Patrick, a finance executive, was diagnosed with bowel cancer after doctors diagnosed anaemia
Patrick McIntosh had given blood every six months for nearly two decades.
Then two years ago, when he went to donate as usual, he was told he couldn't - because his iron levels were too low.
'It came completely out of the blue,' says Patrick, 58, a financier who lives with his wife, Sue, and their two dogs in Smallfield, Surrey.
'I felt very healthy. I sail and I cycle - I've done the London-to-Brighton bike ride more than 25 times.'
At first, he wasn't too concerned. 'The nurse at the donor session said it was nothing to worry about, that I was probably a bit run-down, and I should try taking iron pills - which I did.'
About a month later, Patrick had a routine appointment with his GP and mentioned that his iron levels were low.
'He was pretty reassuring - but just in case, he said he'd measure them again,' says Patrick, a director of KMG financial planners.
'But 36 hours later the doctor rang to say my iron levels were so low - about 35 per cent below minimum - I shouldn't even have the energy to stand up.'
A lack of iron - anaemia - typically causes fatigue, weakness and shortness of breath; it can also lead to headaches, cold hands or feet, and pale skin. 'But I had no symptoms at all,' says Patrick.
His GP thought this was likely to be because he was so fit and his rigorous fitness regimen had helped his body to compensate.
At this point the doctor suggested that bleeding from a stomach ulcer might be to blame, and sent Patrick for tests.
These revealed the true cause was far more sinister: a tumour in his colon.
Anaemia is often thought of as purely a woman's problem, with about three million women affected. But 3 per cent of men, roughly one million, also suffer from it, according to a report last year in the British Medical Journal.
The danger is that - as in Patrick's case - anaemia can be a sign of an underlying problem, but men aren't seeking help.
'Men may not realise they are at risk, and are generally more hesitant to see doctors,' says Dr John Mason, a consultant gastroenterologist at Central Manchester University Hospitals.
The body needs iron to produce red blood cells. Without sufficient iron, not only are there fewer red blood cells, those that are produced lack haemoglobin, an iron-rich protein that transports oxygen around the body.
His iron levels were so low - about a third below minimum - he shouldn't even have had the energy to stand
The lack of oxygen affects almost every function in the body, such as the immune system - which is why frequent infections can be a warning sign. Iron is also vital for the hair, skin and nails.
Often a lack of iron can simply be down to not getting enough from the food we eat. It is found in many foods, including red meat, fish and dark green leafy vegetables. Otherwise, in women the usual cause is heavy periods.
In men, however, anaemia is typically a result of bleeding in the gastro-intestinal tract (the stomach and intestines). This can happen for many reasons, but most often it occurs when taking aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs).
The frightening thing is that the first sign of my bowel cancer was low iron levels... looking back, there were other tell-tale signs
This is the single largest cause of gastro-intestinal blood loss in both men and women, responsible in 10 to 15 per cent of cases, according to the British Society of Gastroenterology.
Daily aspirin is taken for a number of reasons, including lowering the risk of heart disease and stroke.
It works by interfering with platelets, the blood cells that help blood to clot.
A side-effect of anti-clotting action is that it can result in an increased risk of gastro-intestinal bleeding.
'Aspirin is a significant cause of bleeding, especially in older people, who may also not get enough iron because of poor diets,' says Dr Mason.
Other NSAIDs work by blocking enzymes involved in pain and inflammation, but this also stops production of another type of chemical that protects the stomach lining from stomach acid.
This means that NSAIDs increase the risk of developing an ulcer - and thus of anaemia. As well as stomach ulcers, other causes of anaemia in men are bleeding from abnormal blood vessels (angiodysplasia); non-cancerous growths in the colon (polyps); and infection with the stomach bug H. pylori. Treatment for anaemia depends on the cause.
Anaemia is typically a result of bleeding in the gastro-intestinal tract (the stomach and intestines)
Where it is due to a chronic disease causing bleeding, such as ulcerative colitis (an inflammatory bowel condition), treatment of the underlying disease should stop the bleeding and the anaemia. In about 5 per cent to 10 per cent of cases of gastro-intestinal bleeding, the cause is cancer in the colon or stomach.
A fortnight after his anaemia was diagnosed, Patrick went for tests.
'I had an endoscope or tube and cameras stuck into my backside about two weeks after anaemia was diagnosed. And they found a tumour in the colon. They found several smaller ones, too.'
Cancers can cause bleeding because either the tumour itself bleeds or surrounding tissue bleeds as a result of damage caused by the growth.
'I ended up having 17 inches of my large and small colons taken out, as well as lymph glands and stomach muscles,' says Patrick.
'The muscles went in a sort of belt-and-braces approach to make sure everything was got. Because I was pretty healthy, I was discharged after 40 hours, rather than the expected four to five days.
'I did not have any chemotherapy or drugs. Bowel cancer can be cured quickly and efficiently if caught early.'
Where no underlying cause for the anaemia can be found - thought to be the case for about one in four people - iron supplements or diet changes may be effective.
Treating the problem, even when there is no apparent cause, is important because untreated anaemia can put a strain on the heart as it needs to work harder to pump more blood around to make up for the lack of oxygen in the red blood cells.
For people who already have heart disease, this could cause angina (chest pain as the heart is deprived of blood), which is a risk factor for heart attack and stroke.
As Dr Mason explains: 'Anaemia makes the heart work harder and brings out angina, in the same way as running for a bus can bring it out.'
The importance of diagnosing anaemia was brought home to Patrick, who now campaigns to raise awareness of the signs of bowel cancer and has raised funds for Bowel Cancer UK with a sponsored trek to the South Pole.
'The frightening thing is that the first sign of my bowel cancer was low iron levels,' he says.
'Looking back, there were other tell-tale signs,' he adds, recalling a change in stool colour ('pretty black') and odour, 'which I discovered can be symptoms of cancer, but I didn't know at the time'.
'Had I known, I would have seen a doctor. But there was no apparent blood, and I felt so well.
'If the anaemia hadn't been diagnosed when it was - and it was only by chance - who knows what would have happened.'
Read more: http://www.dailymail.co.uk/health/article-2956203/When-tiredness-warning-sign-ignore-peril-s-men-especially-need-wake-danger.html#ixzz3S1ZsKTd4
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