Obesity associated with diminished bone strength, particularly in men

Despite the protective implication often associated with high body weight in terms of fracture risk, recent studies suggest that obesity may in fact raise the risk of fractures, particularly in men with high body fat content.

A comprehensive examination of dual x-ray absorptiometry (DXA) data from a broad spectrum of over 10,000 U.S. individuals revealed an intricate connection between body weight and bone density. Dr. Rajesh Jain and Dr. Tamara Vokes, both from the University of Chicago, discussed these complex findings in the Journal of Clinical Endocrinology & Metabolism.

The duo discovered that each 1 kg/m2 increase in lean mass index correlated with a 0.19 higher T-score in people below 60 years of age. However, every corresponding increase in fat mass index was associated with a 0.10 decline in T-score, with a significant statistical difference (P<0.001).

Their research indicated that while lean mass positively impacted bone mineral density (BMD) equivalently in both genders, the deleterious effect of fat mass was more pronounced in men, leading to a 0.13 lower T-score per additional 1 kg/m2, compared to a 0.08 drop in women (P<0.001 for interaction).

“Our analysis of a large, heterogeneous population presenting a wide range of BMI indicated a clear negative correlation between bone density and fat mass, and a positive correlation with lean mass,” Jain and Vokes stated.

The researchers highlighted that despite lean mass exhibiting a stronger overall impact than fat mass, the detrimental effects of fat on BMD were significantly more evident in men and individuals with excessive fat content.

These insights hold critical clinical implications as they suggest obesity could contribute to declining BMD in patients traditionally not perceived as high fracture risk, and who therefore might not typically undergo DXA screening.

Contrasting previous studies constrained by small sample sizes or referral bias, Jain and Vokes’ findings reflect broader U.S. population data. They emphasise that obesity does not provide immunity against low BMD, advocating for clinicians to assess bone density, especially when other risk factors are present.

To reach their conclusions, the researchers assessed data from the National Health and Nutrition Examination Surveys conducted from 2011 to 2018. This dataset encompassed body composition and DXA measurements for 10,814 individuals aged 20 to 59.

Using linear regression models with total body BMD as the dependent variable, the researchers scrutinised the impact of lean and fat mass, accounting for age, gender, race/ethnicity, height, and smoking status. Notably, they highlighted the challenge of disentangling the interconnected influences of fat and lean mass on bone density.

Prior studies exploring the impact of fat mass on bone density reported varying results due to differing statistical methods and are somewhat outdated, the researchers pointed out. Moreover, the current study benefited from a densitometer with a higher weight limit, allowing for the examination of more severe obesity cases.

However, the study had limitations, including its focus on adults below 60 years, leaving room for potentially different body composition and bone mass relationships in older individuals. It also didn’t evaluate factors besides sex hormones that might elucidate the observed gender differences in the link between fat mass and bone density.

Despite women generally having a higher proportion of body fat, fat accumulation patterns differ by gender, with women typically storing fat in the hip and thigh areas, and men in the trunk and abdomen. Jain and Vokes acknowledged that differences in fat distribution might influence BMD, although their study could not conclusively prove this.