Have there ever been any studies on the effects on the body from space travel?

I know a large percentage of the body is composed of water, adn we know what happens to liquids in space, due to the absence of gravity. Does space travel have detrimental effects on astonaunts? Have there ever been any studies in regards to this? Thanks.
There are some really good answers on here, and some very informative links, thanks all! I'm suprised no one has asked this previously on here.

Zero gravity can cause bones to become weak over time and i also read somewhere that space sickness and kidney stones are a problem as well.

space travel can lead to a number of serious health problems...i know they've done studies of the effects. i don't know the name or details, sorry, i just know that John Glenn asked to participate in the study after he had finished being an astronaut, b/c he was old & felt that if he ended up dying from the negative repercussions and side effects of space travel, it would be a good way to die. they didn't let him participate in the study, though. sorry, that's all i know about it! i know there are a number of serious health concerns associated w/ space travel...that's about all i know, though. sorry, i don't know the name of the study that was done.

Well, if you don't see things from earth like plants, ect, you could go CRAZY! I mean like scycho, overly-drunk type of behaivior.

NASA must have some of that info somewhere.

Astronauts who travel in space are at risk for bone loss in much the same way that cancer patients who receive radiation therapy are, and both groups are more likely to develop fractures than the general population.

Investigators have studied the effects of the space environment on a number of biological processes, including visual and motor functions; regulation of the autonomic nervous system; sleep and daily biological rhythms; and learning and behavior. These experiments could have practical value on Earth as well. An instrument developed to combat motion sickness in space, for example, may be useful to physicians to detect the onset of shock and in diagnosing circulatory disorders such as Raynaud's syndrome.

there have been many studies done on the physiological effects of space flight, many of them focusing on the deterioration of bones and skeletal structure; Johns Hopkins did a study on whether space flight affects blood vessels and if that leads to an increased chance of heart disease for astronauts (http://www.sciencedaily.com/releases/1997/09/970912055945.htm)

If you search the web for medical effects of spaceflight, you will get a lot of resources; this is something the US, Russia (and earlier the Soviet Union) and the European Space Agency are very concerned with so there has been a lot of research into the issue