"In fact, drinking milk and eating dairy products can rob your body of calcium and contribute to osteoporosis. If you eat dark green leafy vegetables like kale, collards, and mustard greens, you can get enough calcium from a vegan diet."

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Other anatomical changes associated with long-duration space flight are definitely negative: the immune system weakens, the heart shrinks because it doesn't have to strain against gravity, eyesight tends to degrade, sometimes markedly (no one's exactly sure why yet). The spine lengthens as the little sacs of fluid between the vertebrae expand, and bone mass decreases as the body sheds calcium. Without gravity, we don't need muscle and bone mass to support our own weight, which is what makes life in space so much fun but also so inherently bad for the human body, long-term.

— Chris Hadfield