Low level of vitamin D does not necessarily result in bone disease in people with lupus
What is the topic?
People with lupus are advised to avoid the sun because the ultraviolet rays can trigger rashes. Some patients experience more widespread flares after sun exposure. However, sun avoidance leads to low levels of vitamin D in the body. Low levels of vitamin D are associated with thinning of the bones, or "osteoporosis." Steroids are often used to treat lupus since they work fast and are highly effective, but they can also increase osteoporosis. For these reasons, among others, people with lupus are at increased risk for osteoporosis.
What did the researchers hope to learn?
The researchers hoped to learn about possible relationships between vitamin D levels in the blood, lupus treatments, and bone mineral density (BMD), a measurement of how thick bones are. BMD is low in people with osteoporosis.
Who was studied?
134 non-pregnant women with lupus were recruited for the study at the University of Toronto Lupus Clinic. The women were mostly Caucasians, an average age of 48, and had lupus for an average of 17 years.
How was the study conducted?
Vitamin D levels in the blood were measured in each woman. About half of the vitamin D measurements were made in the summer and about half in the winter (since there may be more sun exposure in the summer than winter even in people who try to avoid the sun). Vitamin D levels were rated as being "sub-optimal" (if somewhat lower than normal) or "deficient" (if a lot lower than normal).
Most of the women also had their BMD measured by X-rays. BMD measurements were categorized as indicating either "osteopenia" (if BMD was somewhat reduced from normal) or osteoporosis (if greatly reduced from normal).
What did the researchers find?
Vitamin D levels measured in the winter were lower than those measured in the summer even in lupus patients who are usually doing their best to avoid the sun. Sub-optimal levels of vitamin D were found in about 67% of the women, while deficient levels were found in about 18%.
Most of the women had normal BMD, but 28 had osteopenia and 12 had osteoporosis.
There was no direct relationship found between vitamin D levels and BMD. However, vitamin D levels were decreased when there was increased "creatinine" (a test that reflects kidney damage) or increased steroid use.
What were the limitations of the study?
Most of the women were Caucasians, so it is difficult to say how applicable the results are to women of other ethnicities. Also, men were not included in the study. The greatest limitation of the study is that as people get older, osteoporosis tends to get worse, so it may be that many of the lupus patients being studied were too young to find the highest long-term risks. Furthermore, vitamin D levels in these individuals were not compared to those in healthy people or to people with other immune system or rheumatic diseases, so it remains unclear how the patients compare to other people of their same age. There are many variables that can affect vitamin D levels and osteoporosis risk, so there are limits to the conclusions that can be drawn from this study. What this study has been able to do is to make it seem less likely that low levels of vitamin D pose enormous immediate risks for osteoporosis in a population averaging in the 40s.
What do the results mean for you?
People with lupus who are treated with steroids are at increased risk of having low levels of vitamin D. This is not new information, of course, and it has been recommended for some time that people taking steroids receive supplements with calcium and vitamin D. Although reduced levels of vitamin D are known to be directly linked to osteoporosis, this study did not show that connection. There can be many reasons for that, including how much milk people drink, their age, their real sun exposure, what kind of vitamin supplements they take, and their age.
Vitamin D insufficiency in a large female SLE cohort.
Authors: Toloza SM, Cole DE, Gladman DD, Ibañez D, and Urowitz MB. (2010).
Lupus, 19: 13-19.