Amid all of the hoopla that accompanied last week’s press reports about the new Alcohol Consumption Guidelines, something else slipped under the radar. CRUK released a statement, which didn’t receive quite the same level of media hysteria. Which is surprising, frankly, because it involved another popular subject. One which, if it had been released at any other time, would probably have caused a similar Stooshie to the alcohol story.
This one was about obesity. Now, it has been known for ages that increased body weight is linked to increased risks of serious medical conditions. Life-threatening ailments, such as Diabetes, Heart disease and Stroke are well known to be caused by obesity. Lots of work has proven this, beyond a shadow of a doubt.
But what is less well known and, worse, less well understood, is the link between obesity and cancer. It has been known for a while now that there is a correlation between obesity and a wide range of cancers, such as colon, breast, prostate, thyroid, renal, esophageal, gastric pancreatic, gallbladder, and liver cancers, as well as non-Hodgkin lymphoma and multiple myeloma. Yikes! But how obesity is linked to cancer is less well understood. There are several theories that could explain it, but there’s not enough evidence to be sure which (if any) is correct, so the jury’s still out.
The first theory involves tissue inflammation. The presence of high levels of fatty deposits in the organs (known as Adipose Tissue), leads to a low level of chronic inflammation. Now, obviously, inflammation is entirely normal – it’s caused by your body reacting to something that it doesn’t like and involves the activation of parts of your immune response to try and get rid of it. And, normally, once the problem has been dealt with, the inflammation goes away. But, problems can arise if the process doesn’t stop, but just keeps going on and on. This is because the activation of your immune system involves the release of immune-specific signals – basically growth signals. And if you’ve read my other blog posts (especially No Bootees), then you will already know what this can mean. Basically, as cancer is caused by an excess of growth signals, and as chronic inflammation causes the prolonged activation of growth signals……I hope you get the picture. The correlation between chronic inflammation and cancer is long established – and as obesity causes chronic inflammation, it is not a big leap to join the dots and suggest this as the mechanism that links obesity to cancer.
The next theory involves hormone imbalances that can be caused by obesity. Overweight people are often found to have high levels of various hormones. This can be dangerous because, again, hormones can act as growth factors. And, as you may have already guessed, a large number of diseases, such as breast, ovarian, prostate, testicular and thyroid cancers, are known to be linked to unbalanced hormone levels.
For example, in women, the fertility hormone Oestrogen is mainly made in the ovaries. But, post-menopause, Oestrogen production becomes erratic and it can also start to be made in fatty tissues. And, due to Oestrogen’s ability to act as a growth factor, this can lead to an increased risk of cancer for overweight, post-menopausal women.
Another hormone under investigation is Insulin. Now, most folk know about Insulin through its role in the metabolism of fat and carbohydrates, by regulating blood sugar levels. People with type-I Diabetes are unable to make enough Insulin and their metabolism doesn’t work properly. So, they are dependant on Insulin injections. But, also, long-term consumption of fatty and sugary foods can lead to chronic increases in blood sugar levels. The metabolic systems, controlled by Insulin, eventually break down, leading to the onset of type-II Diabetes. All of this is fairly well understood.
But the problem is that Insulin also plays a role in many other metabolic and cellular functions, including control of cell growth. And, as cancer is caused by a lack of control of cell growth….. I hope you can see where I’m going. Obesity leads to a breakdown of Insulin-driven metabolism, leading to a loss of cell growth control, leading to an increased risk of cancer.
The third main theory involves the way that oxygen is carried around the body through the blood system. Now, normally, your body is very good at making sure the oxygen you breathe is distributed around your body, so that each organ – and each cell that makes up each organ – gets enough oxygen to survive. So, your body is full of arteries, veins and capillaries moving oxygen and nutrients around, like a road network.
But, as obesity involves an increase in tissue size, this can lead to the body expanding so much, that some areas end up so far away from the road network that they don’t get access to the nutrients and oxygen that they need. Now, this can be dangerous for several reasons. It can lead to cell death, through nutrient and oxygen starvation, so that the affected organs stop working properly. It can also lead to increased inflammation, as the body tries to fix the problem. But, in the context of cancer, it can also lead to an activation of survival mechanisms in the affected regions, as the nutrient-starved and oxygen-starved cells try to keep going. This can be bad, because cancer is not just caused by cells growing when they shouldn’t, it is also caused by cells not dying when they should.
So, any situation which causes cells to keep trying to survive can be dangerous, because if the survival mechanisms start to go wrong, then the cells will stop listening to signals telling them to, “Stop Growing!”, and this can set them on the path to cancer.
So, there are three possible mechanisms that link obesity to increased risks of cancer. Now, it might not be the case that only one of these is right. It might be a mixture of all three – especially as both hormone imbalances and low oxygen levels are both associated with increased inflammation.
But, remember, being overweight does not mean that you WILL get cancer. As I’ve said many times (and I’m sorry to bang on about this for the umpteenth time), but we are talking about Risk Factors, not Causes.
Still, we are at the start of the New Year, when many people start thinking about their health and their weight, and to think about dieting. So, when thinking about the benefits of a bit of weight loss, it might be good for everyone to consider that, as well as looking better and feeling better, and as well as lowering your chances of well-know health risks like Heart Disease, Stroke and Diabetes, it might also help to remember that you will also lower your risks of developing cancer.
Pérez-Hernández,A.I., Catalán, V., Gómez-Ambrosi, J., AmaiaRodríguez, A., & Frühbeck, G. (2014). Mechanisms Linking Excess Adiposity and Carcinogenesis Promotion Frontiers in Endocrinology, 5 DOI: 10.3389/fendo.2014.00065
Bhimjiyani, A., Knuchel-Takano, A., & Hunt, D (2016). Tipping the scales: Why preventing obesity makes economic sense CRUK