CALORIE RESTRICTION (CR) ALTERS BONE MASS BUT NOT GEOMETRY OR
FAILURE PROPERTIES AND STATIC LOADING DOES NOT PROTECT AGAINST BONE
LOSS DURING CR.
A. Black1*, M. Shea2, J.A. Mattison1, S.A. Shapses3, E.M. Tilmont1, A. Handy1, M. Rios1, M.A.
Lane1
1Nutritional and Molecular Physiology Unit, Laboratory of Neurosciences, National Institute on
Aging/NIH. Baltimore, MD, 21224
2Department of Orthopaedics & Rehabilitation, Oregon Health Sciences University, Portland,
OR 97201-3098
3Department of Nutritional Sciences, Rutgers, The State university of New Jersey, New
Brunswick, NJ 08901-8525
INTRODUCTION: Calorie restriction (CR) slows physiologic signs of aging and reduces the
incidence of age-related disease. However, long-term CR has been shown to result in decreased
bone mass at certain skeletal sites in rodents and rhesus monkeys, possibly due to CR-induced
changes in body weight. Our goal was to determine whether static loading could maintain bone
mass and strength in CR rats. METHODS: Sixty, 12-month old, male Fisher 344 rats were
randomly assigned to one of 5 groups: 1) Ad Libitum (AL), 2) AL + weight jacket (WJ), 3)
40%CR, 4) 40%CR + WJ, and 5) weight stable. Despite CR, all groups received equivalent
amounts of vitamins, minerals and protein throughout the 16-week study. Group 2 rats wore
empty jackets while weight was added to jackets of group 4 rats to replace weight lost due to CR.
Added weight was distributed evenly over the thoracic and lumbar spine and shoulders of the
rats. Changes in body weight, bone turnover, bone mineral density (BMD), vertebral and
humeral geometry and failure properties were compared between groups using multivariate
analysis. Post-hoc analysis was performed as necessary using Fischer PLSD (p<0.05).
RESULTS: By the end of the study, body weight (BW) had increased by 13% in AL rats, and
decreased by 2%, 12% and 29% from baseline in AL+WJ, CR, and CR+WJ rats, respectively.
Final BW was significantly higher in AL rats than all other groups, but not significantly different
between AL+WJ and CR rats. BW was lower in CR + WJ rats than all other groups. Differences
between groups in total body and total humerus bone mineral density (BMD) at the end of the
study mirrored those in body weight. Lumbar vertebrae 5 (L5) and proximal, distal and mid
humerus BMD were lower in both CR groups than AL rats. In the humerus, loss of bone density
was due to endosteal expansion: humeral cortical thickness was higher in AL and CR rats than
CR +WJ rats, while cortical area was higher in AL rats than CR+WJ rats only. Medullary area
was higher in CR+WJ rats than AL and CR rats. Humeral failure load and stiffness were also
significantly higher in AL and CR than CR+WJ rats. Bone strength and modulus measurements
did not differ among the 3 groups tested. There were no effects of CR or static loading on L5
geometric or biomechanical measurements. Bone turnover was reduced in both CR groups.
CONCLUSION: CR lowered BW and total body, vertebral and humeral BMD but did not affect
the quality of bone. Interestingly, 40%CR did not compromise geometric and failure properties
despite lower BMD relative to AL animals. However, the combination of CR + WJ, which
resulted in the lowest BW and BMD measurements, also resulted in endosteal expansion in the
humeral shaft. This resulted in decreased failure load and stiffness in the humerii of these rats,
compared to AL or CR rats. Although static loading did not protect against lower bone mass or
failure properties in the face of 29% BW loss, further study is indicated to determine whether
static loading can maintain bone mass in individuals with more moderate weight loss.
Key words:
calorie restriction, bone loss, loading, rats, strength
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