Abstract:

Background: Phthalates are ubiquitous (e.g., plastics, cosmetics, food packaging), and re-

exposure is continuous despite rapid elimination. Phthalates are linked with adverse health

outcomes, however relationships with dementia risk are not known. This proof-of-concept study

generated fecal phthalate metabolomics to examine gut microbiome ecology, geo-social

determinants of health (area deprivation index or ADI), and brain biomarker outcomes.

Methods: This study integrates participant and biospecimen-level data from the Microbiome in

Alzheimer's Risk Study (MARS), drawn from the Wisconsin Registry for Alzheimer's Prevention

(WRAP) and Alzheimer's Disease Research Center (ADRC) cohorts. Four aims guided this work: (1)

method optimization of fecal phthalate analysis (n = 10); (2) quantification of 19 phthalates and

metabolites; (3) characterization of gut microbiome composition via sequencing; and (4)

description of relationships between phthalate prevalence, microbiome composition, geo-social

factors, and brain health measures. Key outcomes include Alzheimer's diagnosis and plasma

biomarkers (GFAP, NfL, ptau-217). Key predictors include phthalate presence/absence, age, sex,

race, education, Area Deprivation Index (ADI), Bristol score, BMI, MIND diet score, enterotype,

Shannon index, and observed species count.

Results: PERMANOVA confirmed significant differences in microbial community composition

between the Bacteroides dominant enterotype and the Prevotella dominant enterotype (R² =

0.04, F = 14.28, p = 0.001); the modest effect size suggests enterotypes reflect shifts in relative

abundance among shared taxa rather than discrete ecosystems. In this pilot cohort of

ten cognitively unimpaired adults, ADI did not consistently predict within-sample phthalate

burden — samples from both low- and high-deprivation areas spanned wide detection ranges.

Butylbenzyl phthalate and DEHP were detected across nearly all samples regardless of

socioeconomic context. 

Conclusion: This pilot study demonstrates that fecal phthalate measurement is analytically

feasible. Measuring phthalate metabolites in feces, where gut microbes are directly present,

provides the opportunity to examine direct phthalate effects on gut microbiome, compared to

the more common use of urinary metabolites, which primarily reflect downstream metabolic and

excretory processes. Consistent with the Brain Health Synercome framework (Baez et al., 2026),

findings underscore the need to integrate structural and individual-level exposure

characterization to understand plastic-associated risk for brain health.