Phthalate Exposure and Child Development -- The Infant Development and
are a class of chemicals widely used in
manufacturing to increase the transparency, durability, and flexibility
of plastics. They are commonly found in pharmaceutical coatings, food
wrapping, personal care products, and many household items. Since
phthalates are not covalently bound to their product matrix, they can
easily leach into the surrounding environment and are thought to enter
the human body through a number of routes: oral, dermal, inhalational,
intravenous. Phthalate exposure in the modern environment has become
nearly universal as their use in consumer products has become
commonplace. Some studies have suggested that particular types of
phthalates may function as endocrine disruptors and interfere with
To help fund my PhD thesis research, I worked part-time for The Infant
Development and Environment Study (TIDES), under the direction of Dr.
Shanna Swan. In this capacity, I created the code to organize subject
data and conducted some preliminary analyses. During this time I also
conducted an analysis to explore the socioeconomic correlates of
phthalate urinary metabolite levels using the National Health and
Nutrition Examination Survey.
I just finished examining some fairly interesting associations of
prenatal phthalate exposure and behavior in 6-10 year old children, using
Shanna’s Study for Future Families. We found associations between
certain phthalate esters and inattention and problem behavior in boys.
Our paper was accepted by Environmental Health Perspectives and will be
publicly available soon.
is a clip of Shanna discussing phthalate exposure on CBS National News.
Limits of Detection
Environmental health studies often rely upon biomarkers to
estimate exposures. For example, in a study of whether phthalate
exposure during pregnancy was associated with timing of labor, exposure
to phthalates was estimated through quantifying metabolites
in maternal urine samples. Unfortunately, the laboratory techniques
that quantify biomarkers often produce data that are subject to limits
of detection (LOD). Chemical levels below the LOD are difficult to
quanitfy. The presence of these observations complicates the
statistical analysis of environmental health analysis.
While several methods for addressing LODs have been described,
they have rarely been systematically compared. We are conducting a
simulation study to compare the bias associated with each of these
methods. Once we have results we indeed to create a simple and clear
decision tree to help environmental health researchers in their work.
The Seychelles Child Development Study
The Seychelles Child Development Study is a 20+ year
prospective study of Seychellois children and their exposure to
methylmercury. The findings of this study have been published in The
Lancet, Journal of the American Medical Association, and many other
I spent three years working with highly interdisciplinary research
group. I helped determined the direction of future research and
conducted many different analyses relating to socioeconomic status. One
such study was a life course analysis of maternal socioeconomic
position in relation to young adult cognitive function in multiple
domains, which was recently published. In addition, I’ve contributed to
many of their analyses of child neurodevelopment.
PhD Thesis Study
load is a developing epidemiologic concept
that has been used to quantify the physiologic costs of adaptation and
cumulative life stress, whether psychological or physical.
Although various forms of life stress have been linked with late-life
depressive symptoms, the association between allostatic load and
depressive symptoms has rarely been assessed. My thesis project
entailed a cross-sectional study of two different study populations:
older adults from the 2005-2008 National Health and Nutrition
Examination Survey and 125 community-dwelling older adults of
Rochester, NY. The objective was to examine the complex relationship of
life stress, allostatic load, social factors, and psychosocial factors
with the severity of late-life depressive symptoms.
(1) To examine the relationship between multisystem physiologic
dysfunction (renal, immune, hepatic, metabolic, and cardiovascular
function) and the severity of global, cognitive/affective, and somatic
depressive symptoms among a nationally-representative sample of older
(2) To examine the relationship between allostatic load
(neuroendocrine, immune, metabolic, and cardiovascular function) and
the severity of global, cognitive/affective, and somatic depressive
symptoms among a sample of Rochester older adults.
(3) To conduct path analyses to examine the complex causal web of
biological, psychological, and social factors underlying late-life
depressive symptoms. To situate allostatic load within this causal
This study provided evidence in support of the allostatic load
model of late-life depressive symptoms. In both a large, nationally
representative sample and a smaller sample of community-dwelling
Rochester, NY older adults, we observed associations between composite
measures of multisystem bodily dysfunction with late-life depressive
symptoms. In addition to demonstrating that these associations do
exist, the effect sizes we observe indicate a clinically meaningful
difference in depressive symptoms; this difference was comparable to
the average effect size observed in clinical trials of antidepressant
medication use, although occurring in the opposite direction. The full
public health significance of this association remains to be
elucidated, as additional research is needed to confirm these findings.
However, given the prevalence of clinically significant late-life
depressive symptoms observed in the samples represented here and
elsewhere, as well as the debilitating nature of depressive symptoms,
the relationships explored in this project appear to be of broad public
CHILDREN'S TOYS, SUCH AS RUBBER DUCKS, MAY CONTAIN PHTHALATES
THE HYPOTHESIZED LINKS BETWEEN STRESS, PERSONALITY, MOOD, AND ALLOSTATIC LOAD