Abstract
Objective:
To determine the cross-sectional and longitudinal associations of vitamin C and D intake with magnetic resonance (MR) imaging measures of cartilage composition (T2) and joint structure (cartilage, meniscus, and bone marrow) using data from the Osteoarthritis Initiative (OAI) cohort.
Methods:
1785 subjects with radiographic Kellgren Lawrence knee grades 0–3 in the right knee were selected from the OAI database. Vitamin C and vitamin D intakes (diet, supplements, and total) were assessed from the baseline Block Brief 2000 questionnaire. The MRI analysis protocol included 3T cartilage T2 quantification and semi-quantitative joint morphology gradings (WORMS) at baseline and 4 years. Linear regression was used to assess the association between standardized baseline vitamin intake and both baseline WORMS scores and standardized cartilage T2.
Results:
Higher vitamin C intake was associated with lower average cartilage T2, medial tibia T2 and medial tibia WORMS (coeff_standardized range: −0.07 to −0.05, p<0.05). Higher vitamin D intake was associated with lower cartilage WORMS sum score and medial femur WORMS score (coeff_standardized range: −0.24 to −0.09, p<0.05). Consistent use of vitamin D supplements over 4 years of 400 IU at least once a week was associated with significantly less worsening of cartilage, meniscus and bone marrow abnormalities (odds ratio range: 0.40 to 0.56, p<0.05).
Conclusion:
Supplementation with vitamin D over four years was associated with significantly less progression of knee joint abnormalities. Given the observational nature of this study, future longitudinal randomized controlled trials of vitamin D supplementation are warranted.
INTRODUCTION
Osteoarthritis (OA) is a heterogeneous joint disease that affects approximately 250 million people (1) causing severe disability (2), and over 50% of patients diagnosed with knee OA will receive a total knee replacement (TKR) in their lifetime (3). Various vitamin deficiencies have been identified in subjects with OA: including decreased vitamin C and D serum levels (4, 5): one study found that the odds of having hip OA was 1.9 times lower in subjects with recommended or higher vitamin C intake (6) and another study reported that 24% of patients with advanced OA (and upcoming TKR) were vitamin D deficient (<40 nmol/L) (7). Thus, understanding the impact of vitamin deficiency on knee joint health, and the value of nutritional supplements to prevent or treat OA is of significant scientific and clinical interest.
Various studies have investigated the effects of vitamin supplementation on knee OA progression, and most have relied on radiographic outcomes. One randomized controlled trial (n=474) reported vitamin D supplementation did not slow the rate of joint space narrowing compared to a placebo (average difference 0.08 mm/year (95% CI [−0.14–0.29], p = 0.49) (8), and another reported a 3-fold reduction in risk for OA progression (measured using Kellgren Lawrence grade) with mid to high vitamin C intake (9). The primary imaging outcome of these studies has been radiography, and few studies have utilized magnetic resonance imaging (MRI) markers of knee cartilage composition and morphologic knee abnormalities, which provide additional information on the individual knee joint tissues. However, two studies have used MRI outcomes to study the effects of vitamin D supplementation on OA: one reported no effects of vitamin D supplementation on cartilage volume loss (n=146), and another reported that effusion-synovitis volume remained stable in subjects that took vitamin D supplements (n=209) but increased in placebos (n=204) with a significant between-group difference (−1.94 ml, 95% confidence interval (CI): −3.54, −0.33). While these studies both emphasize the importance of using MRI outcomes, they are limited by small sample sizes and short follow-up times (2 years). Thus, the current study aims to enhance knowledge on the impact of vitamin intake on the knee joint using MRI outcomes in a large sample (n=1785) with a longer follow-up time (4 years).
While these previous studies used morphological outcomes, MRI also provides information on cartilage compositional changes in OA using T2 mapping, which provides more sensitive information on the cartilage extracellular matrix including its collagen fiber orientation (10). MRI T2 probes early stages of cartilage degeneration that are not visualized on a standard MRI. Thus, quantifying both cartilage T2 and joint structure features using MR imaging may be beneficial and more sensitive when studying the effects of vitamins on joint pathology in OA.
The purpose of this study was to evaluate the associations of vitamin C and D intake with MR imaging measures of cartilage composition (T2) and joint structure (cartilage, meniscus, and bone marrow) both cross-sectionally and longitudinally, using data from the Osteoarthritis Initiative (OAI).
MATERIALS AND METHODS
Subject Selection
This study utilizes data from the Osteoarthritis Initiative (OAI; http://www.oai.ucsf.edu/) (11), a multi-center, longitudinal study of persons aged 45–79 years at enrollment, aimed at assessing biomarkers in knee OA including those derived from MR imaging. The study protocol, amendments, and informed consent documentation were reviewed and approved by the local institutional review boards of all participating centers.
