Celestial Challenge – Monday, Darkness: December is the darkest month in the north. Bring on the light!

It's a sad fact that death rates increase during the winter months, and the reason for this might surprise you.

Many people have personal experience of this phenomenon. An older relative of mine, who was in his 90s but seemed in robust health, died last week. A friend's uncle died suddenly a few days ago. My father died five years ago today.

Research shows that this is a very real phenomenon. According to the Office of National Statistics, in England and Wales, 27% more people died in the winter months of 2014-15 than in the non-winter months, and 20.9% more people died in winter 2016-17 than in the non-winter months.

National records for Scotland show similar trends – in fact, nearly all countries in the world report "excess winter deaths". You'd expect these deaths to be due to the cold weather, but in fact there is no overall link between an increase in excess winter deaths and cold weather. Countries like Spain and Portugal have more excess winter deaths than the Scandinavian countries.

The phenomenon is also not related to socio-economic status, and there is no single illness responsible for the increased winter death rates – though it's certainly possible that many people's immune systems may be weaker in the cold, dark winter months.

But there is one significant factor that is often overlooked when considering this issue.

Darkness.

As the nights get longer and the days get shorter, there is less sunlight – and therefore, less vitamin D to absorb through the skin.

Vitamin D isn't actually a vitamin at all – it's a hormone that is made by the action of sunlight on our skin.

Shorter days = more darkness = less sunshine and therefore less vitamin D.

Vitamin D is essential for healthy bones, and its importance for other aspects of our health is only just starting to be recognised.

Increased mortality

Recent research conducted in Denmark found a causal relationship between low levels of vitamin D in the genes and increased mortality.

The study of 96,000 Danes looked at mortality rates from 1976 up to 2014, and found that people with low genetic levels of vitamin D had an increased mortality rate of 30 percent.

Too much darkness, it seems, can seriously endanger your health.

We need darkness to help us sleep, but we also need sunlight.

So if you live in latitudes that are distant from the Equator, how do you get enough vitamin D to see you safely and happily through the winter? The best source of vitamin D is sunlight, but in the northern hemisphere, the winter sun is too low to provide sufficient levels of vitamin D for health.

If your shadow is longer than you are, this means that the sun is too low in the sky for your body to make vitamin D. This is my shadow on a sunny winter day in winter. No vitamin D here, sadly!

Unfortunately your body won't make vitamin D if you sit in a conservatory either, as glass blocks the UVB portion of the sun's rays, and it is the UVB rays that your body needs to make vitamin D.

You can build up your stores of vitamin D in the summer months by going out in the sunshine, as Vitamin D can be stored in the body fat.

In the absence of enough sunlight, sunbeds, vitamin D supplementation and eating dietary foods high in vitamin D, such as oily fish or cod liver oil, can help to build levels up.

Roll on December 21st, the winter solstice. From then, the days start to get longer – in the northern hemisphere at least.

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Wishing you all the best of health!

This is my entry for today's Celestial Challenge created by the good @sirknight.

The daily themes are as follows:

Sunday-Light
Monday-Darkness
Tuesday-AnimalKingdom
Wednesday-Structures
Thursday-ForcesinNature
Friday-LoveBeautyFreedom
Saturday-Agriculture