Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are used to manufacture everyday products such as nonstick cookware, food packaging materials, waterproof clothing, and furniture and carpets.¹ PFAS are widely present in ground water and drinking water; it has been estimated that more than 200 million United States residents consume drinking water contaminated by PFAS.² Due to the ubiquity of PFAS exposure, as nearly all persons 12 years and older have detectable concentrations of at least one PFAS in their blood.³ To compound the problem of exposure is the acknowledgement that commonly used PFAS have relatively long elimination half-lives, of 2–9 years depending on the compound.^4,5 Therefore, not only are most individuals exposed to PFAS, but some PFAS can remain in the body for many years.

PFAS exhibit both lipophobic and hydrophobic properties. Due to their structural similarities to fatty acids, PFAS - especially perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) - have been recognized as potential endocrine-disrupting chemicals (EDCs).^6,7 PFAS exposure may alter endocrine regulation and modulate metabolic pathways, possibly through the activation of multiple nuclear receptors such as peroxisome proliferator-activated receptors (PPARs).^8,9 PPARs promote adipogenesis and have a significant impact on inflammation and lipid metabolism.¹⁰

The associations between PFAS and body weight have been explored in adults. Although some studies observed significant relationships between PFAS and increased weight and risks of overweight and obesity,^11–14 the remaining studies did not observe an association.^15,16 Most prospective cohort studies were restricted to overweight and obese persons, or those with elevated glucose concentrations.^13,14 Notably, studies that analyzed their findings by sex observed a more pronounced effect in women.^12,14 Given that the hormonal changes across the menopausal transition (MT) substantially contribute to increased abdominal obesity¹⁷ and gains in fat mass¹⁸, and that PFAS can eliminate from the body through menstrual bleeding,^4,19 women’s midlife years may represent a special period of vulnerability to PFAS exposure. However, no previous study exploring the relationship between PFAS and body size and composition focused on midlife women.

The overarching goal of this analysis was to investigate whether baseline serum PFAS concentrations were associated with body size and composition or their change in midlife women, using longitudinal data from the Study of Women’s Health Across the Nation (SWAN). We hypothesized that women with higher PFAS concentrations had larger weight, waist circumference (WC), body fat mass and proportion fat at baseline, and higher rates of changes in body size and composition over time.

In total, median age of the 1,381 women included in this study at baseline was 49.4 years with an interquartile range (IQR) of 47.3–51.4 years. Half (50.7%) of the women were White, 21.6% were Black, 12.8% were Chinese, and 14.9% were Japanese. The median (IQR) baseline serum concentration was 1.5 (1.0–2.4) ng/mL for PFHxS, 25.1 (17.7–35.8) ng/mL for total PFOS, 4.1 (2.9–5.8) ng/mL for n-PFOA, 0.6 (0.4–0.8) ng/mL for PFNA, 1.2 (0.7–2.2) ng/mL for EtFOSAA, and 1.5 (0.9–2.3) ng/mL for MeFOSAA. Participants had a median of 68.7 (IQR: 58.5–83.9) kg of body weight, 82.3 (IQR: 73.7–94.9) cm of waist circumference, 25.1 (IQR: 19.0–34.2) kg of body fat mass, and 40.4% (IQR: 35.6%−45.1%) of proportion fat mass. Descriptive statistics of other baseline characteristics are presented in Table 1.

Figure 1 shows model-predicted trajectories of all biometrics by tertile of total PFOS concentrations. These are shown for each of the 2-time segments (0 to 9.0 years and 9.0 to 18.6 years since baseline for weight and WC; 0 to 14.5 years and 14.5 to 18.6 years since baseline for body fat mass and proportion fat). Trajectory parameters, i.e. annual rates of changes, are presented subsequently (Table S1). Overall, PFOS was significantly associated with trajectories of all biometrics characterized by greater weight, WC, body fat mass and proportion fat over time (Table 2). At baseline, predicted GM weight was 4.3 kg (ratio=1.06, 95% CI: 1.03, 1.09) higher in women with the highest tertile of total PFOS concentrations than those with the lowest tertile. Similarly, comparing the highest to the lowest tertile, predicted GM was 87.3 vs. 83.7 cm (ratio=1.04, 95% CI: 1.02, 1.07) for WC, 27.9 vs. 25.2 kg (ratio=1.10, 95% CI: 1.05, 1.16) for body fat mass, and 42.4% vs. 40.6% (difference=1.81%, 95% CI: 1.01%, 2.61%) for proportion fat. The significant associations with weight, WC and fat mass became larger during follow-up. As women reached year 15, predicted GM weight was 5.8 kg (ratio=1.08, 95% CI: 1.05, 1.11) in those with the higher tertile of total PFOS concentrations compared to the lowest tertile.

