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How seasonal shifts in light and darkness affect moods, weight gain, and fertility

Living in a northern city like Edmonton, it’s impossible not to notice the wild swings in daylight from season to season. At the summer Solstice in June, we have just over 17 hours of daylight, whereas at the winter Solstice in December, it dwindles to a mere seven and a half hours.

Many cultures have a tradition of gathering with family and friends to eat, drink and celebrate with bright lights as the days grow shorter. Diwali, the Hindu festival of lights, involves decorating homes with lights and candles, and Hanukkah features the lighting of candles on the Menorah for 8 days.

Decorating with strings of lights is a marker of the Christmas season, but what really sets it off for me is when it’s fully dark at 5 pm, and I see the glowing red lights of the cars ahead of me lighting up the traffic as I head home from work. At this time of year, the days are so short that many people are heading to and from work or school in complete darkness, missing the daylight entirely.

As the darkness sets in, the changing light levels affect us in different ways. Some people suffer from seasonal affective disorder, a form of depression triggered during the winter months. To help relieve their symptoms, there are specially designed lamps for use each morning to mimic the intensity of sunlight. These lamps can make a big difference in improving the moods of SAD sufferers, as can taking extra vitamin D when the body is not getting enough sunlight exposure to produce its own.

Many people succumb to the temptation to eat carbs in the depths of winter, and it’s no coincidence that a number of the traditional seasonal treats are sweets. According to the authors of Lights Out: Sleep, Sugar and Survival, these cravings have a great deal to do with the body’s reaction to light – and particularly, the fact that we spend hours every night bathed in artificial light after the sun sets.

Foods with a high sugar or carbohydrate content are mainly available in nature in late summer, when the days are long, and when it makes sense to put on a little extra weight to prepare for the coming winter. The authors say that artificially extending the day with electric lights in the winter months tricks the body into thinking it’s late summer, and therefore, time to consume carbohydrates and gain weight. In our modern lifestyle, high sugar foods are constantly available, making it easy to satisfy these cravings.

There are a few ways to get around this, such as by making sure to eat balanced meals containing protein, vegetables and healthy fats in order to stabilize blood sugar and reduce carbohydrate cravings. This also has the added benefit of keeping moods stable throughout the day, particularly for those who are susceptible to hypoglycemia.

Going to bed earlier makes a difference, especially if you are able to arrange your schedule in order to get nine to nine and a half hours of sleep a night. Getting some extra sleep in the winter months helps the body heal and repair, and is beneficial for the immune system and the endocrine system.

It can also help to dim the lights in the hour or so before you actually go to bed. Turn off screens and devices and glaring overhead lighting, and wind down with softer lighting. This kind of transition mimics the natural gradation of twilight and can make it easier to relax and fall asleep.

There is also evidence that women’s menstrual cycles respond to light exposure at night. Women who are experiencing cycle irregularities often see improvements by sleeping in a completely darkened room. To get results, the room has to be totally blacked out, with no light whatsoever, not even a tiny crack of light from the window or the glow of a clock radio. It should be so dark you can’t see your hand in front of your face.

Eliminating nightly light exposure in this manner can help regulate menstrual cycles, balance a woman’s hormones, and improve her chances of getting pregnant. Through cycle charting (recording daily observations of cervical mucus and temperature), a woman can assess the health of her cycles and determine whether sleeping in total darkness may be of benefit to her.

The authors of Lights Out also make the intriguing suggestion that humans may have at one point been seasonal breeders like other animals, before exposure to firelight at night stimulated our hormones to allow for reproduction year-round.

There is some contemporary evidence for this, since more Canadian babies are born in early spring and summer, with comparatively fewer births between November and February. It is difficult to say whether this is due to seasonal shifts in fertility, or to the preference of would-be parents for summer births. However, there is often a spike in births in September that can be attributed to holiday conceptions, which is certainly one way to celebrate the long, dark nights.

This article was previously published in Wellness Alberta Magazine.