Findings from a new study among mice show a diet high in dried plum (prunes) completely prevents bone loss associated with spinal cord injury (SCI), while also restoring some of the bone lost following SCI.
These findings are a remarkable addition to a decades-long, growing body of evidence that indicates a positive connection between dried plums and bone health.
In addition to the new SCI study, previous clinical research has demonstrated a favorable bone response to prunes among post-menopausal women, along with animal-based research that shows a similar positive response among those exposed to radiation - such as astronauts in space.
We are seeing an exciting 'dried plum effect' on bones. In a variety of unique research scenarios, dried plum is consistently associated with a favorable bone response. No other compound appears to have the same degree of positive impact."
Bernard Halloran, Ph.D., Professor Emeritus, University of California - San Francisco (UCSF)
The latest study, Dried Plum Mitigates Spinal Cord Injury-induced Bone Loss in Mice, was published in the July 2020 issue of the Journal of the Orthopaedic Research Society - Spine. The research was led by Halloran and Xuhui Liu, M.D., San Francisco Veterans Affairs Medical Center, Department of Veterans Affairs and the Department of Orthopedic Surgery, UCSF.
The researchers conducted two separate experiments. In a prevention experiment, they looked at dietary supplementation with dried plum for mitigating the loss of bone induced by SCI. Then, in a recovery experiment, they examined if a dried plum diet could restore bone lost after SCI.
"This evaluation is particularly important as individuals who suffer SCI experience extremely rapid bone loss," said Liu. "The SCI-related bone loss then leads to an increased risk of fractures, osteoporosis, and overall morbidity and mortality."
Experiment #1: Dried plum prevents SCI-related bone loss
Liu explains that in the prevention evaluation, mice underwent SCI and were fed a diet containing 25% dried plum by weight or a control diet for up to four weeks. In vivo microCT scanning was performed three times, including at base line (immediately before SCI) and two and four weeks after SCI.
According to the findings, the dried plum diet completely prevented bone loss compared to control diets. In contrast, the control group diet resulted in 53% and 71% loss of bone volume at two and four weeks post injury, respectively.
Experiment #2: Dried plum restores some SCI-related bone loss
In the recovery experiment, mice were divided into groups and fed a control diet for two or four weeks. Another group was fed a control diet for two weeks to allow bone loss and then switched to the dried plum diet for an additional two weeks. The findings reveal that after only two weeks, the dried plum diet partially restored bone that had already been lost to the SCI. Bone strength was also greater in the mice switched to the dried plum diet when compared to the mice fed the control diet for four weeks.
"There are two types of cells involved with bone metabolism - osteoblasts and osteoclasts. Osteoblasts help to build new bone, while osteoclasts are essentially 'bone eaters,'" and function to tear down bone," said Liu. "At this time, we believe that dried plum functions to inhibit the bone-eating osteoclasts and this results in more bone."
Following the animal study, a pilot clinical trial providing SCI patients with dried plum did not show bone response among those experiencing SCI years prior to the trial. However, investigators indicate that additional research is needed among patients immediately following SCI to determine if dried plum can mitigate the loss of bone and bone strength as it did in the newly injured mice.
Dried plum polyphenols potentially key in positive bone response
According to Halloran and Liu, it remains unclear what bioactive compounds in dried plum are responsible for the beneficial effects on bone. However, the researchers suggest that the polyphenol content in dried plums may play a role.
Non-polyphenolic compounds in dried plum may also be involved, such as vitamin K and manganese. Both nutrients are recognized as contributing to the maintenance of normal bone. Future work will focus on identifying and isolating the bioactive factors in dried plums.
"In summary, dietary supplementation with dried plum or products derived from dried plum may prove to help slow the loss of bone induced by SCI, as well as to improve other bone-related conditions," said Halloran.
"The consistency of bone response to dried plum is remarkable, especially considering that dried plums are a whole food approach to healthy eating, as well as being readily available, economical, safe and - by all indications - effective in supporting healthy bones."
The animal protocol for the study was in accordance with the NIH Guide for the Care and Use of Laboratory Animals and approved by the Animal Care and Use Committee at the Veterans Affairs Medical Center, San Francisco.
The study was supported by a pilot research grant from the UCSF Core Center for Musculoskeletal Biology and Medicine (NIH1P30AR066262-01) and a research grant from the California Prune Board.
Liu, X., et al. (2020) Dried plum mitigates spinal cord injury‐induced bone loss in mice. Journal of the Orthopaedic Research Society - Spine. doi.org/10.1002/jsp2.1113.