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Raymond Lam

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In the spring a young man's fancy

lightly turns to thoughts of love.

– Alfred, Lord Tennyson, Locksley Hall

Between the polar vortex and the late April snowfalls, most Canadians waited impatiently for the ice to melt and the temperatures to climb. Many of us emerged from the winter blues when the dark winter evenings yielded to the longer days of spring. Our mood improves, we have more energy and interest, and we shed those bulky winter clothes to become more active outdoors. For some, this means staying up late and waking earlier. Others can feel giddy. And for a few, seasonal affective disorder is replaced by spring fever – including a marked increase in sexual appetite.

But is spring fever real, and does it have a biological cause?

The Djungarian hamster and the American mink will say yes. Both animals are "long day breeders" and show seasonal changes in mating behaviour with the onset of spring. They get frisky, their sex organs mature, and they mate in the spring.

The seasonal breeding behaviours in hamsters and minks are controlled by melatonin, a hormone produced by the pineal gland in the brain. It's also called the "dark hormone" because it is only produced in the dark, while bright light turns off production. There is higher secretion of melatonin during the longer winter nights and less secreted during the shorter nights of spring and summer. For many animals, the changing levels of melatonin signals their brain to start seasonal mating behaviours.

In humans the role of melatonin is not as clear. We don't show the same clear seasonal changes in mating and breeding behaviour that these animals display. But melatonin may still play a role in people with seasonal affective disorder. After all, during the low mood and energy in winter, sex may be the last thing on your mind.

Melatonin may not be the only biological cause of seasonal mood changes. Some neurotransmitters, chemicals that brain cells use to communicate with each other, also show seasonal rhythms. Serotonin is a well-known neurotransmitter that helps regulate sleep and mood.

The lowest levels of brain serotonin are found in the winter and highest levels in the spring and summer. The changing levels of serotonin may help explain why many people feel better and more energetic in the spring.

Some people with bipolar disorder can overshoot the mark when emerging from winter depression. Manic episodes peak in the spring – feelings of euphoria, racing thoughts and less need for sleep – leading to hyperactivity and impulsive behaviour. Increased sexual appetite can also lead to problem behaviours, including unsafe sex.

But depression and suicide rates are also increased in the spring (and fall).

Maybe the spring doesn't bring the hoped-for improvement in mood in some people, leading to disappointment and depression. Or maybe the rapid changes in light and neurotransmitters can make people more impulsive. Whatever the reason, mood can either improve or worsen with the change from winter to spring.

We may not be Djungarian hamsters, but we can still enjoy spring fever, as long as it is mild. But we need to monitor our springtime moods and seek help if problem behaviours occur. And be sure to practice safe sex!

Dr. Raymond Lam is a professor of psychiatry at the University of British Columbia and medical director of the Mood Disorders Clinic at the Djavad Mowafaghian Centre for Brain Health in Vancouver. He has written nine books on depression, including A Clinician's Guide to Using Light Therapy by Cambridge University Press. Follow him on Twitter @DrRaymondLam.