Why women live longer than men

Why is the life expectancy of an American woman still five years longer than for an American man?  According to new research from the Tokyo Medical and Dental University, it has to do with the way in which the immune system ages.  The study found evidence that a woman's immune system ages more slowly than a man's, protecting her against disease for a longer period of time.

To conduct this study, the researchers analyzed blood samples from 356 healthy men and women between the ages of 20 and 90.  They measured levels of white blood cell and molecules called cytokines, which help regulate the body's response to disease.  In both sexes, white blood cells declined as a person aged.  However, men showed a faster decline of T-cells and B-cells, which protect the body from infection and secrete antibodies to fight infection, respectively.  Men also exhibited a faster rate of age-related decline of two important cytokines.

Scientists hope that testing the strength of the immune systems in both men and women could provide a more accurate picture of a "true" biological age and the stages of aging.

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Sourced from: BBC News, Biological clue to why women live longer than men