October 16, 2023

New Zealand has one of the highest rates of bowel cancer in the world and men are at an increased risk of bowel cancer compared to women. Every year, more than 3,000 New Zealanders are diagnosed with bowel cancer and more than 1,200 die from it.

 And you are never too young to be affected – more than 350 people under 50 are diagnosed with bowel cancer each year.

 We talked to Waitemata Health General and Colorectal Surgeon Andrew Moot about why Kiwi blokes fare so badly in the bowel cancer statistics and what men can do to minimise their risk of dying from this disease.

Why do we have such a high rate of bowel cancer and why are men at higher risk?

Bowel cancer is a disease common in developed countries and it’s thought that the main contributing factor is the diet that we have in the west.

There are genetic conditions that can increase the risk, and this may be a significant factor in up to 20 per cent of bowel cancers, although currently we are able to identify the genetic link in only about five per cent of those.

The World Health organisation has identified processed meat as a carcinogen - people who consume more than 500g of processed meat per week had a higher rate of colorectal cancer. It is less clear whether red meat is carcinogenic, as it may be the nitrates in the bacon and sausages that are more the problem than the meat itself.

Bowel cancer is more common if you are overweight, and live a sedentary lifestyle, and smoke or drink too much. Men are more likely to smoke or drink than women. Men have more ‘visceral fat’, that is fat around their abdominal organs, and this visceral fat is associated with a higher risk of colorectal cancer. A New Zealand man is estimated to have a one in 15 risk of developing bowel cancer at some point in their life! Women are not too far behind, with about a one in 20 lifetime risk of developing colorectal cancer.

Men are especially more likely to develop rectal cancer than women.

The uptake of bowel cancer screening by men has been demonstrated to be lower in NZ and the UK. Women, of course, are more used to screening because they are offered cervical and breast cancer screening, both of which require uncomfortable and rather personal examinations. Men who participate in bowel cancer screening are more likely to benefit, so we do need to encourage men to accept the invitation to participate in our screening programme, currently available to all New Zealanders aged 60 to 74.

What are the symptoms of bowel cancer?

The symptoms of bowel cancer include rectal bleeding, a persistent change in bowel habits, and also weakness and fatigue that occurs if your blood count is low (anaemia) because you are slowly but persistently losing blood

A cancer can slowly ooze blood, and if that is in your colon you will probably not be able to notice it simply by observing your bowel motions. This is why screening tests look for occult blood in the stool - that is blood in your poo that you cannot see with your own eyes. If you are feeling tired and easily fatigued for no good reason, you may be low in iron or anaemic which is detectable on a blood test. 

Rectal bleeding is really common and is most often from a benign anal cause such as a haemorrhoid (piles). You should report bleeding to your doctor so they can check carefully if there is an obvious benign cause. Dark red blood or blood mixed in with the stool is much more concerning then bright red blood (like from a fresh cut) on the toilet paper. A rectal cancer can have a very similar bleeding pattern to a haemorrhoid. Get your doctor to examine you to confirm the source of the bleeding.

A change in bowel habit is also a symptom of bowel cancer. Usually a change in bowel habit is due to changes in what we eat or if we get food poisoning. But if you have diarrhoea that persists for more than a month, or even if you are just passing your bowel movements more frequently without them being loose at all, this could be a symptom of bowel cancer and should be reported to your GP. 

It should be noted that weight loss and pain are not a feature of early (more likely curable) bowel cancer. These symptoms are not specific for bowel cancer, and most patients with these symptoms are likely to have another cause. But the earlier bowel cancer is diagnosed the better the outcome, so see your doctor about your bowel problems. 

When should men (and women) get checked for bowel cancer, how should they do it and how often do the tests need to be repeated?

There is a rising incidence of rectal cancer in younger people, so if you have the symptoms above then you should get checked even if you are a relatively young adult. The older you are the more likely you are to have cancer as a cause for your symptoms. Men are more likely to get rectal cancer. Young men beware!

If you have a family history of bowel cancer, especially more than one close relative (parent, brother or sister) with bowel cancer or a close relative under age 55, then you should discuss a referral for a colonoscopy with your GP because you are at least three times more likely to develop bowel cancer than someone who has no family history. 

For everyone else who has no symptoms or strong family history of bowel cancer, screening is offered currently in New Zealand to all adults aged 60 to 74. This is in the form of a poo test which is done in the comfort of your own home and posted away for testing. It is checked for blood and if blood is identified you will be offered a colonoscopy.

Take up the invitation and do your bowel screen! About 60 per cent of those invited do the test, which means 40 per cent do not. They will not get the benefit of reduced bowel cancer mortality that has been demonstrated by bowel cancer screening programmes. It should be noted that there is evidence for the benefits of bowel cancer screening from aged 50, which is where it should be in New Zealand but unfortunately we do not have sufficient numbers of endoscopists to do the colonoscopy examinations that would be required if we screened from age 50 to 74. 

If you are aged between 50 and 60 and have no symptoms and have not had a colonoscopy but want to be screened, you could discuss your situation with your GP. There are options of doing tests outside of the screening programme, but this may come at a significant cost. 

What diet or lifestyle changes should we consider to prevent bowel cancer?

It is very difficult to prove that lifestyle changes made now will significantly reduce your risk, as it will take a long period of time (years to decades) before these lifestyle factors change your cancer risk. The younger you are, the more likely you are to benefit from these changes. But I would suggest eating significantly less than 500 grams of processed meat a week. Bacon and sausages should be a treat and not the norm. Have your five veg and two fruit per day, and natural fibre (eg oats, legumes, bran, whole grain bread etc.) Stop smoking and drink alcohol within safe limits. If you have a lot of fat around your tummy, you need to try to lose it. Exercise regularly! It might decrease your bowel cancer risk and reduce your chance of becoming diabetic or having a heart attack.

Don’t be prudish. See your GP quickly if you have any symptoms, and make sure you take up the invitation to have that bowel screening poo test.


This blog is part of our Men’s Health Month Series.