Physical health

Sunlight is popularly regarded as beneficial due to the production of vitamin D, but also popularly regarded as non essential since vitamin D can also be gained from diet or supplements. However, the process of producing vitamin D uses up specific raw materials. Those materials, if not used up to make vitamin D, are instead used to make a form of cholesterol. Sunlight exposure leads to lower blood cholesterol. The chemical processes are discussed more in this paper.

More recently other studies have shown further benefits to exposure to ultra violet rays, and it has been suggested that the risk of skin cancer is outweighed by the risks involved with low sun exposure. There are suggestions of benefits to blood pressure and heart health.

Some of these studies were carried out using artificial ultra violet sources, so the benefits do not depend on it coming specifically from Earth's sun. The hypothetical habitat would benefit from having ultra violet lamps, ideally at a frequency or frequencies that bring the benefits without damaging skin cells and risking cancer, if such frequencies can be found through further study. The lamps could either be in treatment rooms which inhabitants would regularly visit, or the general lighting could include enough ultra violet light that everyday life would involve sufficient exposure without having to put time aside for it. This would probably depend on the cost of producing such light. If it's cheap it may as well be everywhere.

Psychological health

As explained in DonyorM's answer blue light is involved in sleep regulation. Studies that deprive people of access to a day/night cycle with which to reset their circadian rhythms are short term, so the effects of long term exposure to such conditions have not been studied. However, there are people who are blind and have no light reception with which to reset their body clocks. Reading up on non-24-hour sleep-wake disorder may help you get a better idea of the long term effects. This would be helpful if you are writing a story in which you want to explore the effects on a society of not having sunlight, but less useful if you just want to decide whether your characters need sunlight - if you want to write about a healthy colony you probably already have enough reasons to include artificial sunlight without having to read further.

posted about 10 years ago

trichoplax‭

16 reputation 11 1 2 0

Yes, living without sunlight can affect the human body and mind negatively. I say can because as mentioned in Githubphagocyte's answer, blind people may be affected differently, and different individuals would experience different effects based on their psychological makeup and physical preparedness.

The best first-person account I can direct you to is that of Michael Siffre, an experienced French caver who voluntarily conducted personal experiments involving isolation in underground caves for extended lengths of time. This was to further understanding of how humans may react to being outside of external cues for sleep/wake cycles and the psychological effects of isolation that may be experienced during space travel. In 1962 he spent two months in a glacial ice cave 375 feet underground, and in 1972 was sponsored by NASA to spend six months in a cave in Texas. The entire time he maintained telephone contact with his research assistants, relating his sleeping, waking and eating times

If you can read French, you can find and read the detailed results of his experiments yourself, but basically: He maintained a normal 24-hour circadian rhythm for the first month, but thereafter varied randomly between 18 and 52 hours. After almost three months in the Texas experiment, he started suffering from depression and contemplated suicide. In both experiments he experienced perturbations in his sense of time, and subsequent short term memory loss (apparently short-term memory is highly dependent on time cues). I don't recall anything interesting regarding his physical health, other than his suffering from hypothermia in the first experiment, as I assume he was well-stocked for nutritional needs otherwise, so no ill effects from vitamin D deficiencies.

Wikipedia article: http://en.wikipedia.org/wiki/Michel_Siffre

Interview with Cabinet magazine here: http://www.cabinetmagazine.org/issues/30/foer.php

posted about 10 years ago

hpp3‭

11 reputation 0 1 1 0

Artificial light could be used instead of sunlight. Much of the basis for this answer comes from this article. The article is mostly about sleep cycles, but it includes some pertinent information.

External cues keep the body in sync.

That's the biggest thing. To be completely successful in mimicking life on Earth, artificial light must fade and come back in a rhythmic manner. This sets are body clock and gives us cues to work with. These cues may not necessarily be every 24 hours, but they do need to be regular. Studies have shown that getting light at the wrong times can mess up your body. (This is true on Earth too).

There would also need to be the proper spectrum of light. Our body especially responds to blue light, which is what sunlight is primarily composed of. Blue light stops the production of melanin, which is what puts us to sleep.

posted about 10 years ago

DonyorM‭

11 reputation 6 1 1 0