During school holidays I usually stay up late because I have a computer in my bedroom with 24 hours broadband Internet connection. Usually I sleep at about 3am and wake up at midday. I have read medical journals that say that lack of sleep is bad for me but even if I sleep at 3am and wake at midday I still get more than 8 hours of sleep so there is no sleep deprivation. However, is sleeping in or staying up harmful for my health? Does my body need to be exposed to sunlight at certain times?

How old are you? Younger kids, teens, and young adults need more sleep because their metabolisms are high and they burn a lot of calories and their bodies need more time to rest and recuperate and regenerate new tissue as they are still growing.

If you are between 15 and 21 years old, you need 10-11 hours sleep each day for proper body function.

As far as the sunlight question: not at certain times. Sunlight is overrated and if you eat right you get everything you need.

Old guys like me can make do with 6-8 hours a day.

If you aren't sleepy during the day, you are getting plenty of sleep.Like Lar-ss said, you only need 10-15 minutes of sun, for Vit D synthesis, and you don't even need that much if you drink milk(it is fortified with A &D.
A few minutes of sun a day is probably a good idea no matter your Vit. status.
Don't worry about sleep, if you aren't sleepy.
Charlie
PS-I'm 55yo, and feel OK on 7 hours.

Sunlight's less of the issue so much as EXERCISE. Even as a geek myself who had that same schedule for YEARS, I made time to get outdoors to talk a walk, go hiking or bicycling or other outdoor activities.

It's all about balance, IMHO.

- Shannon (Geeky, Wild Texan)

Some people have a condition called seasonal-affective disorder, which means that their emotional condition is unusually affected by the weather. If those people don't get enough sunlight, they can have problems. Generally, there are beneficial things about getting enough sunlight for all people, even the ones who don't actually have a disorder- it can make you more cheerful, it can improve alertness or coordination, and natural lighting is better for your eyes, perhaps because human vision evolved under this sun and within its electromagnetic spectrum of ambient light.

However, all of these things are mostly peripheral. If you're doing fine without getting much sun and you sleep enough, exercise enough, eat well enough, and all the rest, there's no particular reason why being awake at one part of the day rather than another should impact you. Plenty of people work the night shift, and you can always think of it as being on a different time zone.