Friday March 25 2011
Levels of PFC may be higher in postmenopausal women because they do not lose blood each month
“Gender-bending chemicals found in non-stick pans and food packaging are linked to early menopause,” reported the Daily Mail. It said researchers have found that perfluorocarbons (PFCs) are associated with hormone disruption in women.
The Mail’s focus on saucepans may give the impression that saucepans or other household objects were analysed in this study. However, the study actually assessed levels of PFCs in people in the US whose drinking water may have been contaminated with high levels of the chemicals. It found that in women of menopausal and pre-menopausal age, those with the highest levels of PFCs in their blood were 1.4 times more likely to have been through menopause than those with the lowest.
These findings do not prove that PFCs cause early menopause, and they need to be interpreted with caution. The study has several limitations, and further, high-quality research is required to assess whether PFCs affect human female hormones.
These chemicals are the subject of ongoing research because there are concerns that they can affect human health. However, the current advice in the UK is that exposure to PFCs is within safe levels. The Health Protection Agency says: “It is very unlikely that the general population will be exposed to a level of PFOS or PFOA (types of PFCs) high enough to cause adverse health effects.”
More information on PFOS and PFOA can be found on the Health Protection Agency website.
Where did the story come from?
The study was carried out by researchers from West Virginia University School of Medicine, US. Funding was provided by a company called Brookmar Inc, which was set up by US courts to conduct the C8 health project. This project was set up and funded by the US courts following a lawsuit regarding PFC contamination of drinking water in six different water districts.
The company has an independent scientific board and is tasked with providing evidence for a class action against the DuPont's Washington Works plant, the plant allegedly responsible for the leak of PFCs into drinking water.
The study was published in the peer-reviewed Journal of Clinical Endocrinology and Metabolism.
The Daily Mail's overall focus on saucepans may also give the misleading impression that saucepans or other household objects were analysed in this study. The study actually assessed levels of PFCs in members of the public following possible contamination of drinking water with the chemical. The newspaper did provide some balance to the piece with some quotes from experts.
What kind of research was this?
This was a cross-sectional analysis of data from the C8 Health project, a survey of more than 69,000 adults and children exposed to contamination in their drinking water of a type of PFC called PFOA. Almost 26,000 of the participants used in this analysis were women over 18 years old. Its aim was to assess whether PFCs are associated with changes to oestrogen levels or timing of the menopause (endocrine disruption) in women.
The authors say that PFCs are used in a variety of household products, and are present in water, air, soil, plant life animals and humans. Previous studies have associated them with “multiple” health outcomes in human and animal studies. One of the effects reported in animal studies is endocrine disruption.
What did the research involve?
The survey was conducted by an independent company. Data was collected on whether women had experienced menopause (though they were not asked at what age) as well as hormone use and medications. Blood samples from within the six affected water districts were also taken. These were analysed for the presence of the PFCs perfluorooctanate (PFOA) and perfluorooctane sulfonate (PFOS). Levels of the oestrogen hormone oestradiol, which is related to ovarian function, were also measured.
The researchers analysed the data for nearly 26,000 women aged over 18, to see whether there was any association between PFC levels, oestradiol levels and whether women had experienced menopause at the time of the survey. They divided the women into five groups (or quintiles) according to PFC exposure and age: 18-42 (childbearing years), 42-51 (perimenopausal) and 51-65 (51 being the average age at menopause). Statistical methods were used to assess any association between levels of PFC, levels of oestradiol and menopausal status.
The results were adjusted for other factors that might influence menopausal status, including age, smoking, BMI, alcohol consumption and exercise. Women who had had hysterectomies were excluded. Women who were pregnant or on hormone therapy were excluded from the analysis of oestradiol levels.
What were the basic results?
The researchers found that among women in the two older age groups (42-51 years and 51-65 years), the odds of having experienced menopause were significantly higher for women in the highest quintile of exposure to both PFOA and PFOS, compared to the lowest quintile.
Among women in the perimenopausal (42-51) age group:
- Those in the highest quartile of PFOS exposure were 1.4 times as likely to have been through menopause as those in the lowest quartile (OR 1.4 [confidence limits 1.1 to 1.8])
- Those in the highest quartile of PFOA exposure were 1.4 times as likely to have been through menopause as those in the lowest quartile (OR1.4 [confidence limits 1.1 to 1.8])
In the menopausal age (51-65) group:
- Those in the highest quartile for PFOS exposure were more than twice as likely to have been through menopause as those in the lowest quartile (OR 2.1 [confidence limits 1.6 to 2.8])
- Those in the highest quartile for PFOA exposure were 1.7 times as likely to have been through menopause as those in the lowest quartile (OR 1.7 [confidence limits 1.3 to 2.3])
Note: the researchers do not say if these were 95% confidence intervals or not.
PFOS was also associated with lower levels of oestradiol among perimenopausal women and menopausal women, but there was no association between PFOA levels and oestradiol.
How did the researchers interpret the results?
The researchers say their analysis shows that women of perimenopausal and menopausal age are more likely to have experienced menopause if they have higher blood levels of PFOS and PFOA, than their counterparts with lower levels. They point out that premature or early menopause is associated with increased risk of heart disease and stroke as well as other health problems.
They also say that while the PFOA levels were much higher in this population than in the rest of the US, the levels of PFOS, which comes from the ambient environment rather than water, were probably typical for the population as a whole.
The findings of this large cross-sectional analysis should be interpreted with caution. It is not possible for this kind of study to prove that PFCs cause earlier menopause. As the authors point out, it is possible that the findings are due to “reverse causation” and that PFC concentrations were higher in postmenopausal women because they are no longer losing blood through menstruation. This possibility is supported by the fact that women who had had hysterectomy had higher-than-average levels of PFCs compared with those who had not (although as the authors say, this might still be cause for concern).
In addition, the information about the menopause came from survey data carried out by a separate company. The data was not independently confirmed.
The researchers only looked at whether women had gone through menopause, and they categorised these women into one of three different age brackets they belonged to at the time of the survey. As such, the study cannot tell us how old the women were when they reached menopause and whether those who had early menopause (i.e. before the age of 40 or 45) were associated with higher PFC levels. Further high-quality research is required to assess whether PFCs affect the regulation of female hormones.
Importantly, this US study was based on a survey of adults living in six water districts where water supplies had allegedly been contaminated with PFCs from an industrial plant.
These chemicals are the subject of ongoing research, because there are concerns that they can affect human health. However, the current advice in the UK is that exposure to them is within safe levels. The Health Protection Agency says:
“It is very unlikely that the general population will be exposed to a level of PFOS or PFOA (types of PFCs) high enough to cause adverse health effects.”
More information on PFOS and PFOA can be found on the HPA website.