For the present study, we analyzed a sample of OAI subjects by selecting all subjects that had a Kellgren Lawrence score (KL) ≤ 3 in the right knee from which we had previously obtained both T2 relaxation time and semi-quantitative joint morphology measures from 3T MR images for other analyses (12–16). The OAI exclusion criteria were: (i) inflammatory arthropathies (including rheumatoid arthritis and seronegative spondylarthropathies), (ii) MRI contraindications, (iii) use of ambulatory aids and co-morbid conditions that may affect the ability to participate in the study. For this analysis we excluded knees with (i) history of knee injury with post-traumatic deformity of the knee joint, (ii) total joint replacements at the lower extremities, (iii) MRI evidence of fractures or abnormalities, that did not fit into the spectrum of OA such as tumor or inflammation at baseline.
Vitamin Intake Measurements
Baseline measurements
Three measurements were each assessed for vitamin C and vitamin D intake, respectively. For vitamin C, we used the Block Brief 2000 food frequency questionnaire (Block FFQ) measurements of a) the average daily vitamin C intake (mg) from food during the past 12 months, b) the number of milligrams of vitamin C supplements usually taken daily in the past 30 days follow-up and c) the sum of (a + b) to determine total average daily vitamin C intake from food and from supplements (if taken).
For vitamin D, the following three measurements from the OAI questionnaire were analyzed: a) Block Brief 2000: daily nutrients from food, vitamin D (IU) during the past 12 months b) Block Brief 2000: vitamin D, number of IUs usually taken daily in the past 30 days follow-up and c) the sum of (a + b) to determine total vitamin D intake from food and from supplements (if taken) (Table 1).
Table 1:
Predictor variables (vitamin C and vitamin D).
| Time-period | Description | N |
|---|---|---|
| Vitamin C | ||
| Cross-Sectional | SAQ:Block Brief 2000: Daily nutrients from food (mg) during the past 12 months | 1785 |
| SAQ:Block Brief 2000: Supplement: Daily dosage (mg) in the past 30 days | 1656 | |
| Daily nutrients from food + nutrients from supplement (mg) | 1656 | |
| Longitudinal | Subjects not taking vitamin C over 4 years (documented yearly) vs. | 612 |
| Subjects taking vitamin C at least 4–6 days/week (in the past 30 days) with a dose of 750 mg over 4 years (documented yearly) | ||
| Vitamin D | ||
| Cross-Sectional | SAQ:Block Brief 2000: Daily nutrients from food (IU) during the past 12 months | 1785 |
| SAQ:Block Brief 2000: Supplement: Daily dosage (IU) in the past 30 days | 1537 | |
| Daily nutrients from food + nutrients from supplement (IU) | 1537 | |
| Longitudinal | Subjects not taking vitamin D over 4 years (documented yearly) vs. | 524 |
| Subjects taking vitamin D at least 4–6 days/week (in the past 30 days) with a dose of 300 IU over 4 years (documented yearly) | ||
Longitudinal Measurements
For vitamin C analysis, subjects were categorized into those who consistently took vitamin C supplements over 4 years (documented yearly), and those that reported not taking any vitamin C supplement over the over the same time period. Subjects were subdivided into groups based on a combination supplement dosage (500 mg, 750 mg, or 1000 mg per dose (on days taken)) and frequency of intake (at least 1–3 days per week or at least 4–6 days per week). The following variables were used for this calculation: frequency of vitamin C supplement use in the past 30 days and number of milligrams taken daily in the past 30 days. Subjects with varying vitamin C intake over 4 years were not included in the longitudinal analysis.
For vitamin D analysis: subjects were categorized into those that had consistent intake of vitamin D supplements over 4 years (documented yearly), and those that reported not taking vitamin D over the same time period. Subjects were subdivided into groups based on supplement dosage (200 IU, 300 IU, or 400 IU per dose (on days taken)) and frequency of intake (at least 1–3 days per week or at least 4–6 days per week). The following variables were used for this calculation: vitamin D frequency in the past 30 days and number of IUs taken daily in the past 30 days (Table 1). Subjects with varying vitamin D intake over 4 years were not included in the longitudinal analysis.
Imaging of the knee
Radiographs:
Fixed flexion knee radiographs were obtained at baseline, and radiographic KL grades (17) were provided in the OAI dataset. Subjects with baseline KL grades of 0–3 were selected.
