All men tend to produce less of the male hormone testosterone as they grow older, but some men produce less than others, which is why there was so much interest--and concern--last week about a new study that showed that older men with particularly low levels of testosterone circulating in their blood may be at higher risk of developing Alzheimer's disease. Other studies have shown that testosterone improves performance on cognitive tests, but this is the first to suggest that low levels of circulating testosterone may provide a warning--as much as a decade in advance--that a man will develop Alzheimer's.
The...