Last Friday, I went to a lecture at UCL, which was on why life is deadlier for males, delivered by Dr Jennifer Regan from the UCL Institute of Healthy Ageing.
In terms of life expectancy, women constantly outlive men by an average of 5 years. However, the gap is narrowing for people who were born in the last couple of years, so the question was put to us: Will the gender gap eventually close?
And why do women live longer? In the past, it was all about behaviour. Men had more dangerous jobs, such as mining, plus they smoked, and were more aggressive and show-offs, so tended to have more physical fights than women. As time passed, women began to smoke and drink too, and men smoked a lot less, and got less dangerous jobs. Men and women’s behaviour became more similar.
We were also asked what ageing is. According to Dr Regan’s presentation, older people report more contentment, happiness, confidence, wisdom and experience. On the other hand, they also report biological senescence, which is deterioration with age. Older people tend to suffer more from conditions such as dementia, type two diabetes, cancer, sarcopenia, macular degeneration, and osteoporosis.
Ageing is a genetically regulated process. Wood mice can live for up to 3 years, chimpanzees 59 years, and bowhead whales 200 years. The quail and the parrot are both similar in that they are birds, but the quail lives for an average of 10 years, whereas the latter can live for about 100 years. Model organisms can be used to study ageing. Genes can be modified, and the environment can be controlled. Fruit flies and worms tend to be used, as they have short lifespans (3 months for fruit flies and 3 weeks for worms), so more results can be obtained. From various experiments, they’ve found that mutations in insulin signalling pathways can extend lifespans.
Ageing is studied so that we can find treatments for diseases where age is a big risk factor. Treatment of ageing could lead to protection against age-related diseases. We want to extend our health span, but in doing so, we also create the side effect of extending our lifespan. We have a current morbidity period of 20 years. Our goal is to compress this morbidity period, but the likely outcome is that we will simply delay the morbidity period. Would we be able to cope with this economically, politically and in terms of relationships?
Aubrey de Grey, an English theoretician in the field of gerontology, once said that “I think the first person to live to 1,000 might be 50 or 60 already.” So why do we age? Natural selection, or survival of the fittest, links to sexual selection, which links to reproductive success. A classic example of this is the peacock, who has an impressive display of feathers to impress the peahen.
Furthermore, why are sex differences in ageing? Males produce small gametes, whereas females produce large gametes, which require a lot of energy, so are only produced once a month. Sperm basically doesn’t provide anything other than the male share of DNA. Making different investments means that different strategies are used. For example, male deer fight with each other to control female groups, while female deer focus their energy on their young, making them choosy.
Testosterone makes you tough, but there’s a trade-off. Records show that eunuchs in the olden days lived longer than men who weren’t castrated. Since testicles are a major source of testosterone, could it be that testosterone is shortening males’ lifespans? Records also show that intact males died more from infectious diseases. It’s well known that males are more prone to infection: dysentery, meningitis, pneumonia flu and tetanus are a few examples.
Wild male mammals have a higher parasite burden, as testosterone suppresses the immune response. Testosterone is directly linked to parasites, fungi, bacteria, and viruses, and regulates genes and behaviours that affect susceptibility to infection. Women have a more active immune system than men. For example, in the 1918 Spanish flu, women survived much better. In addition, women are less likely to develop sepsis after surgery than men, and this result can be induced in a lab. This is all because oestrogen, a hormone found in females, enhances the immune response.
In conclusion, ageing is genetically regulated. Model organisms will help us to understand ageing better as more research is conducted. Dr Regan’s interest is how early life infections can affect lifespan.