The life expectancy of humans has more than doubled since 1900. Global life expectancy has increased from 31 years in 1900 to 73.2 years in 2023 and is expected to further increase to 77.1 years in 2050.

Also increasing is the number of people reaching the age of 100 or more.

In the last 100 years, the life expectancy of Australians has increased by 20 years. 

There are now about 4,250 people aged 100 years or older living in Australia. By 2050, statisticians believe Australia will have more than 50,000 people aged 100 and over. For many seniors, this means more years of being active and being a valuable part of the community. But, of course, that means there will be a lot who don’t live that long.

Why and how some people live to such a ripe age and others don’t is one of medical science’s continuing mysteries.

Latest research has identified the functioning of our immune system, and cell health, as crucial to longevity. Our immunity, designed to protect us, changes over time and can lead to poor functioning in older people – increasing vulnerability to infection, autoimmune disease, and cancers.

Another influencing factor is inflammation, which also increases with age and is linked to diseases including Alzheimer’s disease.

Researchers from Tufts Medical Center and Boston University School of Medicine have found that centenarians possess a unique immune cell composition and activity, giving them a highly functional immune system and allowing them to live longer.

Centenarians tend to have delayed onset of age-related diseases such as cancer, stroke, and cardiovascular disease. This suggests that their immune systems remain healthier for longer compared with other people. But how do they do it?

A previous study in Japan found that immune cells in centenarians differed from that in younger people. It isn’t clear if these results generalise to other ethnicities.

The American study looked at 102,000 cells from 66 people, including people in their 30s and 40s, for comparison.

The researchers observed a decreased ratio of lymphocytes (a type of white blood cell that includes T cells and B cells) to myeloid cells (part of the innate immune system, including monocytes and dendritic cells) with age. This was an expected change with ageing.

Among the lymphocytes, centenarians had more B cells (which produce antibodies) and fewer T helper cells (which help coordinate other immune cells) compared with younger people. This change was unique to centenarians and did not occur in older non-centenarians.

This suggests that over their lifetimes the centenarians developed faster, more effective immune responses to infections. For example, B cells respond faster to infections than T cells.

The team found 35 genes whose expression changed in immune cells with age, including genes involved in repairing DNA damage.

Another 25 genes appeared to be expressed only in centenarians. This included the gene S100A4, which has been implicated in ageing-related diseases and longevity.

So, it could be concluded that centenarians’ longevity is the result of specific immune adaptations –protective factors that enable them to recover from disease and reach extreme old ages.