MR Imaging:
MR images were obtained using four identical 3.0 Tesla (Siemens Magnetom Trio, Erlangen, Germany) scanners in Columbus, Ohio; Baltimore, Maryland; Pittsburgh, Pennsylvania; Pawtucket, Rhode Island. The following four sequences were obtained for the morphological analysis: (i) 2D intermediate-weighted fast spin echo (FSE) sequences with fat suppression in the sagittal plane (3200/30 milliseconds (ms), repetition time (TR)/ echo time (TE)); (ii) 2D proton density-weighted FSE sequences in the sagittal plane (2700/20 ms, TR/TE); (iii) 3D T1-weighted fast low-angle shot (FLASH) gradient-echo sequences (20/7.6 ms/12°, TR/TE/flip angle), 512×512 matrix and (iv) 3D dual echo steady-state gradient-echo (DESS) obtained in the sagittal plane (16.3/4.7 ms/25°, TR/TE/flip angle), 307×384 matrix. Further details about the image acquisition are available in the OAI MR protocol (18). A sagittal 2D multi-slice multi-echo sequence (MSME, TR=2700ms, TE1–TE7=10–70ms, spatial resolution=0.313mmx0.446mm, slice thickness=3.0mm, and 0.5mm gap) was used for cartilage T2 measurements(19).
MR Image Analysis
WORMS Scoring
WORMS scoring was performed at baseline and 4 years. MR images of the right knee obtained at the baseline visit were reviewed on picture archiving communication system (PACS) workstations (Agfa, Ridgefield Park, NJ, USA). Three radiologists with 8-, 6-, and 6-years of experience graded cartilage lesions. In equivocal cases, a consensus reading was performed with a musculoskeletal radiologist with 25-years of experience. Baseline cartilage and bone marrow lesions were assessed in five regions (patella, medial femur, medial tibia, lateral femur and lateral tibia) using a modified semi-quantitative whole-organ magnetic resonance imaging score (WORMS) (20).
Cartilage lesions were evaluated with an 8-point scale: 0 = normal, 1 = normal thickness but increased or otherwise abnormal signal on fluid sensitive sequences, 2 = partial-thickness focal defect < 1 cm in greatest width, 2.5 = full-thickness focal defect < 1 cm in greatest width, 3 = multiple areas of partial-thickness defects (grade 2) intermixed with areas of normal thickness, or grade 2 defect wider than 1 cm but < 75% of the entire region, 4 = diffuse (≥ 75% of the region) partial-thickness loss, 5 = multiple areas of full-thickness defect (grade 2.5) but < 75% of the region, and 6 = diffuse (≥75% of the region) full-thickness loss. Subchondral bone marrow edema pattern was defined as poorly marginated areas of increased T2 signal intensity and graded using a modified 4-point WORMS scale (0, none; 1, diameter 0–5mm; 2, 5–20mm; 3, >20mm) (21). Meniscal lesions were graded separately in 6 regions (medial/lateral and anterior/body/posterior) using the following 4-point scale: 0-normal; 1-intrasubstance signal; 2-non-displaced tear; 3-displaced or complex tear; 4-complete destruction/maceration.
The maximum (MAX) cartilage, meniscus or bone marrow edema pattern (BMEP) score was defined as the maximum score in any region. The summation (SUM) cartilage, meniscus or BMEP score was defined as the summation of WORMS scores in all regions. The reproducibility results for WORMS readings have been previously published (22, 23): the intra-observer reproducibility in all tissues (meniscus, cartilage, bone marrow) was ≥96%, while the inter-observer reproducibility was ≥97%.
T2 measurements
Cartilage T2 measurements were performed at baseline. Semi-automatic cartilage segmentation of lateral/medial femur, lateral/medial tibia, and patella regions was performed as previously described, using an in-house, spline-based software based on MATLAB (MathWorks, Natick, Massachusetts) (23). The average cartilage T2 value in the knee was defined as the average T2 in all the regions described above. Trained investigators segmented the entire cartilage but used rigorous criteria to exclude sections with compromised image quality.
Validated methods for obtaining a T2 map of the cartilage have been previously published by our group (22, 23). T2 maps were computed from the MSME images on a pixel-by-pixel basis using 6 echoes (TE=20–70ms) and 3 parameter fittings accounting for noise (24, 25), and averaged over all of the slices in each cartilage region (lateral/medial femur, lateral/medial tibia, and patella). The first echo (TE=10ms) was not included in the T2 fitting procedure in order to reduce potential errors resulting from stimulated echoes, and a noise-corrected algorithm was implemented (24, 25). The cartilage T2 reproducibility results have been described previously (22, 23). The mean T2 values had root mean square (RMS) coefficients of variation (CV) ranging from 0.83% in the medial femur to 3.21% in the patella for intra-reader reproducibility, and from 1.22% in the patella to 1.86% in the lateral tibia for inter-reader reproducibility.
