Growing body of
research links lead to osteoporosis
Bolstered by recent laboratory findings, researchers at the
University of Rochester Medical Center are embarking on a National
Institutes of Health-funded clinical study to better understand the
deceptive role environmental lead exposure plays in bone maturation
and loss. The clinical trial is the latest in a growing body of
research that is putting yet one more notch in the belt of diseases
attributed to lead, and this time, researchers say, its target is
older adults at risk for osteoporosis.
For decades, scientists have known that the human skeleton is
a repository for lead in people who were exposed to high levels of
this environmental toxin in their childhood, but thought this
storage to be benign. Recently, a growing body of research is
showing that the opposite is true, and that lead in bone actually
sets off a bizarre chain reaction, first accelerating bone growth,
and then eventually limiting it so that a high peak bone mass is not
achieved. Preventing a high peak bone mass will predispose a young
person to osteoporosis later in life.
Now, researchers in the Center for Musculoskeletal Research
at the University of Rochester Medical Center are set to embark on
the next phase of a four-year, $5 million research project funded by
the National Institute of Environmental Health Sciences with a
clinical study aimed at better understanding the deceptive role lead
initially plays in bone development, growth and loss – and how this
all might lead to earlier onset of osteoporosis in those exposed to
high levels of lead as a child.
A metabolic bone disease that predominantly occurs in women,
osteoporosis affects one in three American women over the age of 65.
It is characterized by low bone mass that eventually leads to
fractures, mostly of the hip and vertebrae. These fractures can be
life-threatening; experts say that more women die each year from hip
fracture complications than from cancer of the ovaries, cervix and
uterus combined. Close to $20 billion dollars is spent each year
treating osteoporosis and related fractures.
An Ironic Growth Pattern
The pattern of growth in the skeleton determines the peak
skeletal density of an individual, and this level is established by
the time most people reach 20. Recent research completed at the
University of Rochester Medical Center shows that lead adversely
affects the normal maturation of the growth plate – but does so in
an odd way.
"As a child, lead appears to accelerate bone development and
maturation, so that lead-exposed children actually have a higher
bone density than those not exposed to environmental lead," said
James Campbell, M.D., M.P.H., associate professor of Pediatrics and
a co-investigator of the study. "But, we believe this higher bone
density effect is short-lived, and in fact, we believe it actually
prevents these children from achieving an optimal peak bone mass
later on in life."
J. Edward Puzas, Ph.D., professor of Orthopaedics and
director of the overall project, added that limiting peak bone mass
has dire consequences as a person begins to age.
"When everyone begins to lose bone mass starting at around
age 50, lead-exposed individuals are at a higher risk for bone
fractures and osteoporosis – and probably at an earlier age than the
typical osteoporosis patient."
At what specific age lead-exposed individuals will plateau in
bone growth, and at what age they will begin to lose more bone as
older adults, is the focus of this clinical research. Puzas and
Campbell have used their prior research to guesstimate when these
two milestones occur, but are turning to sophisticated lead
measurement devices to help them pinpoint exact timeframes.
"We believe that somewhere around age 20, we'll begin to see
low-lead exposed individuals surpass high-lead exposed individuals
in bone mass density," Campbell said. "Then, in the 50 to 60 age
group – the age at which any individuals will begin to experience a
natural loss of bone – we expect to see the high-lead exposed
individuals losing more bone sooner."
An X-ray fluorescence spectrometer will be used to measure
the bone lead levels in 500 people, separated into three age groups:
8-9 years old, 18-19 years old, and 50-60 years old. One of only a
few installed machines worldwide, it provides a precise, noninvasive
measurement of the historic accumulated exposure to lead, allowing
researchers to place each of the research subjects into an either
"low-lead exposure" or "high-lead exposure" category within their
age groups. A DEXA-scan will then be used to measure bone density,
and with these data in hand, the investigators will have a better
sense of when lead-exposed individuals might begin to experience
osteoporotic symptoms.