AGEING: PQPULATIONS, ORGANISMS AND CELLS.

There are affiliate links in this article.If you click and buy the products,commissions will be earned by me at no cost to you.Thanks for the anticipated understanding..

Ageing is a reproducible and highly recognizable process. You only have to look at friends or TV and cinema stars and you can guess their age usually correctly to Within a few years. But the process is very variable. Some people look much older than their years and others much younger. What is clear is that the same changes occur but at different rates.

An ageing population is defined epidemiologically as one in which there is an increase in age –specific death rates. Death rates start to increase remarkably early in life from the early 20s. Medical and nursing students are already well into the ageing process by the time they have finished their courses! Male rates are higher than female rates but this is usually attributed to men’s tendency to smoke, drink too much and take part in risky activities, like riding motorcycles.

 

AGEING OR DISEASE?

What is ageing?

Ageing is a developmental process, part of the cycle beginning at conception and ending with death. Ageing is not the same as disease, but diseases do become more common among older people. This association between ageing and disease is  the cause of much confusion about what is in store for us as we age. And it is a confusion that tends to affect doctors more than their patients. Patients complain to their doctors of pain and immobility only to be told that its due to their age – which is seldom true.

For example, a patient develops difficulty getting in and out of the bath. This may be due to ageing: a decline in the number of functioning muscle cells leading to Weakness. It may be due to a disease affecting the peripheral nerves, a metabolic disease (eg. diabetes or osteomalacia), or disease of large joints (e.g. osteoarthritis).

 

 

MEDICAL CARE VERSUS

SOCIAL CARE

In the example given, a social model of care would lead to assessment of the problem and provision of a bath board and rails around the bath. A medical model would sort out disease from ageing, and attempt to treat any underlying disease process. A collaborative approach would lead to both treatment (in its widest sense) of any disease underlying the disability and provision of any aids or lifestyle modifications to overcome the disability. Collaboration and teamwork are the hallmarks of health care for elderly people.

The medical model is often criticized for its preoccupation with diagnosis and drug treatment, for its focus on organ systems, and for its super-specialization. But the medical model has much to offer elderly people. Disease does become so much more common with increasing age and deserves to be diagnosed and treated. Despite much disease being Chronic, degenerative and irreversible, a great deal can be done for its disabling and handicapping consequences. However, the doctor is seldom able to combat disease consequences single-handedly. Teamwork is necessary, and the concept of diagnosis has to be extended to assessment, treatment becomes management, and prognosis becomes monitoring and evaluation of achievement of goals.

An exclusively social model, bypassing the question is this problem due to disease or not?’, is just as inadequate for solving problems as a solely medical model. Collaboration is essential, and is best achieved through comprehensive services for elderly people.

 

IMPAIRMENTS, DISABILITIES

AND HANDICAPS

Although these terms are often used interchangeably, they do have precise meanings that can help in understanding what  comprehensive care means.

 

Impairment:

Damage caused to a cell, organ or system by a disease

Process.

 

Disability:

Difficulty in carrying out tasks - such as activities of daily

living, or driving a car -that are a consequence of the

disease.

 

Handicap:

Effect the disease has on the lifestyle of the patient -- the

disadvantage caused by the disease

 

Some treatment may reduce impairment. For example, exercise against progressively increased resistance may increase muscle strength and joint flexibility in an arthritic joint. The measurement of muscle strength and joint range of movement would be the best indicators of success and failure.

Other treatments may have no effect whatsoever on the impairment caused by disease. For example, no amount of physiotherapy will reduce the amount of brain damaged by a stroke. However, therapy may well reduce the time taken to get independently mobile again. In this case the correct measure of success is the measure of an aspect of disability - mobility.

For many diseases, neither the impairment nor the disability is affected by rehabilitation teamwork. This is not to say that useful management is impossible. It is this type of patient who is often viewed as a ‘no-hoper’ on an acute medical ward, but is transformed into a ‘major rehabilitation challenge’ on a health care of the elderly ward! There is no special magic in this, but simply a more realistic appraisal of the possibilities by the team, and a tendency to focus on handicap or lifestyle.

It is vital that services for elderly people understand their contribution to the overall picture, and do not attempt to demonstrate the supremacy of their particular skills over those of other equally needed and important skills. The impairments, disabilities and handicaps framework is a useful way of ensuring a comprehensive approach.

