Baseline risk factors and long-term changes in BMD
For the study, researchers examined the association between risk factors for bone loss and long-term changes in femoral neck BMD in 2,695 women living in Kuopio who were 47 to 56 years old in 1989. The women were a mean age of 53 years, and 62% were postmenopausal.
They answered questionnaires and had femoral neck BMD measured by DEXA every 5 years.
A total of 2,695, 2,583, 2,482, 2,135, 1,305, and 686 women were assessed at baseline and 5-, 10-, 15-, 20- and 25-year follow-ups, respectively, indicating significant study drop-out by 25 years.
By then, 17% of patients had died, 9% needed long-term care, some were unwilling to continue in the study, and others had factors that would have resulted in DEXA measurement errors (for example, hip implants, spine degeneration).
Researchers divided participants into quartiles of mean initial femoral neck BMD: 1.09 g/cm2, 0.97 g/cm2, 0.89 g/cm2, and 0.79 g/cm2, corresponding with quartiles 1 to 4 respectively (where quartile 1 had the highest initial femoral BMD and quartile 4 the lowest).
At 25 years, the mean femoral BMD had dropped to 0.97 g/cm2, 0.87 g/cm2, 0.80 g/cm2, and 0.73 g/cm2 in these respective quartiles.
Women lost 0.9%, 0.5%, 3.0%, and 1.0% of their initial BMD each year in quartiles 1 to 4, respectively.
And at 25 years, the women had lost 22.5%, 12.5%, 7.5%, and 2.5% of their initial BMD in the four quartiles, respectively.
Women in quartile 1 had the greatest drop in femoral BMD at 25 years, although their mean BMD at 25 years was higher than the mean initial BMD of the other women.
The prevalence of bone-affecting diseases, smoking, and use of vitamin D/calcium supplementation, corticosteroids, or alcohol was similar in the four quartiles and was not associated with significant differences in annual bone loss.
The most important protective factor was HRT
However, body mass index (BMI) and HRT were significantly different in the four quartiles.
On average, women in quartile 1 had a mean BMI of 26.7 kg/m2 at baseline and 27.8 kg/m2 at 25 years. Women in quartile 4 (lowest initial BMD and lowest drop in BMD) had a mean BMI of 24.9 kg/m2 at baseline and 28.4 kg/m2 at 25 years.
Women in quartile 4 (lowest initial BMD and lowest drop in BMD) were more likely to take HRT than women in quartile 1 (highest initial BMD and highest drop in BMD), at 41% versus 26%, respectively.
“The average decrease in bone mineral density was lower than has been assumed on the basis of earlier, shorter follow-ups where the bone loss rate at the femoral neck has been estimated to be even more than 20%,” Dr. Sirola commented in the press release.
“There were also surprisingly few risk factors affecting bone mineral density. The most significant factor protecting against bone loss was hormone replacement therapy. Weight gain during the follow-up also protected against bone loss,” Dr. Sirola added.
The study was funded by the Academy of Finland, Finnish Ministry of Education and Culture, and the Päivikki and Sakari Sohlberg Foundation. The authors and Dr. Ebeling have reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.