L'anxiété peut-elle causer le cancer ?

Why all the worry?

Stress is an occupational hazard of living in the 21st Century. At low levels, we need it to give us the impetus to get out of bed in the mornings and put our best into whatever we’re doing. Our bodies react to stress by producing adrenaline. This ‘fight or flight hormone’ travels through the blood to every nook and cranny of the body, preparing us for battle with the tribe from over the mountain, or flight from that sabre-toothed tiger.

Adrenaline raises your heart and breathing rates, pumping oxygen more effectively to your muscles. It diverts blood away from your gut (you don’t need to digest food in an emergency) to your brain and other vital organs. This ability to run faster and hit harder stood us in good stead when a life-threatening predator lurked around every corner. But all too often today it does more harm than good.

When stress levels rise too high or too long, we can become paralysed by anxiety. It’s hard to see the wood for the trees, and making the smallest decision requires Herculean effort.

If everything makes you anxious to the extent that it interferes with your ability to function, you may be suffering from un trouble d'anxiété généralisée (GAD). 1 in 30-50 people are affected, with women suffering more often than men.

Teasing out GAD from ‘normal’ anxiety can be difficult, but features include:

• Excessive anxiety, on more days than not for at least 6 months, about a wide range of activities

• Finding it hard to control your worry

• Three or more of feeling tired easily; irritability; muscle tension; problems concentrating; irritability and sleep disturbance

• At least four physical symptoms, including pounding or a racing heart, excessive, trembling, bouche sèche, problèmes respiratoires, se sentir malade, vertiges or light-headedness, numbness or tingling sensations, muscle aches and a lump in the throat or difficulty swallowing.

So does stress cause cancer?

There has been much debate over the years whether stress actually causes cancer. Researchers have suggested that people who have an inherited tendency to cancer may be more stressed because they see others in their family suffering from it. In other words, the cancer link is causing the stress and not vice versa. It has been widely assumed that anxiety sufferers were at higher risk because they were more likely to smoke or drink to excess, and less likely to eat healthily or exercise regularly.

However, the study found that even after excluding possible ‘confounding factors’ like alcohol and smoking from the equation, the connection between severe anxiety and cancer remained.

The trouble with studies like this is that they find a connection, but can’t prove that “A” actually causes “B”. Even though this study makes a stronger case for cause and effect by removing factors that might otherwise explain the connection, it doesn’t tell us comment the psychological – stress and anxiety – are directly influencing the physical. But laboratory evidence over the years can give us some clues.

For instance:

• In animal studies, mice with cancer were more likely to have metastases (spread of cancer to other parts of the body) if they were subjected to prolonged stress

• Women using beta blockers, which slow the heart and can trick the body into believing it’s not stressed, have been connected with a lower chance of breast cancer spread in some studies

• Noradrenaline (norepinephrine, closely linked to adrenaline or epinephrine) has been found to increase the rate of inflammation and new blood vessel production, which in turn can promote cancer spreading

• Cancers du sang are influenced by the sympathetic nervous system, which is intimately connected with adrenaline levels

• Stress can downgrade the ability of cells in the immune system to fight off invaders, including infection. Our immune system has sophisticated pathways for neutralising and destroying harmful, potentially cancerous cells, which may also be affected.

Of course, simply discovering that severe anxiety can increase the risk of cancer is enough to make anyone feel anxious. The next step is to work out what to do with that knowledge, and how to fight the connection.

Unsurprisingly, laboratories across the world are hard at work translating knowledge on hormones and stress into potential new targets for cancer – but that is for the future. As yet, we don’t know whether talking therapies such as thérapie cognitivo-comportementale (TCC) can reverse that trend. Pleine conscience, too, may help reduce stress levels and cut the risk of depression, but it is extremely difficult to devise scientific studies to prove conclusively whether it helps prevent cancer.

However, there is very good evidence that they are powerful tools in the fight against mental illness, and can hugely improve quality of life. There's hope that the same tools might combat cancer too. And that is a pretty good start.