Researchers tested whether taking vitamin D supplements could help strengthen bones in people with spinal cord injuries, who often have weak bones. Over one year, 42 people with long-term spinal cord injuries took either vitamin D pills or placebo pills. Even though some people’s vitamin D levels improved, their bone strength didn’t increase. This surprising finding suggests that spinal cord injury affects how the body uses vitamin D in ways scientists don’t fully understand yet. The results show that simply taking vitamin D isn’t enough to fix bone problems in this group.

The Quick Take

  • What they studied: Whether taking vitamin D supplements for one year could improve bone density (bone strength) in people living with spinal cord injuries
  • Who participated: 42 adults with spinal cord injuries lasting at least 3 years (average age 48, mostly men). All had low vitamin D levels at the start. They were split into three groups: one got fake pills, one got medium-dose vitamin D every 4 weeks, and one got higher-dose vitamin D every 2 weeks
  • Key finding: After 12 months, vitamin D supplements did not strengthen bones in any of the groups, even though about one-third of people taking the supplements did raise their vitamin D levels to normal
  • What it means for you: If you have a spinal cord injury and low vitamin D, taking vitamin D pills alone may not be enough to prevent bone loss. Talk with your doctor about other ways to protect your bones, such as exercise programs designed for spinal cord injury or other treatments. This doesn’t mean vitamin D is useless—it may still be important for other health reasons—but it appears to work differently in people with spinal cord injuries

The Research Details

This was a high-quality randomized controlled trial, which is considered one of the best types of research studies. Researchers randomly assigned 42 people with chronic spinal cord injuries into three equal groups. One group received placebo (fake) pills, another received a medium dose of vitamin D3 (24,000 international units every 4 weeks), and the third received a higher dose (24,000 IU every 2 weeks). Nobody knew which group they were in—not the participants and not the researchers measuring the results—which reduces bias. The study lasted 12 months, with bone measurements taken at the beginning and end.

Researchers measured bone density at four different locations: the radius (forearm bone), femoral neck (hip), distal femur (lower thighbone), and proximal tibia (upper shinbone). They also checked vitamin D blood levels to see if the supplements actually raised them. This approach allowed researchers to see if stronger vitamin D levels led to stronger bones.

The study took place at a Swiss spinal cord injury clinic, meaning all participants had access to specialized medical care. The researchers were careful to track other factors that might affect bone health, like smoking status and the level of the spinal cord injury.

This research design is important because it’s the gold standard for testing whether a treatment actually works. By randomly assigning people to groups and using placebos, researchers can be confident that any differences between groups come from the vitamin D itself, not from other factors. The fact that neither participants nor researchers knew who got real vitamin D reduces the chance that expectations influenced the results.

This study has several strengths: it’s a randomized controlled trial (the highest quality type of study), it used a placebo control group, it was double-blind (neither participants nor researchers knew who got what), and it measured bone density at multiple locations. However, the sample size was relatively small (42 people), which means results might not apply to everyone with spinal cord injuries. The study was conducted at one clinic in Switzerland, so results might differ in other countries or settings. The fact that only one-third of people taking supplements achieved normal vitamin D levels suggests the doses used might not have been optimal for this population.

What the Results Show

The main finding was striking: vitamin D supplementation did not improve bone density at any of the four measurement sites (forearm, hip, lower thighbone, or upper shinbone) after 12 months of treatment. This was true for both the medium-dose and high-dose groups compared to placebo. Researchers found no difference in bone density changes between groups, meaning the bones of people taking vitamin D didn’t get stronger than those taking fake pills.

Interestingly, about one-third of people taking vitamin D supplements did successfully raise their blood vitamin D levels to the normal range (above 75 nmol/L). This means the supplements were working to increase vitamin D in the bloodstream, but this increase didn’t translate into stronger bones. This disconnect between rising vitamin D levels and unchanged bone strength is the puzzle that makes this finding so important.

The researchers also checked whether certain factors—like where the spinal cord injury occurred, how long ago it happened, or whether someone smoked—changed how people responded to vitamin D. None of these factors made a difference. Everyone responded similarly: vitamin D supplements didn’t strengthen bones.

