Researchers in China discovered that about 3 out of 4 people getting hip or knee replacement surgery have low vitamin D levels in their blood. This is important because vitamin D helps bones heal and fight infections. The study looked at 384 patients before their surgery and found that almost none of them had been tested for vitamin D beforehand, and very few were taking vitamin D supplements. The doctors think hospitals should start checking vitamin D levels in patients before joint surgery and treating low levels to help patients recover better.

The Quick Take

  • What they studied: How many people needing hip or knee replacement surgery have low vitamin D levels, and whether doctors were checking for and treating this problem
  • Who participated: 384 Chinese patients (244 women and 140 men, average age 64 years) who were scheduled for hip or knee replacement surgery at one major hospital
  • Key finding: About 76 out of every 100 patients had low vitamin D levels, but none had been tested for it before coming to the hospital, and only about 3 out of 100 were taking vitamin D supplements
  • What it means for you: If you’re planning to have hip or knee surgery, ask your doctor to check your vitamin D level beforehand. Low vitamin D may slow healing and increase infection risk, so getting your levels up before surgery could help you recover better

The Research Details

This study looked at information collected from 384 patients who had hip or knee replacement surgery at one hospital in China. The researchers checked each patient’s medical records to see if they had been tested for vitamin D before coming to the hospital and whether they were taking vitamin D pills. They also measured everyone’s vitamin D level the day before surgery by taking a blood sample. The doctors then organized the results into three groups: people with very low vitamin D (deficiency), people with somewhat low vitamin D (insufficiency), and people with normal vitamin D levels (sufficiency).

The researchers used clear cutoff numbers to define each group. Vitamin D deficiency meant less than 20 ng/mL (a measurement of vitamin D in the blood), insufficiency meant 20 to 29 ng/mL, and sufficiency meant 30 ng/mL or higher. This approach allowed them to see exactly how many patients fell into each category and compare the hip surgery patients to the knee surgery patients.

This type of study is important because it shows what’s actually happening in real hospitals with real patients. By looking at medical records and blood test results, the researchers could see a clear picture of how common low vitamin D is before joint surgery. This information helps doctors understand whether they should start screening and treating vitamin D problems as part of preparing patients for surgery, similar to how they check blood pressure or blood sugar.

This study has some strong points: it looked at a large group of 384 consecutive patients (meaning they included everyone who came in during a certain time period, not just selected patients), and it measured actual blood vitamin D levels rather than relying on what patients remembered. However, the study only looked at patients from one hospital in China, so the results might be different in other countries or populations. The study also didn’t follow patients after surgery to see if low vitamin D actually caused more problems with healing or infections, so we can’t be completely certain about the connection yet.

What the Results Show

The main finding was striking: about 3 out of every 4 patients (76.3%) had low vitamin D levels when tested the day before surgery. This broke down into two groups—about 1 out of 3 patients (33.6%) had severe deficiency (very low levels), and about 4 out of 10 patients (42.7%) had insufficiency (somewhat low levels). The average vitamin D level across all patients was 24.1 ng/mL, which is below the healthy range of 30 ng/mL or higher.

When the researchers compared hip surgery patients to knee surgery patients, the results were very similar. Hip surgery patients had an average vitamin D level of 24.2 ng/mL, while knee surgery patients had 24.1 ng/mL. About 36% of hip surgery patients had severe deficiency, compared to 32% of knee surgery patients. However, knee surgery patients were more likely to have insufficiency (48% versus 35%).

Perhaps most concerning was what happened before surgery: not a single patient out of the 384 had been tested for vitamin D levels before arriving at the hospital. This means doctors weren’t routinely checking for this problem. Additionally, only about 3 out of 100 patients (2.6%) were taking vitamin D supplements, and even those few were only taking them for bone health, not specifically to prepare for surgery.