In addition, total PFOS was also significantly associated with accelerated increases in weight during 0 to 9.0 years of follow-up (Table S1). Women with the lowest tertile of total PFOS concentrations had an annual rate of increase of 0.10% (95% CI: 0.04%, 0.17%) in year 0 to year 9; a significant increase with annual rates of 0.33% (95% CI: 0.27%, 0.40%) observed in women with the highest tertile of total PFOS concentrations (P for interaction<.0001). Similarly, compared to those with the lowest tertile, women with the highest tertile of serum concentrations had a 1.4-fold acceleration in annual rate of increases in WC (P for interaction=0.002). Total PFOS was also significantly associated with accelerated gains in body fat mass (P for interaction=0.0002), but not proportion fat mass (P for interaction=0.32) in year 0 to 14.5. Similar results were detected for n-PFOS (Figure S2 and Tables S2, S9) and Sm-PFOS (Figure S3 and Tables S3, S10). Weight, body fat mass and proportion fat had slight decreases in the 2^nd segment of follow-up, while there was a continued increase in WC. PFOS was associated with higher weight, WC, body fat mass, and proportion fat over time. PFOS was also related to different rates of gains or loss in body size or body fat.

n-PFOA was also significantly associated with larger body size and body fat (Figure 2 and Table 3). At baseline, comparing the highest to the lowest tertile of n-PFOA concentrations, predicted GM was 74.0 vs. 69.4 kg (ratio=1.07, 95% CI: 1.03, 1.10) for weight, 87.6 vs. 83.9 cm (ratio=1.04, 95% CI: 1.02, 1.07) for WC, 87.6 vs. 83.9 cm (ratio=1.04, 95% CI: 1.02, 1.07) for fat mass, and 42.5% vs. 40.6% (Diff=1.91%, 95% CI: 1.07%, 2.75%) for proportion fat. At follow-up, the differences remained similar to the differences observed at baseline as n-PFOS was not associated with change rates in outcomes (Table S4).

Trajectories of all biometrics for other PFAS are shown in Figures S4–S7, rates of change in Tables S5–S8, and predicted values in Tables S11–S14. Two PFOS precursors, i.e. EtFOSAA and MeFOSAA, had similar effects to PFOS. PFHxS was not related to body size or body fat during follow-up (Table S11). Nonetheless, PFHxS was significantly associated with higher rates of increases in weight (P for interaction<0.0001) and WC (P for interaction=0.003) in years 0 to 9, as well as body fat mass (P for interaction<0.0001) and proportion fat (P for interaction=0.0009) in years 0 to 14.5 (Table S5). No significant findings were found for PFNA.

In the sensitivity analyses, the results of log-transformed PFAS were similar to our main findings using tertiles of PFAS concentrations (Tables S15–S16). Log-transformed PFOS, n-PFOA, EtFOSAA and MeFOSAA were positively associated with weight, waist circumference (WC), fat mass, and proportion fat at baseline. Higher PFOS concentrations were also associated with larger increase rates of weight (P for interaction <0.0001), WC (P for interaction=0.01), and fat mass (P for interaction <0.0001). EtFOSAA and MeFOSAA showed similar effects to PFOS (data not shown). Although PFHxS were not related to body size or body fat at baseline, PFHxS were associated with faster increases in weight (P for interaction <0.0001), fat mass (P for interaction=0.0005), and proportion fat (P for interaction=0.02) (data not shown). An additional adjustment for baseline body mass index did not impact the change rates (Tables S19–S20). The results remained almost the same after controlling for pizza, salty snacks, fries, and fish consumption (Table S21–S23). Further adjustment for time-varying menopausal status did not change the results (Tables S24–S26). The results also remained similar after censoring women at the visit when they developed diabetes or cancer (Tables S27–S29).

In this study, PFOS, PFOA, MeFOSAA and EtFOSAA was related to greater body weight, WC, fat mass and proportion fat mass at baseline; the associations persisted through the follow-up visits. Our study also quantified the effects of PFAS exposure on longitudinal trajectories of body size and composition and determined how PFAS was associated with the rates of changes during follow-up. Exposure to PFOS and PFHxS was significantly related to accelerated gains in weight, WC, and body fat.

Although an association between PFAS and larger body size has been reported in previous studies, our study provides a precise estimate of the timing of alterations in body size and body fat in midlife women. Previously, Cardenas and colleagues¹³ found a significant association of PFOS, PFNA and MeFOSAA with larger weight at baseline and during follow-up in a study of 802 adults with overweight or obesity; whereas no association was observed for other PFAS or for skinfold thickness and subcutaneous and visceral fat. Liu and colleagues¹⁴ found weight regain was significantly related to higher baseline plasma concentrations of PFOS, PFOA, PFNA, PFHxS and PFDA after a 6-month weight loss program followed by 18-month follow up in a group of 621 adults with overweight or obesity; whereas PFAS were not significantly related to weight or weight loss during the weight loss period. However, those prospective cohort studies did not include normal weight adults. A cross-sectional study of 1,612 Chinese adults found PFAS exposure associated with obesity and larger WC.¹² In contrast, a retrospective cohort of 8,764 residents from communities with drinking water contaminated with PFOA aged 20–40 years from the C8 Health Project reported no relationship between early-life PFOA exposure and obesity risks.¹⁵ Two other studies^11,16 also reported no significant association of body size with PFAS exposure. The main distinction between previous studies and ours is long-term follow-ups with the average number of repeated measurements of 10.9 in midlife women during and after the menopausal transition, a life-stage that confers susceptibility to metabolic changes in women. This rich data allows us to evaluate whether longitudinal trajectories of body size and composition over 15 years differ by different PFAS serum concentration groups. The present study supports the hypothesis that PFAS exposure may be associated with greater body weight and body fat, and contribute to higher rates of change in body weight, WC, and body fat.

