As we head into the cooler months, many of us have found our alarms go off while it's still dark outside.

It can make getting up in the mornings a complete battle, and yes, it makes us more tired, according to president of the Australasian Sleep Association, Dr Maree Barnes.

"When the sun comes up in the morning, the light turns off or suppresses melatonin, which is the naturally occurring body hormone which helps us go to sleep," Dr Barnes told news.com.au.

"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."

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So normally when we wake up and the sun has already risen, our melatonin is switched off and our cortisol is switched on, which physically keep us awake.

But that isn't happening right now, with the sun rising in some eastern states as late as 7.30am, by which time many of us are already on the bus to work. For context: On January 1 the sun rose at 5.47am.

"That makes it hard to stay awake and it also affects our mood considerably," Dr Barnes said.

If you've been feeling extra grumpy during the past few weeks, the late sunrise could have something to do with it.

A drop in mood caused by the weather is very common - it's even a diagnosable mood disorder.

Seasonal affective disorder (SAD) is listed in the DSM 5 and mainly affects people living in the northern hemisphere.

Some Nordic countries only experience a few hours of daylight during the colder months and residents can slip into a winter depression.

"Your body is not set up to cope with that lack of sunlight and yes, it makes us feel tired and depressed," Dr Barnes said. "If you don't get enough daytime hours, that can happen."

But there is good news.

With daylight savings ending on Sunday, the sun should start to rise before most of us have to switch the alarm off. Phew!

- news.com.a