A Secret to Women's Longer Life Revealed New study finds that women's immune systems decline more slowly By Evann Gastaldo, Newser Staff Posted May 15, 2013 8:26 AM CDT 26 comments Comments White blood cells. (Shutterstock) (Newser) – Why do women typically walk the Earth longer than men? According to a new Japanese study, the immune system is to thank—or blame, depending on your gender. It found that men's immune systems weaken more quickly than women's, leaving males more susceptible to disease, the BBC reports. Researchers believe this could be due to the fact that female sex hormones (like estrogen) give the immune system a boost, the Telegraph reports. The nuts and bolts of the study: Researchers took blood samples from 356 healthy men and women ranging between ages 20 and 90. They expected to see white blood cells decrease in number with age, as shown in previous studies, and did. But here's the surprising part: They found that two white blood cells that are key to immune function, T-cells and B-cells, declined more quickly in men than in women; men also experienced a quicker decline in the levels of two cytokines, which help the body respond to disease. Meanwhile, two other types of immune system cells increased with age, and women experienced a faster rate of increase than men.