New research from the UC San Francisco Veterans Affairs Medical Center shows that eating high doses of dried plums (prunes) increases bone volume in adult and elderly male mice. Prunes have many advantages over other treatments for normal bone loss and osteoporosis, including low cost and high nutrient density. They could also prove useful in preventing bone loss in younger animals.
During normal aging, mice lose approximately 60% of bone volume between 6 weeks and 24 months of age. Bone loss can also occur from disease states such as osteoporosis, and can be caused by hormone deficiencies and particular medications. Previous research has shown dried plums to be effective at limiting bone loss in a mouse model of estrogen deficiency. This is the first study to show that dried plum can actually restore bone that has been lost due to normal aging in males.
In the study, mice were started on the experimental diet at either 6 (adult) or 18 (elderly) months of age. All diets had the same number of calories and nitrogen ratio, but were supplemented with either 0, 15%, or 25% dried plums. Bone volume and density were measured directly, as were various markers of bone resorption and bone formation in blood samples.
After 6 months both the adult and elderly animals on the diet with 25% prunes had 50% and 40% increases in bone volume, respectively. Bone mineral density was unchanged in any condition. The 15% prune diet increased bone volume in adult animals, but not in elderly animals. Blood markers indicated that both increased bone formation and decreased bone resorption may be responsible for the increase in volume, though these changes occurred primarily in the first 3 months of the experiment. The mechanism of action of prunes on bone volume is still unknown.
Though encouraging, the study has several limitations. Work on the value of dried plums in preventing bone loss is still in its early stages, and much more research is needed to determine if prunes are useful in different animal models (including female mice). Furthermore, the study mentions weight loss as one side effect of dietary prunes, but the possibility of other side effects was not examined. Also, the authors do not explore if the bone changes are due to increased prune intake or the large decrease in consumption of traditional mouse chow. Mouse metabolism is not the same as it is in humans, so we cannot extrapolate the effects shown here. Likewise, it is not reasonable for a human diet to be comprised of 25% prunes.
It should also be noted that the research was partially funded by the California Dried Plum Board. Though this doesn't imply any flaws in the science, it makes it especially important that the work be replicated by an independent research group before too much is made of the findings.