The secret to why women live longer than men is due to their superior immune systems, according to a new study published in the journal Immunity & Ageing.
The study, conducted by Professor Katsuiku Kirokawa and his colleagues of the Tokyo Medical and Dental University, revealed that women live longer than men partly because their immune systems age more gradually and are able to fight off infections for a longer time.
The Japanese scientists discovered that as the body’s defenses diminish over time, men’s elevated risk of disease can shorten their lifespans. Therefore, tests of immune function could reveal true biological age.
The investigators aimed to examine whether age-related changes in the immune system could be the reason for the difference in average life expectancy between men and women.
In the UK, the average life expectancy for men is 79 years and 82 years for women. In Japan, this gap between men and women is even greater, with women living approximately six years longer, on average.
The researchers analyzed blood samples from 356 healthy women and men who ranged in age between 20 and 90 years. They calculated levels of white blood cells and molecules called cytokines, which interact with immune system cells to control the body’s response to disease.
Results showed that in both males and females, the number of white blood cells per person fell with age, which the scientists had expected.
Closer analysis showed that there were two differences between men and women in parts of their immune systems – B-cells, which produce antibodies, and T-cells, which protect the body from infection.
The rate at which T-cell and B-cell lymphocytes fell was faster in males, and men also exhibited a quicker age-related reduction in two cytokines.
Additionally, two kinds of immune system cells that fight intruders – CD4 T- cells and natural killer cells – increased in number with age, with a greater rate of increase in females than in males.
Therefore, the authors believe that a person’s immunological framework could indicate a person’s real biological age.
Prof Hirokawa concluded:
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.”
A study conducted by the MRC/CSO Social and Public Health Sciences Unit in Europe, suggested that in 60% of cases where females outlive males, it is 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.
Written by Kelly Fitzgerald