Declining blood levels of two molecules that occur naturally in the body track closely with worsening Alzheimer's disease, particularly in women. Levels were found to drop gradually, from women with no signs of memory, disorientation, and slowed thinking to those with early signs of mild cognitive impairment. Decreases were more prominent in women with moderate or severe stages of the disease. Declines in men were evident in only one molecule, revealing a disease-specific difference between the men and women.