Jane Walkinton, of Nga Tawa School, asks :-

What causes aging?

Richard Sainsbury, the Professor of Health Care for the Elderly at the Christchurch School of Medicine, responded

The exact cause or causes of ageing are not known. There is general agreement that ageing is to some extent determined by the genes we are born with. Each animal species has a specific lifespan. Marion's tortoise can live over 150 years. Golden hamsters live two to three years. The maximum recorded lifespan in humans is 115 years. In many species females live longer than males. In humans there has been a marked increase in life expectancy during the 20th Century.

There are a number of theories about what causes ageing. An early theory suggested that humans had a fixed amount of energy available to them and when this is used up death follows. If this were true, then higher mortality rates would be expected amongst the most active people which, of course, doesn't happen.

Another theory called the 'free radical theory' suggests that energy producing processes within cells make toxic substances called 'free radicals'. Over time the cell becomes less able to deal with these until it is permanently damaged.

Another experiment has shown that cells from the human body are capable of only a cer- tain number of divisions. They cannot reproduce indefinitely and die off after a certain time. Perhaps this means that the cells in the body are programmed to divide a set number of times and then stop.

It has also been suggested that the RNA in cells, which is responsible for making protein, undergoes gradual change with time which eventually leads to the death of the cell.

The questions of why we age and who adjusts best to ageing are still not answered. What we do know is that life expectancy is increasing as are the numbers of older people. The challenge is to provide them with the best quality of life in their later years.