**6.3 Cardiovascular system**

These changes have been observed:


**71**

*Vitamin D in Space*

*DOI: http://dx.doi.org/10.5772/intechopen.82314*

• Changes in venous function [42]

advantages and disadvantages) [9].

**6.6 Central nervous system (CNS)**

**6.7 Autonomic nervous system**

**6.4 Respiratory system**

**6.5 Blood**

Earth [49].

**6.8 Sleep**

**6.9 Eye**

infarcts [51].

**6.10 Skeletal system**

traveling to other planets [52].

• More sensitive to space radiation (opposite to previous studies) [12]

• Spaceflight anemia (reported frequently) [43, 44]

arrangement, and (6) mental and/or physical factors [50].

• Sustained increase of RBC and platelet [45]

sensorimotor, and vestibular brain regions [48].

The heart does not work against gravity, so it has less work (with associated

Different results have been published by studies, so the comparison would not be easy due to the environmental bias and the variability of experimental protocols [9].

Currently, there is little known about CNS alterations in space [46, 47]. The following structures are more affected than other parts of the CNS: cerebellar,

Orthostatic stress has been reported, but its severity is less than on the

Sleep problem is a common issue in space. It may affect the health of astronauts, so the safety of the mission would be endangered. Six causes for sleep alterations might be (1) factors related to cabin environment, (2) schedule adjustment, (3) impaired sleep discipline, (4) disordered circadian rhythm, (5) unreasonable work

Spaceflight-associated neuro-ocular syndrome has been reported which is associated with optic disk edema (unilateral and bilateral), flattening of the eyeball, folds of choroid and retina, hyperopic refractive error shifts, and nerve fiber layer

Most changes occur in the skeletal system. Osteoporosis can be a major obstacle to the actions and activities of astronauts, especially in long-term missions and/or

Skeletal changes in spaceflights seem to be the most important alterations because they may limit or even stop a space program [53]. Rate of monthly 1–2% bone loss has been postulated during spaceflights [52] and 0.5–1.5% by some other investigators [54]. It could be up to 15%. Returning to normal values after landing

• Loss of arterial pressure gradient [9]


The heart does not work against gravity, so it has less work (with associated advantages and disadvantages) [9].
