Question

Commander Scott Kelly landed in Kazakhstan on Mar. 2, 2016 after 340 days on the International Space Station. Medical tests found his heart rate and blood pressure elevated, that he had significant atrophy of his skeletal muscle and that his DEXA scan Z-score was -1.8. His total body calcium was 83.85% of that before launch.

Why did he experience loss of total body calcium and have a low Z-score?

Answer 1

Generally, bones constantly reshape themselves in relation to the stress that is put on them. Just sumilar to muscles, when bones are not used, they eventually weaken. Bone loss occurs in the microgravity environment of space because bones no longer have to support the body against gravity.

Dexa scan is used usually used to determine the bone density.It is reported as T-scores and Z-scores, in which,T-score is a comparison of a person's bone density with that of a healthy 30-year-old of the same sex and Z-score is a comparison of a person's bone density with that of an average person of the same age and sex. So, low Z score means low bone density. Studies show that in the microgravity environment of space, astronauts lose on average 1% to 2% of their bone mineral density every month.

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