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
Virginia, USA

 

 

References

1.W.J. Rowe.  A better way to exercise in space SPACEFLIGHT 45, p 480,2003.

2.W J RoweThe 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.( Vichy, France) London:John  Libbey :pp.177-190, 2001.

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.