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Does cosmic weather affect infant mortality rate?

Introduction

Galactic cosmic rays are highly energetic particles, originating from unknown sources outside our solar system and hitting the Earth's surface at an extremely high speed. Although the atmosphere shields the Earth's surface from cosmic rays, some of these highly penetrating particles can still reach the ground, and their presence can be detected even more than a mile below the Earth's surface (Dorman, 2003).

Energetic cosmic rays have a damaging effect on living organisms, which is substantially greater than X-rays or gamma-rays (Goldman, 1982; Shimada, Shima, Nojima, Seino, & Setlow, 2005). Cosmic rays have been reported to affect gene mutation and genome instability (Arenz, Hellweg, Meier, & Baumstark-Khan, 2005; Yang, Mei, George, & Craise, 1996), break DNA strands (Baumstark-Kahn, Heilmann, & Rink, 2003), and degrade the immune system (Todd, Pecaut, & Fleshner, 1999). The effect of cosmic rays has also been linked to sudden cardiac death (Soupel, 2006), and convincing evidence exists that irradiated cells can send out signals that can result in damage to nearby unirradiated cells (Brenner & Elliston, 2001). Other studies suggest that cosmic rays are among the causes of cancer in pilots and aircrew (Badrinath & Ramaiah, 1999), due to their exposure to cosmic rays in the higher atmosphere.

Considering its damaging effect on living organisms, one can reasonably assume that galactic cosmic radiation (CR) can also damage embryos in their early stages of development. The number of cosmic rays hitting an embryo is dependent on its size, so that the number of cosmic rays hitting the fetus increases as the fetus enlarges. Damage is expected to have a greater impact, however, if the embryo is hit at an earlier stage of development. With ~2 primary cosmic ray hits per [cm.sup.2] per minute (Johnson, 1938), and assuming an average surface size of the embryo of 0.0075 [mm.sup.2] in the first week, the order of primary cosmic rays hitting an embryo before the end of the first week is ~1.5, and around 15 hits in the second week, assuming an average embryo surface size of 0.075 [mm.sup.2].

The frequency of galactic cosmic rays hitting the earth is inversely correlated with solar activity (Wang, Sheeley, & Rouillard, 2006), which peaks once about every 11 years when the sun flips its magnetic pole (Howard & Labonte, 1980). When galactic cosmic rays approach the sun, they encounter the magnetic field of the heliosphere. This interaction results in the loss of some of the energy of the cosmic ray, making it less energetic and therefore less likely to ever reach the ground (Dorman, 2003). Solar activity during the magnetic polarity flip reduces the energy of galactic cosmic rays, so that the number of cosmic rays at sea level during the peak of the solar activity is smaller than the number of cosmic rays when the solar activity is at its minimum.

Methods

The analysis is based on the correlation between the change in CR density and the infant mortality rate (IMR) decrease in the following year. Assuming that a cosmic ray hit can damage an embryo in its early stages of development, a sharper IMR decrease is expected in the year following a sharp decrease in CR flux. Figure 1 shows the CR density at terrestrial altitude, as measured in Oulu Cosmic Ray Station, and Figure 2 shows the IMR recorded in the U.S. between 1977 and 2006.

Results

As can be seen in Figure 2, the year 2001 had a very low infant mortality rate, followed by a surprising increase (of nearly three per 1,000 births) in 2002. These data are in agreement with the intensive solar activity in 2000, which provided a better shield against cosmic rays during that time.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Examining the previous solar cycle, peaking in 1989, infant mortality rate in 1990 was 0.6 (per 1,000 live births) lower than the one recorded in 1989. This sudden drop of more than 6% followed five consecutive years of decrease of less than 2% per year, and is the highest IMR decrease recorded in nearly 30 years.

Figure 3 shows the CR flux decrease and the IMR decrease in the following year. Since IMR is a function of very many parameters (Frey & Field, 2004), a perfect correlation between the two variables is not expected. A partial correlation is noticeable, however, and the Pearson correlation between the two variables is ~0.36 (p < .05).

Discussion

This article presents a correlation between CR flux and IMR decrease in the following year. In particular, sharp IMR decreases were recorded in the years following the end of the solar cycle. The decrease is followed by an increase (or an unusually small decrease) in the following year, when the solar activity was getting less intensive.

The effect of cosmic rays may be even more significant on the number of miscarriages. Unlike IMR, however, miscarriage statistics are not well recorded, and therefore no conclusion can be established based on these data.

Cosmic rays are significantly stronger and more frequent at higher altitudes. For instance, at an altitude of one mile above sea level, the cosmic ray density is 3.7 times greater than at sea level, and it is 12.8 times greater at two miles in altitude (Ziegler et al., 1996). These data are in agreement with the observation of higher IMR at altitudes of two miles above sea level (Keyes et al., 2003).

Since cosmic rays are highly penetrating particles, no mechanism that can effectively protect embryos from cosmic rays is yet available. Since the magnetic field of the earth is consistently weakening (Sabaka, Olsen, & Purucker, 2004), its effectiveness as a shield is degrading. This trend might also contribute to infant mortality rate in future years.

Acknowledgments: This research was supported entirely by the Intramural Research Program of the NIH, National Institute on Aging.

References

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Lior Shamir, PhD

Corresponding Author: Lior Shamir, Research Fellow, Laboratory of Genetics, National Institute on Aging, NIH, 251 Bayview Boulevard, Baltimore, MD 21224. E-mail: shamirl@mail.nih.gov
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Title Annotation:GUEST COMMENTARY
Author:Shamir, Lior
Publication:Journal of Environmental Health
Article Type:Report
Geographic Code:1USA
Date:Jul 1, 2010
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