Think of the day you get at work and that woman, who is always on a bad mood smiles at you and asks if you need something, and does all those deeds that she would normally ignore? There's an explanation for that. In fact, there can be two: either she finds out that you are going to get a promotion and wants to be your friend so that she can be promoted too, or - most likely - she leaves a kind of "sex glow" around her. Then, you get to the logical conclusion: she had sex the day before.

It's a fact that sex can improve mood. People tend to get happier, more relaxed, and even subtle to deal with after a sexual relation. It happens in both genders, and it's a healthy thing. So, based on these facts, scientists from all over the world made themselves a question: could sex improve not only people's mood and spirit, but also their bodies? And then began the studies and theories to prove that yes, sex can be a healthy exercise for the mind and for the body, leading to a longer life, better cardiopulmonary health and even protection against some kinds of cancer - not to mention the fact that people who have active sex lives decreases the likelihood of depression onset.

Of course, it's not an easy thing to prove such associations, scientifically speaking. But these studies are leading the scientists to a hormone called oxytocin. That hormone increases efficiency five fold during orgasm, in comparison to its usual blood ratio. When released in the cerebrum, it reaches - through ongoing blood - extreme segments, where it regulates body core and blood pressure, healing and pain relief. However, other factors do contribute to such enhancement. Some scientists compare sexual relations to some exercises: calories get burned during sex, for an example, and heart and blood pressure typically double during orgasm. So, it's logical to conclude that sex, as any other exercise, can protect against problems like heart disease. It also can control pain: the pain-killing centre in the midbrain is activated during peak arousal, instructing the body to release endorphins and corticosteroids, numbing temporarily the nerves responsible for things like arthritis.

It's proved then that sexual relations not only increase people's humour, but also act on people's body, improving their defences and health. Studies show that married people live longer than singles. Sure, there is another thing to consider - like companionship - but sex is definitely one of them. Therefore, next time that you see someone with a big smile, maybe you will understand the reason. And you will want to smile along.