The study found that vitamin D problems were equally common in both men and women, and they occurred across all age groups, including younger patients. The fact that even patients in their 20s and 30s had low vitamin D levels suggests this isn’t just a problem for older people. The similarity between hip and knee surgery patients indicates that low vitamin D is a widespread issue for anyone needing major joint surgery, not specific to one type of procedure.

While this is one of the first studies to specifically look at vitamin D levels in joint surgery patients, previous research has shown that vitamin D is important for bone healing and immune function. Other studies have found that low vitamin D is linked to slower wound healing, more infections after surgery, and more pain after surgery. This new study confirms that low vitamin D is extremely common in this patient group, which suggests that previous findings about vitamin D’s importance might apply to many more patients than doctors currently realize.

The biggest limitation is that this study only looked at patients from one hospital in China, so the results might be different in other countries or regions with different sun exposure or dietary habits. The study also didn’t follow patients after surgery to see whether those with low vitamin D actually had more problems healing or more infections—it only showed that low vitamin D was common. Additionally, the study didn’t look at why patients had low vitamin D or what factors contributed to it, such as sun exposure, diet, or other health conditions. Finally, because this was a single snapshot in time (measuring vitamin D the day before surgery), we don’t know if these low levels were temporary or long-standing.

The Bottom Line

If you’re scheduled for hip or knee replacement surgery, ask your doctor to check your vitamin D level at least a few weeks before surgery (HIGH confidence recommendation based on this research). If your level is low, ask about taking vitamin D supplements to bring it up to normal before your operation (MODERATE confidence—this study suggests it’s important, but we need more research to confirm it reduces complications). The typical recommendation would be to get your vitamin D level to at least 30 ng/mL before surgery. Your doctor can tell you the right dose of vitamin D supplements for your situation.

Anyone scheduled for hip or knee replacement surgery should care about this research. People living in areas with less sunlight, those who spend most of their time indoors, people with darker skin (which makes it harder to produce vitamin D from sun), and those over age 65 should be especially interested. People with bone disease, digestive problems, or kidney disease should definitely talk to their doctor about vitamin D testing. However, this research is less relevant to people having other types of surgery, though vitamin D is still important for overall health.

It typically takes 4 to 8 weeks to significantly raise vitamin D levels with supplements, so ideally you’d want to start vitamin D treatment at least 6-8 weeks before your scheduled surgery. If your surgery is sooner, talk to your doctor about higher doses. Even if you can’t completely normalize your vitamin D before surgery, getting it higher than it currently is will likely help.

Want to Apply This Research?

  • If you’re preparing for joint surgery, track your vitamin D supplement intake daily (dose and time taken) and record your vitamin D blood test results when you get them. Set a goal to reach a vitamin D level of 30 ng/mL or higher before your surgery date, and monitor progress with repeat blood tests every 4-6 weeks.
  • Set a daily reminder to take your vitamin D supplement at the same time each day (such as with breakfast). If your doctor prescribes vitamin D, log each dose in the app immediately after taking it. Also track any sun exposure time, as this helps your body make vitamin D naturally. Aim for 10-30 minutes of midday sun exposure several times per week if possible.
  • Create a pre-surgery health dashboard that tracks: (1) vitamin D supplement adherence as a percentage, (2) your vitamin D blood test results over time with a target line at 30 ng/mL, (3) days until surgery, and (4) other pre-surgery health metrics your doctor recommends. Share this dashboard with your surgical team to show you’re preparing properly for your procedure.

This research suggests that low vitamin D is common in people having joint surgery and may affect recovery, but it does not prove that vitamin D supplements will prevent complications. Always consult with your surgeon and primary care doctor before starting any supplements or making changes to your health routine, especially if you’re preparing for surgery. This information is educational and should not replace professional medical advice. Individual vitamin D needs vary based on age, health conditions, medications, and other factors that only your doctor can assess. If you’re scheduled for surgery, discuss vitamin D screening and supplementation with your surgical team as part of your pre-operative planning.