By Markham Heid
September 17, 2014
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Evenings are chillier, the leaves are starting to turn, and every guy you know is yapping about football. Fall is right around the corner. And as the days grow shorter and the weather cools, your brain and body will react to the changing season in more ways than one. From your mood to your sleep, here's how fall may throw you for a loop.

Autumn and Your Energy Levels

Ever heard of hypersomnia? It's the technical term for sleeping too much (the opposite of insomnia) and it tends to crop up during the fall months. In fact, most people sleep more in October-roughly 2.7 hours more per day-than during any other month of the year, shows a study from Harvard Medical School. A little extra shuteye may sound like a good thing. But the same Harvard study found the quality and deepness of your sleep also suffer, and people report feeling groggier during the day. Why? Thanks to shorter (and often rainier) days, your eyes aren't exposed to as much bright sunlight as they enjoyed during the summer, the authors say.

When ultraviolet light hits your retinas, a chemical reaction takes place in your brain that firms up your circadian sleep rhythms, ensuring you sleep soundly at night and feel energized during the day, the study authors say. So, like switching from a daytime to an evening work schedule, the sudden shift in sun exposure caused by the advent of autumn may knock your sleep cycle off balance for a few weeks, the research suggests. The sun doesn't just set your sleep clocks; when it hits your skin, it also fortifies your vitamin D levels. In the autumn (and winter) the lack of sunlight means your D stores may become depleted, which can leave you feeling fatigued, shows research in the New England Journal of Medicine.

Moody Blues

You've probably heard of (and maybe even experienced) seasonal affective disorder, which is a blanket term for depression-like symptoms that crop up when the weather cools. From a slightly down-in-the-dumps feeling to major melancholy, multiple reports have linked seasonal affective disorder, or SAD, to both lower vitamin D levels and poor sleep. While multiple studies have all but cemented a link between vitamin D and your mood, the mechanisms that tie D to depression aren't well understood, according to a research review from St Joseph's Hospital in Canada. Those researchers found depressed women who took a vitamin D supplement pill for 12 weeks experienced a significant lift in spirits. But they can't say why that happens, apart from a possible connection between "vitamin D receptors" in your brain and your noodle's mood circuitry.

Not only can fall leave you sad and sleep-deprived, but you also tend to eat more carbs and spend less time socializing in the autumn compared to the summer, shows a study of young women from the National Institutes of Mental Health. While fatigue may explain your lack of sociability, the cooler weather could somehow encourage your brain and belly to seek out insulating calories, like a bear preparing to hibernate, the research suggests.

But It's Not All Negative

The end of scorching summer temps may benefit your brain too. Your memory, temper, and ability to problem solve all take a hit when the thermostat shoots above 80. Why? As your body works to cool itself, it draws energy away from your brain, undercutting its ability to operate optimally, shows a study from the U.K. Also, nearly all of the above studies point out that different people experience the seasons in different ways. If you hate the heat of summer, you may actually spend more time outside in autumn, and so experience a boost in mood and energy. Plus, you've gotta love a little apple cider, the color change, and breaking out all your favorite sweaters. So don't fear the fall. Just keep your friends close (and your vitamin D supplements closer).