We evolved 150 to 200 thousand years ago in eastern Africa. The climate was lovely, like a permanent beach holiday, which had two consequences that are of interest to us. Firstly our ancestors were black (even the ancestors of the Klu Klux Clan were black) this is because their skin produced very large quantities of the pigment called Melanin which was necessary to protect their naked or near naked bodies from the UV radiation in the sun. The second consequence was that they used the sun to synthesise a vital chemical that the human body needs in order to work properly. That chemical is known as vitamin D.
Vitamins are chemicals that cause diseases if we are deficient in them and a lack of vitamin D leads to about 30 different diseases. These include rickets, inadequate hair growth, peripheral vascular disease, cancer, multiple sclerosis, rheumatoid arthritis, juvenile diabetes, Alzheimers, Parkinsons, osteoporosis, heart disease, cognitive impairment and depression. So it is pretty important that we get enough of the stuff.
Of course there was no danger of vitamin D deficiency whilst our ancestors were running round naked in the African sun, but around 60,000 years ago some of them became more adventurous and went exploring, leaving Africa. Gradually they spread, north, south, east and west to occupy most of the planet, but the people who interest this story at the moment are those who set up home in northern Europe.
When they migrated to the north there were a couple of pretty major problems, firstly there was a lot less sun, especially in winter, and secondly it was colder, so it was necessary to cover up most of that black skin with clothes and to spend more time sheltering in a cave or hut. It is easy to imagine what these both did to vitamin D production, it must have been a disaster with all those nasty diseases afflicting the population.
Then evolution came to the rescue. Melanin was no longer needed for sun protection in the north so individuals who happened to have less of it had a competitive advantage because they could make more vitamin D, a classical survival of the fittest situation, Darwin’s natural selection. This meant that they were more likely to survive to breed and to pass on their low melanin genes. Repeat this process many times and we have people with white skin, purely because it gives a vitamin D production advantage when living in the north. Exactly the same process happened with homo neanderthalensis (neanderthal man) who had evolved before us and who also populated Europe before us. So when we first arrived in Europe we were black and the neanderthals were white.
This same evolutionary mechanism happened to a lesser or greater extent everywhere that mankind settled, dependent on the amount of sunshine that the climate provided. So people of the Indian subcontinent tend to have a somewhat lighter skin than the native Africans they were descended from, whilst Chinese people are somewhat lighter again. It is all just a matter of adapting to the environment.
These days the white people of the north (who are now, as a consequence of Empire, spread around the world) have another problem, their ancestors were hunter gatherers who were forced to spend much of their lives outdoors in the environment that provided their sustenance. Nowadays we get that sustenance from the supermarket and spend most of our lives indoors, where there isn’t much sunshine. And when we do go out, in a massive over-reaction to health scares, we often put on sun screen which makes the situation even worse. Hardly surprising then that so many of us are vitamin D deficient and are suffering from all those diseases as a result.
Doctors at the Canadian McGill University Health Centre found that about 59 percent of people tested suffered from vitamin D deficiency and in about 25 percent this was severe. Many other studies in other countries have come to similar conclusions, so worldwide this is causing huge amounts of diseases with the consequent suffering.
Obviously the darker our skin pigmentation is, all other factors being the same, the more likely we are to be vitamin D deficient, as the dark melanin pigment stops the sunlight from doing its job. This is borne out in the worldwide studies, so the darker a person is and the less sunlight they receive the more likely they are to be in danger.
The answer to the Vitamin D problem is obvious, get out more and when we do, uncover more of our skin and go easy on the sun screen. It doesn’t even need to be sunny as lots of UV light from the sun gets through clouds. In the summer, whilst wearing light clothes with arms and face exposed, about ten minutes of sun exposure per day is needed. With less light and more clothes in the winter considerably longer is needed. We cannot overdose on vitamin D from sunshine because there is a feedback loop in our bodies that cuts off production once sufficient has been made.
There is another way and that is to eat foods or take supplements that are rich in dietary vitamin D, fish oils are best for this, most notably cod liver oil, but the vitamin content levels are pretty low. It is probably better if we get vitamin D3 in tablet form. It is also available as D2, but this is chemically less accessible by our bodies, especially as we get older.
Vitamin D has a half life of about three weeks in our bodies. So after 3 weeks half of an initial dose is consumed, after a further three weeks half the remaining dose is consumed (so there is a quarter left), a further three weeks sees half of the remaining dose consumed, and so on. This means that we don’t have to go out in the sunshine or pop a pill every single day.
If we do the sensible thing by supplementing our Vitamin D, especially in the winter, then it is important to realise that large doses are poisonous and will cause us harm. Dosage is measured in International Units (IUs) and most adults need around 600 IUs daily with a maximum of 4,000 IUs, some of this will come from light on our skin, so we need to adjust our dose according to our circumstances.
We have seen how sunshine in our lives prevents loads of diseases by enabling us to produce vitamin D, yet there is even more of importance that it does.
It is noticeable that most people are awake during the day and sleep at night. This is governed by an internal clock known as the circadian rhythm or diurnal cycle. One of the mechanisms that controls this is a hormone called melatonin which is produced by the pineal body which lives in the middle of our brain and which receives messages from our eyes about the presence or absence of light.
The mechanism is very simple, our body doesn’t make Melatonin when there is light and does make melatonin when it is dark. In fact in countries where it is legally available some people use melatonin as a sleeping tablet and if we lived in the land of the midnight sun this could prove very useful.
The big problem comes in the winter when our bodies can start producing melatonin during the day. This helps to cause a common (suffered by 9.7% of the population in New Hampshire) and major mental depression called Seasonal Effective Disorder (SAD), winter depression or seasonal depression. The answer, once more of course, is to get outside as much as possible, exposing ourselves to lots of natural light.
When we travel across time zones our circadian rhythm becomes mightily confused in a phenomenon known as jet lag. But with the knowledge we now have we can see that there are ways to reset our body clocks more quickly to our arrival destination. Travelling west the answer is to stay outside in the bright light in the late afternoon and early evening (not wearing sunglasses!), till dusk basically, this gives our body the information it needs about its new time zone. Likewise travelling east we need to get up at a normal time in the morning for where we are and then get outside as soon as possible to halt melatonin production. Also, whilst sorting our jet lag out, melatonin pills are very effective just before going to bed.
So it is possible to see that sunlight is wonderful stuff which makes us healthier and happier. But unfortunately it has its dark side. Excess exposure to sun can cause DNA damage, premature skin ageing, a variety of cancers, cataracts in the eye and sundry other problems, especially in light skinned people, who as we know are evolved for a relative absence of sunlight.
What we have here is a matter of balance and common sense, of ensuring we have enough sun for the fantastic health benefits that it brings whilst not exposing ourselves to damaging levels. Certainly we shouldn’t put on high factor sunscreen and dark sunglasses every time we go out, this is unhealthy. But definitely we need to stay in the shade during the summer and whilst in the tropics and to avoid exposure in the middle of the day when the light is at its most intense.