Anemia (lack of suitable protein), respiratory issues (from inadequate atmosphere filtration and scrubbing), faster passing of airborne diseases (again, inadequate atmosphere filtration, combined with the closed environmental systems), not to mention the serious issue of getting help quickly when something goes horribly wrong, either through accident or a pre-existing health condition.
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"You know how parents tell you everything's going to fine, but you know they're lying to make you feel better? Everything's going to be fine." - The Doctor
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"You know how parents tell you everything's going to fine, but you know they're lying to make you feel better? Everything's going to be fine." - The Doctor