Astronaut health

Question
I don't know if your the person to ask this question, but I'll give it a shot.  As I understand it, the majority of our vitamin D comes from exposure to the sun.  How, when the astronauts aboard the International Space Station are never exposed to the sun, are said astronauts supplemented their vitamin D needs. Is is just added to their diets or do they take vitamin pills like we do on Earth?  Also, could there be any correlation to possible vitamin D deficiency accelerating bone loss from zero gravity? If your not the person for this question, please forward it to the proper expert.

Answer
Hello, this is an interesting question.  I will do my best to answer the question based on my area of expertise. My background is not in space science so you may want to consider passing your question along to an expert in this field for additional information.

You are correct that Astronauts need to have their diets carefully monitored and Vitamin D must be consumed by dietary sources. Based on the research, it seems that weightlessness during a flight to space does accelerate calcium, vitamin D, and vitamin K deficiencies. It may be that the bone lost in space is never fully replaced once the Astronauts return to Earth. In some cases, bone loss has been fully restored after spending time back on Earth.  

A high calcium intake and vitamin D supplementation during space flight does not affect bone metabolism but it does prevent an elevation of the serum calcium level.  Whether or not the calcium is taken in from foods or through supplementation is not specified but I would expect that RDI's for all nutrients are taken into account when preparing for space exploration.

Hope this helps you out.  

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