Statistical Analysis
Statistical analysis was performed using STATA version 14 software (StataCorp LP, College Station, TX). For the cross-sectional analysis, linear regression models were used to assess the relationships between baseline vitamin C and D intake (predictors) and baseline WORMS scores and cartilage T2 (outcomes). To make interpretation easier, we report standardized coefficients – the change outcome per standard deviation change in the predictors. In addition to standardized predictors, standardized T2 outcomes were used to aid interpretation. All models were adjusted for baseline age, gender, BMI, race, education, and total calorie intake.
For the longitudinal analysis, logistic regression models were used to assess the relationship between consistent vitamin intake over 4 years (predictor, described in the methods section) and worsening of joint morphology over 4 years (outcome). Worsening of joint morphology was designated as binary variable, and positive if WORMS score at year 4 was greater than the WORMS score at baseline. All models were adjusted for baseline age, gender, BMI, race, education, and total calorie intake. Total calorie intake was included to adjust for potential intestinal malabsorption.
The outcome variables were subdivided into primary and exploratory in order to address potential multiple testing issues. The three primary cartilage T2 outcomes were T2 in the medial femur and medial tibia, and T2 averaged over all 5 regions. The seven primary WORMS regional outcomes were medial femur and medial tibia cartilage and bone marrow lesion scores, and medial anterior, body and posterior meniscus scores. The 3 primary WORMS sum score outcomes were cartilage, bone marrow lesions and meniscus. We focused on the medial compartment as medial OA occurs more frequently than lateral OA (26–28). The remaining regions were considered exploratory, and those results are presented in the supplementary tables.
RESULTS
Subject Characteristics
The 1785 participants included in the cross-sectional analysis of daily nutrients from food this study had a mean age of 59.8±9.0 years and a mean BMI of 28.6±4.4 kg/m2 at baseline (Table 2). Sixty percent of the subjects were female, and a majority of the subjects had KL0 (n = 677, 37.9%), while 17.1% (n=306) had KL1, 30.0% (n=536) had KL2, and 14.9% (n=266) had KL3 in the right knee.
Table 2:
Participant Characteristics
| All Participants | |
|---|---|
| n# | 1785 |
| Age (years, mean ± SD) | 59.8 ± 9.0 |
| BMI (kg/m2, mean ± SD) | 28.6 ± 4.4 |
| Gender (female) | 1086 (60.8%) |
| WOMAC% pain (mean ± SD) | 2.4 ± 3.2 |
| Family history of knee replacement^ | 251 (14.2%) |
| Race* | |
| Other Non-white | 27 (1.5%) |
| White or Caucasian | 1387 (77.7%) |
| African American | 359 (20.1%) |
| Asian | 11 (0.6%) |
| Highest grade or year of school | |
| Less than high school graduate | 52 (2.9%) |
| High school graduate | 226 (12.6%) |
| Some college | 421 (23.5%) |
| College graduate | 387 (12.6%) |
| Some graduate school | 150 (8.4%) |
| Graduate degree | 549 (30.7%) |
| SAQ:Block Brief 2000: daily nutrients from food, calories (Kcal, mean ± SD) | 1390.8 ± 605.8 |
| Vitamin C | |
| SAQ:Block Brief 2000: Daily nutrients from food during the past 12 months (mg, mean ± SD) | 110.6 ± 63.3 |
| SAQ:Block Brief 2000: Supplement: Daily dosage in the past 30 days (mg, mean ± SD)@ | 256.7 ± 451.4 |
| Vitamin D | |
| SAQ:Block Brief 2000: Daily nutrients from food during the past 12 months (IU, mean ± SD) | 137.4 ± 106.2 |
| SAQ:Block Brief 2000: Supplement: Daily dosage in the past 30 days (IU, mean ± SD)& | 109.5 ± 228.0 |
note that n is based on subjects with data available for the following predictor variable: vitamin C Daily nutrients from food (mg) during the past 12 months)
WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index
one subject did not have race information available
20 subjects did not have family history of knee replacement information available
n = 1656
n = 1537
Cross Sectional Results
Vitamin C
Higher daily total vitamin C intake (from diet + from supplements) was associated with lower average cartilage T2 (an estimated drop of 0.05 SD of T2 (95% CI = −0.09 to −0.002) with each SD increase in vitamin C, p =0.04) and lower medial tibia cartilage T2 (coeffstandardized = −0.05, p = 0.03, 95% CI = −0.09 to −0.01). In addition, higher daily vitamin C supplement intake was associated with lower baseline medial tibial cartilage WORMS score (coeffstandardized = −0.07, p = 0.05, 95% CI = −0.14 to −0.001). No significant associations were found between baseline vitamin C intake and the remaining primary cartilage T2 or WORMS parameters; however, there was a nonsignificant trend for association of vitamin C supplement intake with meniscus WORMS in the medial posterior horn (coeffstandardized = −0.06, p = 0.06, 95% CI = −0.12 to 0.003), Table 3. The results for the exploratory outcomes are presented in Supplementary Table 1.
