May 16, 2013
Sturdier Immune System May Explain Why Women Live Longer
redOrbit Staff & Wire Reports - Your Universe Online
Women's immune systems age more slowly than men's, which may contribute to their longer average lifespans, according to new research published Wednesday in the journal Immunity & Ageing.
The study by Japanese researchers found that levels of key white blood cells responsible for fighting off infections decline faster in ageing men than they do in women.
The average life expectancy in the US is 76.0 years for men and 80.9 for women, according to figures from the US Centers for Disease Control and Prevention. In some countries, such as Japan, the disparity is even greater, with women living on average nearly six years longer than men.
A number of theories have attempted to explain this gap, including a recent finding that the tiny, energy-producing mitochondria in cells tend to have fewer faults in women than in men.
But the current study has uncovered another potential explanation for the gender-longevity discrepancy, finding that levels of white blood cells and cytokines, which help to carry messages in the immune system, decrease faster in men than in women.
The researchers believe this might be due to female sex hormones such as estrogen, which can boost the immune system´s response to infections.
“Women have more estrogen than men, which seems to also protect them from cardiovascular disease until menopause. Sex hormones also affect the immune system, especially certain types of lymphocytes,” said the study´s lead author, Professor Katsuiku Hirokawa at Tokyo Medical & Dental University.
The researchers examined the blood of 356 healthy men and women between the ages of 20 and 90 years old, and examined levels of white blood cells and cytokines. In both sexes, the number of white blood cells fell with age, but two key types of cells —T-cell and B-cell lymphocytes — declined slower in women than in men. Both of these white blood cells are involved in fighting off bacterial infections.
The researchers also found that another type of cell that attacks viruses and tumors — CD4+ T cells and NK cells — increased with age, with a higher rate of increase seen among women than men. Additionally, men showed a decline in two types of cytokines that help to keep the immune system under control and prevent inflammation from damaging surrounding tissue. Finally, the researchers also observed an age-dependent decrease in red blood cells for men, but not women.
“It is well known that ageing is associated with a decline in the normal function of the immune system, leading to increased susceptibility to various diseases and shortened longevity,” Hirokawa said.
“However, specific dysfunctions in the immune system directly responsible for this have yet to be identified. Among the important factors, T cells are central to the immune response, and their function is significantly altered with increasing age."
The difference in the aging of immune systems between men and women is just one of many biological processes that alter as we grow older, Hirokawa explained.
"The process of aging is different for men and women for many reasons. Women have more estrogen than men which seems to protect them from cardiovascular disease until menopause. Sex hormones also affect the immune system, especially certain types of lymphocytes.”
Hirokawa said the study could someday help experts predict the "biological age" of people based on the state of their immune system.
"Because people age at different rates, a person's immunological parameters could be used to provide an indication of their true biological age.”