According to the World Health Organization (WHO), depression is the most common illness worldwide and the leading cause of disability.
It is estimated that 350 million people are affected by depression, globally.
But what causes it?
Although depression may never fully be understood, there is evidence to suggest that hormone imbalances can be a major contributing factor.
In this article we discuss the varying factors that might contribute to depression and how hormones may be implicated.
Depression is remarkably common affecting approximately one in five adults in the Western world. It is considered a disease that could eventually pose a greater burden on the health industry than heart disease and tuberculosis.
The effects of depression can be mild, moderate or extreme and the causes are multifactoral.
Experts suggest that, medications, genetic vulnerability, biological, environmental, and psychosocial factors can all play a part.
There are a wide range of symptoms and some functional disabilities that characterize depression.
Symptoms can vary between individuals and it is important to seek medical guidance to rule out other possible health conditions.
While researchers strive to understand the full complex biology of depression a lot is already known about the link to hormone imbalance.
Evidence suggests that hormonal changes may promote the onset of depression. Hormones that are out of kilter are known to lead to significant fluctuations in moods often brought about by changes in the central nervous system, altered metabolism and by the action of hormones within the cells.
These factors point to the endocrine system as a partial player in depressive episodes. Imbalances of key endocrine hormones such as corticotrophins, oestrogen progesterone and thyroid may have a significant impact on the development of depression.
Given that these hormones are essential for the normal function of the metabolism, it is likely that any imbalance may contribute to the development of mental health issues.
Some of the key health conditions that are linked to hormone imbalance and depression include:
On a worldwide scale, the prevalence of depression amongst young adolescent females appears to be rising.
Epidemiologic studies suggest that there is a higher risk for major depressive disorders in women than men, this disparity begins at puberty which suggests a significant link to hormonal changes.
In fact some research shows that twice as many women as men suffer from depressive disorders which appears to be linked to their reproductive cycle.
This is possibly because women undergo constant hormonal influences during their reproductive years.
Evidence points to sex hormones because they affect mental status,
mood and cognition. Particularly oestrogen and progesterone which are responsible for female sexual development and menstruation.
Because hormones and neurotransmitters share common pathways and receptor sites in sections of the brain that control mood, it is thought that women sufferring from PMS may be more susceptible to depressive symptoms.
Progesterone and estradiol are also thought to be implicated in the depression women experience after childbirth. Many women experience ‘baby blues’ at this time, but post natal depression is significantly more severe.
It has been suggested by some scientists that post natal depression is caused partly by sudden changes in progesterone and estradiol levels immediately after giving birth.
Women experiencing depression at these reproductive points in their life may have a heightened sensitivity to intense hormonal fluctuations.
The menopausal transition seems to represent a period of time during which some women might be more vulnerable to the development of depressive symptoms and major depressive episodes.
Approximately 20% of women have depression at some point during the menopause. This risk seems to increase during the perimenopause and decrease post menopause.
During this transition there are a number of hormonal changes that may contribute to depression. Women as well as men produce the hormone testosterone, which naturally declines around the menopause. Decreasing levels of testosterone have been linked to fatigue, a loss of libido and depressive symptoms.
Low oestrogen levels are also thought to contribute to depression, possibly because oestrogen facilitate the actions of serotonin and norepinephrine, both neurotransmitters that raise mood.
Serotonin is a chemical that has a wide variety of functions in the body but is often referred to as the ‘happy hormone’ because of its influence on mood and wellbeing.
Recent research has shown that oestrogen pays a key role in the central nervous system affecting the hypothalamus, hippocampus and cerebellum - regions of the brain where most cognitive functions and mood are controlled.
Depression, mood swings, anxiety and irritability are common symptoms of hypothyroidism and as such, a relationship between low thyroid function and depression has been assumed for years.
The importance of thyroid hormones on brain development and function are evident by the devastating neurological consequences of severe iodine deficiency and untreated hypothyroidism.
Animal studies have identified that serotonin levels in the brain increase after administration of the thyroid hormone T3.
A reduction in thyroid hormones is also directly linked to a decrease in serotonin levels.
Thyroid hormones are sometimes prescribed alongside antidepressant medications to improve mood. It is thought that the thyroid drugs boosts chemical activity in the brain that improves mood and concentration.
One of the medical causes frequently cited for depression is the overproduction of stress hormones.
Evidence suggests that if stress is continued or prolonged it can result in adverse effects on many systems in the body including, the immune, neuroendocrine and central nervous system.
One study has identified that prolonged exposure to the stress hormone cortisol contributes to symptoms of depression.
Furthermore, according to other research, depressed people often have higher levels of cortisol in their blood circulation, which is thought to decrease serotonin - manifesting in low moods and depression.
What is also known is that prolonged stress can cause insomnia.
The importance of sleep for restoring the body implies that chronic insomnia is likely to create a significant pathway to disease.
Insomnia and depression often go hand in hand. Several studies show that insomnia is a risk factor for the onset of depression and for worsening depression.
Nutrition and depression are intricately and undeniably linked, as suggested by the mounting evidence by researchers in neuropsychiatry.
Depleted nutrients can therefore have a significant effect on brain chemistry.
Supporting thyroid, adrenal and brain function through diet can help to balance hormones and reduce the risk of depressive symptoms.
Foods rich in fibre such as broccoli, green beans, pulses, lentils, beans and bananas are also rich in chromium and B-vitamins which enhance mental processes
Research has established a relationship between depleted levels of magnesium in stress and depression.
Oily cold water fish contain high levels of omega 3 essential fatty acids which are known to play a critical role in the development and function of the brain.
Emerging research suggests that omega-3 fatty acids may be of therapeutic value in the treatment of depression.
It is suggested that low glycemic index (GI) carbohydrates such as some fruits and vegetables, as well as whole grains are more likely to provide a moderate but lasting effect on brain chemistry and mood.
READ: BBC News: Mediterranean diet 'may help prevent depression'
Written by: Jacqueline Newson BSc (Hons) Nutritional Therapy
Charity providing support if you've been diagnosed with an anxiety condition.
Phone: 03444 775 774 (Mon-Fri, 9.30am-5.30pm)
A charity helping people living with manic depression or bipolar disorder.
Charity for sufferers of depression. Has a network of self-help groups.
Promotes the views and needs of people with mental health problems.
Phone: 0300 123 3393 (Mon-Fri, 9am-6pm)
Young suicide prevention society.
Phone: HOPElineUK 0800 068 4141 (Mon-Fri,10am-5pm & 7-10pm. Weekends 2-5pm)
Confidential support for people experiencing feelings of distress or despair.
Phone: 116 123 (free 24-hour helpline)
Information on child and adolescent mental health. Services for parents and professionals.
Phone: Parents' helpline 0808 802 5544 (Mon-Fri, 9.30am-4pm)