Stress causes heart disease. We can live our lives avoiding beefburgers, chips and eggs, but if we are very stressed, we are still at risk of developing heart disease. The most accessible study to show this is the Whitehall study ,2002, done on 10,308 civil servants. This blog is about what happens to us physically when we get stressed and how this damages the heart and arteries.
Put simply, stress comes in 2 forms, acute and chronic. Acute is something that happens suddenly, like discovering a grizzly bear in the bushes in the average UK garden. This would be surprising, frightening, involve a lot of running and screaming. After a while, the bear would be taken away or shot – and the immediate stress would be gone. The other form of stress is chronic, meaning it lasts for a long time. So post-traumatic bear disorder could lead to depression, which is one form of chronic stress. One of the things the Whitehall study found was that the less control we have over our job or lives, the more we suffer from chronic stress and the worse our health.
Returning to the bear in the bushes. If a bear is found at the bottom of the garden, we immediately release stress hormones to help us get out of there. The prime stress hormone released is called cortisol. As cortisol levels shoot up, it not only raises the heart rate but also increases the force with which the heart beats. It does this by stiffening or constricting the veins returning the blood to the heart, so the blood enters the heart at a much greater pressure, slamming into the heart walls, which makes the heart walls stretch like rubber bands then snap back with great force. The arteries leading out of the heart dilate, allowing for more blood flow to the fleeing legs1 . With this much greater blood flow, blood pressure rises.
Other things also happen. Digestion is shut down to divert blood away and increase supply to those pumping legs and arms. Blood sugar levels go up for energy. In the kidneys, in order to conserve water to maintain blood volume in case the bear claws us so we bleed, they stop forming urine and instead reabsorb water into the blood stream. 2 We also release various blood clotting agents, again if the bear claws us, these will help stem the bleeding. The production of sex hormones is ramped down. All repair projects taking place inside are put on hold, for example the repair to the damage to the artery wall that happened when the bear last jumped out at us.
A short sharp burst of stress is actually good for us. Provided the stress comes to an end and we relax when the bear is gone. Of course in reality the chances of the stress being a simple physical stressor like a bear down the garden are not high and our stress reaction is rarely physical. Normally the stress is lack of control at work, tiredness, not enough money to live on, divorce, moving house- especially against our will, death and depression. This list is far from exhaustive3. The common stressors we deal with on a daily basis are not physical but mental. Yet the stress hormones released are the same as the ones we release to get away from said bear. The physical response is the same – only we sit and stew not run away or thump the bear. And the stress for many is relentless.
So now the body has constantly raised pressure in the arteries and veins, the blood vessels, and a constantly elevated heart rate and heart force. Plus lowered digestion, elevated blood sugar levels, thicker blood for better clotting, water retention, lowered sex hormones leading to lowered sex drive, chronic inflammation from partially mended damage to the body. The body is forced to adapt. One way it does this happens in the blood vessels. The arteries leading away from the heart are relatively large, getting rapidly smaller as they get further from the heart until they reach the capillary beds. As they get smaller, the relative pressure in them rises, so they have to work harder to circulate the blood making them more muscular and therefore thicker which, in turn, raises blood pressure even more.
In order to get smaller, the blood vessels regularly divide into 2. Where they divide causes turbulence in the pressurised blood and it is around these junctions that damage often occurs, the damage is called endothelial damage or damage to the blood vessels. This damage sets off the chain reaction for repair mentioned in the blog on what clogs up arteries. Immune system cells rush to the spot, clotting agents clump there, LDL cholesterol is drawn to the site4 as is Lp(a) cholesterol, bits of fibrous gunk and goo collect there and now we have built ourselves a big scab on the blood vessel wall – which will be an artery for reasons too long winded to go into now. This scab is called an atherosclerotic plaque.
In the last few years it is becoming clear that the amount of damaged inflamed blood vessels is a better predictor of cardiovascular trouble than is the amount of circulating crud. Robert Sapolsky. Why Zebras Don’t Get Ulcers.
By circulating crud he is referring to things like cholesterol.
Here on the right we have a pulmonary embolism. Pulmonary refers to the lungs. So a big old plaque has built up in one of the arteries feeding the lungs, following a long period of stress and eventually it bursts squirting its contents into the blood stream. These travelling clots are called embolisms. The embolism will trundle through the arteries eventually lodging where the artery gets too narrow for it to pass through, blocking the artery possibly straight away or a little later as time and increasing damage continues. Then we experience a heart attack or stroke, depending upon where the artery is blocked.
The other simple way that chronic stress damages the heart is due to the left side of the heart, the side that receives blood from the veins, constantly reacting to high pressure blood being squirted in, so it gets much more muscular, leading to an imbalance between the right and the left side of the heart. This too is a predictor of future heart attacks. It can lead to an irregular heart beat or, worst of all, the arteries supplying the heart with its blood may not be up to the job on the left hand side, so the blood supply is inadequate for the heart to beat properly. This is called chronic myocardial ischemia – long term blood shortage to the heart – and this leads to angina.
Of course, not everybody develops heart disease. How people respond to stress is critical and very varied. One persons stress is another’s challenge. The reason for this blog is the endless false connection made between eating saturated fat and developing heart disease. The basic mechanism for developing heart disease lies in our response to stress. We were designed to be out on the savanna in small autonomous groups. The stress we lived under was primarily physical from attack or food shortage. We would not have got stressed from a looming big presentation or from being delayed on the train or in traffic for 3 days running. We were designed to be physical and not mental. And so the relentless stress of western life brings a great physical toll including heart disease.
- This description is taken from Robert Sapolsky’s book Why Zebras Don’t Get Ulcers. Generally in literature the stress response reports vasoconstriction in the blood vessels with vasodilation at the capillary beds – to supply the muscles with oxygenated blood. I cannot work out which is right, but Sapolsky’s view makes more sense than a general constriction of both veins and arteries. Incidentally, veins take the blood into the heart – the vay-in – whilst arteries take oxygenated blood away from the heart [↩]
- The reason we wet ourselves if severely scared is that wee is stored in the bladder, not the kidneys. So if we have to leg it from an angry bear, we hardly need to carry a big bag of widdle inside us and are better off jettisoning it to make us a bit lighter. [↩]
- So added to the list of stressors are commuting, deadlines, queueing, driving ie daily minor stressors, but they build up [↩]
- LDL cholesterol. The word cholesterol means bile and sterol. Sterols are natural anti-inflammatories. When there is inflammation going on, an natural anti-inflammatory is a good thing to have floating about I would have thought [↩]