BACKGROUND: Vitamin D deficiency is associated with poorer functional outcomes and increased complication rates after total knee arthroplasty (TKA). Yet, there is no longer term study evaluating vitamin D levels and supplementation after TKA. Our study aimed to compare quantitative vitamin D levels and supplementation regimens after TKA stratified by patient sex and race. METHODS: A retrospective cohort study of primary TKA patients at a single hospital from 2015 to 2022 was conducted. We analyzed vitamin D preoperatively and postoperatively up to 2 years. Vitamin D deficiency was defined as <
30 ng/mL. A subgroup analysis was conducted in patients with vitamin D <
21 ng/mL. Supplementation categories included none, low (<
1,001 IU), medium (1,001 to 5,000 IU), and high (>
5,000 IU). RESULTS: A total of 400 (66.0% female) patients who underwent 430 primary TKA procedures were included, and 65.3% received supplementation. Patients who were vitamin D sufficient preoperatively demonstrated higher vitamin D levels and ability to maintain sufficiency postoperatively using low-dose supplementation compared with no supplementation ( P = 0.004). Those who were vitamin D deficient preoperatively demonstrated higher vitamin D levels postoperatively using medium to high doses ( P = 0.02). For patients who became deficient postoperatively, supplementation was associated with achieving repletion at an average of 10.2 months ( P <
0.001). Black patients demonstrated 2.8 times higher odds of having a vitamin D level less than 30 ng/mL ( P = 0.03). CONCLUSION: Our study demonstrated that low-dose vitamin D supplementation (<
1,001 IU) was beneficial for vitamin D-sufficient TKA patients to achieve higher levels and maintain vitamin D sufficiency. Vitamin D-deficient TKA patients benefitted from medium-to-high dose supplementation (1,001 to 5,000+), but only 33.7% achieved vitamin D repletion. This work highlights the need to continue vitamin D surveillance postoperatively and the need to continue vitamin D repletion.