September 5, 2006

Greater Risk of Bone Loss in HIV-Positive Women

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.