Depression affects around 10% of the population at any given time, according to the Office for National Statistics, and is now second only to high blood pressure among the most common conditions recorded by GPs.
But while bereavement, unemployment and illness are common triggers for low mood, experts say everyday activities – from what we eat and drink to spending too much time online – could also contribute to leaving you feeling down.
So what are the causes? And what can you do about them?
Certain groups of antibiotics, including quinolones and penicillin, are linked to depression, say scientists.
A large Tel Aviv University study of British patients found that taking just one course of antibiotics can raise the risk of depression and anxiety by around a quarter.
And taking between two and five courses raises the risk by nearly half, they reported in The Journal of Clinical Psychiatry.
It’s thought that disrupting the balance of bacteria in the gut can harm the way in which the brain cells communicate.
Boost your mood: A major proportion of your immune system actually lies in your gut in the form of friendly bacteria, and antibiotics can wipe these out – automatically weakening your immune system.
Restore the balance by promoting the production of good bacteria when taking antibiotics by eating live yogurt (containing lactobacillus, for example), but also fermented foods, such as sauerkraut, kefir and miso.
Your online activity
Addicted to your smartphone? Always online?
Swedish researchers found that women who spend long hours in front of a computer screen or on their phones (up to 150 hours a week) reported more depression, possibly due to sleep deprivation and lack of face-to-face communication.
And a separate study by University of Michigan psychologist Ethan Kross found a direct correlation between time spent on social media and feelings of dissatisfaction, loneliness and isolation.
Boost your mood: Don’t visit a social network when feeling sad or dissatisfied with your present situation as, chances are, it will only make you feel more sorry for yourself and more depressed.
Consider deactivating your account temporarily or unfollowing those who make you feel worse.
And pick up a bestseller instead. Those who read books regularly are, on average, happier and more satisfied with life, according to a study by reading charity BookTrust.
Whether it’s from the streetlights outside or the dim glow of your TV, being exposed to light while trying to sleep can have a negative effect on the brain.
This is because lights can interfere with secretion of the hormone melatonin, which helps let the body know it is nighttime and time to sleep, an Ohio State University study found.
Invest in blackout blinds if you have a street lamp outside your bedroom window.
Switch off all electrical appliances and either turn your electrical alarm clock away from you at night if it has a light-up display, or change to an old-fashioned one with no lights.
Not eating your greens
Those who eat the least fresh fruit and vegetables are most likely to become depressed, according to a University College London study.
The high levels of antioxidants found in fresh produce help prevent free radical damage to cells, including those in the brain.
Boost your mood: Find ways to sneak extra fruit and veg into meals.
Eating just one extra portion of berries, greens or salad boosts someone’s mental wellbeing by the same amount as walking for an additional 10 minutes for seven days over four weeks, say researchers.
And adding 10 additional portions of fruit and vegetables to your daily diet has the same effect on our emotional wellbeing as going from unemployment into a job.
Professor Karen Pine, of the University of Hertfordshire, found that what we choose to wear is heavily dependent upon our emotional state.
She found that when women are feeling depressed, they are more likely to wear jeans and a baggy top.
Boost your mood: Wear clothes you associate with happiness, even if you’re feeling low, because of the strong link between clothing and mood state.
Professor Pine’s study found “happy” clothes that make us feel good are well-cut, figure-enhancing and made from bright and beautiful fabrics.
Ironically, studies show the colour blue has a positive impact on mood, lowering blood pressure and instilling calm.
Your cigarette habit
Smoking increases your depression risk by 41%, according to scientists who spent six years monitoring 8,556 adults.
Nicotine sends the “elation” brain chemical dopamine soaring, then plummeting, leaving you feeling down.
Boost your mood: Quit to revive your health, mood – and finances!
People using e-cigarettes to quit smoking are about 95% more likely to report succeeding than those trying without, according to a large, UCL-led survey of smokers in England.
Skipping the fish course
Large population studies have also confirmed a link between low consumption of fish and an increased incidence of depression. In a Norwegian study of almost 5,000 volunteers, fish eaters reported having better mental wellbeing than those who did not eat fish at all. It’s thought the poly-unsaturated fatty acids in fish act as a mood stabiliser.
Boost your mood: Aim to eat oily fish – salmon, mackerel, kippers, sardines and fresh tuna – twice a week. Don’t like fish? Take a supplement instead. A four-year Canadian double-blind randomised trial, involving 432 patients, found that omega-3 supplementation was as effective as antidepressants for patients diagnosed with depression. Try Healthspan High Strength Omega 3
While many millions of women take the pill without problems, a significant minority say it has an effect on their mental health. Several studies, including a recent one from the University of Copenhagen of more than a million women, found a clear link between hormonal contraception and subsequent diagnoses of depression. Those using the combined pill were 23% more likely to be diagnosed with depression, and those on the mini-pill 34% more likely.
Boost your mood: If you have experienced (or have a family history of) anxiety or depression, speak to your GP about alternative, non-hormonal, contraception options.
Too many coffee breaks
In the same way that sugary and fatty foods can leave you on a rollercoaster of emotion, so too can coffee and high-caffeine energy drinks, warns nutritionist Patrick Holford, author of Feel Good Factor (Piatkus, £12.99).
Consuming caffeine sets off a stress response to your brain which then stimulates the production of adrenaline, making you more alert, he explains.
“In the long term, however, too much caffeine throughout the day causes constant adrenal overload,” he says.
“As a consequence, an increasing number of people are suffering from chronic anxiety, panic attacks, low mood, insomnia and stress-related weight gain.”
Boost your mood: Cut back on caffeinated drinks and eliminate them completely after 4pm.
Try non-stimulating herbal teas, such as chamomile.