PARTIAL
SOLUTION TO BONE LOSS DILEMMA
SPACEFLIGHT. 48:352, 2006
Even with 2 hours of exercise a
day and a “ good diet “, astronauts return to earth weakened after a few months
in space with some crew members unable to get out of their seats or walk, according
to Jeffrey Jones, director of NASA’s medical operations for exploration at the
Johnson Space Center. I have emphasized that for a Mars mission, a total of 4
hours of exercise a day (15 minutes out
of every waking hour) might be required.(1) but this countermeasure alone would certainly not be sufficient to prevent
osteoporosis. With loss of the bone reservoir there is in turn loss of
magnesium (Mg.) which serves as a bone protector since it plays a vital role
along with calcium ( Ca.) in the synthesis of bone. Mg. also serves as “nature’s
Ca. blocker”, thereby blocking an
excess amount of Ca. from entering and destroying the energy- producing
machinery of the cell (mitochondria ).(2)
In addition to insufficient
exercise (hypokinesia) there is the predisposing
factor of invariable malabsorption responsible for a progressive deficit of both
Mg.(2 ) and Ca. The fractional Ca. absorption (based on the percentage of the
dose administered) is markedly reduced to only 4. 4 % on the
19th.flight day, in comparison with 13. 4 % fractional Ca.
absorption before flight.(3)
Compounding this is the problem
with Spaceflight-reduced appetite with the pattern of space osteoporosis,
similar to the pattern of Anorexia Nervosa patients (4) .For example on 3 missions
(Spacelab D2, Euromir 94, and Euromir
95) the energy intake in 8
astronauts was reduced by over 20 % in most of them in relationship
to the astronauts’ calculated energy expenditure. (5)
I believe several measures are necessary
to correct these problems:
First: In addition to increasing
exercise duration (1), the total Ca. intake should NOT be greater than a 2: 1
ratio in comparison with the total intake of Mg. If the Ca / Mg. ratio exceeds
this 2: 1 level, there will be a reduction in the gastrointestinal absorption
of Mg.. which, as I have pointed out, is also
essential in preventing osteoporosis by its important role in the synthesis of bone (6 ))and would
accentuate the problem of SF- malabsorption (2).On
earth the recommended total intake of daily
Ca. need not exceed 1000-1200 mgm. with
the total intake of Mg. 500-600 mgm./ day. (7). No specific spaceflight recommendations as
to Ca. and Mg. requirements on a daily basis can be made since the requirements
will change with duration of the mission.
Second: In addition to the
requirement for subcutaneous Mg. (2), similarly Ca. must be given
subcutaneously for long missions and both will require a subcutaneous delivery
device to serve as a substitute for progressively diminished Ca. and Mg.
reservoirs. Such a device is not yet available because it can not be
replenished after leaving the manufacturer. (2)
Third: Both Ca. and Mg. and Ca / Mg ratios can be very accurately measured with
the availability of intracellular assays by obtaining – as often as necessary-
serial smears from the buccal mucosa. The equitmaent
can be made small enough for spaceflight requirements and one can be readily
trained to perform these studies.(2)
Finally by adhering to a total
intake of 2:1 Ca./ Mg. ratio there are vitally
important cardiovascular dividends. A ratio above this level is conducive not
only to impairment in Ca. absorption, but to impairment in bone perfusion,
triggered by an increase in the release of adrenaline, enhancing the
invariable elevations of adrenaline in space (8) and conducive to
dangerously high heart rates( particularly during space walks ), spasm of blood
vessels, oxidative stress and clot formation, along with progressive
damage to the lining of the blood
vessels (endothelium)(2).It is noteworthy that Finland with the highest Ca./Mg.
intake ratio – much higher than the
ideal 2: 1 ratio – has the world’s highest
cardiovascular morbidity and mortality rate. ( 6,
7)
William J Rowe M.D. FBIS
References
1.W.J. Rowe. A better way
to exercise in space SPACEFLIGHT 45, p 480,2003.
2.W J Rowe. The case for
a subcutaneous magnesium product and delivery device for space missions J Am Coll Nutr 23, pp 525 S-528
S, 2004
3.Zittermann A, Heer M, Caillot-Augusso
A et.al. Microgravity inhibits intestinal calcium
absorption as shown by a stable strontium test. Eur J
Clin Invest 30, pp. 1036-1043, 2000
4. Heer
M, Kamps
N, Biener
C et.al.
Calcium metabolism in microgravity Eur J Med Res 4 :pp. 357-360, 1999
5. Heer
M. Nutritional interventions related to bone turnover in European space missions
and simulation models. Nutrition 18, pp.853-856, 2002
6.. Seelig MS. Epidemiologic data on
magnesium deficiency-associated cardiovascular disease and osteoporosis :consideration
of risks of current recommendations for high calcium intake . In :Rayssiguier Y, Mazur A, Durlach J eds.Advances in magnesium
research :Nutrition and Health. Proceedings of the ninth international symposium
on magnesium.(
7.WJ Rowe. Calcium-magnesium- ratio intake and cardiovascular
risk Am J Cardiol
98 p. 140, 2006
8. Eckberg
D for the Neurolab autonomic nervous system team.Bursting into space: alterations of sympathetic control
by space travel. Acta Physiol Scand 177, pp 299-311, 2003.