The secret to living longer is having a better immune system, suggests new research published in the journal Immunity & Ageing.
A study conducted by Professor Katsuiku Kirokawa and his colleagues of the Tokyo Medical and Dental University revealed women tend to live longer than men, at least partly because their immune systems are able to fight off infections for a longer period of time.
The Japanese scientists found that as a body's defenses diminish over time, there is an elevated risk of conditions that can shorten lifespans, reports Medical News Today.
The investigators set out to test whether age-related changes in the immune system could help account for the difference in average life expectancy between men and women.
In the United States, while the average lifespan of all residents an approximate 78 years, American women live to an average age of 81 years while men last an average 76 years, according to data supplied by National Geographic.
The scientists examined blood samples taken from 356 healthy women and men who ranged in age between 20 and 90 years and calculated levels of white blood cells and molecules, called cytokines, which interact with immune system cells to manage the body's response to disease.
Results revealed the number of white blood cells per person fell with age in both males and females, which is what the scientists anticipated.
However, a closer analysis revealed two significant immune system differences between men and women, mainly in B-cells, which produce antibodies, and T-cells, which protect the body from infection.
The study team found T-cell and B-cell lymphocytes, or, white blood cells, fell faster in males. At the same time, men showed a quicker age-related reduction in two types of cytokines.
The study determined the numbers of two other kinds of immune system cells increased with age, but there was a greater rate of increase in females than in males.
Hirokawa and his team concluded "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."
A study conducted by the Chief Scientist Office and Medical Research Council's Social and Public Health Sciences Unit in Europe suggested that in 60% of cases where females outlived males, it was due to smoking.
A separate study in the Journal of Women's Health suggested that although women live longer than men, they experience a greater incidence of disability during old age than men do.