Deep vein clots after knee replacement 3X more likely if low vitamin D - cohort
Association of preoperative serum 25-hydroxyvitamin D levels with deep vein thrombosis after total knee arthroplasty: a hypothesis-generating analysis of coagulation function mechanisms
Frontiers in Surgery, 27 August 2026, https://doi.org/10.3389/fsurg.2026.1756540
Shang H, Li J, Ma T, Wei Y, Liang J, Ding Y, He X, Ma B, Ma Y, Wang R, Wang Y, Chen D
Summary by Claude - September, 2026 Patients who went into a total knee replacement with a vitamin D level below 20 ng/mL had roughly three times the odds of developing a deep vein clot in the first week afterward.
This is a retrospective chart review of 193 consecutive knee replacement patients at one hospital in Ningxia, China (2020-2023) - not a trial, and nobody was given vitamin D. Preoperative 25(OH)D sorted them into deficient <20 ng/mL (106 patients), insufficient 20-29 (47), and sufficient 30+ (40). Everyone got standard clot prevention (heparin, compression, early movement) and everyone was scanned by ultrasound on day 5-7 whether or not they had symptoms.
26 clots turned up, 13.5% overall: 18.9% of the deficient group, 10.6% of the insufficient, 2.5% of the sufficient. The eye-catching odds ratio of 9.1 rests on a single clot in the sufficient group and the authors themselves call it unstable; their more solid estimate is 3.1 (95% CI 1.2-8.2, P = 0.020), confirmed at 2.9 by a penalized-regression check.
The blood work moved in step. On day 5 the deficient group had the highest D-dimer (2.57 vs 1.56 mg/L) and the shortest prothrombin time (11.2 vs 12.4 s) - "significantly higher postoperative D-dimer and shorter PT than the sufficiency group." Adjusting for D-dimer shrank the vitamin D association to 2.6 (P = 0.065), which fits D-dimer sitting on the causal path rather than confounding it.
What this does not show / limitations
- No supplementation was tested, so this says nothing about whether raising a level before surgery prevents clots - anyone who had taken vitamin D or calcium in the prior 3 months was excluded.
- Single center, retrospective, and no data on sun exposure, diet, or how mobile patients were beforehand; frail immobile people tend to be both low in D and clot-prone, and that alone could produce this pattern.
- 21 of the 26 clots were below-knee and all were found by screening with no symptoms, so their clinical importance is uncertain. Follow-up ended at discharge (7-10 days), missing later clots. The authors label the whole analysis hypothesis-generating.