WHAT DID THE AUTHORS STUDY?

It has been shown that older women have a greater chance of developing bone loss.¹ In the article “Reduced bone resorption and increased bone mineral density in women with restless legs syndrome,” the authors asked whether women with restless legs syndrome had changes in bone heath compared to women of similar ages and weights.²

WHY IS THIS STUDY IMPORTANT?

We know that women with restless legs syndrome have increased stress hormones in their blood stream.³ This led the authors to think that there might be more bone loss in women with restless leg syndrome symptoms. Other studies have shown that stress hormones send messages to bone-creating cells, signaling them to reduce bone production.⁴

HOW WAS THIS STUDY PERFORMED?

The authors tried to answer the question by measuring bone mineral density in the lower part of the spine in 78 women with restless legs syndrome. They also studied 78 women who were similar in age and weight but did not have restless legs syndrome as a control group. The researchers included only women with primary restless legs syndrome (not the secondary form that is caused by medications or chronic medical conditions). Primary restless legs syndrome often occurs within families. Those with restless legs syndrome have both the urge to move the legs as well as an uncomfortable feeling in the legs (prickling or crawling feelings). These feelings usually occur when the patient sits down or lies down, and they can be relieved by walking or pacing. The women enrolled in this study had not yet been treated for their restless legs syndrome symptoms. As soon as they were enrolled, the strength of the bones in the lower spine was measured (bone mineral density test). Because bone health depends on different issues, the authors looked at several factors. Blood was drawn to measure vitamin D₃ and a protein that is a marker for bone resorption, c-telopeptide of type 1 collagen (CTX). Resorption is when the bone tissue breaks down and decreases. Having adequate vitamin D₃ levels is important for bone health. Bone density is also affected by activity level.

WHAT WERE THE RESULTS OF THE STUDY?

The authors found an increase in the bone mineral density of women with restless legs syndrome compared to healthy controls. CTX levels were lower in women with restless legs syndrome, which may mean that there was less bone resorption in these patients. Levels of vitamin D₃ were lower in patients with restless legs syndrome than in controls.

WHAT DID THE AUTHORS CONCLUDE?

Despite the lower levels of vitamin D₃, there was less bone resorption and increased bone density in women with restless legs syndrome. The authors decided that the involuntary leg movements in these women may explain their stronger bone profiles.

WHAT ARE SOME OF THE STRENGTHS AND LIMITATIONS OF THIS STUDY?

This was a prospective cross-sectional case-control study that was performed over the course of 1 year. “Prospective” means that patients from both groups were enrolled into the study as they were initially seen in the clinic. “Cross-sectional” means that each patient was evaluated only once (no subsequent measurements were made over time). A “case-control” study is one in which patients are matched with healthy controls who are similar in certain aspects, such as age and weight.

The cross-sectional study design might be considered a weakness. A longitudinal study—one that follows people with multiple measurements over time—might be better, because it could help establish a true cause and effect relationship between the presence of restless legs syndrome and the protection from bone loss. A strength of this study is the prospective design, which allowed patients with restless legs syndrome to be examined before they were started on any medications. Treated patients with restless legs syndrome might not have shown the same changes in bone metabolism when compared to controls. Another strength is the case-control study design that matched patients and controls with respect to age, weight, and smoking status, because bone loss is known to be greater in those who are older, those who are thinner, and those who smoke.

WHAT IS NOT KNOWN YET?

Researchers might perform overnight sleep studies to see whether the severity of leg movements in patients with restless legs syndrome relates to bone density changes or CTX differences compared to controls. A longitudinal study of these patients might also be interesting, because it is possible that the protective effect of the involuntary movements on the bones might disappear as the patients are treated for the symptoms of restless legs syndrome.