By Eleanor McDermid
Contrary to the researchers' expectations, a study shows that women with restless legs syndrome (RLS) have increased bone mineral density (BMD) in some sites.
Patients with RLS reportedly have increased sympathetic nervous system activation, which, in turn, is believed to have a negative effect on bone metabolism.
This suggests that RLS patients could have reduced BMD, which the authors of an accompanying editorial - Linda Hershey (University of Oklahoma Health Sciences Center, Oklahoma City) and Mehmet Karan (Istanbul Medical School, Capa, Turkey) - describe in Neurology as "a plausible hypothesis".
However, Mehmet Cikrikcioglu (Bezmialem Vakif University Medical Faculty, Fatih, Turkey) and colleagues found that 78 women with RLS had significantly better bone health than 78 control women matched for age and body mass index.
The RLS patients had significantly lower levels of 25-hydroxy vitamin D3 than the controls, at 35.44 versus 45.53 nmol/L, but despite this they were significantly less likely to have lumber osteopenia, with 13% versus 25% having a T score between -2.5 and -1.0. Likewise, lumber BMD was 1.36 versus 1.06 g/cm2.
The researchers note that RLS patients have been shown to have increased physical activity levels, assumed to be because it alleviates their symptoms.
"The better bone findings in our patients with RLS than in controls may be accounted for by the increased physical activity in the night and morning hours that may serve as a form of unintended exercise", they suggest.
Levels of the bone formation marker procollagen 1 N-terminal peptide were similar between the groups, and there were no significant differences in femoral BMD between the groups, Cikrikcioglu and team report.
But they suggest this could change with longer duration of disease; the women's average RLS duration was 45 months.
However, levels of bone resorption markers were significantly lower in patients than controls, at 176.91 versus 340.32 ng/mL for C-telopeptide of type 1 collagen and 8.72 versus 14.93 ng/mL for sclerostin.
Sclerostin is known to reduce with exercise, which the team says lends weight to their theory that voluntary or unintended physical activity underlies the increased BMD in the patients in their study.
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