Control Shot May Weaken Bones
(HealthScoutNews) -- Could
your choice of birth control at age 18 come back to haunt you
when you're 45? It might -- if your choice is the popular injectable
contraceptive known as Depo-Provera.
New research confirms that the main ingredient in the shots
-- depo medroxyprogesterone acetate or DMPA -- can cause significant
bone loss when used long term. And, say experts, the younger you
are when you begin using this contraceptive, the greater your
risk of bone-related problems later in life.
"This is not the first study to observe that use of DMPA
may result in bone density loss, [but] our study confirms the
results of others," says study author Dr. Abbey Berenson,
professor of Obstetrics and Gynecology at University of Texas
Medical Branch. What makes this study stand out, adds Berenson,
is the design, which was able to detect even subtle differences
between the groups of patients who were studied.
From the time we are born, well into middle age, our bone mass
is constantly breaking down and re-building, usually in a well-balanced
design that keeps bone density -- the thickness and strength of
our bones -- in check. In women, one of the key factors involved
in the bone-making process is the hormone estrogen.
As we age, however, we start to lose more than we make, causing
our skeleton to grow more fragile. In women, the start of this
process is often marked by menopause, a time when, not coincidentally,
estrogen levels dramatically decline.
Now, researchers say that DMPA, which blocks pregnancy by suppressing
estrogen production and stopping ovulation, has the same effect
on the bones as menopause -- preventing a woman from making new
bone fast enough to keep up with the level of bone loss.
"After menopause, bone is resorbed [lost] at a faster rate
than it is made. The mechanism is probably similar in women using
DMPA," says Berenson.
The most significant dangers linked to DMPA, say other experts,
occur when taken by young women whose skeletons are not yet fully
"A woman's skeleton continues to develop until she is about
25 years of age. To decrease bone mass during this time means
maturing with a weaker bone structure, and that can translate
into really serious problems by the time she reaches menopause,"
says Dr. Rogerio Lobo, chairman of Obstetrics and Gynecology at
Columbia Presbyterian Medical Center.
Those problems, he says, include a high risk of the bone-thinning
disorder osteoporosis, as well as increased risk of broken bones,
including hips, knees and ankles.
If you're wondering if all forms of this kind of progesterone
therapy have the same risks -- including Norplant, another form
of progesterone-only birth control, or even natural progesterone
treatments often prescribed for peri-menopausal dysfunctional
bleeding disorders -- both Berenson and Lobo say there's nothing
"An injection of DMPA releases progesterone into the blood
stream every day for at least three months [with four injections
usually used in a year ]. We do not think that a loss in bone
density would be observed with other progesterone-only therapies,
in which the duration of use is much shorter, smaller in amount,
or not every day," says Berenson.
Lobo agrees: "The levels are much lower, and, particularly
in the case of progesterone-only therapy for peri-menopausal symptoms,
it's only used for part of the month, mimicking a natural cycle
The new study involved a total of 155 women between the ages
of 18 and 33. An injection of DMPA was given to 33 women once
every three months for a period of one year. Other women in the
study group were given their choice of two different oral contraceptives
(both containing estrogen) plus one of two different forms of
progesterone: norethindrone (chosen by 28 women) and desogestrel
(used by 35). Fifty-nine women who did not use any hormonal contraception
served as the control group.
At the start of the study all the women were given bone density
tests, measuring the lumbar (lower) spine. Other factors figured
into the study included body mass index, calcium intake, exercise
and smoking -- all known to have an effect on bone formation and
After 12 months, the bone mass of the women was measured once
The result: Overall, the group using DMPA experienced a 2.74
percent rate of bone loss, compared to the pill users who actually
gained bone mass during the study time. Women using the norethindrone
pill gained 2.33 percent bone mass, while those taking the desogestrel
formulation gained 0.33 percent bone mass -- about equal to that
of the control group.
"Some women in [the DMPA] group did have an overall increase
in their bone density, [but] on average, the DMPA group experienced
a loss in their measured bone density," says Berenson.
For Lobo, the question now is whether the bone loss would continue
at the same rate, grow worse, or stop completely, if DMPA were
"For the most part, the bone density effects are reversible
if you stop taking DMPA. But we don't know the degree to which
it would continue with continued use of DMPA for more than a year,"
Berenson speculates that bone loss would increase over time
with continued use of DMPA, but the degree may also be influenced
by other factors including ethnicity, smoking, exercise and nutrition.
What To Do
To learn more about all forms of birth control, visit Planned
For information on teens and birth control, click
To learn more about preventing osteoporosis, visit the National
Osteoporosis Foundation, click
Reference Source 101