a frosty, fiery sleepy-head;

Blinks but an hour or two,

and then; A blood-red orange, sets again.

Sunlight is powerful stuff,

perhaps more powerful

than most people realise.

Every aspect of how we function is controlled by light.

In winter we are seeing a lot less sunlight.

The perils of living without sunlight are really quite real.

In some ways, modern life

has driven us back to the Stone Age,

when we lived in caves.

In the 60s there were several experiments

by French people who went into caves and stayed there.

They all began to sleep either for extraordinarily long periods of time

or extraordinarily short periods of time,

and they couldn't tell the difference.

They all said they had severe mood disturbances and depression,

so much so that some of them had to leave

long before they really had planned to.

In winter, we often feel somewhat out of sorts at this time of the year.

A lack of sunlight means that your immune system doesn't work as well,

your defence mechanisms don't work as well.

An effect on mood, increased depression,

more metabolic disorders,

and all of these things are offshoots

of a disrupted circadian clock.

It times all of our physiology and all of our behaviour.

All of the active sorts of processes

are compartmentalised to the day,

and all of the restorative processes are kept to the night.

The wavelengths that have the most powerful impact

are the bluish-coloured ones.

Within our eyes there are these cells

that have a pigment that's sensitive to this blue light,

that then signals to the body clock to tell it what time of day it is.

Before the stars have left the skies,

At morning in the dark I rise;

and shivering in my nakedness,

by the cold candle, bathe and dress.

Many people don't realise what an artificial life we live.

That's because artificial life depends on artificial light.

So by seeking out artificial light,

what that is doing is giving your body a time cue

that is incorrect.

Then you might end up feeling far more alert at night,

or a lot more depressed during the day.

Your systems within your body tend to desynchronise

and so you tend to have a higher incidence of diabetes,

obesity, cardiovascular disease.

The World Health Organization sees shift work

as a threat to health, and it is.

Many British people spend less than half an hour a day in the open air.

So it's no good staying inside and looking at the Sun

and saying this is doing me good, because it isn't.

So it's probably, on a day like today,

about four or five times less light

simply being on this side of the glass.

A good dose of bright sunshine at any time during the day

has a huge impact on elevating mood

and general feelings of wellbeing.

There was a study at the Broadmoor institute

where they looked at the effects of the equivalent

of 20 minutes of bright sunshine in the morning on mood.

What they found was the bright light

had a much greater effect

on elevating mood

than even some anti-depressants.

When to go out, my nurse doth wrap me in my comforter and cap;

The cold wind burns my face,

and blows its frosty pepper.

So our skin's not just a barrier, it's a living organ.

When our skin sees sunlight, that is when it starts making vitamin D,

which is an essential component

of many different signalling pathways in our body.

You can get vitamin D in several ways.

You can do what I do, and take a vitamin D pill.

A diet of wild salmon and mushrooms and you won't get rickets.

But overwhelmingly the best way is through the Sun.

It's coming back for genuinely depressing reasons.

The amount of sunlight we're getting

has gone down dramatically in the last 20 years.

It's gone down particularly fast in the last two or three years.

We're not getting outside, and this is going to have an impact

on how well the body clock is aligned.

It makes us even more like hermits in a cave relying on artificial light.

Have meals at the right time, go to bed at the right time,

and get out, even if it's freezing, for that daily 20-minute walk

and some light exposure.

Simply being outside and exposing yourself to light,

so that you strengthen your circadian clock

is going to have a hugely beneficial impact on health and wellbeing.

Don't retreat into your cave.

In other words, when the sun comes out,

go out and have a good time, that's the medical advice.

Black are my steps on silver sod;

Thick blows my frosty breath abroad;

And tree and house, and hill and lake,

Are frosted like a wedding-cake.