Depression biology

Depression is not just ‘all in the mind’. The mind and the body are not separate entities, and both body and mind together are affected by depression.

Brain chemistry

Brain chemicals called neurotransmitters send messages around the brain. Several specific neurotransmitters, including one called serotonin, are responsible for regulating moods, as well as appetite, sleep and stress response functions. Lowered mood happens when the brain can’t access enough of the right combinations of these neurotransmitters.

Neurotransmitters are affected by various biological and environmental factors:


Vulnerability to the more severe forms of depression does seem have a genetic component. In other words, if depression runs in your family you may have inherited a tendency for problems with levels of the brain’s mood chemicals, so you may be more likely to be affected by depression yourself.

Early experiences

Because the brain is still developing when we are young children, it is now believed that some early experiences may have an effect on how the brain chemistry deals with stress throughout life.


Hormones are another part of body chemistry which interact with neurotransmitters and affect moods. Illnesses or conditions (such as pregnancy and birth) which affect hormones can trigger depression as well: chronic fatigue syndrome, glandular fever, and diabetes are a few examples.

Blood sugar

What and how we eat can have a profound effect on mood. For example, low levels of blood glucose can result in aggression, anxiety, confusion, fatigue and irritability as well as low mood.


An important factor seems to be related to the body’s stress responses and how well they cope with chronic stress or stress build-up in particular. There is evidence that in some forms of depression the body’s ‘fight or flight’ response seems to remain ‘switched on’ or hyperactive, rather than returning to a resting state*.

Managing our biology

Depression does not have simple causes and effects. Most biological processes are in constant flux, and can be changed and managed by interaction with each other and by outside intervention. Thus even having a genetic vulnerability to depression should not be seen as an ‘inescapable doom’.

There is a lot that can be done to modify the effect of brain chemistry.

Activity levels, eating habits, sleeping patterns, alcohol and drug consumption, and medication all have a direct effect on brain chemistry. Most importantly, thinking patterns and coping habits have a very important effect on stress levels and the body’s stress responses.

Our biological processes interact with thoughts, behaviour, mood and environment to form habit spirals, often without us realising it. The depression habit spiral can be modified by intervening in many small ways.

Next: Depression psychology

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Stress spirals
Understanding food and mood