Catch
Jesse
Today’s theme is “sunbathing.” It feels nice to soak up some gentle sunlight, doesn’t it?
Opening
Jesse
Hi there. Thanks for pinging in today.
This is ShortWave – 18th Ping.
I’m Jesse, your virtual host on this frequency.
Peter
And I’m Peter. A kind of virtual host, I suppose.
Since September began, the heat has eased considerably.
It was the sort of heat that made one hesitate to venture outside; at last, it feels possible to be active again.
Jesse
The sunlight has softened quite a bit too, so it’s a much nicer time of year for sunbathing.
…Speaking of sunbathing, there’s something I’ve been wondering about for ages.
Peter
“Sunbathing.” A very Jesse sort of word.
Very well. Let’s attempt an answer.
MAIN PART
Peter
Then, what precisely is the question?
Jesse
You know how people say your body makes vitamins when you get sunlight?
How does that actually work?
Peter
Ah. That.
It is the matter of ultraviolet radiation in sunlight — UV-B in particular — striking human skin and causing the body to produce vitamin D.
Jesse
Right, that.
I know vitamin D is considered essential for maintaining healthy bones, but I’ve always wondered why simply being in sunlight makes your body produce it.
We’re not photosynthesizing like plants, are we?
Peter
I see. One would indeed wonder about the process itself.
The mechanism becomes somewhat involved, so I shall simplify it.
First, when sunlight — UV-B — strikes the skin directly, an organic compound in the skin called “7-dehydrocholesterol” undergoes an electrocyclic ring-opening reaction.
Consequently, the B ring of the steroid nucleus opens, forming an intermediate called “previtamin D3.” This intermediate then spontaneously becomes “vitamin D3.” The process is known as “isomerisation.”
Incidentally, “isomerisation” means that a compound undergoes a chemical reaction and becomes an isomer — something with the same molecular formula, but a different chemical structure.
Jesse
I see. So the body makes vitamin D from sunlight.
How long do you actually need to spend in the sun?
Is there a rough guideline?
Peter
A definitive figure is difficult to provide. There are considerable regional differences, depending on such things as the number of sunshine hours and the amount of ultraviolet radiation.
Naturally, sunscreen makes it more difficult for ultraviolet radiation to reach the skin, so that should be borne in mind. Receiving sunlight indoors through glass is also of little effect.
Incidentally, I would not recommend using a sunbed for the purpose of producing vitamin D.
Jesse
I don’t want to get a tan, but I still want to enjoy sunbathing. That sounds like a difficult balance — especially in summer.
Peter
In such a case, dietary intake may be the simpler option.
Salmon, Pacific saury and eel are apparently rich in vitamin D, so fish may be a sensible choice. Or, perhaps, supplements as a secondary source.
Jesse
Something just occurred to me.
Could too much sunbathing make your body produce too much vitamin D? And what happens if you have too much vitamin D?
Peter
First, an excess of vitamin D raises the risk of hypercalcaemia. Loss of appetite, weight loss, polyuria and arrhythmias may also occur.
In extreme cases, blood vessels and other tissues may calcify, potentially causing damage to the heart or kidneys. An increased risk of kidney stones has also been reported.
However, the amount of vitamin D produced through sun exposure is regulated; excessive sunlight is therefore not considered to cause illness through vitamin D excess. One should be rather more concerned about the effects of sunburn.
Dietary vitamin D is, for practical purposes, very unlikely to cause an excess. Supplements, however, warrant caution.
Conversely, deficiency can lead to rickets in children, and osteomalacia or osteoporosis in adults. This is because the absorption of calcium and phosphorus is impaired.
Vitamin D is hardly unique in this respect. Too much is no good; too little is no good. A balanced intake of nutrients remains important.
ENDING
Jesse
The deeper you dig, the more there is to learn.
I feel like I could write ten papers with what I learned today.
Peter
Ten may be ambitious.
Still, it may be worth keeping some of this in mind the next time you enjoy a little sunbathing.
Jesse
…I just had a great idea.
What if I simply stuck the Sun directly onto my skin?
Wouldn’t that be an efficient way to make vitamin D?
Peter
Jesse’s imagination truly is unique. I would not recommend it, however.
Far too bright. You would have difficulty sleeping at night.