Patients with rheumatoid arthritis have lower levels of vitamin D

This study assessed the levels of vitamin D in adults with rheumatoid arthritis. It also investigated whether vitamin D levels were associated with bone weakness or disease activity. 

Osteoporosis is a bone disease which causes bone loss (decreased bone mass and bone density). This in turn leads to the bones becoming brittle and fragile and increases the risk of them breaking. Patients with rheumatoid arthritis have a higher risk of developing osteoporosis and as a result have a higher risk of suffering from bone fractures.

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 muscle loss. It is unclear whether vitamin D levels are low in rheumatoid arthritis patient, or if low levels are linked with disease severity or bone weakness.

This study assessed vitamin D levels in 34 women with rheumatoid arthritis and 41 healthy women for comparison. Patient vitamin D levels were measured at the start of the study and after 1 year of taking vitamin D supplements. To assess vitamin D levels blood samples were taken to measure 25-hydroxyvitamin D (currently the best test available to monitor vitamin D levels). Participants also had an x-ray to measure bone density. Lower bone density indicates the weaker bones that are more likely to break. Rheumatoid arthritis disease activity was assessed by measuring the number of joints affected. 

Women with rheumatoid arthritis had lower levels of vitamin D (20.4 ng/ml of 25-hydroxyvitamin D) than healthy women (26.3 ng/ml of 25-hydroxyvitamin D). Patients with moderate to severe disease activity (19.5 ng/ml of 25-hydroxyvitamin D) had lower levels of vitamin D than patients with low disease activity (23.7 ng/ml of 25-hydroxyvitamin D).

Patients with rheumatoid arthritis had lower bone density than healthy women. 41.6% of the patients had osteoporosis while only 5.9% of the healthy women had low bone density scores. Vitamin D levels were not linked to lower bone density scores in patients.

After 1 year of taking vitamin D supplements, average 25-hydroxyvitamin D levels had increased in rheumatoid arthritis patients, from 20.4 ng/ml to 35.2 ng/ml. This increase in vitamin D was paralleled with a decrease in average disease activity scores after 1 year.  

The authors concluded that patients with rheumatoid arthritis had lower levels of 25-hydroxyvitamin D than healthy individuals. Low levels of vitamin D were associated with more severe disease activity, but not with lower bone density. 

This study only included women with rheumatoid arthritis, therefore we cannot be sure the same results would be seen in men with rheumatoid arthritis. This was also a very small study, more research is needed to ensure the results are widely generalizable.