Women live longer than men and it is all about having a better immune system. A study published on "Immunity & Ageing" on May 15 cites the slower decline of immunological parameters such as the levels of white blood cells in women as the main reason why they outlive the opposite sex.

The study titled "Slower Immune System Ageing in Women Versus Men in the Japanese Population" was able to establish that the immune system of women age more slowly. The Japanese proponents suggest that testing one's immune function is a good measure of true biological age.

"Age-related changes in various immunological parameters differ between men and women. Our findings indicate that the slower rate of decline in these immunological parameters in women than that in men is consistent with the fact that women live longer than do men," the abstract of the study points out.

The immune system is responsible for fighting diseases ranging from a common cold to dreaded conditions such as cancer. The immune system may also cause illnesses if not properly regulated.

Prof. Katsuiku Hirokawa, from the Tokyo Medical and Dental University, and his team analyzed blood samples from 356 male and female subjects between 20 through 90 years old.

Hirokawa and his colleagues looked into the levels of white blood cells (WBC). They also measured the levels of cytokines, molecules that interact with the human immune system to respond to diseases.

The health experts confirmed that the level of WBC of a person goes down as one ages regardless of gender. This was also the conclusion of previous studies.

A closer look into the immunological parameters revealed significant differences between the levels of T-cells and B-cells in men and women. The T-cells are responsible for fighting infection while the B-cells secrete the antibodies. The decline of these important lymphocytes is faster in men than women.

Women, on the other hand, showed higher levels of natural disease fighting cells and CD4 T-cells as they grow older.

"The process of aging is different for men and women for many reasons. Women have more oestrogen than men which seems to protect them from cardiovascular disease until menopause. Sex hormones also affect the immune system, especially certain types of lymphocytes. Because people age at different rates a person's immunological parameters could be used to provide an indication of their true biological age," Hirokawa expounded in a press statement.