Basic information on ageing

Ageing is a natural part of our lives and not just ours: from humans to animals, plants and fungi, few organisms are spared. In short, ageing involves gradual changes to our bodies that cause it to work less effectively over time. For example, as we get old, our muscles get weaker and our hearing, eyesight and memory become poorer. We are more likely to get sick, and illnesses can be more severe.

The human body does amazing things. A wide variety of cells together form our organs, for example the liver, the skin and the brain. Every cell is made up of proteins, the building blocks that fulfil all important functions of the cell. In addition, every cell contains DNA - the master code with instructions on how it should grow and what it should do. If the DNA or proteins are damaged, the cell can no longer function properly, stops growing or even dies. As a result, our body ages.

Scientists have defined the basic characteristics of ageing, which they named "hallmarks of ageing". A hallmark is a process that (1) occurs during normal ageing, (2) accelerates ageing when it worsens, and (3) slows, halts or even reverses ageing when it is therapeutically "improved". Five such hallmarks are considered the main causes of ageing:

• Damage to the DNA. The DNA in our cells can be damaged by chemicals or UV rays from sunlight. If this damage is not repaired properly, the cells lose important information they need to function.
• Shortening of the DNA ends. The ends of the DNA (telomeres) are protective caps for our genetic information. However, they wear down and when the cell divides, each time a piece of the telomeres is lost. When they become particularly short, they lose their protective effect. They can no longer correctly pass on the instructions on the DNA and the cell stops growing. If the number of these old, non-dividing cells increases, the body is less able to replace damaged cells - as a result, the organs do not work as effectively as before.
• Uncontrolled switching on or off genes. Our DNA contains numerous genes, or instructions, for proteins that keep the processes in the cell running. However, cells can only work properly if the required genes are switched on in the correct cell: genes for liver function should only be switched on in liver cells, while genes for the skin should only be switched on in skin cells. With age, the signals that control which genes are switched on and off can change, so that specialised cells (e.g. liver or skin cells) work less effectively.
• Damage to proteins. Chemicals or UV rays from the sun can also damage proteins causing them to stop working properly and form toxic clumps, so that the cells die. If this happens in brain cells, it can result in diseases such as Alzheimer's.
• Impaired recycling system. Cells have an efficient recycling system (called autophagy) to dispose of proteins and other molecules when they are damaged. This system works less and less well with age, so that cellular waste accumulates and the cell no longer works properly.

Older people fall ill more frequently and often more seriously than younger people. Their cells are less able to fight viruses and bacteria. In addition, older cells divide more slowly, so the body is less able to replace cells and repair itself. If these cells have important functions in organs, they work less effectively. Unrepaired damage to the DNA accumulates over time. This increases the risk of cells getting out of control and becoming cancerous. All of these reasons make the elderly more susceptible to diseases.

Diseases that become more common with age are known as age-related or age-associateddiseases. Some examples include cardiovascular disease, neurodegenerative disease (e.g. Alzheimer's), cancer and arthritis. Many of these are chronic illnesses that do not yet have any cure so far and which can stop elderly people from leading fulfilling, productive lives.

Our eyesight gradually deteriorates with age. This is due to age-related damage to the cells that make up the lenses of our eyes. While our body is able to constantly regenerate some cell types such as blood, skin or intestinal cells, other cell types such as nerve or heart muscle cells cannot simply be replaced with new cells. Unfortunately, the cells in our eye lenses cannot be replaced - even when they become old and get damaged. Over time, damaged cells accumulate and the lens becomes less elastic and can no longer change its shape as well. As a result, the eye can no longer focus on objects close-up, making it difficult to read. This condition often affects people over the age of 40.

The proteins in the cells of the lens also become more and more damaged over time. They form clumps that cloud the lens cells. This can eventually result in a cataract - a cloudy, whitish lens that makes it difficult to see. Fortunately, cataracts can be treated by surgery. More than half of people over the age of 74 have had a cataract.

Around 25-40% of people over the age of 65 experience hearing loss. People with this condition hear sounds (especially high-pitched sounds) as muffled or unclear. This loss of hearing is caused by age-related changes in the inner ear and brain. Hair cells in the inner ear, which are responsible for perceiving sounds and transmitting them to the brain, become damaged with age. The areas of the brain that process sound also cease to function properly at some point. In contrast to other body cells such as skin or blood cells, hair cells are non-renewable cells - once they are destroyed, hearing loss is inevitable. It is still unclear why only some people suffer from age-related hearing loss. However, it is assumed that a combination of genetic factors, exposure to noise during life, as well as smoking and diseases such as diabetes, cardiovascular, thyroid and kidney diseases contribute to the development of hearing loss in old age.

Everyone ages, but we do not all age in the same way. Some people develop physical problems and illnesses while they are relatively young, while others remain fit, healthy and free of chronic disease well into their 60s and beyond. People who go on to live over 100 years are known as centenarians; most of them are relatively healthy until shortly before they die and do not suffer from chronic illness even in old age.

Healthy ageing is about ageing successfully: to stay healthy as we grow older, so that we remain free of illnesses and our bodies and minds continue to work well in old age. We study the causes of ageing to find out why some people age more healthily than others - and to develop new ways to help us all stay healthy and fit in old age.