Older adults with higher levels of saturated bone marrow lipids have a higher risk for fractures, whereas those with more unsaturated marrow lipids have a lower fracture risk, according to study findings.

“It has been established that greater bone marrow adiposity is associated with aging and osteoporosis,” Gina N. Woods, MD, associate professor of medicine at University of California, San Diego, told Healio. “The aim of this study was to evaluate whether the type of fat within bone marrow, not just the total amount, influences bone. The take-home message is that saturated and unsaturated marrow lipids have distinct and opposing effects on skeletal health in older adults.”

Woods and colleagues analyzed data from the AGES-Reykjavik study, a longitudinal observational study of community-dwelling older adults. Participants underwent quantitative CT scans of the spine and hip at baseline, and DXA scans of the hip, anteroposterior spine and lateral spine at baseline and during follow-up visits. MRI scans were conducted to measure bone marrow lipids. Incident fractures were identified between baseline and Dec. 31, 2012, using data from the Reykjavik study fracture registry. Fractures occurring from January 2013 to March 15, 2019, were obtained from hospital records. Participants had sex steroid and bone biomarkers measured through serum collections at baseline.

The findings were published in The Journal of Bone and Mineral Research.

There were 465 older adults included in the study cohort, including 243 men (mean age, 82.6 years) and 222 women (mean age, 80.7 years). Men had an areal bone mineral density reduction of 0.3 mg/cm² per year, and 18.9% had at least one fracture during 4.7 years of follow-up. The annual areal BMD reduction among women was 3.5 mg/cm², and 23.9% reported a fracture during a mean follow-up of 5.5 years.

Saturated lipid content lowers BMD

In adjusted analyses, each standard deviation increase in vertebral marrow saturated lipid content was associated with a 23.6% reduction in lower spine trabecular bone density and a 26.8% reduction in lower spine compressive strength index. There was also a 13% reduction in trabecular BMD and a 1.2% reduction in cortical BMD at the total hip, and a 23.5% reduction in trabecular BMD and a 1% reduction in cortical BMD at the femoral neck with each standard deviation increase in vertebral marrow saturated lipid content.

Each standard deviation increase in vertebral marrow unsaturated lipid content was associated with a 17.5% increase in trabecular spine BMD, a 26.2% increase in spine compressive strength, an 11.5% increase in total hip trabecular BMD and a 22% increase in femoral neck trabecular BMD.

Saturated and unsaturated lipid content were not associated with changes in any bone parameters for the full cohort. For women, each standard deviation increase in saturated lipid content was linked to a 3.82 mg²/cm⁴ reduction of spine compressive strength index each year, and each standard deviation increase in unsaturated lipid content increased the loss of femoral neck trabecular BMD by 1.39 mg/cm³ each year.

Increased fracture risk with higher saturated lipids

Each standard deviation increase in saturated lipid content increased the odds for a prevalent vertebral fracture (OR = 1.46; 95% CI, 1.11-1.92) and incident radiographic vertebral fracture (OR = 1.55; 95% CI, 1.03-2.34). Each standard deviation increase in unsaturated lipid content decreased the likelihood for incident radiographic vertebral fracture (OR = 0.58; 95% CI, 0.38-0.89).

“We did not find marrow lipid composition to be significantly associated with bone loss, although we did find associations with prevalent and incident fractures,” Woods said. “These findings suggest that marrow lipid composition may influence fracture risk through a mechanism that is independent of bone density.”

There were no associations observed between saturated lipid content and bone biomarkers.

Each standard deviation increase in unsaturated lipid content was associated with a 6.87% reduction in procollagen type 1 N-terminal propeptide (P1NP) and a 6.97% reduction in C-terminal telopeptide of type 1 collagen (CTX).

Woods said more research is needed on the factors regulating marrow lipid accumulation and lipid composition, as well as whether marrow lipid interventions can affect bone health.