Thank you for all of your hard work Aunt Scripty <3 My characters are part of a city that has lived underground for security reasons for a 100 years or so. My question is, if a group of 20 or so of them head out into the sunlight for the first time, what range of impacts could it have on their health? They have a physician among them taking notes and comparing it to their condition back underground
Hey there nonny! This is an interesting question, and while it’s an unusual one for me, I’m going to give it a go.
First, I don’t think it’s possible for them to have survived completely underground without sunlight of any kind unless all they’re eating is fish. You didn’t mention whether this is future, present, or past, so I’m going with present and I apologize if I got the time frame wrong.
What Are They Like Underground?
Here’s what the what: remember that these humans need to eat, and mostly what they’ll be eating is plants, and plants need so much sunlight to grow, which means either a) they have at least one area where they get and use sunlight – I’m thinking a big hole in the roof of one area (I’m imagining caves, sorry if this is wrong) and arable soil underneath, b) they only eat what they brought down there with them, bunker style, or c) they are relying on fish from an underground river, which may or may not work and may or may not be enough to sustain your population. Humans can survive almost entirely on fish, but it’s not exactly a pleasant survival to eat the same thing over and over and over again – but I’m sure all of this is stuff that you’ve thought through and already solved.
One of the big questions is Vitamin D. The body uses sunlight to produce Vitamin D from its base components. It’s not found in the human diet so much except in products that we’ve fortified, such as milk, and vitD deficiency is common even in our above-ground world for those of us (like me!) who work indoors.
One thing to look at is therefore a disease called Rickets, in which the bones fail to mineralize properly due to VitD deficiency, and the bones are soft, easy to break, and often deformed. Asthma is another health problem associated with VitD deficiency, especially in children, and VitD deficiency has been implicated in hypertension, heart disease, high cholesterol, and cancer.
Fish does contain a certain amount of vitamin D, but not an enormous quantity, as do egg yolks, so if your characters are eating eggs and fish they might have lesser forms of the disease.
Also, remember that these people will have paler skin regardless of their skin color; that is, even those with heavily pigmented skin won’t tan in the caves because they won’t have sunlight, so they’ll default to only what their genes have given them. Once outside they’ll start to tan – even those with dark skin – and get a bit darker.
Let’s not forget scurvy as another form of malnutrition. Scurvy is Vitamin C deficiency taken to an extreme, which causes weakness, lethargy, sore limbs, bleeding gums, and a general tendency towards bleeding and difficulty stopping bleeding. Scurvy is a big problem that is fairly easily solved; citrus fruits are a natural source, and ascorbic acid, a common preservative, is just another name for Vitamin C. If your characters are eating large amounts of preserved food, and that food is preserved with ascorbic acid, it’s likely that they won’t have horrendous vitamin C deficiencies, especially if they’re eating canned citrus on the regular.
In short, your characters might be fairly sick from living the lifestyle that they’re living, depending on what they’re eating and how much.
Here Comes the Sun (doo-do-doo-do!)
And I say, it’s alright…
There are a lot of impacts seeing the sun for the first time could have on their physical welfare, and it’s worth taking a look at all of them.
For one, their eyes are going to have to take some time adjusting to the brightness. I don’t think there would be any actual damage per se, but headaches and vision troubles could be a problem in the first few days.
Myopia might be A Thing, since, having never been outside, these characters may never have had to use their distance vision; they may be near-sighted. They may have trouble focusing on things at a distance.
For another, VitD deficiency is going to get a lot better because, well, humans make Vitamin D in the presence of sunlight.
A whole mess of them are going to get sunburns, including those with dark skin, and depending on the time of year and the latitude at which the characters’s underground home was made, they might wind up with blisters or sun poisoning. Heat exhaustion during the summer is going to be A Thing.
If it’s winter, there’s actually a different problem, which is – the temperature underground tends to be remarkably resistant to changes in temperature above the surface, so their cave / bunker might be a very consistent temperature, and they might not be prepared for winter up above. Frostbite, frostnip, hypothermia might all be common, since temperatures underground tend to be in the 50s-60s(F), where temperatures above can be…. extremely cold, by comparison.
Next question: what do they eat when they’re Above? Are they eating the flora? is the flora safe to eat? Consider what they might decide to eat, and look at the health consequences of that. Blueberries might be fine, and if they hunt, hunting animals might be fine, but if they went underground to escape, say, radioactivity, and they start eating radioactive plants, they miiiiight wind up with radiation poisoning. Also, those with genetic allergies might discover those allergies Up Above that might not have bothered them in the cave, though most allergies will take time to develop.
Lastly, where are they getting their water? Is their water safe to drink? If they’re downstream of a place with poor sanitation, cholera could definitely become a problem, as could various forms of worms; if they’re smart they’ll have some form of purification system (iodine tablets, UV purifiers, boiling) but if not, they may get sick from the water.
In short, the sunlight itself isn’t really that big of an issue beyond sunburns (which no one will know how to prevent), but there are a lot of nutritional issues that you might want to consider when building your story and your world.
I hope this has been useful and I’ll gladly see you later. Bye bye!