For the past two decades, the age-adjusted incidence of hip fractures has decreased in the United States and other high-income nations. Initially, this was attributed to the treatment of osteoporosis, but research suggests this doesn't fully explain the magnitude of the decrease in hip fracture rates. Researchers used data from the long-term, multigenerational Framingham Heart Study to analyze the potential factors contributing to the decreased incidence of hip fracture.

The original study cohort was enrolled from 1948 to 1952. An offspring cohort was enrolled beginning in 1971. The researchers tabulated the number of people ages 60 and older at risk of first fracture and tallied the incidence of hip fracture in five-year calendar periods, beginning in 1971. The study included more than 105,000 person-years from 10,552 individuals, with a gradual shift toward the offspring participants in the 1980s and 1990s. Women made up more than 55% of the study sample.

During this 40-year study, the age-adjusted incidence of hip fracture decreased by 4.4% per year in both men and women. Both the time period and birth cohort associations were significant. The incidence of hip fracture for a given age range was lower among members of the offspring cohort. For example, among participants 85 to 89 years old, the incidence of hip fracture was 759 per 100,000 person-years in the offspring cohort compared with 2,018 per 100,000 person-years in the original cohort. Although most risk factors for hip fracture remained stable throughout the study period, the prevalence of smoking and heavy drinking declined.

The authors note that their findings don't suggest bisphosphonates are ineffective in reducing the risk of hip fracture but highlight the possible role of other factors. To reduce the hip fracture burden, both treatment of osteoporosis and public health measures to reduce smoking and heavy drinking are important, they advise.

Lack of contemporaneous bone mineral density data throughout this study is a major limitation, according to the authors. Also, data on bisphosphonates were only recorded in the 2000s. In addition, the Framingham Heart Study population is exclusively white and has a lower incidence of obesity than the general population and a somewhat lower incidence of hip fracture, which limits the generalizability of this study's findings.