Table 3:
Linear regression models of the associations between baseline vitamin C intake and baseline cartilage T2, cartilage WORMS scores, meniscus WORMS scores, and bone marrow WORMS scores (adjusted for age, gender, BMI, race, education, and total calorie intake) with p values and 95% confidence intervals (CI). Abbreviations: MFC (medial femoral condyle) MT (medial tibia), SUM (Summation of WORMS scores across all regions). Note that cartilage T2 is a standardized outcome.
| Vitamin C | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Daily nutrients from food (mg) n = 1785 | Supplement: daily dosage (mg) n = 1656 | Daily nutrients from food + from supplement (mg) n = 1656 | ||||||||||
| Outcome | Coefficient | p | 95% CI | Coefficient | p | 95% CI | Coefficient | p | 95% CI | |||
| Cartilage T2 (standardized outcome) | ||||||||||||
| Average T2 | −0.01 | 0.69 | −0.06 | 0.04 | 0.03 | 0.31 | −0.02 | 0.08 | −0.05 | 0.04 | −0.09 | −0.002 |
| MFC T2 | −0.01 | 0.84 | −0.06 | 0.05 | 0.02 | 0.54 | −0.04 | 0.07 | −0.03 | 0.18 | −0.07 | 0.01 |
| MT T2 | −0.01 | 0.66 | −0.06 | 0.04 | 0.01 | 0.71 | −0.04 | 0.06 | −0.05 | 0.03 | −0.09 | −0.01 |
| WORMS SUM Scores | ||||||||||||
| Meniscus Sum | 0.08 | 0.34 | −0.09 | 0.26 | −0.07 | 0.41 | −0.25 | 0.10 | 0.00 | 0.97 | −0.13 | 0.14 |
| Cartilage Sum | −0.11 | 0.39 | −0.35 | 0.14 | −0.18 | 0.14 | −0.42 | 0.06 | −0.09 | 0.40 | −0.28 | 0.11 |
| Bone Marrow Sum | 0.04 | 0.42 | −0.06 | 0.15 | −0.05 | 0.36 | −0.15 | 0.05 | 0.01 | 0.90 | −0.08 | 0.09 |
| Regional Cartilage WORMS | ||||||||||||
| MFC Cartilage | −0.04 | 0.40 | −0.12 | 0.05 | −0.06 | 0.17 | −0.15 | 0.03 | 0.00 | 0.92 | −0.07 | 0.06 |
| MT Cartilage | −0.04 | 0.25 | −0.11 | 0.03 | −0.07 | 0.05 | −0.14 | −0.001 | −0.03 | 0.23 | −0.09 | 0.02 |
| Regional Bone Marrow WORMS | ||||||||||||
| MFC Bone Marrow | 0.00 | 0.88 | −0.04 | 0.03 | 0.00 | 0.97 | −0.04 | 0.04 | 0.01 | 0.63 | −0.02 | 0.04 |
| MT Bone Marrow | 0.01 | 0.70 | −0.03 | 0.05 | 0.00 | 0.92 | −0.04 | 0.04 | 0.01 | 0.72 | −0.03 | 0.04 |
| Regional Meniscus WORMS | ||||||||||||
| Medial Anterior | 0.02 | 0.15 | −0.01 | 0.04 | −0.02 | 0.19 | −0.05 | 0.01 | 0.01 | 0.52 | −0.01 | 0.03 |
| Medial Body | 0.04 | 0.20 | −0.02 | 0.10 | −0.04 | 0.24 | −0.10 | 0.02 | 0.00 | 0.97 | −0.05 | 0.05 |
| Medial Posterior | 0.03 | 0.40 | −0.03 | 0.09 | −0.06 | 0.06 | −0.12 | 0.003 | −0.02 | 0.42 | −0.07 | 0.03 |
Vitamin D
Overall, higher vitamin D intake was associated with lower WORMS scores, particularly in the medial femur. Higher dietary vitamin D (IUs) had a significant negative association with lower baseline cartilage WORMS sum score (an estimated drop of 0.24 WORMS score (95% CI = −0.46 to −0.02) with each SD increase in Vitamin D, p = 0.03). In addition, daily vitamin D supplement intake had a significant negative association with cartilage WORMS score in the medial femur (coeffstandardized = −0.09, p = 0.04, 95% CI = −0.18 to −0.003), Table 4. No significant associations were found between baseline vitamin D intake and the remaining primary cartilage T2 or WORMS outcomes. The results for the exploratory outcomes are presented in Supplementary Table 2.
