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Phosphatidylcholine is a ubiquitous phospholipid. It contains a phosphocholine (PC) headgroup and polyunsaturated fatty acids that, when oxidized, form reactive oxidized phospholipids (PC-OxPLs). PC-OxPLs are pathogenic in multiple diseases and neutralized by anti-PC IgM antibodies. The levels of anti-PC IgM increase as the levels of PC-OxPLs increase and, in humans, are inversely correlated with the incidence of cardiovascular diseases and steatohepatitis. PC-OxPLs also decrease bone mass in mice. Overexpression of anti-PC IgM ameliorates atherosclerosis and steatohepatitis, increases bone mass in young mice, and protects against high fat diet- and age-associated osteoporosis. We investigated the relationship between anti-PC IgM plasma levels and bone mineral density (BMD) in a cross-sectional study of 247 participants [mean age: 65.5 (± 8.6) years] without medical conditions known to influence BMD or antibody production. Anti-PC IgM levels negatively correlated with both T- and Z-scores at the lumbar spine, femur and, to a lesser extent, the forearm. These correlations were maintained after adjustment for age, race, and sex. These results raise the possibility that higher levels of anti-PC IgM in patients with lower BMD reflect exposure to higher levels of PC-OxPLs, which are known to affect bone mass, and could be a novel risk marker for osteoporosis. [ABSTRACT FROM AUTHOR]