The study didn’t report major secondary findings, but the fact that vitamin D levels improved in some people while bone density didn’t is itself an important secondary observation. This suggests that in people with spinal cord injuries, the normal relationship between vitamin D and bone health may be broken or altered. The researchers noted that spinal cord injury creates unique biological conditions that might prevent vitamin D from working the way it normally does in people without spinal cord injuries.

In people without spinal cord injuries, vitamin D supplementation typically helps maintain or improve bone density, especially when people have low vitamin D levels. However, people with spinal cord injuries lose bone density much faster than other people, even when vitamin D levels are normal. This study confirms that the bone loss in spinal cord injury is more complex than just vitamin D deficiency. Previous research suggested that vitamin D might help, but this well-designed trial shows it doesn’t—at least not on its own. This finding aligns with growing evidence that spinal cord injury causes bone loss through multiple mechanisms that vitamin D alone cannot address.

The study had several limitations worth considering. First, only 42 people participated, which is a relatively small number. Results from larger studies might show different outcomes. Second, the study only lasted 12 months; longer follow-up might reveal delayed effects. Third, only one-third of people taking supplements achieved normal vitamin D levels, suggesting the doses might not have been strong enough for this population. Fourth, the study was conducted at one Swiss clinic, so results might not apply to people in different countries or healthcare settings. Fifth, the study didn’t test other bone-strengthening treatments alongside vitamin D, so we don’t know if vitamin D combined with exercise or other therapies might work better. Finally, the study focused on bone density but didn’t measure bone quality or fracture risk, which are also important for bone health.

The Bottom Line

Based on this research, taking vitamin D supplements alone is unlikely to strengthen bones in people with chronic spinal cord injuries (moderate confidence). However, vitamin D may still be important for other aspects of health, so discuss with your doctor whether you should continue taking it. Instead of relying on vitamin D alone, people with spinal cord injuries should ask their doctors about comprehensive bone health strategies, which might include specialized exercise programs, other medications designed to prevent bone loss, and adequate calcium intake. This research suggests a multi-pronged approach is needed rather than depending on one supplement.

This research is most relevant to people living with spinal cord injuries who have low vitamin D levels and are concerned about bone health. Healthcare providers treating spinal cord injury patients should be aware that vitamin D supplementation alone won’t prevent bone loss in this population. Family members and caregivers of people with spinal cord injuries should understand that bone health requires more than just vitamin D. People without spinal cord injuries shouldn’t assume these findings apply to them—vitamin D remains important for bone health in the general population.

If you have a spinal cord injury and are considering vitamin D supplementation, don’t expect to see improvements in bone strength within 12 months. The research suggests that even with a full year of supplementation, bone density doesn’t improve. However, changes in bone density can take years to become noticeable, so longer-term studies might show different results. If you’re concerned about bone health, talk with your doctor about starting a comprehensive program that might include exercise, other medications, and adequate nutrition—results from these approaches might take several months to become apparent.

Want to Apply This Research?

  • Track vitamin D supplementation intake (yes/no daily) and any bone-related symptoms like pain or falls. Also note participation in bone-strengthening activities like physical therapy or exercise. While this study shows vitamin D alone won’t strengthen bones, tracking helps you and your doctor see if a comprehensive approach is working
  • If you have a spinal cord injury, use the app to schedule and track participation in specialized exercise programs designed for spinal cord injury, which may be more effective for bone health than supplements alone. Set reminders to discuss bone health strategies with your healthcare provider beyond just vitamin D
  • Over 6-12 months, track any changes in bone-related symptoms, participation in bone-strengthening activities, and medication adherence. Use the app to log conversations with your doctor about bone health and any new treatments started. This long-term tracking helps identify what actually helps your bone health, since vitamin D supplementation alone appears insufficient

This research applies specifically to people with chronic spinal cord injuries and should not be interpreted as advice for the general population. Vitamin D remains important for overall health in all people. If you have a spinal cord injury and are concerned about bone health or vitamin D levels, consult with your healthcare provider before making changes to your supplementation or treatment plan. This study shows that vitamin D supplementation alone doesn’t improve bone density in spinal cord injury, but it doesn’t mean vitamin D is unimportant or that you shouldn’t take it for other health reasons. Your doctor can help determine the best approach for your individual situation.