so an individual can supplement with selenium if needed.
- Spiller H. Rethinking mercury: the role of selenium in the pathophysiology of mercury toxicity. Clin Toxicol 2017 Nov 10;1-14. doi: 10.1080/15563650.2017.1400555
New study finds U.S. deaths from lead exposure might be 10 times higher than previous estimates
Contributed by Kathi Head, ND
A study published March 12 in The Lancet Public Health estimates that lead exposure contributes to significantly more deaths from cardiovascular disease than previously estimated – as much as 10 times more. The study followed 14,289 adults for 19 years and found that even low levels of lead in the blood (below 5 mcg/dL) contributed to increased mortality, particularly from heart disease.
Is it time to start testing blood lead levels as part of a routine cardiovascular health screening – along with cholesterol and triglycerides?
- Lanphear B, Rauch S, Auinger P, et al. Low-level lead exposure and mortality in US adults: a population-based cohort study. Lancet Public Health 2018 March; doi.org/10.1016/S2468-2667(18)30025-2
Effects of cadmium exposure on DNA methylation could reveal a mechanism for cadmium toxicity
Contributed by Sheena Smith, MS (Biol)
Gene regulation is managed through the DNA code – genetics – and from outside it – epigenetics. One form of epigenetic regulation is methylation. Analogous to redacting a document, methylation blocks the ability of cells to read the genetic code contained in the DNA.
Alterations in methylation patterns can result in aberrant genetic expression and cellular dysfunction.
A 2018 study found that higher levels of cadmium exposure can cause differential methylation in maternal and newborn genomic DNA. The study found both hypo- and hypermethylation in the DNA of women and newborns exposed to higher levels of cadmium, with these alterations tending to occur near genes or regulatory elements. Furthermore, strong representations of genes associated with metabolic and cardiovascular functions were found.
Although statistical significance was weak, possibly owing to the small number of genes assessed, this corresponds with known toxic effects of cadmium exposure. The authors propose that epigenetic disruptions might contribute to the mechanisms of cadmium toxicity, especially contributing to long-term impacts on growth and metabolism.
- Cowley M, Skaar D, Jima D, et al. Effects of cadmium exposure on DNA methylation at imprinting control regions and genome-wide in mothers and newborn children.Environ Health Perspect 2018 Mar;126(3):037003. doi: 10.1289/EHP2085
Meta-analysis supports link between cadmium exposure and urolithiasis risk but highlights open questions
Contributed by Stephen Phipps, ND, PhD
A meta-analysis of six observational studies including 88,000 participants provides support for the hypothesis that cadmium exposure is linked to increased risk of urolithiasis. Four studies assessing occupational cadmium exposure and two studies assessing dietary cadmium exposure were included.
Overall analysis showed an increased odds ratio of 1.32 for the highest levels of cadmium exposure compared to the lowest.
Segregating the studies by route of exposure, however, found significant results only from occupational exposure with an odds ratio of 1.56. The authors conclude that cadmium exposure is associated with higher urolithiasis risk, especially from occupational sources, and that further study is required to more accurately characterize the conditions with the most potential risk.
- Guo Z, Wang J, Gong L, et al. Association between cadmium exposure and urolithiasis risk: A systematic review and meta-analysis. Medicine (Baltimore) 2018 Jan;97(1):e9460. doi: 10.1097/MD.0000000000009460.
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