The associations between PFAS and increased body size and body fat are biologically plausible. PFAS can activate PPARs. PPARα may be less responsive to PFAS exposure in humans than in mice; nonetheless, most perfluoroalkyl acids (e.g., PFOA and PFOS) can activate both PPARα and PPARγ.^33,34 PPARs are known to involve in adipogenesis, inflammation, and lipid metabolism.¹⁰ Therefore, PFAS have the ability to promote metabolic disturbances and increase adipocyte differentiation.³⁵ Further, epidemiologic studies have suggested that PFAS were associated with lower thyroid hormone levels; however, the findings are inconsistent.^36,37 Moreover, PFAS exposure may also disrupt leptin signaling pathways, which could contribute to increased weight in mice when they reached midlife³⁸; however, the underlying mechanisms of PFAS and leptin are not completely understood.

Growing evidence pinpoints estradiol (E2) and follicle stimulating hormone (FSH) as targets of PFAS toxicity.^6,7 FSH and E2 affect energy homeostasis pathways. For example, mice with FSH blocked show increases in energy expenditure and oxygen consumption which are accompanied by increased physical activity as well as reductions in resting metabolic rate and body fat.³⁹ Longitudinal data from women in SWAN displayed a positive association between FSH and body fat during menopausal transition.^18,40 Thus, alterations in FSH are possible mechanisms of obesogenic toxicity of PFAS because PFAS were associated with increased FSH concentrations and accelerated ovarian aging in midlife women. PFAS had impact on steroid hormone synthesis.⁷ Besides interacting with specific receptors, PFAS can also exert metabolic effects by acting on non-specific molecular targets. For instance, PFOA and PFOS may cause decreases in global DNA cytosine methylation, while these chemicals may also contribute to increases in long interspersed nuclear element 1 (LINE-1) DNA methylation, and alterations in the expression of genes responsible for lipid metabolism in humans.^41,42

Weight, WC, body fat and proportion fat increased in the 1^st segment of follow-up. Interestingly, we observed slight declines in weight, body fat mass and proportion fat in the 2^nd segment of follow-up, and yet a continued increase in WC (as a surrogate marker of visceral fat). Previous studies have shown that both men and women gain weight and fat mass until middle age and begin to lose weight and fat mass near age 60–65.^43–45 Even in healthy, active older people, men and women may lose weight and body fat.⁴⁴ It is similar to what we observed in SWAN (Figure S1). Weight and body fat decreased in midlife women over time, whereas waist circumference steadily increased with aging. The weight loss among older adults might be due to the loss of lean mass, while visceral fat (as represented by waist circumference) increased. A previous toxicologic study showed that exposure of human visceral preadipocytes in vitro to 5 and 50 μM PFOS promoted adipocyte differentiation and increased cellular lipid accumulation.⁴⁶ It is possible that PFAS exposure may also determine fat distribution during the menopausal transition. Future studies are warranted to examine the associations between PFAS and fat distribution.

Study strengths are several. First, this analysis included a large cohort of midlife women followed for up to 18 years. Standard annual follow-up visits also provided reliable estimates of changes in body size and composition. Second, we analyzed DXA-quantified body composition and measured body weight and waist circumference, thus providing more convincing evidence for the potential obesogenic effects of PFAS. However, we cannot rule out residual confounding, although we have controlled for many known confounders. Also, some women lost to follow-up in the later years which may impact the precision of the study results. Finally, there is a lack of well-established statistical methods to assess the combined effects of chemical mixtures on longitudinal trajectories of outcomes.^47,48 Given that people are exposed to a myriad of chemicals daily, it is critically important to examine the joint effects of PFAS mixtures in future research.

In a large, longitudinal cohort of multi-racial/ethnic midlife women with 18 years of follow up, higher serum concentrations of PFOS, PFOA, EtFOSAA, MeFOSAA were significantly associated with greater body weight, WC, body fat and proportion fat, accompanied by accelerated increased during follow-up. Our findings suggest that PFAS may be an underappreciated contributing factor to women’s obesity, especially during the critical time windows for the development of metabolic and cardiovascular risks. Following the discovery of polytetrafluoroethylene (Teflon) in 1938, thousands of different PFASs have been synthesized and used in industrial and consumer products. These chemicals, also known as “forever chemicals”, may predispose people to weight gain in later life and could play a significant role in the global obesity epidemic. Although PFOA and PFOS in the USA has been largely phased out of use,^49,50 these compounds are still found in the blood of most people. Since PFAS is ubiquitous in the environment, especially in drinking water and ground water, it poses a significant and immediate threat to the general population in the United States and around the world. Consequently, there is a pressing need to raise awareness of PFAS toxicity and potential adverse human health effects.