(30-10-10) TORONTO -- Low serum sodium may be a risk factor for fractures in the elderly, a researcher said here.

In a long-running cohort study in Holland, mild hyponatremia was associated
with an increased risk of nonvertebral fractures and prevalent vertebral
fractures, according to Carola Zillikens, MD, of Erasmus Medical Center in
Rotterdam.

The condition is usually considered benign, but cross-sectional studies have
shown it can lead to gait instability, falls, and fractures, Zillikens reported
at the annual meeting of the American Society for Bone and Mineral Research.

But there have been no prospective studies to look at the issue, she said. To
help fill the gap, she and colleagues turned to the longitudinal prospective
Rotterdam Study, which had 5,208 participants, ages 55 and older, who had serum
sodium levels at baseline in 1991 through 1993.

When the study started, the researchers collected data on bone mineral
density, recent falls, comorbidity, medication, and vertebral fractures,
Zillikens said. For this analysis, she reported, the researchers had more than
six years of follow-up data on both vertebral and nonvertebral fractures, as
well as all-cause mortality.

The vast majority of the participants had normal sodium levels -- defined as
136 minimoles per liter or above -- but 399 fell below that level, she said.

Those with hyponatremia were more likely to be diabetic, to be using
diuretics, and to have had a recent fall, she reported, with the difference
from the majority reaching significance at P<0.01 for all three comparisons.

But there was no difference at baseline in bone mineral density, or in such
factors as smoking, heart attack, or dementia.

Over the follow-up, the researchers found:

The risk for incident nonvertebral fractures was increased by 34% for those
with low sodium, a difference that was significant at P=0.009.
There was a trend of similar magnitude for incident hip fractures, but it did
not reach significance.
Overall, the risk for vertebral fractures was increased by 61%, which was
significant at P=0.049.
That was driven by a 75% increase in the risk of prevalent fractures,
significant at P=0.037.
But the risk of incident vertebral fractures, while increased by 8%, was not
significant.
The risk of recent falls was increased by 34%, significant at P=0.029, while
mortality was increased by 21%, also significant at P<0.05.
Zillikens cautioned that the findings need to be replicated in other groups,
and said that the mechanism involved remains unknown. But if the results are
repeated, she said, it may be possible to reduce the risk of fractures by
treating the low sodium.

She added that the researchers only had sodium levels from the participants at
baseline and had no prospective information on falls during the follow-up.

The study is "exciting" but it's premature to suggest it should affect
clinical practice, said Elizabeth Barrett-Connor, MD, of University of
California San Diego, who was not part of the study but who moderated the
session at which it was presented.

"First of all, we need to see if someone else can find it again," she told
MedPage Today. If the finding is replicated, she said, "we need to know what
the mechanisms are."

"It's an original observation and there could be lots of different
mechanisms," she added.

Zillikens did not report external support for the study. She said she had no
disclosures.

Barrett-Connor had no disclosures.

Primary source: American Society for Bone and Mineral Research
Source reference:
Zillikens M, et al "Mild hyponatremia as a risk factor for fractures: The
Rotterdam study" ASBMR 2010; Abstract 1092.

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