Obesity and space flight Spaceflight 52: 73, 2010.

Those subjected to space flight (SF) invariably lose weight in the presence of normal weight among astronauts prior to a mission. The weight loss is probably related to decreased appetite, malabsorption, and elevations of adrenaline. It is indeed remarkable however, that the complications of obesity on earth (1) and those SF- complications conducive to potential kidney disease are similar. Recently I published a paper describing an hypothesis showing that very prolonged space flight or colonization might ultimately cause kidney disease, triggering in turn hypertension with ongoing vicious cycles between the two. (2) Although hypertension does not always occur during space flight, it is noteworthy that the blood pressure does not fall significantly ( <10 %) during sleep and it may rise with sleep (3) This is believed to be related to elevations of adrenaline with levels twice as high in comparison with the levels on earth in the supine position. In addition there is both with SF and obesity insulin resistance which is conducive to albuminuria and portends kidney disease. (2)

With SF a peptide ( atrial natriuretic peptide ) (ANP) deficiency invariably occurs which could also precipitate kidney disease. (2) For example after just 7-12 days on Spacelab-2, the plasma ANP was reduced by more than 40 %. (4) ANP plays a very important role as a vessel dilator and clot buster. Furthermore in the presence of a significant reduction of ANP the effects of various constrictors, as for example adrenaline, are enhanced -conducive ultimately to the development of impairment in the circulation of the kidneys and ultimately leading to hypertension.(2)

Similarly obese individuals have been shown to have low circulating levels of ANP and it has been reported that this may contribute to the susceptibility for kidney disease with hypertension (5, 6). I have postulated that the severe hypertension Irwin showed after return from his 12 day lunar mission, was triggered not only by lunar dust inhalation in the habitats for a total of almost 7 days , but also was triggered by a postulated reduction in ANP whereas on earth exposure to dust may not trigger hypertension because of the protection by significantly higher levels of ANP with its vasodilator function.(2)

Obesity and space flight share not only reductions in ANP and insulin resistance but also both have been shown to have magnesium ion deficits.(2, 4, 7) Magnesium is necessary for the synthesis and release of ANP.(2) Therefore it is reasonable to speculate that both space flight and obesity may ultimately trigger kidney disease and hypertension. In the case of space flight however this complication may take a much longer time – perhaps several years. Since pharmaceuticals can’t be used with SF, gene therapy may be required to prevent these complications.(2)

William J. Rowe M.D. FBIS

References

1. W.J. Rowe. Obesity or space flight-the heart can’t see the difference. Spaceflight 47: p 274,2005.
2. W.J. Rowe. Potential renovascular hypertension, space missions and the role of magnesium. Internat. J Nephrol And Renovasc. Dis 2 : pp 1-7, 2009.
3. M. Shiraishi ,T. Kamo , M. Kamegai et al. Periodic structures and diurnal variation in blood pressure and heart rate in relation to microgravity on space station Mir. Biomed and Pharmacotherap 58: pp S31-34, 2004.
4. C.S. Leach Huntoon . A.I. Grigoriev , Y.V.Natochin. American Astronaut Society. Fluid and electrolyte regulation in Spaceflight ( Science and Technology series 94) San Diego, CA : Univelt; 1998.
5. C.K. Abrass. Overview : Obesity : What does it have to do with kidney disease ? J Am Soc Nephrol 15: pp 2768-72, 2004.

6. T.J. Wang , M.G. Larson ,D. Levy et al. Impact of obesity on plasma natriuretic peptide levels. Circulation 109: pp 594-600, 2004.

7. M.A.Farhanghi , S. Mahboob , A. Ostadrahimi. Obesity induced magnesium deficiency can be treated by vitamin D supplementation. J Pak Med Assoc 59: pp 258-61, 2009.