September 5, 2006 (AIDSmeds)—A report published in the August issue of The Journal of Clinical Endocrinology and Metabolism
has confirmed that HIV-positive women are more likely to suffer from
low bone mineral density (BMD) compared to HIV-negative women. However,
the study also suggests that the bone loss in HIV-positive women does
not appear to significantly worsen over time and is often related to
traditional risk factors, including low body weight and cigarette
smoking.
Osteoporosis and osteopenia
are familiar terms to many older adults. A diagnosis of osteoporosis, a
serious loss of BMD, can bring on a lot of anxiety, as it generally
means that a person's bones have become weaker and are more likely to
break. And while a diagnosis of osteopenia, a less serious loss of BMD,
does not mean the same thing as an osteoporosis diagnosis, it can be of
concern just the same.
Previous studies have reported
increased rates of osteopenia and osteoporosis among HIV-positive
people. However, most of these studies were "cross sectional" in their
design, meaning that they relied on a one-time "snapshot" of all
patients enrolled and didn't follow patients to see if the problem
worsened. What's more, the studies were generally too small to evaluate
the risk factors for decreased BMD in the HIV-positive volunteers.
In
the newest study, conducted at Harvard Medical School in Boston,
changes in BMD among 100 HIV-positive women – compared to 100
HIV-negative women similar in age and race – were monitored over a
two-year follow-up period.
Dual energy X-ray
absorptiometry (DEXA) scans, used to measure BMD, were conducted in all
of the study volunteers upon entry and every six months for a total of
24 months.
At the start of the study, the HIV-positive
women had significantly lower BMD at three important skeletal
locations: the spine, the hip, and the femoral neck (the ball part of
the hip joint). The differences between the two groups were
statistically significant, meaning that the differences in BMD between
to two groups weren't likely due to chance.
Approximately
41% of the HIV-positive women had osteopenia and 7% had osteoporosis.
Oddly, the paper did not summarize rates of osteopenia or osteoporosis
in the HIV-negative women for comparison purposes.
While
the differences between the HIV-positive and HIV-negative women
persisted for two years, BMD actually remained stable in both groups of
women. This stability, the Harvard group pointed out, argues against
worsening bone loss in HIV-positive women compared to HIV-negative
controls.
Blood markers of bone metabolism – notably
osteocalcin and N-telopeptide of type 1 collagen – were higher in
HIV-positive women compared to HIV-negative women.
Bone
metabolism is better known as "remodeling," with two important types of
bone cells to be familiar with: osteoclasts and osteoblasts.
Osteoclasts are responsible for removing old or worn bone, which can
leave cavities (lacunas). The removal of bone, and the creation of
lacunas, is known as bone resorption. It is the job of the osteoblasts
to fill these lacunas with new collagen and mineral, a process known as
bone formation.
Just as healthy bone structure requires
adequate amounts of collagen and mineral, there must also be a healthy
balance of bone resorption and formation. If the amount of new bone
deposited by osteoblasts equals the amount of bone taken away by
osteoclasts, the bones stay strong. However, the Harvard research
suggests that the bone resorption and formation seems to prematurely
shift in HIV-positive women, resulting in more bone being taken away
than deposited.
Many of the risk factors for low BMD
were not directly related to HIV, including low body weight, smoking
history, low vitamin D levels, and high levels of bone metabolism
markers. However, the longer women had been infected with HIV or had
been treated with at least one nucleoside reverse transcriptase inhibitor (NRTI), the greater the association with decreased BMD.
Based
on these findings, the study authors concluded that HIV-positive women
with easy-to-document risk factors for bone loss, including low body
weight and blood markers of bone metabolism, should be screened for
bone loss with DEXA scanning.
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