- Researchers investigated the effects of social isolation on bone loss in mice.
- They found that social isolation was associated with increased bone loss in male, but not female, mice.
- Further studies are needed to understand whether the same happens in humans.
Social isolation is linked to worse health outcomes, including increased all-cause mortality, cardiovascular problems, and mental health conditions.
Previous research has also shown that psychological stress is a risk factor for osteoporosis and poor bone health.
Social isolation, closely linked to loneliness, may lead to psychological distress. How social isolation affects bone health, however, remains unknown.
Recently, researchers investigated how social isolation affects bone health in male and female mice. They found that social isolation was associated with bone loss in male, but not female, mice.
The study was presented at ENDO 2023, the Endocrine Society’s annual meeting in Chicago.
Medical News Today spoke with Dr. Nahid Rianon, an assistant professor of geriatrics with McGovern Medical School at UTHealth Houston, not involved in the study, about the findings.
“This study reports an important finding in animals. A translational study to see findings in humans, especially in older adults who often suffer from social isolation would be important to understand if risk of bone loss is higher in this vulnerable group. Identifying people at risk is the first step to prevent a health problem like bone loss that may lead to fracture and disability,” she told us.
Dr. Rebecca Mountain, a postdoctoral fellow at the Center for Molecular Medicine at MaineHealth Institute for Research, lead author of the study, also told MNT:
“[The findings] may also have clinical implications as we grapple with the long-term health impacts of the rise in social isolation related to the COVID-19 pandemic, although future studies are needed to understand the effects in humans.”
Isolated mice had lower bone density
For the study, the researchers split 32 16-week-old male and female mice into two groups. One group simulated social isolation by keeping one mouse per cage. In the other group, each cage was shared by four mice.
The researchers monitored the mice for 4 weeks in their respective living conditions.
Ultimately, isolated male mice experienced reductions in bone mineral density. Bones containing fewer minerals are less dense, and are thus more likely to break.
The researchers also found that bone volume fraction and cortical bone thickness fell by 26% and 9%, respectively, in isolated male mice. Both measures indicate reduced bone quality.
Further analysis revealed that male mice had signs of reduced bone remodeling, a process that includes the formation of new bone, which can increase fracture risk.
The researchers noted that bone loss seen in isolated males was similar to that seen in previous studies following orchiectomy (removal of the testicles) and ovariectomy (removal of the ovaries).
By contrast, female mice in the current study did not experience any bone loss following social isolation.
The researchers found, however, that isolated females had increased bone resorption-related gene expression, although their bone mass was unaffected. Increased bone resorption can result in bones breaking down faster than they can renew, increasing fracture risk.
Dr. Mountain noted that the precise mechanisms for how social isolation may lead to bone loss are unknown. However, her team is exploring different possibilities, including the role of various stress hormones and the body’s sympathetic nervous system.
MNT also spoke with Dr. William Buxton, board-certified neurologist and director of Neuromuscular and Neurodiagnostic Medicine and of Fall Prevention at Pacific Neuroscience Institute at Providence Saint John’s Health Center in Santa Monica, CA, not involved in the study, about the mechanisms underlying the effects of social isolation on bone health.
“My first thought about the link is that one of the best ways to maintain bone health and prevent osteoporosis is engaging in weight-bearing exercises. If one is isolated he or she is less likely to be out of his or her home and as a result be on their feet less,” he told us.
Dr. Rianon added: “Both depression and weight loss can lead to frailty, disability, decreased mobility which can contribute to bone loss. All of these are risks for bone loss and future research is needed to understand underlying metabolic changes that lead to bone loss in these medical conditions.”
Why the sex differences?
Dr. Mountain noted that they are currently investigating why social isolation affected males and females differently. She noted that estrogen is known to have a protective effect on bone, and so may play a role.
“It’s also possible that isolation is working in different ways, or on a different time scale, in male and female mice,” she added.
MNT also spoke with Dr. Douglas Landry Jarvis, an orthopedic surgeon with Novant Health in Charlotte, NC, not involved in the study, about what may explain the sex differences.
“Lack of social interaction [may have affected] testosterone production and hormonal balances, changing bone metabolism in a negative way. [It may be that] the female hormonal cycle is less affected over a 4-week span,” he noted.
Dr. Mountain said that the study’s limitations include its small sample size and lack of behavioral data to understand how isolation affected depressive or anxious behavior in mice.
Dr. Buxton further noted: “The study is limited by the use of animals in cages, so it’s not a perfect model of human activity. I don’t know if the authors reported on how often animals were on their feet in the cages, but I would expect that those in the community were on their feet more.”
Dr. Rianon added that although the researchers indicated that there might be differences between male and female mice regarding bone formation, the study does not explain how these differences occur.
She noted however: “[It’s pretty normal] to not have [such] details in the early stages of any research.”
Implications for future research
“If these results are also later demonstrated in humans, I am also guessing that alcohol plays a role,” noted Dr. Buxton.
“We know that drinking increases [the] risk of osteoporosis. Isolation is a risk factor for increased alcohol use, so alcohol is probably a link between isolation and decreased bone mineral density in humans,” he surmised.
Dr. Jarvis added: “Based on the study, no one should change their habits. The only implication of the study is that more studies need to be conducted. Social interaction is too broad of a variable. We need to know how much the […] cortisol levels of the mice changed; the study can then be extrapolated to primates and maybe even humans.”
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