Feeling down? The reasons why will surprise you Believe it or not, a healthy sex life can send your mood spiralling downward. MORE than ever people are suffering from the blues. Millions of people around the world are using antidepressant to treat depression and the epidemic just seems to be growing. The traditional triggers for depression are well-known ... stress, money and relationship worries. But there are some more surprising reasons you might be feeling low. Sex may be pleasurable, but the post-coital blues less so. A survey of more than 200 Australian women found a third had experienced sadness after sex. Richard Friedman, a psychiatrist at Weill Cornell Medical College in New York, treated the problem in his patients using a type of antidepressant that boosts levels of the feel-good chemical serotonin in the brain. He speculated that the depression after sex could be down to the amygdala - the emotional brain region that is less active during orgasm - rebounding strongly afterwards, or simply to the let-down following intense pleasure. Avoiding meat can leave you low in iron which may make you depressed. If you've cut down on burgers for health reasons, a lack of iron could be making you gloomy. This key nutrient is essential for the formation of haemoglobin, which is present is red blood cells and transports oxygen around the body. 'This helps oxygenate all your major organs, so if you're deficient in iron, you feel sluggish and tired, and that can impact on your lifestyle, preventing you from socialising and affecting your mood,' says Alana MacDonald, an NHS dietitian and spokeswoman for the British Dietetic Association. A woman should aim for 14.8mg of iron a day, while men need 8.7mg. Although red meat is a good source, you can also boost your iron intake by stocking up on greens such as broccoli and kale. Sleeping in front of the television is a mood upsetter. If you find that the gentle glow of the television helps send you off to sleep, it may be time to think again. Research has suggested sleeping in front of the dim light emitted from TVs and other electronic devices such as computers may affect our mood. Dr Guy Meadows, clinical director of The Sleep School, a West London clinic, says: 'We're designed to sleep in the dark. When the sun comes up, the light receptors in the retina at the back of the eye tell us it's time to wake up by inhibiting the release of melatonin, the hormone that makes us sleepy. 'The reverse happens at night, so it's ideal to dim down the lights as bedtime approaches as sleep is vital for the regulation of our mood.' Any light in the bedroom, even that produced from a TV, will disrupt these sleep hormones and lead to us becoming sleep-deprived, which triggers a low mood. Tiredness dampens down the effect of the prefrontal cortex in the brain, which is responsible for more rational thought, and causes us to use the part of the brain responsible for emotion, called the amygdala, more. This is the more primitive emotional regulator in the brain which exaggerates our emotions and causes us to be more prone to anger, aggression and sadness. A study at Ohio State University found that hamsters who spent their nights exposed to dim light - the equivalent of having a television on in a dark room - displayed more signs of depression. Penny pinching can make you unhappy. It seems money can buy you happiness - as long as you spend it on other people. In a study, published in the journal Science in 2008, participants were asked to rate their happiness levels in the morning and then given an envelope containing either $20 or $5. Some were instructed to spend the money on themselves, whereas others were told to buy someone else a gift or make a charitable donation. After they rated their happiness levels again, the people who had spent the money on a good cause were cheerier than those assigned to personal spending, with the size of the windfall making little difference to the results. Read about the other reasons which may be causing your depression. Here's a hint: Too many bananas or not enough?