Hormones play a vital part in keeping our bodies working properly. But they can also have a powerful – and sometimes negative – effect on our mood and mental health.

We all like to think that our feelings and emotions are under our control, but are they? Scientists have long known that chemical messengers called neurotransmitters exert a huge influence on our brain. Yet as scientists learn more, they are finding that hormones too can mess with our heads in unexpected ways.

Now, some are trying to harness this knowledge to find new treatments for conditions like depression and anxiety.

Hormones are chemical messengers released by certain glands, organs, and tissues. They enter the bloodstream and travel around the body, before binding to receptors in a specific place. The binding acts as a kind of biological "handshake" which tells the body to do something. For example, the hormone insulin tells liver and muscle cells to suck up excess glucose from the blood and store it as glycogen.

Scientists have identified more than 50 hormones in the human body so far. Together they manage hundreds of bodily processes, including a person's growth and development, sexual function, reproduction, sleep-wake cycle and – importantly – their mental wellbeing.

"Hormones really impact our mood and our emotions," says Nafissa Ismail, professor of psychology at the University of Ottawa, Canada.

"They do this by interacting with the neurotransmitters that are produced and released in specific brain regions, but also by influencing processes like cell death or neurogenesis – when new neurons are created or born."

The prevalence of mental health disorders, such as depression, anxiety, and post-traumatic stress disorder (PTSD) is higher during major hormonal transitions. This is particularly true for women. Rates of depression are essentially equal between boys and girls during childhood, but by adolescence, girls are twice as likely as boys to be depressed – a difference which persists across the whole life course.

So could hormones be to blame? It may not be a surprise to learn that, if you are a woman, sex hormones exert a striking influence on mood. In the days and weeks preceding a woman's period, levels of oestrogen and progesterone fall, coinciding with feelings of irritability, fatigue, sadness and anxiety for some, but not all. Some women can even experience premenstrual dysphoric disorder (PMDD), a severe, hormone-related mood disorder characterised by extreme mood swings, anxiety, depression, and sometimes suicidal thoughts during the two weeks before menstruation.

"For a lot of women with PMDD it's a very chronic issue that they deal with every month, and it can have a really profound effect on people's lives," says Liisa Hantsoo, assistant professor of psychiatry and behavioural sciences at The Johns Hopkins University School of Medicine, US.

Conversely, high levels of oestrogen immediately before ovulation have been linked to feelings of wellbeing and happiness. Meanwhile allopregnanolone, a product of the breakdown of progesterone, is also known for its calming effects.

"If you give someone an injection of allopregnanolone, it will relax them," says Hantsoo.

It's not just the "time of the month" that women have to deal with. Hormonal fluctuations in pregnancy, perimenopause and menopause can also wreak havoc with mental health. Up to 13% of women who have just given birth experience depression.

But why is this? Immediately after giving birth, women experience a precipitous drop in hormones progesterone and........

© BBC