Analysis: No Link Between Talc and Lung Cancers
There are many stories of the possible health dangers of inhaled talc throughout the media, the most recent appearing in the New Yorker. These anecdotes are alarming to people who work in the mining and milling of talc, along with the thousands who have previously used baby powder containing talc for infant care and their own personal hygiene.
Among the first research areas the Center for Truth in Science has addressed is an effort to bring clarity to the science underlying the health problems resulting from talc exposure.
One of the deliverables of this effort is a high-quality and independent systematic review of talc, dealing with its relationship to respiratory cancers. This work has been published in a special issue of the journal Frontiers in Public Health, and it provides much that scientists, regulators, policymakers, legal professionals, and the public need to know about this issue.
The systematic review was conducted using a hybrid framework built on the strongest elements of EPA, Toxic Substances Control Act (TSCA), and Institute of Medicine of the National Academies of Science frameworks. It also used PRISMA guidelines, considered the “gold standard” for reporting results of systematic reviews and meta-analyses.
In this review, a team of highly regarded epidemiologists, toxicologists, and risk specialists conducted a search of the studies on inhaled talc and its association with lung cancers and mesothelioma published up to September 2021. Three types of studies were collected: epidemiological, experimental animal, and mechanistic.
After applying inclusion and exclusion criteria, which had been decided a priori (aka. before the search was begun), the researchers ultimately included 19 epidemiology and four animal studies focused on pulmonary cancers in the systematic review. Next, these studies were evaluated for quality and the research team integrated results for all three types of studies to reach their conclusions. [A full summary of the study findings and quality evaluation methods and results are described in the paper and its supplementary materials.]
Due to the rigorous methods of the search and analysis of the papers for this review, including study quality, results should be seriously considered by anyone who needs to know what good science is currently telling us about inhaled talc and respiratory cancers. I have summarized the most important points below:
Overall, in available animal studies, there is indeterminate evidence that talc is associated with lung tumors in rodents based on negative findings in several high-quality studies and species.
Talc was found negative for an ability to cause genetic mutations in cells (mutagenicity). While the evidence for possible carcinogenic mechanisms of talc is limited, a genotoxicity mechanism of action (a way to damage cell growth, leading to cancer) can be ruled out with confidence.
Data from studies of how talc acts in the body over time indicate there is a rapid clearance from the lung and body after it is inhaled in single doses, and there is no translocation of talc to other organs after either single or repeated exposure. This means overall, that current mechanistic evidence does not support a means by which talc induces lung cancer.
Human epidemiological studies
No excess of malignant mesothelioma has been reported in any of the available epidemiological studies of talc miners and millers heavily exposed to talc.
When considered together, the findings, large study populations, long duration of follow up, and consistency of non-positive results demonstrate that talc exposure is not associated with mesothelioma.
Lung cancer mortality was not elevated among most cohorts of talc miners and millers exposed to high levels of inhaled talc and accessory minerals. The available epidemiological evidence does not show a causal association between talc exposure and lung cancer deaths.
Asbestos in talc?
There has been worry from consumers and professionals in mining and milling, that very small amounts of asbestos or asbestiform materials, known carcinogens, might be in talc, as the two substances come from mines that can be in close proximity to each other.
I spoke to lead author of the systematic review, Heather Lynch, and she informed me that their review criteria did not specifically include or exclude any particular types of talc. So, some of the talc that study participants inhaled, theoretically may have been contaminated by asbestos, while others were known to be asbestos-free.
The investigators were looking for associations with any talc type. If they could have made any conclusions specific to “pure” talc or with “trace other minerals” they would have. “However, when the evidence is all unequivocally null (associated with 0) then it doesn’t really matter,” she explained. “We did not need to specify, because even if some theoretical small amount of asbestos were actually in talc, there was no excess of lung cancers or mesothelioma in any of the studies.”
Studies of talc miners that report excesses of deaths from non-cancer lung diseases find that these are not associated with either lung cancer or malignant pleural mesothelioma.
Based on the integration of evidence from human epidemiological studies, animal experiments, and mechanistic studies (all with good methodological quality), it is not likely talc and cosmetic talcum powders at human-relevant exposure levels, cause human pulmonary cancers, including lung cancer and mesothelioma.
The body of human epidemiological evidence is reasonably large and robust for lung cancer and mesothelioma, and it provided the most weight in the integration of the team’s review findings. It was complemented by a number of high-quality animal studies, as well as the lack of convincing mechanistic evidence.
To learn more about the significant conclusions of this systematic review, published in Frontiers in Public Health, you can access our Top Takeaways here.
The Center for Truth in Science remains committed to bringing clarity to the existing body of scientific research on the potential human health effects of talc exposure. A second independent paper examining potential links between talc and reproductive cancers, such as ovarian cancer, is under review and expected to be published later this year.