 

POPULATION AGEING

Most people know that we are living in an ageing society, indicated by such phenomena as the greying of America, the rise of the Grey Panthers, the growth of retirement and nursing homes. One of the major justifications for health care for elderly people is the increased number of them. This is highlighted by the tremendous increase in the number of centenarians in the UK who receive a birthday telegram from the Queen each year.

The spectacular population changes over the last century are due to two major factors: declines in fertility and decreases in death rates at all ages. Fertility declines because of a smaller number of babies born and increasing maternal age at first birth. These trends began with the industrial revolution and the associated socio-economic development which made large families less advantageous. Family planning has accelerated the process in many developing countries. A willingness to use family planning methods depends on culture, education and religion, but with increased economic wealth a move to smaller families is inevitable. Prosperity is no longer measured by the size of the family.

Deathrates have also declined dramatically over the last century and the decline has affected the old and the young. The explanation for the decline is found in improved nutritional status, better social and economic conditions and the major public health reforms of clean water and sewage disposal. Medical care was not responsible for the changes. Over the last century, the world has - despite appearances - become a healthier place to live, and more of us are doing it for longer.

It is paradoxical that an ageing population is a consequence of living in a successful society that ensures that babies do not die, that promotes the autonomy of women to control their fertility, and that has reduced the chances of death over the entire lifespan. The large numbers of elderly people are our heritage, and the rewards of socio-economic development. Turning back the clock to the turn of the century when old age was not a ‘problem’ is impossible, and countries where high fertility and infant mortality rates occur do not wish to stay at that point in development. A better understanding of ageing, removing the myths and stereotypes, and at improving the health, social and economic lot of elderly people are keys to the solution.

 

RECTANGULARIZATION OF SURVIVAL

Survival curves have changed in shape over the  last few hundred years. This process has been called the ‘rectangularization of survival’.  One Of the Consequences of the increased chances of survival is that average life expectancy begins to approach maximum lifespan. The maximum lifespan is around 115 years, but the average expectation of life at birth is around 80 years for women in the most successful countries (Japan, USA). Deaths, instead of being spread across a fairly long part of the human lifespan, are now compressed into a shorter time. This should mean that people are sicker for a shorter time as well, and in essence will tend to be healthier for longer. 

 

This optimistic scenario for the next century may come true, but for the foreseeable future it is more likely that increased survival will be associated with increased risk of non-life-threatening, but disabling chronic diseases. At present, the rectangularization of survival is associated with a far greater number of very old people, which is producing an explosion of morbidity, and an increased pressure on health and social care resources.

 

INDIVIDUAL AGEING

We have become used to hearing how things change, usually for the worse as we get older. Blood pressure goes up with age, hearing and vision get worse, bone density declines, intelligence declines, and so on. As humans grow and develop they reach a peak in physiological and anatomical capacity in their late teens, but subsequently capacity declines. It seems to matter little which type of capacity is considered: muscle strength, stamina, lung volume, kidney function, brain volume. All show age-related declines.

 

Cross-sectional and longitudinal studies

There is a large trap for the unwary here. Most of the studies of age-related declines are not really studies of ageing at all. In fact they are studies of a number of young people, a number of middle-aged people, and a number of old and very old people, all examined at the same point in time. None of the subjects has aged at all during the study, they are simply of different ages at the time of the study. Such studies are cross-sectional - snapshots -- and we have to make some assumptions before we can accept that they are a good indication of true ageing changes.

The first assumption is that what is true for 60-year- olds now will be true for 50-year-olds in I() years’ time. We have to believe that the effects of belonging to a group _ or cohort - of people born around the same time, and living through a unique set of life experiences, is not relevant to the factor (e.g. blood pressure, brain volume) under study. The effects of belonging to a cohort have been extremely important over the last century. For example, women born at the turn of the century had far fewer chances for marriage than those born later because of World War I. Men who went to light in that war, if they survived, were subsequently much more likely to die of lung cancer because of smoking habits acquired during the war. Cohort effects can be powerful, and are impossible to detect in a simple cross-sectional study.

The second assumption to be made is that conducting the study at a particular point in time is irrelevant. It is unlikely that a cross-sectional study of changes in, say, muscle strength and age conducted in 1989 would come up with different results to one conducted in 1990. But over a period as short as five years, differences in the relationships between blood pressure and age have been found.