Table 4:
Linear regression models of the associations between baseline vitamin D intake and baseline cartilage T2, cartilage WORMS scores, meniscus WORMS scores, and bone marrow WORMS scores (adjusted for age, gender, BMI, race, education, and total calorie intake) with p values and 95% confidence intervals (CI). Abbreviations: MFC (medial femoral condyle) MT (medial tibia), SUM (Summation of WORMS scores across all regions). Note that cartilage T2 is a standardized outcome.
| Vitamin D | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Daily nutrients from food (IU) n = 1785 | Supplement: daily dosage (IU) n = 1537 | Daily nutrients from food + from supplement (IU) n = 1537 | ||||||||||
| Outcome | Coefficient | p | 95% CI | Coefficient | p | 95% CI | Coefficient | p | 95% CI | |||
| Cartilage T2 (standardized outcome) | ||||||||||||
| Average T2 | 0.15 | 0.15 | 0.15 | 0.03 | 0.03 | 0.33 | −0.03 | 0.08 | 0.003 | 0.91 | −0.044 | 0.049 |
| MFC T2 | 0.15 | 0.15 | 0.15 | 0.03 | 0.02 | 0.45 | −0.03 | 0.08 | 0.001 | 0.97 | −0.045 | 0.047 |
| MT T2 | −0.02 | −0.02 | −0.02 | 0.02 | 0.02 | 0.48 | −0.04 | 0.07 | −0.009 | 0.72 | −0.056 | 0.038 |
| WORMS SUM Scores | ||||||||||||
| Meniscus Sum | 0.00 | 0.99 | −0.16 | 0.15 | −0.06 | 0.50 | −0.22 | 0.11 | −0.038 | 0.63 | −0.191 | 0.115 |
| Cartilage Sum | −0.24 | 0.03 | −0.46 | −0.02 | −0.15 | 0.24 | −0.41 | 0.10 | −0.159 | 0.15 | −0.378 | 0.059 |
| Bone Marrow Sum | −0.06 | 0.19 | −0.16 | 0.03 | −0.07 | 0.21 | −0.17 | 0.04 | −0.069 | 0.16 | −0.163 | 0.026 |
| Regional Cartilage WORMS | ||||||||||||
| MFC Cartilage | −0.07 | 0.13 | −0.17 | 0.02 | −0.09 | 0.04 | −0.18 | −0.003 | −0.044 | 0.25 | −0.119 | 0.031 |
| MT Cartilage | −0.06 | 0.08 | −0.12 | 0.01 | −0.02 | 0.57 | −0.10 | 0.05 | −0.021 | 0.50 | −0.083 | 0.041 |
| Regional Bone Marrow WORMS | ||||||||||||
| MFC Bone Marrow | −0.01 | 0.51 | −0.04 | 0.02 | −0.01 | 0.68 | −0.05 | 0.03 | −0.004 | 0.83 | −0.037 | 0.029 |
| MT Bone Marrow | 0.00 | 0.99 | −0.03 | 0.03 | −0.01 | 0.71 | −0.05 | 0.03 | 0.003 | 0.88 | −0.032 | 0.037 |
| Regional Meniscus WORMS | ||||||||||||
| Medial Anterior | 0.00 | 0.76 | −0.02 | 0.03 | −0.01 | 0.41 | −0.04 | 0.02 | 0.002 | 0.85 | −0.021 | 0.025 |
| Medial Body | 0.01 | 0.71 | −0.04 | 0.06 | 0.00 | 0.92 | −0.06 | 0.06 | −0.003 | 0.92 | −0.056 | 0.051 |
| Medial Posterior | 0.03 | 0.27 | −0.02 | 0.08 | 0.03 | 0.26 | −0.02 | 0.09 | 0.047 | 0.09 | −0.007 | 0.101 |
Longitudinal Results
Vitamin C
Compared to those who did not use vitamin C supplements over 4 years, no significant associations were found between consistent vitamin C supplement intake over 4 years at any combination of typical frequency (at least 1–3 days per week or at least 4–6 days per week) and daily dose (500 mg, 750 mg, or 1000 mgs) and worsening of joint degeneration in the cartilage, meniscus, or bone marrow over 4 years.
Vitamin D
Consistent vitamin D supplement intake over 4 years was associated with significantly less joint degeneration in subjects that took vitamin D consistently over 4 years. The smallest dose and lowest frequency with a statistically significant association with WORMS progression was 300 IU taken at least 4–6 days per week. Thus, subjects that consistently took vitamin D supplements over 4 years had a significantly lower odds for WORMS cartilage and bone marrow progression (n=524, cartilage SUM: OR = 0.56, p = 0.04, 95% CI = 0.32 to 0.97; bone marrow SUM: OR = 0.48, p = 0.02, 95% CI = 0.25 to 0.89) compared to subjects that did not take vitamin D over 4 years. In addition, taking at least 400 IU at least 1–3 days per week was associated with lower odds for cartilage (OR = 0.56, p = 0.04, 95% CI = 0.32 to 0.98), meniscus (OR = 0.51, p = 0.04, 95% CI = 0.27 to 0.97), and bone marrow (OR = 0.40, p = 0.01, 95% CI = 0.21 to 0.75) worsening over 4 years. Similarly, taking 400 IU of vitamin D supplements at least 4–6 days per week was associated for lower odds of joint structure degeneration (Table 5).
