P‐156: Low serum bioavailable testosterone levels are associated with mild cognitive impairment in Chinese older men

dementia to their unaffected twin sibling, thus testing the importance of depression as a risk factor while controlling for genetic background and early shared environmental experiences. Results: Case-control results showed that individuals with a history of depression were 1.72 times more likely to develop dementia than those without a history of depression (CI 1.07, 2.76, p 0.0212). Risk was greater for depression when the first episode was closer to dementia onset; for each one-year increase in the difference between age of onset of depression and age of onset of dementia or censored age, the risk of developing dementia decreased by 8.1% (p 0.0031). Co-twin control analysis found that individuals with a history of depression were 3.19 times more likely to develop dementia (CI 1.35, 7.55, p 0.0082). Conclusions: These findings suggest that depression is a prodrome, rather than a risk factor for dementia.