Doctor's Casebook:A salute to old age and the biological elite

The media has been full of tributes to him, and to his lifetime of duty and devotion to his wife, Her Majesty the Queen. He had been unwell in hospital for a month and had only recently been discharged home.

Gerontology is the study of ageing. It is a field in which we still have many questions, but few answers. One thing that does seem to stand out, however, is that people age at different rates.

Biological age is not the same as chronological age. Those people who live long lives like Prince Philip and the late Captain Sir Tom Moore are undoubtedly members of the biological elite.

Their biological age has never been in phase with their chronological age.

There are broadly speaking two categories of theories about ageing. Firstly, programmed theories. These are theories that imply an individual has a biological timetable that is regulated by changes in gene expression.

Essentially, they suggest that particular organ systems such as the nervous system and immune system begin to fail, so allowing degeneration to begin.

Secondly, a category called damage and error theories. These cover the impact of the environment, harmful habits we develop and biochemical theories, including such processes as free radical reactions.

This is why antioxidants seem so important to health. The cross-linking or glycosylation theory of ageing also suggests that binding of sugars to proteins impairs their ability to function.

It is suggested that senile cataract formation and the thickening and yellowing of skin with age are examples of such cross-linking.

Common sense would tell us that there is probably something in all of these theories.

But when we look at the biological elite, those people like Prince Philip and Captain Sir Tom Moore, there are additional factors. The characteristic seems to be self-discipline.

They never seem to have abused their bodies. They seem to have a more optimistic view of life and they tend not to over-indulge in anything, and seem to have thrived on smaller quantities of food than what might be considered normal.

We should look to our centenarians for inspiration.