Why do women live longer than men? According to a 2010 Scientific American article, women outlive men by about five to six years. There are roughly six women to every four men at age 85. At 100, the ratio is more than two to one. According to some scientists, this is because a majority of women, in comparison to men, lead healthier lives. For instance, women smoke and drink less than men. Evolutionary scientists argue that men, just like other male animals, have to compete for female attention. As a result of this, men are more aggressive and thus prone to engage in risky and sometimes violent behaviour, ultimately raising their overall death rate.
However, according to a new study, the precise reason why women outlive men is that their immune system ages slower than that of men’s. The study, which was conducted by Tokyo Medical and Dental University and published in Immunity & Ageing, found that the increased susceptibility of men to disease shortens their lifespan.
For the study, the researchers analysed the blood samples of 356 healthy men and women aged between 20 and 90. They wanted to check if age-related changes in the immune system could be affecting the difference in average life expectancy between men and women.
The study found that the number of white blood cells per person, in both sexes, declined with age, as expected. However, it found certain differences in the immune system of men and women. In men, the rate of decline of T-cells, which perform the task of protecting the body from infection, and of B-cell lymphocytes, which secrete antibodies, was faster. Males also displayed a more rapid age-related decline of two cytokines. These are molecules that interact with cells of the immune system to regulate the body’s response to disease.
The researchers write in the journal: ‘The process of ageing 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.’