Table 5:
Logistic regression models testing the associations between consistent intake of vitamin D over 4 years and worsening of WORMS scores over 4 years (binary) with p values and 95% confidence intervals (CI).
| Frequency | n (take / did not take) consistently over 4 years | Outcome | Odds ratio | p | 95% CI | |
|---|---|---|---|---|---|---|
| 200 IU vitamin D | ||||||
| At least 1–3 days/week | 583 (142 yes / 441 no) |
ΔMeniscus SUM | 0.83 | 0.48 | 0.50 | 1.38 |
| ΔCartilage SUM | 0.77 | 0.28 | 0.48 | 1.23 | ||
| ΔBone Marrow SUM | 0.73 | 0.22 | 0.44 | 1.21 | ||
| At least 4–6 days/week | 571 (130 yes / 441 no) |
ΔMeniscus SUM | 0.78 | 0.36 | 0.47 | 1.32 |
| ΔCartilage SUM | 0.73 | 0.19 | 0.45 | 1.17 | ||
| ΔBone Marrow SUM | 0.71 | 0.20 | 0.43 | 1.20 | ||
| 300 IU vitamin D | ||||||
| At least 1–3 days/week | 532 (91 yes / 441 no) |
ΔMeniscus SUM | 0.57 | 0.07 | 0.31 | 1.05 |
| ΔCartilage SUM | 0.60 | 0.06 | 0.35 | 1.03 | ||
| ΔBone Marrow SUM | 0.48 | 0.02 | 0.26 | 0.88 | ||
| At least 4–6 days/week | 524 (83 yes / 441 no) |
ΔMeniscus SUM | 0.56 | 0.07 | 0.30 | 1.05 |
| ΔCartilage SUM | 0.56 | 0.04 | 0.32 | 0.97 | ||
| ΔBone Marrow SUM | 0.48 | 0.02 | 0.25 | 0.89 | ||
| 400 IU vitamin D | ||||||
| At least 1–3 days/week | 523 (82 yes / 441 no) |
ΔMeniscus SUM | 0.51 | 0.04 | 0.27 | 0.97 |
| ΔCartilage SUM | 0.56 | 0.04 | 0.32 | 0.98 | ||
| ΔBone Marrow SUM | 0.40 | 0.01 | 0.21 | 0.75 | ||
| At least 4–6 days/week | 516 (75 yes / 441 no) |
ΔMeniscus SUM | 0.49 | 0.04 | 0.25 | 0.96 |
| ΔCartilage SUM | 0.50 | 0.02 | 0.28 | 0.89 | ||
| ΔBone Marrow SUM | 0.38 | 0.01 | 0.19 | 0.74 | ||
DISCUSSION
Cross-sectionally, a higher intake of both vitamin C and D was associated with less cartilage degeneration, as evidenced by an inverse relationship with cartilage T2 values (particularly for vitamin C) and with cartilage WORMS scores (for both vitamin C and D). In addition, consistent intake of vitamin D supplements (and not vitamin C) over 4 years had a protective effect on joint degeneration; however, this relationship was dose-dependent. The lowest dose and frequency of vitamin D intake with a statistically significant protective effect was 300 IU at least 4–6 days per week, which was beneficial for cartilage and bone marrow tissues. While decreasing the frequency of intake to at least 1–3 days per week did not have a significant protective effect on joint degeneration, increasing the dose to 400 IU at least 1–3 days per week was not only beneficial for the cartilage and bone marrow, but also for meniscus tissue.
Both the cross-sectional and longitudinal results of this study suggest that vitamin D intake is associated with less joint structure degeneration. While various studies have shown similar beneficial effects of vitamin D, others found no associations. In a randomized controlled pilot trial, patients that received oral vitamin D supplements had less knee pain than those receiving a placebo (29), and imaging x-ray studies have reported that lower levels of vitamin D are associated with increased risk of joint space narrowing and cartilage loss (30–32), which is consistent with our results. However, Felson et al. published a longitudinal study which demonstrated no associations between baseline vitamin D (measured using blood draw) and structural worsening of JSN and cartilage loss by MRI (33). The varying results of these studies may be attributed to factors such as self-reported vitamin D intake vs. serum levels measured in the laboratory as well as varied ethnic backgrounds of study populations (34). Thus, a large-scale randomized control study or meta-analyses on pre-existing findings may yield more comprehensive interpretations.
