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SEONGNAM, South Korea, March 23 -- Low bone mineral density may increase the risk of benign positional vertigo, researchers found.

Patients with osteopenia had double the risk of the condition unrelated to head trauma or other known causes (P=0.011), Ji Soo Kim, M.D., Ph.D., of Seoul National University Bundang Hospital, reported in the March 24 issue of Neurology.

In the case-control study, osteoporosis tripled the risk of idiopathic benign positional vertigo (P=0.007).

These findings add to evidence from animal and limited observational studies implicating calcium metabolism in this common cause of dizziness, they said.

The sensation of vertigo comes from shifting debris in the inner ear canals. These particles are composite calcite crystals that break off from calcium carbonate deposits.

Why this happens isn't clear, the researchers said, but because bone contains 99% of the calcium found in the body, a link between bone health and vertigo has been suspected.

So, the researchers looked at bone mineral density among 209 consecutive patients -- 142 women and 67 men -- diagnosed with idiopathic benign positional vertigo and seen at Dr. Kim's hospital over a one-year period.

These cases were compared with a matched group of 202 controls seen for bone mineral density measurement at the same hospital but who had no history of dizziness.

The researchers found the lowest bone mineral density T scores among cases compared with controls for both men (-1.1 versus -0.7, P=0.030) and women (-1.7 versus -1.0, P<0.001).

Likewise, both women and men with benign positional vertigo had significantly higher rates of low bone mineral density than controls (P=0.036 and P<0.001, respectively).

The findings included:

• 47.2% of female cases versus 33.3% of controls had a T score in the osteopenic range between -1.0 and -2.5
• 40.3% of men with the condition versus 27.4% of controls had osteopenia
• 25.3% of female cases compared with 9.4% of controls had osteoporosis with a T score of -2.5 or less
• 11.9% of male cases versus 5.7% of controls had osteoporosis

After adjustment for age, sex, alcohol, smoking, and high phosphate levels, low bone mineral density was the only significant risk factor for idiopathic benign positional vertigo (HR 2.0 for osteopenia, P=0.011, and HR 3.1 for osteoporosis, P=0.007).

Although bone mineral density was depressed among women with benign positional vertigo whether younger or older than 45, women with recurrent episodes of vertigo had significantly lower bone T scores than those diagnosed with their first episode (-2.1 versus -1.6, P=0.035).

The researchers noted that prior studies have shown a sharp rise in benign positional vertigo incidence among women in their 50s compared with incidence patterns in men.

"This steep increment may reflect that women experience an abrupt reduction in bone mass around menopause due to an estrogen deficiency, whereas men lose bone in a steady manner," they wrote.

Estrogen ranks high among the hormones that influence calcium and bone metabolism, the investigators said.

Estrogen deficiency may change the internal structure of calcium carbonate deposits in the inner ear and make them more likely to break off, and increased free calcium circulating in the body may make it more difficult to dissolve this debris, they said.

However, hormonal changes around the time of menopause cannot be the only cause of benign positional vertigo, because bone mineral density was also decreased in men with the condition, the researchers added.

Dr. Kim reported support by the Brain Korea 21 project in 2006. The researchers reported no conflicts of interest.

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