A couple of years ago, I wrote about how we all have unique body clocks called chronotypes, which explain why some of us like to rise at first light and others consider the early-bird routine a daily torture. You can't control your chronotype; it's genetic. This was a revolutionary finding for me personally, as I had always beat myself up for not being an early riser. But I never beat myself up again after writing that article. Instead, I adjusted my life to my internal sleep/awake cycles. No guilt and better sleep? It was a win-win.

But even if you're a naturally early riser, sleep experts say waking up really early can be hard on your body. That's because the hormones that govern our sleep-awake cycles (melatonin and cortisol, respectively) are connected to light cycles — that is, the sun.

Sleep expert Dr. Maree Barnes told the New York Post: “When the sun comes up in the morning, the light turns off or suppresses melatonin, which is the naturally occurring body hormone that helps us go to sleep. At the same time, our internal cortisol levels start to rise in the mornings. Cortisol is the same hormone that’s released if you have a fright and get that jolt of energy.”

The potential problem arises if you have to wake up before the sun rises. Your melatonin isn't suppressed, and the cortisol hasn't had a chance to rise high enough — both of which make it really hard to wake up. That can lead to grogginess and moodiness for hours. The fact that it may be cold in your home during darker, cooler winter months doesn't lend any extra motivation. (Tip: if you can, set your thermostat to rise just before you wake up so your house is warmer when you crawl out from under the covers.)

What you can do

Try adjusting your wake-up time closer to when the sun rises, and see how it affects you. Don't forget to keep your blinds or curtains open so you get that morning light into your bedroom.

If you can't adjust your wake-up time, consider getting a full-spectrum light, and turn it on first thing in the morning. Or better yet, get one with a timer that will bring light to your room gradually each morning like the sun would. My partner and I share one of these lights in the winter, and turning it on first thing on dark winter days really helps us wake up — and I swear it improves my mood. I do 10 minutes of yoga and gentle stretching in front of it before I head for the shower or make tea.

And if you're using caffeine to get you going, be judicious about when you drink it. You could be quaffing your caffeine at the wrong time. However, if you time it right, you'll consume less caffeine overall, which means it's less likely to interfere with your sleep when you do hit the sack.

Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.