Elderly men with low serum levels of vitamin D are at increased risk for developing hip osteoarthritis, a prospective cohort study found.
Men whose levels of 25-hydroxyvitamin (OH)D were between 15.1 to 30 ng/mL had twice the likelihood of prevalent radiographic hip osteoarthritis than those whose levels were normal (OR 2.19, 95% CI 1.21 to 3.97), according to R. Krishna Chaganti, MD, of the University of California at San Francisco, and colleagues.
Conversely, after adjusting for age, season at blood draw, and clinic site, higher vitamin D levels were associated with a lower prevalence of hip osteoarthritis (OR 1.39 per 1 SD decrease in 25(OH)D level, 95% CI 1.11 to 1.74), the researchers reported in the February issue of Arthritis & Rheumatism.
Because the role vitamin D may play in the pathogenesis and progression of osteoarthritis is unclear, Chaganti and colleagues analyzed data from the Osteoporotic Fractures in Men Study, which enrolled a large cohort of elderly men between 2000 and 2002 from six centers across the U.S.
A total of 1,104 men whose mean age was 77.2 years had baseline measurements of serum vitamin D, and about 4.5 years later pelvic radiographs were obtained.
Radiographs were scored to reflect joint space narrowing, osteophyte formation, cysts, subchondral sclerosis, and femoral head deformity.
Vitamin D levels were categorized as deficiency (≤15 ng/mL), insufficiency (15.1 to 30 ng/mL), and sufficiency (>30 ng/mL).
Mean vitamin D level was 23.38 ng/mL in men who had radiographic hip osteoarthritis, compared with 26.04 ng/mL in men without radiographic abnormalities (P=0.0002).
Men with hip osteoarthritis had a higher prevalence of both vitamin D insufficiency (77% versus 65%, P=0.002) and deficiency (10.2% versus 7.5%, P=0.012).
Moreover, they had slower six-meter walking speed (P<0.0001) and reported more hip pain (P=0.0001).
Men who were vitamin D deficient also tended to have an increased likelihood of hip osteoarthritis (OR 1.99, 95% CI 0.83 to 4.74), but after adjustment in multivariate models, statistical significance was lost with this level of the vitamin.
"The association of low 25(OH)D levels with prevalent radiographic hip [osteoarthritis] underscores the potentially important role of vitamin D in the pathogenesis of [osteoarthritis]. Vitamin D metabolites have been found to be associated with the regulation of the Wnt pathway, products of which play important roles in the development and maintenance of bone and cartilage," the investigators explained.
Furthermore, in vitro studies have suggested that serum levels of 25-hydroxyvitamin D3 can affect the ratio of RANKL to osteoprotegerin and thereby influence bone deterioration and repair.
Previous investigations have yielded conflicting results. One study found that low levels of vitamin D were not associated with worsening of knee osteoarthritis, as reflected in loss of articular cartilage on MRI.
Another study, however, linked knee osteoarthritis with low vitamin D levels, particularly in patients who also had decreased bone mineral density in the lumbar spine.
"Vitamin D influences the mineralization of bone matrix, and low serum levels of vitamin D may result in poorly mineralized bone that might alter forces across the joint and reduce joint deterioration," the authors suggested.
On the other hand, low levels may interfere with chondrocyte metabolism and thereby increase degeneration.
Further studies will be needed to more fully clarify the effects of the vitamin on the development and progression of osteoarthritis, the investigators cautioned.
Strengths of the study include the large cohort of participants, careful classification of radiographic osteoarthritis, and reliance on the gold standard of vitamin D measurement, the 25(OH)D level.
Limitations include the cross-sectional design, precluding the inference of causality, and the gap in time between measurement of serum vitamin D and radiography.
The authors concluded that therapeutic interventions to increase vitamin D serum levels in the elderly "are warranted," with the goal of improving skeletal health in this vulnerable age group.
The study was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases, the National Institute on Aging, the National Center for Research Resources, and the NIH Roadmap for Medical Research.
The lead author was supported by a grant from the American College of Rheumatology Research and Education Foundation.
- Reviewed by Dori F. Zaleznik, MD Associate Clinical Professor of Medicine, Harvard Medical School, Boston and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner