Vitamin D levels are inversely associated with osteophyte formation in elderly women, but not men - a population-based cohort study “The Bunkyo Health Study”
L. Liu Osteoarthritis and Cartilage 28, SUPPLEMENT 1, S293-S294, APRIL 01, 2020
Purpose: Osteoarthritis of the knee (knee OA) is a slowly progressive joint disease and a leading cause of impaired mobility in elderlies. Vitamin D insufficiency and deficiency are common in elderly women. As vitamin D plays an important role for formation and mineralization of both bone and cartilage in growth plate, vitamin D insufficiency and/or deficiency has been speculated to affect not only osteoporosis but also knee OA. However, it is still controversial whether or how vitamin D insufficiency and deficiency is involved in the pathophysiology of knee OA. Osteophyte formation has considered to be a secondary phenomenon in knee OA. However, osteophyte has been recently paid attention, as osteophyte has been revealed to have a distinct and unique role in OA pathogenesis. Osteophytes develop at the peripheries of the articular cartilage by following the process similar to that in an endochondral ossification in growth plate. Histologically, osteophytes are composed of the cartilage and bone parts. Because of the limitation in detectability of the cartilage part of osteophytes by radiography or conventional magnetic resonance imaging (MRI), we have recently reported that the cartilage part of osteophytes can be detected by using not only T2 mapping MRI (Arthritis Res Ther 2017) but also proton density weighted fat suppression (PDFS) images on MRI (OARSI 2020). The aim of this study was to examine whether there was any association between vitamin D status and osteophytes development in elderlies.
Methods: This cross-sectional study was conducted by analyzing data of the “The Bunkyo Health Study” which was started at 2015 in Juntendo University Graduate School of Medicine. The aim of the study is to find out associations between the metabolic and cognitive function disorders and motor organ disorders, such as osteoporosis and OA, of the elderlies aged 65 years of age or older. The participants of this study were collected using a residential registration administrated by Bunkyo-ward office, Tokyo, where our university is located. 1,629 subjects (F/M: 942/687, 73.1 years of age on average) who did not have knee pain, which is needed to consult medical institution, and did not experience any traumatic episodes for the knee joints were analyzed in this study. A written informed consent was obtained all participants of this study. Blood samples, MRI and a standing, extended antero-posterior view radiograph of both knees were taken at the time of study entry. Serum 25-hydroxy vitamin D [s25(OH)D] level was assessed by ELISA method. Postero-anterior long-leg standing X-ray of the patients was conducted to measure femoro-tibial angle (FTA), medial proximal tibial angle (MPTA), and medial joint space width (mJSW). We evaluated osteophytes width by PDFS images on MRI (OARSI 2020), which can evaluate osteophyte length accurately, similar to T2 mapping MRI, which enables us to detect cartilage- (cartilage OP) and bone-parts of osteophyte (bone OP) separately (ART 2017). All subjects were divided into two groups according to s25(OH)D levels; the vitamin D deficiency group: s25(OH)D <20 ng/ml and the vitamin D insufficiency or sufficiency group: s25(OH)D≧20 ng/ml. A liner regression analysis was analyzed to examine the associations between s25(OH)D and imaging findings.
Results: As 484 subjects were excluded due to either valgus lower limb alignment or lateral type of knee OA, a total of 1,145 [72.9 (SD 5.4) years of age on average among 1,629 subjects were enrolled in the present study. 634 among 1,145 subjects (55.4%) were women, while remaining 511 (44.6%) were men. 86.0% of the subjects showed the radiographic knee OA with Kellgren-Lawrence (K/L) grade 2. The FTA, MPTA, and JSW of the subjects were 177.6 (SD 2.5) °, 84.6 (SD 3.1) °, and 4.9 (SD 1.1) mm on average, respectively. Seven hundred and thirty-six of 1,145 subjects (64%) were classified as the vitamin D deficiency group, while remaining 409 subjects (36%) were classified as the vitamin D insufficiency or sufficiency group. While the s25(OH)D levels of the subjects were 19.1 (SD 5.0) ng/ml, a significant difference of s25(OH)D levels were observed between male [19.8 (SD 5.0) ng/ml] and female [18.5 (SD 4.9) ng/ml] subjects. Mean serum calcium (sCa, adjusted for the serum albumin level, if it was 4.0 g/dl or less), phosphorus (sPi) and bone alkaline phosphatase (BAP) levels of the subjects were within the reference range. No one was diagnosed with osteomalacia. A linear regression analysis indicated that no association was observed between s25(OH)D levels and bone OP length (β=0.02, p=0.691), cartilage OP length (β=0.06, p=0.187), and their summation (β=0.06, p=0.199) in male subjects. No significant differences of the bone part (1.74 mm vs 1.77 mm), cartilage part (1.70 mm vs 1.79 mm) and their summation (3.44 mm vs 3.56 mm) of osteophyte width were observed between vitamin D deficient groups and vitamin D insufficiency/sufficiency groups in male subjects. In contrast, s25(OH)D levels were inversely associated with bone part (β=0.09, p=0.018), cartilage part (β=0.08, p=0.032), and their summation (β=0.12, p=0.002) in female subjects. The osteophyte width in vitamin D deficient group (4.37 mm) was significantly shorter than that in insufficiency/sufficiency group (4.89mm) in female subjects (p=0.008). In female subjects, the cartilage part of osteophyte widths in vitamin D deficient group (2.04 mm) were significantly shorter than that of those in vitamin D insufficiency/sufficiency group (2.25 mm) (p=0.046), while no significant differences of bone part of osteophyte width were observed between vitamin D deficient (2.33 mm) and vitamin D insufficiency/sufficiency groups (2.64 mm).
Conclusions: Vitamin D levels are inversely associated with osteophyte formation in elderly women, but not in men.