Just a Thought
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What this series is about … As we age, keeping physically active is essential. It not only improves the appearance of the body, it also prevents the occurrence of health complications in the future. Join the discussion in this series as we research the various programs that can help maintain a healthy mind and body. |
Staying Young: Hormones
Is it possible to slow or stop ageing – or even reverse it?
The idea of an elixir of youth has fascinated humans throughout history. The unglamorous reality is that our bodies have inbuilt obsolescence. Will the science of anti-ageing ever deliver an extended lifespan? Or is staying healthy in old age a lot simpler than that?
Would you like to live forever? Unfortunately, it is just not possible. Due to a combination of genetics and the effects of the environment on our bodies, we gradually wear out. Fortunately for the survival of the human race, we are replaced – not by new versions of our own bodies, but by our offspring. Also, with the advancement in medical science we are continuing to have a longer lifespan compared to most other animals.
HormonesHormones are chemicals that have specialised functions in the body. As people age, the glands that produce hormones begin to function less, for example, sex hormones, responsible for sexual characteristics and muscle and bone health. Other hormones, like growth hormones and thyroid hormones, responsible for keeping the body's regular functions, also slow down.
The reduced levels of hormones affect the abilities of other organs influenced by hormones. In women, the drop in levels of sex hormones start around the age of 50; ovulation ceases, the uterus and ovaries shrink, commencing the process of menopause. In men, reduced levels of hormones decrease normal sexual functions.
The only people who are spared the process of ageing are those who die young or in early middle age. For the rest of us, the process is relentless. But, how does ageing happen? Peter Lavelle of the Australian Broadcasting Corporation (ABC) discusses some ideas on the biology of ageing, http://www.abc.net.au/health/bio/lavelle_p.htm.
Biology of ageing
As cells and body tissues go about their business–reproducing, staying alive, doing whatever specialist jobs they are programmed to do–they undergo decline from a wide range of sources. The damage can come from outside or it can come from within, from the by-products of metabolism within the cell itself. The cell can fight back, using its own mechanisms to limit the damage, but these mechanisms are not perfect.
Cells can only function within a very controlled environment. They need the right temperature, pH and chemical composition of fluids to survive. Over time the body has developed systems for maintaining this environment – kidneys to filter wastes, lungs to keep oxygen coming, skin to stop fluid loss by evaporation, and so on.
But it is an uphill battle. Skin is exposed to ultraviolet light, to chemicals, and to extremes of temperature. Lungs are exposed to toxins in the air like cigarette smoke and inhaled chemicals, and other organs are exposed to toxins that are ingested and absorbed into the bloodstream.
Waste products of metabolism
At the same time, there are dangers from inside the body too. Inside the cells are billions of chemical reactions that carry on essential functions – like generating energy, making proteins and reproducing the cell itself. These processes are subject to wear and tear and to damage from waste products.
A lot of the damage comes from so-called “free radicals”. These are by-products of metabolism, consisting of oxygen molecules that are missing an electron. These are very destructive because they take electrons from other molecules, destabilising them and damaging vital tissues like proteins, membranes and DNA.
Free radicals would do a whole lot more except that the body has evolved ways of dealing with them–enzymes that break them down, and other substances that “mop” them up by donating the missing electron. These substances are called antioxidants. Another name for the process of taking an electron from another molecule is “oxidation”; hence substances that stop this from happening are called antioxidants.
Many antioxidants are vitamins found in fruit and vegetables, which is why vitamins help prevent degenerative diseases such as heart disease and cancer. But antioxidants do not stop the damage altogether. Free radicals can damage cell membranes, organelles like mitochondria (the tiny factories inside cells that produce energy) and important proteins like enzymes. They can also damage the cell's DNA, which is especially serious because DNA is the genetic blueprint of the cell that programs its functions. Knock out the DNA and the cells cannot function or reproduce.
Fortunately the cell does have repair mechanisms that help to fix the damage. One of the reasons we do live a relatively long time compared to other animals is that we have very low rates of oxidation, plus powerful antioxidant enzymes, DNA-repair enzymes and an excellent immune system. However, it is not perfect and the older we get, the more the cell damage accumulates.
Programmed to destructEven if a cell could repair itself completely – and avoid damage from toxins, infections, heat and cold – it would not last indefinitely. Cells are programmed at a certain stage to self-destruct.
At the end of every chromosome are specialised stretches of DNA called telomeres. After each cell division, the telomeres shorten, and when they get to a certain length (after about 50 divisions), they trigger cell death.
Why, some might ask–surely that is biological madness? It is thought that the telomeres are one inbuilt protection against a cell mutating and dividing uncontrollably–becoming cancerous, in other words. Programmed cell destruction is a safety valve against cancer. Without it we would probably die of cancer before we reached reproductive age.
Cell and tissue deathThe process of self-destruction that occurs when a cell has sustained too much damage, or its telomeres have shortened to the critical point is known as apoptosis. Over a 12 to 24-hour period, the cell's energy powerhouses (the mitochondria) shrink. Its genetic material fragments into pieces, and the remains of the cell are devoured by scavenger cells called macrophages.
