Paul Vallely: The powers that bloom in the spring

We lost an hour's sleep overnight, but, energised by more daylight, we can eat less and achieve more

This is a public service message. You have had an hour's less sleep than usual. This could affect you over the next few days more than you think. Unless you are of Icelandic descent. The clocks went forward at 2am this morning and chronobiologists – pay attention – suggest that the after-effects on your circadian body clock can last for weeks. So watch out for drastically lower productivity, increased susceptibility to illness and general tiredness. You are at greater risk of having a heart attack or committing suicide over the next three days. Perhaps you should just go back to bed.

When I was a boy, I loved the wintertime with its darkening afternoons. I can remember sitting in my primary school classroom by the big old iron radiator, making woollen pom-poms, the school wrapped securely in a blanket of night. But, as the years have passed, my favourite season has shifted inexorably to the spring.

These days, my spirits lift towards the end of January, when the working day no longer begins in the dark and the iris-tipped crocuses first pierce the iron soil. Next comes the forsythia and the early camellia, an unknown white blossom on the tree next door, and now the daffodils. The greyness disperses and blue comes to the sky along with a rejuvenated spirit of optimism. Hullo clouds, hullo sky, as Fotherington-Thomas, no fule he, would put it.

The thing about having missed an hour of sleep is that your serotonin may be depleted. One hour might not seem that significant, but most of us are chronically sleep-deprived already these days. Serotonin is a neurotransmitter that relays information to different parts of the brain. It can have a direct impact on emotions, mood, behaviour, sexual appetite and much more. It is the happy hormone, which the body produces only in daylight but which governs the production of its polar opposite melatonin, the hormone of darkness, which prompts us to sleep as the evening descends. Between them these two maintain the body's diurnal rhythm.

Scientists in China have just discovered something startling about serotonin. Male mice bred without it lose their preference for the opposite sex. Presented with a choice of partners, these serotonin-free beasties were far more likely to mount a male mouse introduced into their cage, emitting the mating call normally sounded when a straight mouse sees a female. A preference for lady mice can be restored by injecting serotonin into the brain. According to the scientific journal Nature, it is the first time that a neurotransmitter has been shown to play a role in sexual preference in mammals.

"No matter gay, straight or bi, lesbian, transgendered life, you were born this way," as Lady Gaga puts it – though that lyric was last week banned by radio stations in Malaysia fearful of government disapproval. Indignant at this censorship, the avant-garde techno-rockist responded by urging her Malaysian fans to protest on the streets. This may sound a good idea to a glam-rock US citizen safely ensconced in Google's Californian HQ. But it is an altogether different prospect in a country with a dodgy human rights record, where bloggers and peaceful demonstrators are subject to arbitrary arrest and abuse in detention camps. It may be brain chemicals other than serotonin that Gaga is low on.

But back to the gay mice. It's important not to make a species leap to humans here, because sexual behaviour in mice is largely driven by their sense of smell, and human sexual preference is governed by a more complex cocktail of factors than what the scientists delicately call "odour cues", notwithstanding Walter Davis's 1930s Mississippi blues classic, "I Can Tell by the Way You Smell".

The most graphic instance of the impact of serotonin can be seen in people who use the recreational drug Ecstasy, which floods the brain with all the body's available serotonin. This produces a heightened awareness of emotion and an intensified sense of intimacy, followed by a low caused by the resulting serotonin deficiency, which can lead to depression.

That feeling, in a form which is less intense but more prolonged, is what is experienced by people who suffer from "winter blues". Now known as Seasonal Affective Disorder (SAD), it was first described by a 6th-century Goth scholar as being common among the inhabitants of winter-darkened Scandinavia, though the people of Iceland seem to have developed genetic immunity. At its worst in December, January and February, its symptoms include lethargy, anxiety, irritability, loss of libido, withdrawal from company, finding it hard to stay awake during the day and difficult to sleep through the night. There is also a craving for carbohydrates and sweets which makes sufferers fatter. In the UK, around seven per cent of people are affected, women more than men, young more than old. It is said to particularly affect those in their twenties.

SAD is also common among creative types. The poet Emily Dickinson wrote three times as many poems in the spring and summer as she did in the autumn and winter, the former being more joyful and the latter dwelling on loneliness and death.

Small wonder, then, that legislators have tried to amend Daylight Saving regimes in the hope it will reduce road accidents, cut electricity consumption, lessen global warming, boost tourism and increase the general happiness quotient. Last autumn, the Energy and Climate Change select committee considered a three- to five- year trial in which clocks are not put back in autumn 2011 but are put forward in the spring of 2012 so that the country operates on GMT+1 in winter and GMT+2 in the summer.

Whatever the economic arguments, the impact on our psychological health could be yet more confusing. Light doesn't do the same things to the body in the morning and the evening, insists Professor Till Roenneberg, a chronobiologist at Ludwig-Maximilians University in Munich. More light in the morning would advance the body clock, which would be good. But more light in the evening would even further delay our circadian body clocks, which would be bad.

We could do something more radical, and revert to the Roman idea of 12 hours of daylight whatever the time of year – so that an hour lasts 44 minutes at the winter solstice but goes on for 75 minutes on the longest day of the year. This might, however, throw the fine timetabling of modern life into some confusion.

So, as the delicate white flowers of the amalanchia tree in my garden are followed by the blossoms of the plum, greengage and then apple trees, I shall be watching for a change. In the folk around me, the symptoms of the winter blues – finding it hard to wake in the morning, overeating, lack of energy leading to an ability to take pleasure in life, pessimism, depression and general feelings of hopelessness – should be dissipated by a warming sun and blue skies. Unless, of course, it has not been the lack of daylight which has been causing all that, but George Osborne's looming slash-and-burn public spending cuts. In which case, we may expect the general SADness only to increase.