New Research Evidences Suggest Key Role Of Immune System In Longevity

Another hypothesis, and one that has been the object of a very recent study conducted by Japanese investigators, attributes women’s longer lifespan to age-related differences in the immune system between genders.

In this study, both women and men presented with lower levels of white blood cells as they aged – a decline that is all but surprising. The real finding came when the researchers took a more careful look at the lab data. As it turns out, the rate of decline of most T-cell and B-cell lymphocytes, the two main types of white blood cells, was faster in men, while men also showed a more rapid age-related decline in two cytokines (which are molecules involved in the immune response). And if the overall levels of lymphocytes decreased with age, two specific types, the CD4 T-cells and natural killer cells actually appear to proliferate with age. Once again, this proliferation occurs at a higher rate in women than in men.

Higher level of estrogen might be another factor contributing for longer survival

Still, theories abound. Yet another hypothesis states that female sex hormone estrogen somehow protects females at a cellular level, so that females - whether they are rats or mice or whales or bats or humans - will be generally longer lived. The positive effects of estrogen are wide-ranging and include maintaining muscle strength and promoting skeletal muscle repair, glucose and lipid metabolism, and lowering the risk of cardiovascular disease, particularly atherosclerosis. In addition, estrogen reduces serum levels of low-density lipoprotein (LDL or ‘bad cholesterol’) and increases serum levels of high-density lipoprotein (HDL or ‘good cholesterol’).

A recent report of striking longevity in eunuchs at the Korean Imperial court is strongly suggestive of a role for testosterone in limiting male lifespan in humans.

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Genetics may play a role too

And if we look as deep as to the genetic determination of sex, there also seems to be some sort of link. In species that have XX/XY chromosomal determination, such as most mammals, the X chromosome is ‘unprotected’ in the male, implying that if he inherits a mutation on the X chromosome, there is no second, normal copy of the gene on the Y chromosome to compensate. Thus men are more exposed to recessive X chromosome-linked diseases, such as as Duchenne muscular dystrophy.

As we have seen, theories on why women live longer than men abound. The scientific literature is full of attempts at providing with a single, mechanistic explanation for this widespread observation. Nevertheless, it seems that the matter is way too complex for a definite conclusion to be drawn at this stage. We now know that a myriad of pathways and physiological characteristics are at play. Further research in experimental model systems, for example, is a possible method for scientists to discover the secret of female longevity.