Various mechanisms through which vitamin D deficiency may impact cartilage degeneration have been postulated. Vitamin D receptors are present in articular cartilage chondrocytes, especially in the superficial zone (35); these vitamin D receptors can stimulate proteoglycan synthesis (36), and inhibit metalloproteinase activity (which degrades the extracellular matrix) (37). In addition, adverse effects of vitamin D deficiency on subchondral bone calcium metabolism and matrix ossification (38) may trigger cartilage damage since cartilage tissue is adjacent to subchondral bone through calcified cartilage (39). Thus, vitamin D deficiency may adversely impact the pathogenesis of cartilage degeneration in OA, both directly through its impact on ECM activity and indirectly through its negative effects on bone metabolism.
The results for the cross-sectional and longitudinal vitamin C analyses were disparate: the cross-sectional results found a beneficial effect of vitamin C on joint degeneration (having inverse associations with cartilage T2 and WORMS scores), while the longitudinal results showed no significant associations. The effects of vitamin C on OA are multifaceted, and similar to vitamin D, the mechanisms through which vitamin C impacts joint degeneration are unclear. Vitamin C is an anti-oxidant, which may combat free-radical damage (resulting from mechanical stress) and subsequent cartilage degeneration that are often present in the osteoarthritic joint (40). In addition, since vitamin C is a sulfate carrier in glycosaminoglycan (GAG) synthesis, its depletion may contribute to GAG loss in early OA (41). Thus, it can be hypothesized the vitamin C may benefit the OA joint by decreasing oxidative damage as well as GAG loss. However, this hypothesis needs further confirmation, as previous studies have published varying results on the impact of vitamin C on the arthritic joint with some showing benefits (9), others showing no effects (42), and others reporting that high levels are associated worsening of knee OA (43, 44).
The primary limitation of this study is its observational design and use of self-report of dietary intake and vitamin supplements over the previous 12 months. A randomized controlled design would be better-suited to account for confounding and other factors; thus, the presented results should be interpreted with caution. However, as the OAI dataset can only be analyzed retrospectively, we have performed statistical adjustment in order the address any potential biases due to confounding by indication. Total calorie intake was included to adjust for potential intestinal malabsorption, and education was included to adjust for potential differences in knowledge about vitamin supplements. We examined the effects of potential unmeasured or uncontrolled confounding on the associations reported in this study using the E-value statistic (45). The observed odds ratio of 0.38 (Table 5) could be explained away by an unmeasured confounder that was associated with both the predictor (vitamin D status) and the outcome (cartilage WORMS) by an odds ratio of 4.7 each, above and beyond the measured confounders. Given these results, is highly unlikely that other potential unmeasured variables are strongly associated with the treatment and outcome. Thus, the reported associations in this study are unlikely to be due to unmeasured or uncontrolled confounding. In addition, we only analyzed baseline T2 measurements of cartilage composition as provided by the OAI, and it would be beneficial to study other quantitative cartilage assessments such as T1rho mapping. We were unable to assess baseline vitamin plasma concentrations, as this data was not available in the OAI. Despite these limitations, we feel that this study is valuable given its large sample size and use of advanced MR imaging outcome measures that include cartilage T2.
Overall, the cross-sectional results showed that some measures of vitamin C and D intake from food and supplements were associated with less cartilage degeneration. While consistent vitamin C supplementation over 4 years did not have a significant association with changes in joint morphology, consistent use of at least 300 IU of vitamin D at least 4–6 days per week) over four years was associated with less progression of knee joint abnormalities in the cartilage and bone marrow, and consistent use of at least 400 IU at least 1–3 days per week was beneficial for cartilage, bone as well as meniscus tissues.
Supplementary Material
SIGNIFICANCE AND INNOVATIONS:
A higher intake of both vitamin C and D was associated with less cartilage degeneration.
Supplementation with vitamin D over four years was associated with significantly less progression of knee joint abnormalities.
Acknowledgements
We would like to acknowledge Felix Liu for his help in obtaining information on the variables from the OAI.
Funding
This study was funded by NIH R01-AR064771. The OAI is a public-private partnership comprised of five contracts (N01-AR-2-2258; N01-AR-2-2259; N01-AR-2-2260; N01-AR-2-2261; N01-AR-2-2262) funded by the National Institutes of Health, a branch of the Department of Health and Human Services and conducted by the OAI Study Investigators. Private funding partners include Merck Research Laboratories; Novartis Pharmaceuticals Corporation, GlaxoSmithKline; and Pfizer, Inc. Private sector funding for the OAI is managed by the Foundation for the National Institutes of Health.
Financial Support: This study was funded by NIH R01-AR064771.
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