I caught myself staring out the window, watching the birds play and realized that my mind had taken a long walk from the computer – and work – yet again today!

I began to wonder if perhaps there really is “something in the air” at this time of year that sets the world a quiver – and I’m not talking about pollen here.

Research has shown that there does seem to be something that causes us to feel restless, excited or even just plain lazy! This internal “itch” is being called Spring Fever – and it is probably the result of a physiological response to a powerful but little recognised aphrodisiac – light!

Spring rush

While causes for spring fever still remain unclear, the popular explanation is that when seasons change, the retina -- the inner layer of the eye that connects to the brain through the optic nerve -- naturally reacts to the first subtle changes in the amount of daylight. This triggers a chain of reactions originating in the pineal gland, so-called the 'third eye', located in the centre of the brain. As a result hormonal changes take place, including altered secretion of melatonin, a hormone that affects sleep cycles, mood changes and energy levels.

The internal body clock which controls circadian rhythms - the 24-hour cycles of body temperature, hormonal secretion and sleep - is directly affected physiologically by bright light. Darkness acts as a signal to the pineal to start making melatonin and light as a signal to stop. As there is more daylight, melatonin secretion decreases, which means people have more energy, and sleep a little less.

We also become more aware of our body image when the sun shines. The good news is that the winter craving for carbohydrates tends to diminish naturally in the spring.

Why is this? Well – it could be a hangover from our ancestors who had a hibernation-type biology. In the autumn, they began putting on weight to see them through the lean times of winter when food was scarce.

The end of winter blues

Another explanation is that spring fever is the end of the ''winter blues'' that many people experience to some degree. During the long darkness of winter months, the body naturally produces more melatonin. Most of us are now familiar with the term SAD (Seasonal Affective Disorder), a severe form of winter blues linked to sun and daylight starvation. SAD is estimated to affect half a million Britons.

For people prone to seasonal affective disorder, all that melatonin triggers a winter depression. In spring, when melatonin production eases up, so does depression. Confidence returns, along with a reduced desire to eat and sleep and an increase in sexual appetite.

Light therapy is often recommended by physicians to lift some of the melancholy created by the darkness of winter. While some doctors have been highly sceptical of light therapy, a comprehensive analysis published in the American Journal of Psychiatry found not only that the treatment was effective for seasonal depression but that it also eased moderate depression nearly as effectively as the class of antidepressant drugs known as SSRIs (e.g. prozac) which focus on serotonin- the 'mood enhancing' hormone.

And if light affects those who are depressed, it also affects those who aren't. A study of 101 healthy men that was published in the British medical journal The Lancet revealed that the turnover of serotonin in the brain was at its lowest during the dark winter months.

The production of serotonin was "directly related to the prevailing duration of bright sunlight and rose rapidly with increased luminosity." Dazzling spring sunshine during daylight savings time can make even the healthiest people feel as if they have experienced the ideal response to Prozac.”

In spring a young man's fancy turns to thoughts of love

Lord Tennyson, of course, had his mind on that other imperfect science - love - when, in 1842, he wrote his famous ode to spring. Sex drives and energy levels surge for many people in the spring, but we are only now beginning to understand why that is. Studies have shown conclusively that levels of testosterone, the male sex hormone that is attributed with giving us the sexual urge, are higher in the fall. So what is the reason for this spring-time sexual burst?

For hamsters, elephants, mice and other mammals, smell plays a strong role in mating choices; they secrete pheromones indicating sexual readiness, and a member of the opposite sex responds. And while humans are far more complex in their choice of partners, scent does still make a difference. As usual, men and women respond differently.

Warm weather, fewer garments, the gleam of perspiration — not to mention the heady odours of buds and blooms — run riot over the more than 1,000 different olfactory receptor proteins found on neurons in the nose. Our reactions to smells then

mingle with other parts of the brain that govern reasoning, memory and social cues to create an often unconscious, but intensely powerful, emotional response. Part of the feverish quality of spring involves a greater desire to socialize and, perhaps, even to fall in love.

Then, what is spring fever?

This natural high that some of us experience in the spring can also be problematic. Some people experience too much of the elevated feeling and become irritable and irrational at this time of the year. In fact hospital admissions for depression and alcoholism reach a peak during April – as do suicides.

A possible explanation may be that some people simply have a hard time adjusting to all the seasonal changes. If the changes are rapid they don’t have time to adapt physiologically to the new weather, which may lead to physical and emotional breakdown.

Most researchers seem to agree, if only by default, that spring fever may best be characterized as a combination of conflicting emotions, including a sense of comfort, warmth and renewal, amiability and lack of ambition.