Researchers studied 328 people getting hip or knee replacement surgery in New Zealand and found that 72% of those not taking vitamin D supplements had low vitamin D levels. People presenting for surgery in winter were much more likely to be vitamin D deficient than those coming in other seasons. While the study found slightly higher readmission rates in the deficient group, the differences were small. The good news: taking a monthly vitamin D supplement before surgery significantly reduced the chances of being deficient, suggesting this might be an easy way to prepare the body for joint replacement surgery.

The Quick Take

  • What they studied: Whether people getting hip or knee replacement surgery have low vitamin D levels, and if this affects their surgery outcomes
  • Who participated: 328 patients in New Zealand waiting for elective hip or knee replacement surgery over a 2-year period. Average age was around 69 years old.
  • Key finding: About 7 out of 10 patients not taking vitamin D supplements had deficient levels. Patients presenting in winter were 3.6 times more likely to be deficient than those in other seasons. Those with deficiency had slightly higher readmission rates (7% vs 1%), though the actual number of cases was small.
  • What it means for you: If you’re scheduled for joint replacement surgery, especially in winter, getting your vitamin D levels checked and possibly taking supplements before surgery may be worth discussing with your doctor. This appears to be a simple, modifiable factor that could help prepare your body for surgery.

The Research Details

This was a retrospective cohort study, which means researchers looked back at medical records of patients who had already gone through hip or knee replacement surgery. They collected information on 328 patients from a single hospital in New Zealand’s South Island over a 2-year period. The researchers gathered data on each patient’s age, sex, vitamin D blood levels before surgery, whether they were taking vitamin D supplements, and what happened after their surgery (like how long they stayed in the hospital, any complications, and whether they needed another surgery).

The researchers then compared outcomes between two groups: patients with normal vitamin D levels and those with deficient levels. They also looked at whether the season when patients had their surgery affected vitamin D levels.

This study design is useful because it looks at real-world surgical patients and their actual outcomes, rather than just laboratory measurements. By examining medical records that were already collected, researchers could identify patterns without needing to do expensive or time-consuming new testing. This approach helps doctors understand which factors might be important to address before surgery.

This study has some strengths: it included a reasonable number of patients (328) and looked at actual surgical outcomes. However, there are limitations to keep in mind. It only included patients from one hospital in one region of New Zealand, so results might not apply everywhere. The study looked backward at existing records rather than following patients forward in time. The number of complications was small, making it harder to draw firm conclusions about surgery outcomes. The researchers didn’t randomly assign people to take or not take vitamin D, so we can’t be completely certain vitamin D supplements caused the better outcomes.

What the Results Show

The study found that vitamin D deficiency was very common among joint replacement patients. Of the 236 patients not already taking vitamin D supplements, 170 (about 72%) had deficient vitamin D levels. In contrast, only 92 patients (28%) were taking monthly vitamin D supplements before surgery, and these patients had much better vitamin D status.

Interestingly, patients with deficiency tended to be slightly younger (average age 68 vs 70 years) and were more likely to be male. The most striking finding was the seasonal effect: patients coming in for surgery during winter were 3.6 times more likely to have vitamin D deficiency compared to other seasons. This makes sense because vitamin D is produced when skin is exposed to sunlight, and winter has less sunlight.

When looking at surgery outcomes, patients with vitamin D deficiency had higher readmission rates (7% compared to 1% in the normal group). However, the actual number of readmissions was small, so while this difference is statistically noticeable, it’s important not to overstate its practical significance.

The study found that regular vitamin D supplementation was highly effective at preventing deficiency. Among the 92 patients taking monthly vitamin D supplements, the vast majority maintained adequate vitamin D levels. This suggests that supplementation is a practical and accessible intervention for at-risk patients. The study also noted that younger patients and males were at higher risk for deficiency, which might help doctors identify who should be screened or offered supplements.

This research adds to growing evidence that vitamin D deficiency is common in surgical patients and may affect outcomes. Previous studies have suggested vitamin D plays a role in bone health, immune function, and inflammation—all relevant to surgery recovery. This study is one of the first to specifically examine the seasonal pattern of vitamin D deficiency in joint replacement patients and to show that simple supplementation can address this issue.

Several important limitations should be considered. First, this study only included patients from one hospital in New Zealand, so findings might not apply to other regions or populations with different climates and sun exposure. Second, the study looked backward at existing medical records rather than following patients forward, which limits what we can conclude about cause and effect. Third, the number of surgical complications was small, making it difficult to draw firm conclusions about whether vitamin D deficiency truly affects surgery outcomes. Fourth, the study didn’t randomly assign people to take or not take vitamin D, so we can’t be completely certain that the supplement itself caused better outcomes rather than other differences between the groups. Finally, the study didn’t measure other factors that might affect vitamin D levels or surgery outcomes, such as diet, sun exposure, or overall health status.

The Bottom Line

For patients scheduled for hip or knee replacement surgery, especially those presenting in winter or with risk factors for deficiency (male, younger age), discussing vitamin D screening and supplementation with your surgeon or doctor is reasonable. The evidence suggests that taking a monthly vitamin D supplement before surgery is safe and effective at correcting deficiency. However, this should be done under medical supervision, as your doctor can check your vitamin D levels and recommend the right dose for you. Confidence level: Moderate—the evidence is promising but based on a single-center study with some limitations.

This research is most relevant to people scheduled for hip or knee replacement surgery, particularly those having surgery in winter months or those at higher risk for vitamin D deficiency. It may also be relevant to anyone undergoing major surgery who wants to optimize their health beforehand. People living in regions with limited sunlight year-round should pay particular attention. However, this study doesn’t necessarily apply to people not having surgery or those with other medical conditions that affect vitamin D metabolism, so individual medical advice is important.

Vitamin D levels can be corrected relatively quickly with supplementation—typically within weeks to a few months, depending on the dose and individual factors. If you’re planning surgery, starting vitamin D supplementation 2-3 months before your procedure would give adequate time to correct any deficiency and potentially optimize your body’s healing capacity. However, benefits for surgery recovery may take longer to become apparent, with most healing occurring over several weeks to months after surgery.

Want to Apply This Research?

  • Track your vitamin D supplement intake (yes/no daily) and note the season and any pre-surgery blood test results showing vitamin D levels. If you have surgery, track readmission or complication events in the 30 days post-surgery.
  • Set a daily or weekly reminder to take your vitamin D supplement, especially if you’re scheduled for surgery. Log your supplement intake in the app to ensure consistency. If you’re having surgery, discuss vitamin D screening with your doctor and log the results.
  • For long-term tracking, monitor vitamin D supplement adherence monthly. If having surgery, track post-operative outcomes (hospital stay length, readmissions, complications) for at least 30 days after surgery. Consider seasonal tracking if you live in a region with significant seasonal sunlight variation.

This research summary is for educational purposes only and should not be considered medical advice. Vitamin D deficiency and surgical preparation are individual medical matters that require personalized assessment by your healthcare provider. Before starting any vitamin D supplementation or making changes to your pre-surgery preparation, consult with your surgeon or primary care physician. They can assess your individual risk factors, check your vitamin D levels if appropriate, and recommend the right approach for your specific situation. This study shows an association between vitamin D deficiency and higher readmission rates, but does not prove that vitamin D supplementation will prevent complications in your case. Always follow your doctor’s pre-operative instructions.