women have low levels of the now-banned pesticide DDT in their blood, which
is reducing their bone mineral density and putting them at greater risk of
The research was done as part of a PhD project by Sonya Marshall-Gradisnik,
in the University's School of Exercise Science and Sport Management.
Dr Marshall measured DDE, which is formed when DDT breaks down in the body.
DDE has been shown to affect the levels of women's hormones, oestrogen and
androgen, which regulate bone density.
"We found three quarters of the women had detectable levels of DDE in their
blood," she said.
"When women had detectable levels of DDE, there was a significant reduction
in their bone mineral density, compared to women who had no detectable
levels of DDE.
"As DDE levels increased, the women's bone mineral density decreased. This
may predispose the women to increased fracture rates, and osteoperosis in
The other main investigator in the study was Professor John Beard, from the
Lismore-based Northern Rivers University Department of Rural Health, which
is a joint venture between the University of Sydney and Southern Cross
Dr Marshall and Professor Beard tested 89 women aged 45-65 from the NSW
northern rivers region.
DDT was widely used in Australia and worldwide as a pesticide and
insecticide until it was banned in most countries in the 1970s because of
its damaging effects on the environment. It continues to be used in some
third world countries for malaria control. DDT takes more than 70 years to
break down. It accumulates in the body when people consume meat or milk
from cows, sheep or other animals that have grazed on grass in soil
containing DDT residues.
The researchers were the first in the world to examine if there was a
relationship between DDT and bone mineral density. "It's an interesting
finding and the outcomes can be applied worldwide," Dr Marshall said.
DDE accumulates in the fat cells of the body, and circulates in the blood.
"The level we found in the blood is not toxic in your body, but this study
shows that level is affecting one parameter, and that's bone mineral
density," she said.
Another part of the study found that taking part in a six-month walking or
resistance (weight) training program made no difference to retention of
bone mineral density, compared to a control group who did no exercise program.
"That is consistent with the recent literature saying you need at least
eight to 12 months to promote changes in bone retention," Dr Marshall said.
However they did find that resistance training was associated with a
reduction in the levels of a substance associated with inflammation in the
body, called Interluken-6. That reduction was not seen in the walking group
or control group.
"It shows that if you can increase your strength, presumably you're not
getting as much muscle damage happening," she said. "The common perception
is older women and men can't really lift heavy weights. Well, this study
shows they can, with no damage, and in fact greater benefit from resistance
training exercise compared to other exercise programs."
Dr Marshall lost a year's work of her PhD when the funding for it ran out
at a Queensland University. With the help of Professor Peter Baverstock,
Pro Vice-Chancellor (Research) she transferred to SCU's School of Exercise
Science and Sport Management and became involved in the DDT study.
For more information contact Sara Crowe, Southern Cross University Media
Unit, Ph: 6620 3144.