Organs and tissues vary as to how quickly dead cells within them are replaced. In skin and bowel tissue, for example, cell turnover is fast–cells die early and are replaced quickly. In others, like muscles and the brain, they last a long time but when they do die, they are not replaced at all.
Over time, more and more dead cells are not replaced with new cells, but instead with fibrous tissue that causes organs to contract and shrink. Muscles for instance, lose their bulk. The brain shrinks. Bones become demineralised.
As cells, tissues and organs progressively deteriorate the body gradually loses its ability to respond to external shocks. We get more and more susceptible to changes in extremes of temperature, infectious diseases, or mutations in our DNA that can give rise to tumours within the body.
Eventually, one or more of these events overwhelms us and we die. The maximum age we can get to before this happens is about 120 years–the limit of human longevity.
Extra-cellular tissues age tooWe have talked a lot about cells, but it is not just cells that age. Connective tissues outside the cells, such as elastin and collagen, also degenerate. Chemical cross-links form between strands of tissue, reducing their strength and elasticity. This process especially affects skin, lungs, muscles, and blood vessels. In our skin, we see the visible result of this process as wrinkles.
We do have powerful enzymes to break these cross-links as they form, but again, they are not perfect. So, tissues designed to give elasticity (as in the artery wall) or transparency (as in the lens of the eye) or high tensile strength (as in ligaments) all degenerate. Muscles lose their strength, the heart does not pump as hard when challenged by exercise, arteries do not deliver as much blood as they used to, and lungs lose their elasticity. Bones grow brittle.
HealthWhat walks on four legs in the morning, two in the afternoon, and three in the evening? In Greek mythology, that was the riddle posed by the Sphinx to the young Oedipus, who got the answer right and went on to become King of the city of Thebes.
The answer, of course, is that people do. They crawl on all fours as a baby, walk on two legs as an adult, and walk with a cane in old age.
However, in this day and age, not everybody may walk with a cane in old age but most people do come to terms with the fact that their body is not functioning as well as in early adulthood. It is all to do with the biological changes. Little by little, so slowly that we barely notice it, our major organs–heart, lungs, skin and muscles–become less effective.
Some of the signs become obvious and we are fully aware of them. For example, some people:
. lose their hearing ability, particularly for higher frequencies;
. their joints wear out–a third of men and half of women over 65 develop symptoms of arthritis;
. experience loss of teeth (especially those over 65);
. lose weight due to loss of muscle and bone;
. lose height due to the bones of the spine losing calcium and shortening;
lose muscle bulk, strength and power;
. have vision difficulties. They become short sighted with reduced ability to focus on close-up objects. This condition (called presbyopia) may begin in the forties; the ability to distinguish fine details may begin to decline in the seventies. From 50 years on, many people have increasing difficulty in seeing at low levels of illumination;
. sleep more lightly, more frequently and for shorter periods;
. men lose capacity for normal sexual functions;
. women decline in reproductive capacity around the age of 50 as levels of sex hormones fall drastically, and the changes of menopause set in;
. bladder capacity begins decline with symptoms of incontinence (prostatic hypertrophy in men);
. fat becomes redistributed from below the skin to deeper parts of the body. Women are more likely to store it in the lower body (hips and thighs), and men in the abdominal area.
Then there are other changes we do not notice, or we are only dimly aware of them. For example:
. blood pressure rises because of narrowing of the arteries;
. heart grows slightly larger because it has to pump against higher blood pressure caused by narrowing arteries;
. lung capacity decreases because of loss of elasticity of lung tissue, so we get puffed more easily on exertion;
. brain cells are affected as reaction times slow and short-term memory deteriorates; some may have difficulty concentrating or become confused more easily;
. kidneys do not function as well, becoming less efficient at clearing wastes from the body;
. the immune system declines and we become more prone to illness;
. the metabolism slows down, so we notice the cold more.
What is surprising is that the age at which these changes begin varies so much. In some people they begin in the late forties, while others can reach their seventies without noticing the effects of ageing. This variation has a lot to do with our genes–if our parents aged well then the chances are that we will too.
But eventually, age catches up with everybody. And vices catch up such as smoking, drinking too much, eating wrong foods. Damage from these lifestyle choices accumulate over the years and depending how much we are at risk from our family history, we are more prone to cardiovascular disease (heart attack and stroke), cancer and diabetes. And to make matters worse, some people also develop other degenerative diseases like osteoarthritis, osteoporosis, Alzheimer's disease, Parkinson's disease and retinal degenerative diseases.
About Peter Lavelle …
Peter Lavelle studied medicine at the University of Sydney and graduated in 1983. He practiced as a GP for several years before becoming a full-time medical writer. For many years he wrote for national medical newspapers and magazines. Lavelle now works for the Australian Broadcasting Corporation (ABC). http://www.abc.net.au/health/bio/lavelle_p.htm.
The final issue in this series will discuss successful … graceful … youthful ageing.
Monika Bhatia
Project Manager and Editor, Quality4life
13 December 2006
