Vitamin D levels are low in patients with juvenile idiopathic arthritis

This study assessed the levels of vitamin D in children, adolescents and young adults with juvenile idiopathic arthritis (JIA). They also investigated whether low vitamin D levels are associated with worse disease activity.

Vitamin D is produced by the skin during exposure to sunshine and is also taken in through diet or supplements. Foods high in vitamin D include tuna, salmon, beef liver, fortified cereals and egg yolks. Low levels of vitamin D can lead to bone problems and increased risk of fractures. Vitamin D may also have anti-inflammatory properties.

Adults with rheumatoid arthritis are reported to have low vitamin D levels and lower levels of vitamin D have been linked to higher disease activity and physical disability. Whether patients with JIA have lower vitamin D levels is unclear. 

This study assessed vitamin D levels in 152 patients with JIA and 188 healthy age matched participants for comparison. Patients with arthritis were also divided into subgroups based on their subtype of JIA. 63.2% had oligoarticular onset, 23% had polyarticular, 4.6% had systemic arthritis and 9.2% had enthesitis-related arthritis. All participants had blood tests to determine their levels of vitamin D (the blood test measures 25-hydroxyvitamin D to assess vitamin D levels). Participants also had an x-ray to measure bone density, which indicates the strength of bones and how likely they are to break.

Patients with JIA had significantly lower levels of vitamin D than healthy participants. On average healthy subjects had 29.8 ng/ml of 25-hydroxyvitamin D, while patients with JIA had 21.8 ng/ml. These lower levels of vitamin D were seen in all subtypes of JIA.

Patient age or gender did not affect the levels of vitamin D. Male patients had average blood 25-hydroxyvitamin D levels of 20.7 ng/ml and females had 22.4 ng/ml. Children had 22.4 ng/ml, adolescents had 21.6 ng/m and young adults had 21.0 ng/m on average. The decreases in vitamin D were most severe in winter. Patients with JIA had an average of 16.7 ng/ml of 25-hydroxyvitamin D in winter compared to 26.5 ng/ml in healthy participants.

Patients with lower levels of vitamin D had more active disease and/or more frequent relapses compared to patients with higher levels of vitamin D. Patients with lower vitamin D levels also had significantly lower bone density compared to patients with higher vitamin D levels.

The authors concluded that children, adolescents and young adults with JIA have lower levels of vitamin D compared to healthy participants. Lower levels were associated with more severe disease and lower bone density. They suggest that patients with more severe disease might require higher supplementation of vitamin D to maintain normal levels.

This was a short-term study. Further long-term studies are needed to investigate the relationship between serum 25-hydroxyvitamin D levels and disease activity in JIA.