Per- and polyfluoroalkyl substances (PFAS) are manmade chemicals with a fully or partially fluorinated alkyl chain that is connected to different functional groups (e.g., carboxylate, sulfonate). PFAS have been used for various applications, including water-resistant fabrics, carpet, food packaging, and firefighting foams.1,2
Because of their industrial applications and chemically stable characteristics, PFAS have contaminated the global environment over decades.3,4
These environmentally persistent chemicals are detected in human populations5–8
and linked to adverse health effects such as liver injury,9
kidney and testicular cancer,2,10
and reproductive disorders.2,11
PFAS exposure has been associated with less-favorable blood lipids, including higher low-density lipoprotein (LDL) cholesterol and triglycerides concentrations in epidemiological studies including cross-sectional6,12–18
and longitudinal studies.6,17,19–22
Longitudinal studies of PFAS manufacturing workers19,20
and residents living near PFAS manufacturing plants21,22
reported positive associations between serum PFAS and cholesterol or triglycerides. Several recent studies have explored adults with prediabetes status17
and adults age 70 y6
and found associations of PFAS exposure with less-favorable lipids profiles (i.e., higher total cholesterol and triglycerides). The prospective epidemiologic studies on this topic to date have used a population-mean approach to analysis instead of a trajectory-based approach, which allows researchers to capture heterogeneity in lipid trajectory in the population.
Women in menopausal transition undergo important physiological changes (e.g., changes in hormones and lipids levels),23,24
and they have substantial heterogeneity in such changes.23,25
Because of the physiological changes across the menopausal transition, this life stage may be particularly vulnerable for exposure to factors that may lead to metabolic alterations. Moreover, serum PFAS concentrations increase in postmenopausal women because of cessation of menstruation.5,26,27
However, little is known about the potential role of PFAS in longitudinal changes in lipid profiles during this critical life stage except a study reporting a weak association of perfluorooctanoic acid (PFOA) exposure with hypercholesterolemia among women age 40–59 y.22
To address this data gap, we evaluated serum PFAS concentrations at baseline with trajectories of lipids measured for about 15 y of follow-up in a cohort of women 45–56 y of age, with a hypothesis that PFAS exposure has association with less-favorable lipid trajectories.
In this prospective study of a population of women age 45–56 y, we found serum concentrations of several PFAS (including PFAS mixture groups clustered by k-means algorithm) was predictive of higher total and LDL cholesterol trajectories, which were characterized by an early high peak in the trajectories. We also found that Sm-PFOS were inversely associated with HDL cholesterol trajectory.
The associations of several individual PFAS and PFAS mixture with total and LDL cholesterol trajectories observed in this study are generally in line with previous epidemiological findings (Table S17),2,10
providing a line of evidence that supports harmful effects of PFAS on blood cholesterol profile. Positive associations of blood concentrations of PFAS (e.g., PFOA, PFOS) with blood total or LDL cholesterol levels have been consistently reported in cross-sectional studies of general populations.12–14,16,45,46
Similar observations have been reported in longitudinal studies. Occupational exposure to PFOA was positively associated with higher level of total cholesterol.19,20
PFOA/PFOS exposure has been associated with higher levels of total and/or LDL cholesterol among residents living in a PFAS-contaminated area.21,22
Associations of PFAS exposure with higher cholesterol have been reported in recent longitudinal studies with general populations such as U.S. adults with prediabetes status (
) or Swedish older adults (
although insignificant associations have been also reported in Swedish adults (
Our findings on total and LDL cholesterol are supported by results from relevant experimental studies. Alterations in gene or protein expression regarding lipid metabolism was observed along with lipid accumulation in 3T3-L1 preadipocytes exposed to PFAS such as PFOA, PFOS, and PFHxS during their adipocyte differentiation.48,49
Although rodents studies generally showed lower serum cholesterol levels after PFAS exposure,50
results from mouse studies with human-relevant diet (i.e., high fat diet) were generally aligned with our observations, showing increased serum cholesterol levels after the exposure.51,52
Several mechanisms for PFAS-induced cholesterol dysregulation have been suggested. PFAS have been reported to be associated with liver injury, and PFAS-induced hepatic lipid accumulations have been shown in experiments with mice,53
including peroxisome proliferator-activated receptor
Because of the link between PFAS and liver injury,9
researchers have suggested that liver injury may be mediating the relationship between PFAS and increased cholesterol levels. Other possible mechanisms include epigenetic control of lipid metabolism56,57
and activation of nuclear receptors such as constitutive androstane receptor, pregnane X receptor, and liver X receptor.52,58
Sex hormone disrupting effects of PFAS may be another potential mechanism underlying their effects on lipid regulation. It is known that estrogen decreases circulating LDL cholesterol and increases HDL cholesterol.59
Ovariectomized rats showed increased cholesterol blood levels, which were decreased by estrogen treatment.60,61
Stimulation of hepatic LDL receptor62
and hepatic lipase63
and enhanced cholesterol efflux from peripheral tissues64
are proposed mechanisms for the effects of estrogen on cholesterol. Total and LDL cholesterol levels increase as estrogen decreases during the menopausal transition.23,24
Estrogen therapy in postmenopausal women increased their LDL cholesterol levels and decreased HDL cholesterol levels.65
On the other hand, PFOS has been inversely associated with estrogen levels in female populations.11
In a previous analysis of the SWAN-MPS PFAS data, PFOA and PFNA were inversely associated with estradiol, although the association between PFOS and estradiol was not significant.66
Given the association of PFAS exposure with estrogen and the effects of estrogen on cholesterol regulation, we hypothesize that PFAS exposure increases blood total and LDL cholesterol levels mediated by a PFAS-induced decrease in estrogen. However, exposure to PFOA or PFOS increased estrogen levels in rats67
and a human adrenal carcinoma cell line.68
Species difference in PFAS-induced estrogen change may be another reason for the discrepant associations of PFAS with cholesterol between humans and animals, but further investigation is needed.
The direction of the associations of PFAS with HDL cholesterol or triglycerides in previous epidemiological studies has been mixed (Table S17),2,10
but longitudinal studies mostly have shown primarily associations of serum PFAS with higher triglycerides levels. PFOA, PFNA, PFOS, and PFHxS were associated with hypertriglyceridemia among U.S. adults with prediabetes status (
Similar positive associations of serum PFAS and triglycerides were observed in longitudinal studies of Swedish older adults (
U.S. adults exposed to PFOA contaminated drinking water (
and occupationally exposed workers (
whereas a study of Swedish adults (
) reported inverse associations of PFNA and PFOS with triglycerides.47
It is unclear whether our observation of the inverse association of Sm-PFOS with HDL cholesterol trajectory was by chance or a result of a causal relationship. Further investigation may help to understand the reasons behind this observation.
It was an unexpected finding that the second tertile of n-PFOA (vs. first tertile) was inversely associated with the odds of high trajectory of total cholesterol. We do not have clear reasons for this observation. This inverse association with total cholesterol trajectory might be partly attributed to the inverse association of PFOA with HDL cholesterol, although it is known that the majority of total cholesterol consists of LDL cholesterol rather than HDL cholesterol.69
This might also be a result of chance, given that the association was nonlinear (only significant in the second tertile, not in the third tertile).
This study has numerous strengths. First, to the best of our knowledge, this is the first study investigating associations of PFAS exposure with lipids trajectories in midlife women. The trajectory analysis of this study allowed us to incorporate not only the levels of lipids but also the change patterns in lipids with PFAS exposure. For example, we identified that the high LDL cholesterol trajectory had an early rapid increase and a subsequent decrease, whereas the low trajectory had a slow increase. Because of such fluctuations in lipids in midlife women and individual differences in the patterns, a conventional population-mean approach with rate of changes in lipids levels during a certain period of time, as done in several previous studies, may not fully capture complex patterns in lipid change, which may vary between individuals. Our cross-sectional analyses using the population-mean approach did not show any significant associations of PFAS concentrations with baseline LDL cholesterol or the rate of change in LDL cholesterol during follow-up (Tables S15 and S16). These results emphasize the importance of using group-based trajectory analysis to secure a comprehensive understanding of the relationship between PFAS exposure and longitudinal changes in lipids.
Second, we accounted for lipid-lowering medication. Studies with lipid outcomes often exclude participants with lipid-lowering medication, which can, however, lead to selection bias.70
We accounted for the effects of lipid-lowering medication using two different methods, which yielded similar classifications of lipids trajectories. Third, we evaluated multiple PFAS compounds as a mixture. We used k
-means clustering to identify three clusters of PFAS mixtures (low, medium, high). The observed monotonous positive associations between PFAS mixture clusters and total and LDL cholesterol trajectories further our understanding of the combined effects of PFAS on lipid disruption. In addition to previous studies using k
-means clustering for PFAS mixture,37,71
our results suggest that k
-means clustering is a useful method to cluster the participants with similar exposure status. Fourth, the present study was based on a multiethnic population with about half of the participants from minority race or ethnicity groups. There are limitations to this study. First, PFAS were measured only once at baseline. Although most PFAS considered in this study are biologically persistent with half-lives of the order of several years, our previous analysis of a subpopulation of SWAN-MPS (
) showed relatively low intraclass correlation coefficients among four repeated measurements of PFAS in serum collected 1999 through 2011, indicating relatively high within-subject variability over time.5
Therefore, a single measurement of PFAS at baseline might not be sufficient to represent overall PFAS exposure through follow-up. Second, serum PFAS concentrations can be affected by kidney function,27
which may lead to exposure assessment measurement error and associations toward null. However, even though we lacked information on kidney function, prevalence of kidney disease among women age 45–56 y is expected to be small. Third, although the present study was conducted in a racially/ethnically diverse female population, the results of this study may not be generalizable to males and other racial/ethnic groups, in particular Hispanic populations. Finally, we cannot rule out the possibility of unmeasured residual confounding.
