Does Obesity Affect Risk for Vertebral Fracture?

Increased weight circumference is associated with a significantly higher vertebral fracture incidence, according to study results published in JMBR Plus. Body mass index (BMI), however, did not carry this association.

Obesity may have positive or negative effects on bone health. The mechanical loading conferred by body weight can have a beneficial effect on bone formation, but increased fat mass may also have a detrimental effect on bone metabolism, particularly visceral adiposity. Furthermore, these associations between obesity and bone health may be different between men and women.

The goal of the current study was to investigate the association between several different measures of obesity and vertebral fracture risk, as well as to predict the risk for vertebral fractures using various clinical factors and explore the association between vertebral bone mineral density (BMD) and geometry and measures of body fat.

To assess the relationship between obesity measures and vertebral fracture incidence, the researchers used data from the UK Biobank cohort of 502,543 participants (229,138 men and 273,405 women) aged 40 to 69 years who completed questionnaires and physical measurements from 2006 to 2010. The assessment of BMD and geometry of the vertebrae was based on subset of this cohort that included 5189 individuals (2473 men and 2716 women) with available dual-energy x-ray absorptiometry data from 2014 to 2019.

Overall, there were 479 vertebral fractures in the men in the UK Biobank cohort and 645 in the women over 5 years, equaling an incidence rate for vertebral fracture of 4.2 per 10,000/y in men and 4.7 per 10,000/y in women.

In both sexes, no association between BMI and incident vertebral fracture was seen. However, there was a significant association between weight circumference and incident vertebral fracture in men (P =.0014) but not in women. The incidence of vertebral fractures was higher among men classified as obese based on waist circumference (≥102 cm; incidence, 5.0 per 10,000/y) compared with men categorized as normal weight (94-<102 cm; 3.7 per 10,000/y) and underweight (<94 cm; 3.8 per 10,000/y).

The results from the imaging data subset showed that in both sexes, there were negative associations between visceral adipose tissue mass, trunk fat mass, and limb fat mass with vertebral body BMD and geometry. However, the results from the full dataset showed that weight circumference, which is related to visceral fat, was the only measure that was linked to the risk for vertebral fracture in men. Hence, the researchers claimed these findings suggest that BMD does not adequately assess the risk for vertebral fracture, especially in patients with obesity.

The researchers acknowledged several limitations to the study, including identification of vertebral fracture from self-report questionnaires, analyses of data collected over a relatively short period of time, and missing data on vitamin D levels.

“This study may be useful to clinicians for the prediction of vertebral fracture risks, and may provide further information to supplement the fracture risk assessment tool, which assesses general fracture risks,” noted the researchers.

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Reference

Luo J, Lee YWR. How does obesity influence the risk of vertebral fracture? Findings from the UK Biobank participants [published online March 10, 2020]. JBMR Plus. doi:10.1002/jbm4.10358