A third assumption is that older subjects are disease free. For example reductions in air flow with age may be due to changes in the elasticity of the lung, but inclusion of older people with chronic bronchitis will lead to much greater age-related reductions in air flow due to the combined effects of age and disease.

The reason that scientists continue to examine the effects of age by cross-sectional studies is because such studies are generally much cheaper than cohort _ follow-up or longitudinal – studies. Provided such studies give more or less the same answer, no harm is done. However, in the few cases where comparisons can be made between cross-sectional and cohort studies, the answer can be strikingly different. The best example of a discrepancy between cross-sectional and cohort effects are the changes in performances on intelligence tests at different ages.

The general conclusion of cross-sectional studies is that intelligence declines with age, supporting stereotyped images of confused old people. The cohort changes are strikingly different: far from getting more stupid over the years, people tend to improve on some aspects of intelligence and remain more or less the same on others, and decline in only a few areas (Fig. 1.3).

 

So why the difference? It probably arises out of a cohort effect. People born in 1920 had limited schooling and access to educational mass media like television and newspapers. People born in 1930 enjoyed better education. When studied cross-sectionally in 1990, those born in 1920 are 70 years old and will do worse on the intelligence tests than the 60-year-olds born in 1930.

 

Describing true ageing effects

Describing true age effects requires complicated studies of successive cohorts of people over long periods of time – so – called  ‘cohort-sequential’ studies. This is because a single cohort invariably experiences a unique set of circumstances thrown up by the age they live through (e,g. wars, economic depression) – period effects that have an impact at all ages. The task is to separate the effects of ageing from the effects of the era in which people age. This can only be done by studying a succession of cohorts to determine whether age-related changes are consistent across each cohort. Very few studies like this have ever been set up, so we have to make do with the information from cross- sectional studies. However,  never take such information at face value: always ask – could this be due to cohort or time period effects?

Statistically, ageing can be defined as facing an increased risk of death over time. What does this mean? If you take 1000 glasses and count how many ‘survive’ over a period of years you would not be surprised if many of them ‘died’. The death rate of the glasses can be calculated as the number broken divided by the number at the outset. However, a small adjustment has to be made for the fact that once a glass is broken it cannot be broken again, and must be removed from the denominator of the calculation of the ‘death’ rate. If this is done, a glass survival curve can be drawn, giving the percentage of glasses surviving at the end of each year (Fig. 1.4).

 

Now glasses do not age: their molecules contain no ability to replicate, they are inert. And yet a population of glasses appears to ‘age’, and has a survival curve. The key is that the rate of breakage of glasses is constant – there is a constant accident hazard that systematically removes glasses until they are all gone. Death rates of populations do not show a constant rate, but an ever increasing rate with increasing chronological age. This gives population survival curves their characteristic rectangular shape. The point at which death rates start to rise can be viewed as the start of human ageing. It comes as a surprise to see how early in life this starts - late teens, early 20s!

Many factors change as people get older. Some people get richer, most get poorer. Their homes age with them, often becoming hazardous. Social contacts and status within the family alter. These factors are called ‘extrinsic’.

 

 

 

THE MECHANISMS OF

HUMAN AGEING

Ageing has fascinated scientists, philosophers and poets for centuries. What is ageing? Why do we age? What is ageing for? How can we slow down or stop the process? These are weighty questions and need unravelling into smaller questions that are more easily tackled. An inherent difficulty in the study of ageing is that the findings from easy-to-study animal species (bacteria, paramecium, mice) are not directly transferable to humans.

Strehler’s framework of ageing states that, for a process to be truly due to ageing (rather than due to pathology), it must be universal, progressive, intrinsic and deleterious.

Cellular and molecular ageing

Are you struggling to lose weight no matter how much you diet or exercise? 

Scientists have discovered a remedy LEARN MORE

Cells get old and die just like the whole organism, but they do it at a more rapid rate. The cells of the epidermal layer of the skin shed themselves within a few days. The red blood cell lives for about four months. Theories of ageing have to accommodate the following observations about ageing.

Hayflick limit to cell division

The Hayflick limit is the number of cell divisions that human fibroblasts - connective tissue cells – grown in a cell culture can undergo before stopping. They stop after about 50 cell divisions. By contrast, many human cancer cells continue to replicate unchecked, and are called immortal.

 

Mercyvill.