In this first study examining longitudinal associations of PFAS with lipids trajectories among midlife women, we showed that PFAS serum concentrations were associated with less-favorable lipids trajectories, particularly total and LDL cholesterol trajectories. These findings suggest that PFAS exposure is a potential modifiable risk factor for lipid metabolic disorders, even though the underlying mechanisms of action are still poorly understood. Further studies investigating potential mechanisms of PFAS-induced lipid alteration (e.g., estrogen-mediated pathway) would expand the scientific knowledge in this area.
The authors thank the study staff at each site and all the women who participated in the SWAN.
The authors also thank the late X. Ye at the U.S. CDC for her support in PFAS assessment.
The SWAN has grant support from the National Institutes of Health (NIH), the Department of Health and Human Services (DHHS), through the National Institute on Aging (NIA), the National Institute of Nursing Research (NINR), and the NIH Office of Research on Women’s Health (ORWH) (Grants U01NR004061; U01AG012505, U01AG012535, U01AG012531, U01AG012539, U01AG012546, U01AG012553, U01AG012554, U01AG012495, and U19AG063720). The study was also supported by the SWAN Repository (U01AG017719). This publication was supported in part by the National Center for Research Resources and the National Center for Advancing Translational Sciences, NIH, through UCSF-CTSI Grant Number UL1 RR024131.
This study was also supported by grants from the National Institute of Environmental Health Sciences R01-ES026578, R01-ES026964, R01-ES035087, and P30-ES017885, and by the U.S. CDC/National Institute for Occupational Safety and Health grant T42-OH008455. H.K. was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2020R1A6A3A03037876).
The content of this article is solely the responsibility of the authors and does not necessarily represent the official views of the NIA, NINR, ORWH, or the NIH.
Clinical Centers: University of Michigan, Ann Arbor—C. Karvonen-Gutierrez, PI 2021–present, S. Harlow, PI 2011–2021, and M. Sowers, PI 1994–2011; Massachusetts General Hospital, Boston, Massachusetts—J. Finkelstein, PI 1999–present, and R. Neer, PI 1994–1999; Rush University, Rush University Medical Center, Chicago, Illinois—H. Kravitz, PI 2009–present, L. Powell, PI 1994–2009; University of California, Davis/Kaiser—E. Gold, PI; University of California, Los Angeles, Los Angeles, California—G. Greendale, PI; Albert Einstein College of Medicine, Bronx, New York—C. Derby, PI 2011–present, R. Wildman, PI 2010–2011, and N. Santoro, PI 2004–2010; University of Medicine and Dentistry–New Jersey Medical School, Newark—G. Weiss, PI 1994–2004; and the University of Pittsburgh, Pittsburgh, Pennsylvania—K. Matthews, PI.
NIH Program Office: NIA, Bethesda, Maryland—R. Correa-de-Araujo 2020–present, C. Dutta 2016–2020, W. Rossi 2012–2016, S. Sherman 1994–2012, and M. Ory 1994–2001; NINR, Bethesda, Maryland–program officers.
Central Laboratory: University of Michigan, Ann Arbor–D. McConnell (Central Ligand Assay Satellite Services).
U.S. CDC Laboratory: Division of Laboratory Sciences, National Center for Environmental Health, U.S. CDC, Atlanta, Georgia.
NIA Biorepository: R. Correa-de-Araujo 2019–present; SWAN Repository: University of Michigan, Ann Arbor—S. Harlow 2013–2018, D. McConnell 2011–2013, and M. Sowers 2000–2011.
Coordinating Center: University of Pittsburgh, Pittsburgh, Pennsylvania—M. Mori Brooks, PI 2012–present, K. Sutton-Tyrrell, PI 2001–2012; New England Research Institutes, Watertown, Massachusetts—S. McKinlay, PI 1995–2001.
Steering Committee: S. Johnson, current chair; C. Gallagher, former chair.
The findings and conclusions of this report are those of the authors and do not necessarily represent the official position of the U.S. CDC. Use of trade names is for identification only and does not imply endorsement by the U.S. CDC, the Public Health Service, or the DHHS.